Styrene-Ethylene-Butylene-Styrene (SEBS) is one type of different types of Styrene thermoplastic elastomers. In chemical structure of SEBS terpolymer, the terminal blocks are styrene (thermoplastic) and the middle blocks are ethylene-butylene (elastic) (figure 1). This new thermoplastic elastomer is very resistant to environmental conditions such as temperature, UV radiation and mechanical wear. The lack of double bonds in this thermoplastic elastomer makes it suitable for use in cases where styrene butadiene styrene cannot be used. SEBS is a thermoplastic elastomer which that has the properties of an elastomer along with the low cost of the thermoplastic process at the same time. Excellent wear resistance in SEBS-based mixtures is due to the absence of double chains in their polymer structure.

 

 

Due to the flexibility in the formulation, it is possible to prepare products in a wide range of hardness for different applications from SEBS in the industry. The multitude properties of these materials have led to the expansion of global markets for these materials, including in various tools and accessories (figure 2).

 

 

The most remarkable features of this polymer are: wide range of hardness and excellent resistance to aging, wide range of colorability, very good processability at low temperatures and resistance to high temperatures. Besides, this polymer as a thermoplastic elastomer has high impact resistant and it is used as an impact modifier in some compounds. To process SEBS, like any other polymers, different additives is used. These additives during the process, or immediately after polymerization are added to the system to prevent possible defects during the process of parts and during use. These additives are used in several categories of antioxidants, light stabilizers, fillers, reinforcements and softeners. Antioxidants are mostly used in the production of polyolefins and styrene-based compounds. In addition, because the elastic modulus and hardness of SEBS is low, mineral reinforcements such as glass fibers, talc, calcium carbonate, etc. are used in it. But SEBS are not compatible with most mineral fillers and reinforcing materials such as glass fibers, talc, calcium carbonate, etc., because they are different from each other in terms of polarity, and there is a need for the presence of polymer compatibilizers.

Compatibilizers or coupling agents reduce the mixing enthalpy and interfacial free energy. Also, they are chemically similar to both phases and thermodynamically compatible with one or both phases. In many applications, SEBS grafted with maleic anhydride has been used as a compatibilizer. The chemical structure of SEBS grafted by maleic anhydride is shown in Figure 3.

 

 

The function of this compatibilizer is that it is connected to minerals from the side of the maleic anhydride molecule with high polarity and interacts with the polymer in the compound from the side of its polymer chain, and in this way, the connection between the mineral particles and the polymer is established.

In the rest following, we will examine the compatibilizing effect of maleic SEBS on the properties of compounds containing SEBS and calcium carbonate, as well as on the properties of compounds containing polypropylene and polyamide.

In the first stage, compounds with the same polymer base as the coupling agent were tested, and the raw materials used included styrene-ethylene-butylene-styrene terpolymer (SEBS), maleic anhydride, calcium carbonate modified with stearic acid and other additives. To prepare the above compounds, first, the coupling agent SEBS-g-MA was prepared by an internal mixer, and then 6 compounds including SEBS components, calcium carbonate, SEBS-g-MA and other additives were prepared in a twin screw extruder. The names and formulas of these compounds are listed in Table 1.

Table 1. Names and formulas of prepared compounds

Name	SEBS/ PHR	CaCO3/ PHR	SEBS-g-MA/PHR
SN0	100	0	0
SN1	100	3	0
SN2	100	5	0
SN3	100	3	1.5
SN4	100	5	1.5
SN5	100	3	3
SN6	100	5	3

The compounds prepared for 3 minutes at a temperature of 170 degrees Celsius and a pressure of about 200 bar were molded in the form of a sheet under a hot press, and after making standard samples and preparing dumbbell-shaped samples from the obtained compounds, tensile tests were performed according to the ASTM D638 standard and hardness according to ASTM D2240 standard were performed to obtain the properties of the above compounds. The results of tensile and hardness tests for the prepared compounds are given in Table 2.

 

Hardness/Shore A	Tensile strength/Mpa	Elongation at break (%)	Compound
65	4	370	SN0
69	4.4	319	SN1
70	4.5	296	SN2
71	5.3	267	SN3
72	5.1	254	SN4
75	4.8	241	SN5
76	4.5	229	SN6

Tensile strength values in Table 2 indicate that with the addition of calcium carbonate, the tensile strength increases to a small amount, but with the addition of the SEBS-g-MA coupling agent, the increase in tensile strength will be higher as follows that by adding 1.5 phr of SEBS-g-MA coupling agent to the compound containing 3% calcium carbonate, the tensile strength increases by 32.5% and this increase is due to two reasons: Firstly, a strong chemical bond is established between the polar group of stearic acid and calcium carbonate, and calcium stearate is formed, which improves the compatibility between the polymer matrix and calcium carbonate particles. Secondly, the SEBS-g-MA coupling agent, due to the presence of the polar carbonyl group in maleic anhydride, has the possibility of establishing a hydrogen bond with the ester group of the stearate coating on the surface of calcium carbonate, and its polymer chains are mixed with the SEBS matrix from the other side. In one hand, the strength and resistance of the above compounds depends on the amount of adhesion between the reinforcing particles and the polymer. On the other hand, by increasing the coupling agent to 3 PHR, the tensile strength decreases compared to 1.5 PHR, and the reason is that by increasing the compatibilizer percentage and since the compatibilizer is considered a hard component compared to the polymer, as a result, it declines flexibility and tensile strength.

Elongation at break percentage in the case of prepared compounds is reduced compared to SN0 control sample, because on the one hand, calcium carbonate mineral particles can act as stress concentration points or initiate cracks in the samples and as a result reduce the elongation to breaking point and on the other hand, the reduction of the elongation at the breaking point can be attributed to the plastic nature of SEBS-g-MA because it has less elastomeric properties than SEBS.

By adding the SEBS-g-MA coupling agent to the amount of 3 PHR in the compound containing 5% calcium carbonate, the hardness increases up to 17%, and in general, the hardness of all samples increases due to the addition of the coupling agent SEBS-g-MA to SEBS. In order to explain this phenomenon, it should be pointed out that the dispersed particles of calcium carbonate act as hard particles and prevent the penetration of the needle into the sample. If the particles are not completely distributed and remain in the polymer in the form of clusters, they act like a two-phase system, so that these particles act as a hard phase and the polymer acts as a soft phase, so finally the hardness of the system decreases, but due to the uniform distribution of calcium carbonate particles due to the presence of SEBS-g-MA within the polymer system, the indentation resistance increases. In the second step, the effect of SEBS-g-MA coupling agent on the properties of polypropylene/polyamide compounds was investigated, and for this purpose, SEBS-g-MA agent was added in amounts of 5 and 10% to compounds containing 80% polypropylene and 20% polyamide, and compounds containing the opposite ratio, i.e. 20% polypropylene and 80% polyamide, were added, and the impact properties of the above compounds were measured by the izod impact test according to ASTM D256, the results are shown in Table 3.

Table 3. Impact strength amounts of polypropylene/polyamide compounds

Item	Izod impact strength (kJ/m2)
PA/PP (80:20) without compatibilizer	4
PA/PP (80:20) with 5% SEBS-g-MA	15.1
PA/PP (80:20) with 10% SEBS-g-MA	29.5
PA/PP (20:80) without compatibilizer	2.2
PA/PP (20:80) with 5% SEBS-g-MA	6.3
PA/PP (20:80) with 10% SEBS-g-MA	12.2

From the data in Table 3, it is clear that the impact resistance increases with the addition of SEBS-g-MA agent to polypropylene/polyamide compounds, and when 10% is added, the impact resistance increases about 6 folds. This is for two reasons: Firstly, SEBS-g-MA is used to increase impact properties due to its elastomeric nature, and secondly, SEBS-g-MA acts as a binding agent between polypropylene and polyamide and makes the compound homogenous. The mechanism can be seen in figure 4.

 

 

In another case, the effect of SEBS-g-MA coupling agent on the properties of polyamide 6 and polyamide 66 compounds with glass fibers was investigated, the results of which are shown in Tables 4 and 5:

Table 4. Effect of adding 5% SEBS-g-MA on the impact of Polyamide6/glass fibers compound

Item	PA6/GF	PA6/GF/5% SEBS-g-MA
Tensile strength/ MPa	138	135
Elongation at break (%)	2.1	2.6
Izod Impact, Notched/ KJ/m2	9	27.5

Table 5. Effect of adding 5 and 10% SEBS-g-MA on PA6/GF compound

Item	PA66/GF	PA66/GF/5% SEBS-g-MA	PA66/GF/10% SEBS-g-MA
Tensile strength/ MPa	162	117	98
Notch impact strength/ KJ/m2	11	22	30

From the data in Tables 4 and 5, it is clear that the impact resistance property increases with the addition of SEBS-g-MA agent to polyamide/glass fiber composites, and in the case of polyamide 6, by adding 5% of SEBS-g-MA to the impact resistance of compound increases about 3 times, and this increase in the case of polyamide 66 is achieved by adding 10% of SEBS-g-MA agent, and the reason for the improved impact property can be attributed to the elastomeric nature of SEBS-g-MA agent and its compatibility with polyamide and glass fibers.

Author: Emad Izadi Vasafi

The glass transition temperature is the temperature at which the material changes from a solid state to a rubbery state. The difference between this temperature and the melting temperature is that at the melting temperature, the state of matter changes from solid to liquid. The importance of knowing the glass transition temperature is in changing the mechanical properties of the material at this temperature, which may not meet the consumer’s expectations.

The glass transition temperature is usually defined for amorphous (disordered) and semi-crystalline polymers, and the more crystalline the polymer or the more ordered, this temperature increases. Figure 1 shows the amorphous and crystal regions in a polymer. If a polymer is completely amorphous, there will be no melting temperature in it, but because all polymers have amorphous regions, although very small; In this case, it will definitely have a glass transition temperature. In Figure 2, the difference between melting temperature and glass transition temperature in a polymer can be seen.

 

 

As mentioned, the glass transition temperature is one of the most important physical properties of polymers. Since the behavior of a polymer above or below this point is very different, the properties affecting this temperature and how to obtain this point are of great importance. Therefore, in the following, the factors affecting this temperature and measurement methods have been discussed.

 

 

Factors affecting glass temperature

The glass transition temperature depends on the mobility and flexibility of the polymer chain (the ease of the chain segment to rotate along the main chain). If the polymer chain can move easily, the glassy state can change to the rubbery state. Now, if for any reason the rotation of the chains encounters resistance; To exit the glass state, more temperature will be needed and the glass temperature will increase.

Now let’s examine some parameters affecting this temperature:

1. Intermolecular forces

Strong intermolecular forces increase the glass transition temperature. For example, the glass transition temperature in PVC material (Tg=80 ℃) is much higher due to the stronger intermolecular force compared to polypropylene, which has a glass transition temperature (Tg=-180 ℃). The reason why the intermolecular bonding of PVC is strong is the existence of the C-Cl dipole-dipole bond.

2. Main chain stiffness

The presence of heavy groups in terms of molecular weight in the main chain increases the glass transition point; Because it reduces the flexibility of the chain. For example, polyethylene terephthalate (Tg=69 ℃) has a higher glass transition temperature than polyethylene adipate (Tg=-70 ℃) due to its benzene ring.

 

3. Crosslinking

Cross-linking between chains restricts movement and rotation; Therefore, the glass transition temperature increases. Hence, cross-linked polymers have a higher glass transition point. For example, the glass transition temperature of cross-linked HDPE, in its maximum state, is 125 °C, which is very close to the melting temperature of this polymer in its raw state. However, without cross-linking, this temperature reaches -90 degrees Celsius.

 

 

4. The group attached to the main chain

The groups attached to the main chain, depending on their nature, can lower or increase the glass transition temperature. The effect of these groups can be analyzed in two general categories.

Bulk connecting group: The presence of a bulk group in the main chain, such as a benzene ring, can make it difficult for the main chain to rotate and lead to an increase in the glass transition temperature.

 

 

Flexible connecting group: The presence of a flexible group in the main chain, such as an aliphatic chain causes the main chain to move more easily; Because it adds space for the rotation of the chain. In this case, the glass transition temperature decreases.

 

 

5. Plasticizers

Plasticizers are non-volatile and have a low molecular weight that are used to increase the effectiveness of chains and are widely used to reduce costs. Plasticizers reduce the adhesion of polymer chains; For this reason, they reduce the glass transition temperature. For example, DOP plasticizer is used for vinyl chloride polymer (Figure 7).

 

 

As it can be seen in figure 7, with adding the plasticizer to 10% wt, T_g climbed from 71 to 40.8 ℃ and with increasing amount of plasticizer to 20% wt, T_g reached 16.8℃.

6. Molecular weight

The molecular weight increases the glass transition temperature due to increasing the stiffness in the movement and rotation of the polymer chains. As seen in Figure 8, with the increase in the molecular weight of the polymer up to 20,000, the glass transition temperature has also increased; But after that, increasing the molecular weight does not have a significant effect on this temperature.

 

Methods of measuring T_g

Measurement methods are important because they are tied to different chemical and physical properties. For example, as the temperature increases and reaches the glass transition region, the mechanical properties, including the Young’s modulus, start to decrease abruptly; which represents the glass transition region. Therefore, by using the change of these properties in a jump form, it is possible to determine the glass transition temperature. In this section, some conventional methods of measuring this temperature will be introduced.

1. Thermodynamic Analysis (TMA)

In the thermodynamic analysis method, a small sample of the desired polymer is used. A rod is placed on the sample with a small force and the sample itself is placed on a surface in an oil bath. After that, the heating of the oil bath is started and the amount of changes in the length of the rod connected to the sample is measured by the LVDT linear variable transformer device. The temperature of the oil bath typically increases by 5°C per minute. In this case, the slope of the graph of length changes in terms of temperature indicates the coefficient of thermal expansion. Any temperature at which the slope of the line or the coefficient of thermal expansion changes, is called the glass transition zone.

 

 

2. Differential Scanning Calorimetry (DSC)

In this method, a small sample of polymer is prepared and heat is given to it. Meanwhile, the amount of energy required to heat the sample is measured. Since the physical properties change in the glass transition region, the energy required to heat the sample also changes. This is shown as a bend in the diagram.

 

 

3. Dynamic Mechanical Analysis (DMA)

The basis for measuring the glass transition temperature in this method is the measurement of mechanical properties. At first, a sample of prepared polymer is putted under a frequency of 1 Hz and a heating rate of 5 °C/min. Then, storage modulus, loss modulus and heating coefficient are measured in terms of temperature in a graph. As the temperature increases, the mechanical properties deteriorate until it reaches a specific transition region, and the beginning of that region is known as the glass transition temperature (in the red area of Figure 12).

 

Conclusion

In this article, the definition of glass transition temperature, factors affecting it, and measurement methods were discussed. At this temperature, the mechanical and chemical properties of the material change, and it is possible to predict these properties by knowing the glass transition temperature. However, sometimes the conditions are such that the use of a certain polymer at a certain temperature is unavoidable. That is why, how to change the glass transition temperature and the effect of changing this temperature on other properties of the material is one of the topics studied by researchers today.

At the end, the glass transition temperature of some commonly used polymer materials is given as examples.

References

1-A Materials Science and Engineering Perspective, First Edition.Edited by Kantesh Balani, Vivek Verma, Arvind Agarwal, Roger Narayan.

2-The glass transition temperature Tg of polymers—Comparison of the values from differential thermal analysis (DTA, DSC) and dynamic mechanical measurements (torsion pendulum)

3-glass transitions in polymers M. S. Shen and A. Eisenberg

Author: Emad Izadi Vasafi

Nowadays, due to the importance of maintenance of oil and gas pipelines, new methods have replaced old mechanical and traditional methods such as complete replacement of pipelines or welding that require high cost and very difficult installation operations, along with many risks of life and financial. Therefore, repair of pipelines using composite walls, which are mainly done through manual layering in the pipes or complete baking of composite walls (spring clock), has increased day by day, these methods also cause problems such as lack of proper adhesion, dirt of the place, etc. due to the variety of weather in the crossing of the lines. Oil and gas transmission pipes have increased the importance of manufacturing composite coatings with the ability to use concurrently in On Shore and Off Shore environments and their quick and easy installation, so the world’s major companies have conducted extensive research on the construction of composite walls by pre-impregnated method with the least environmental pollution and high flexibility to install at any level, especially in underwater environments. They did. In the new generation of composite coatings, innovation is in its flexibility and prefabricated, which makes it possible to use it at different levels and conditions.

According to a 2014 report by the North American Center for Oil and Gas Pipelines, the life of more than 60 percent of oil and gas pipelines worldwide is projected to be over 40 years old because these worn-out pipes have problems such as explosions, leaks, etc.  Efforts to repair these pipelines in North America, where three of the six countries with the highest oil and gas pipelines are located, were the explosion caused by a spill of oil pipelines in the San Francisco suburbs that killed and injured 128 people and destroyed thirty-eight homes, paying attention to the issue of repairs of the oil and gas pipelines. Therefore, nowadays, due to the high volume of oil, gas and petrochemical activities in the world and the desperate need for repairs of transmission pipelines, considering the economic importance of these products, repairs of oil and gas pipelines are one of the concerns of major industries and international oil companies in the world.

The first methods in repairing oil and gas pipelines, old mechanical and traditional methods such as pipeline replacement and later welding metal steel method, due to high costs and very difficult installation operations, along with the risks of life and financial damage caused by explosion during repairs, have a very high risk. Therefore, pipeline repair was replaced by mechanical and traditional methods using pipeline repair composite wrap technology. This technology, which is carried out using composite coatings, was very welcomed in the world because it does not require the pipeline to be removed. This technology is mainly done through two methods of manual layering at the hand lay-up site or the complete baking of composite coatings at the factory site, which was invented by Clock Spring ­Company.  These methods also cause problems such as lack of proper adhesion, filth of the place, lack of skilled workforce, etc. during installation of the wall­. On the other hand, due to the variety of climate of the crossing site of oil and gas pipelines, the construction of composite coatings with the capabilities of concurrent application in On Shore and Off Shore environments and their quick and easy installation has increased, which is using manual layering methods in the repair site of the pipes (Hand-lay-up), or complete sintering of composite coatings at the factory site are difficult or unworkable. Therefore, the world’s major companies have conducted extensive research on the construction of composite walls in a pre-impregnated manner with the least environmental pollution and high flexibility to be installed at any surface, especially in underwater environments

In the new generation of composite coatings, innovation is in its flexibility and prefabricatedness, which makes it possible to use it on different surfaces and conditions. In the pre-impregnated process which is done with specially designed devices, the reinforcing fibers are impregnated with resin, but by applying certain baking conditions, the resin is partially cooked which leads to the formation of composite form due to the lack of complete resin cooking. In this method, by exposing the composite wall to moisture or UV light, the composite wall is cooked in a very short time and this method is the only molding method of composites that has the ability to use at the same time in aquatic and dry environments, it is worth mentioning in these coatings, using technology to improve the physical and mechanical properties of the composites with the aim of reducing the weight of the product and controlling the duration of the product. And the amount of pre-impregnated gelling is done.

Methods

As mentioned in the history of technology section, currently, due to numerous problems that traditional mechanical methods including pipe replacement and welding of metal sleeves in the repair of oil and gas pipelines have created, various technologies in the production of composite coatings for repairing oil and gas pipelines have replaced traditional mechanical methods. These technologies include:

1. Complete cooking method in the factory
2. How to bake at the pipe repair site
3. Pre-impregnated method

So how each product is produced will be as follows:

Curing technology at the pipe repair site

Reinforcing fibers (usually glass fibers) are soaked by liquid resin at the repair site of the pipes and then soaked on the pipe (manual layering method). After applying composite coating on damaged pipelines, with baking conditions, the composite is formed and tightened.

 

 

Complete curing technology in the factory

Composites, which include reinforcing fibers and polymer thermoset resins, are cured with common methods of forming composites at almost complete production stage and composites are produced in the factory. These composite coatings produced in diameters slightly less than the outer diameter of the damaged pipes are wrapped and wrapped around the pipe when applied on the composite casing pipe and wrapped by layer-by-layer glue around the pipe. This technology was invented by Clock Spring under the same title.

 

 

Pre-impregnated technology

Reinforcing fibers are soaked with a certain percentage of resin and are semi-baked­­.  Then, this pre-impregnated composite is baked and molded during use by applying special conditions such as UV light, heat or humidity in a short time.

 

 

In order to investigate the status of pre-impregnated technology and compare it with other common technologies in repair method with composite coatings, the following table has been adjusted.

Table 1. Comparison of common technologies in the manufacture of composite coatings for repair of oil and gas pipelines

Method Type	Advantages	Disadvantages
Complete cooking method in the factory	– Controlling the direction of fibers and percentage of resin and fibers – Removing the adjustment of variable parameters with the outer diameter of the pipe – Better and more uniform mechanical properties – High speed of applying composite coating after accurate measurements of pipe dimensions and damage­ – Clean process	– Requires accurate measurements and expert force before applying the coating – Inability to apply on surfaces with irregular shapes or pipes with low diameter – No changing the size and diameter of the coating in case of any changes in the conditions of the damaged pipe
How to bake on-site	– Ability to determine and change the amount and length of composite coating in place – Ability to repair pipes with non-regular shapes, T-shaped pipes  , fittings, flanges and valves – No need for accurate measurements before applying the coating – Time and sintering process as a broadcast of coating installation operations – Cheap price	– By changing the environmental conditions of the pipe, the amount of resin consumed, the cooking conditions change – The construction of the wall and its actions requires expert forces – Dirty process – High consumption of resin
Pre-impregnated method	– Precise control of fiber percentage – Controlling the thickness of the layers­ – Reduce labor costs­ – Clean process – Higher quality – Higher flexibility compared to the complete production method in the factory	– Requirement for special machine for composite production –Technical Special Hi-Tech – Requiring special storage conditions in order to prevent early cooking

Fabrication of pre-impregnated composite

In the first stage of the construction of the mentioned composite, in the pre-impregnated process, which is done with specially designed devices, the reinforcing fibers are impregnated with resin, but by applying certain baking conditions, the resin is partially cured, which leads to the formation of composite form due to the lack of complete resin curing. This pre-impregnated composite wall can be placed in certain packaging’s until its service, and when needed, this composite wall is easily completed and hardened under moisture, and a composite wall with mechanical properties such as other walls will be achieved. In this method, by exposing the composite wall to moisture, the composite wall is cured in a very short time and this method is the only molding method of composites that has the ability to be used at the same time in aquatic and dry environments.

As mentioned below, the price of raw materials of traditional products (buying metal sleeves and tubes for replacement) is lower than the purchase price of composite coating raw materials. The final costs of mechanical repairs due to the costs of waste of oil or gas materials, the need to stop, the high cost of manpower due to the high duration of repair and high machine costs, are higher than composite coating methods.

Also, one of the most important factors in valuing products is the added value that creates added value for the main customer of this product, i.e. oil and gas pipeline maintenance company. In addition to the topic of competitive analysis of composite coatings, the­ example of the created value added of composite coatings in comparison with traditional methods in repairing oil and gas pipelines is discussed­­.

In a report from the Natural Gas STAR Center of America, a comparison was made between the costs of repairing gas pipelines in two traditional ways of replacing the pipeline and repairing with composite coatings on gas pipelines with a diameter of ­ 24 inches for a length of 6 and 234 inches equivalent to 15 and 594 cm, as shown in the diagrams below.

 

As mentioned in the diagrams above, a major share of the costs of repairs belonging to gas waste and the cost of human resources are needed in such a way that repairing gas transmission lines by composite coatings for meters less than 3 meters, between 10 and 20% of the repair cost will be replaced by a replacement method, this ratio of costs for meters above 3 meters will be between 75 and 85%. In order to repair 6 meters of pipe with a diameter of 24 inches (about 61 cm) the amount of about 350 million Rials is calculated the difference in costs of the two methods.

Conclusion

Common methods are used in repairing oil and gas pipelines, among which traditional methods of welding metal sleeves and replacement methods due to high overhead costs, life and financial risks and their incompleteness are being analyzed gradually. In composite methods that are used in three ways, complete baking in the factory, baking method at the pipe repair site, the pre-impregnated method is used.

Author: Emad Izadi Vasafi       

 

 

Polymers are divided to four categories: thermoplastics, thermoset rubbers, thermosets and thermoplastic elastomers (TPE) which are a group of copolymers or physical combination of plastic and rubber and have both thermoplastic and elastomeric properties (figure1). While the majority of elastomers are thermoset, the most important feature of thermoplastic elastomers is their processing ability. These polymers show both advantages of plastic and rubbers. The benefit of using thermoplastic elastomers is their ability for starching and return to the initial sate, which increase their durability. The main difference between thermoset elastomers and thermoplastic elastomers is the type of crosslinking in their structure. In fact, crosslinking is the key factor which leads to high elasticity properties [1].

 

1. TPU Types

Thermoplastic elastomers like thermoset rubbers are soft and flexible, and like thermoplastics are processable. In term of structure, they are divided to two main categories: block copolymers, and elastomer compounds. Block copolymers are made by separate crystalline fragments and amorphous regions containing similar polymer chains (Figure 2-a), and blends are mechanical mixtures of semi-crystalline and amorphous polymers (Figure 2-b).

These materials have six commercial types which was at figure1. In this study, three kinds of them will be investigated.

1.1 Polyurethane Thermoplastic (TPU)

This polymer is based on poly ether or poly ester. As it can be seen in figure 3, it has both soft and rigid areas.

1.2 Polyolefin-rubber blend (TPO)

In the modified polyolefin elastomers, as it can be seen in figure4, there is a few elastomeric regions in thermoplastic matrix [2].

1.3 Volcanized Thermoplastic (TPV)

The biphasic combination of polypropylene and rubbers, as shown in Figure 5, contains large areas of non-spherical and cross-linked rubbers.

Each one of commercial thermoplastic elastomers has significant advantages, and due to them for use of them, those benefits should be considered. Applications of thermoplastic elastomers with considering their specific properties are shown in table1.

Table 1. benefits and applications of some commercial thermoplastic elastomers

Thermoplastic elastomer Advantages Applications

• TPU Tear resistance and high hardness, Resistance to wear and bending fatigue Shoe soles, industrial belts, ski boots and wires and cables
• TPO Processability, UV resistance, dimensional stability and good thermal strength To increase the toughness and durability of polypropylene copolymer
• TPV Can be used in a wide range of temperature and hardness, processability, elasticity, UV and chemical resistance and good bending fatigue It can be used when elasticity and bending fatigue are needed, such as car sealing systems, weather stripping, industrial seals and gaskets.

2. Properties of thermoplastic elastomers

Elasticity is one of the main properties of TPEs, but there are mix of properties to make them useable in different industries. Whenever it is required to select a TPE, functionality and price of materials must be compared with expected engineering properties. The morphology and chemistry of this polymeric material defines its overall performance. Recent progresses in processing and blending polymers, has expanded the functionality of TPEs. In this section, the most important properties of TPEs are discussed [2].

2.1. Operating temperature and resistance to oils

For the classification of thermoplastic elastomers, their usage/price chart is shown in Figure 6, and as can be seen, the performance range of amorphous and semi-crystalline polymers depends on their price.

While the cost/performance classification is a general way of classifying thermoplastic elastomers, within this classification, there is considerable variation among its members. Resistance to swelling in hot oil is another criterion that is a suitable classification for the functional properties of these materials. Figure 7 shows the oil resistance of various thermoplastic elastomers compared to their maximum applied temperature [3].

2.2 Hardness

Another major functional comparison between thermoplastic elastomers is their hardness range. Figure 8 shows the hardness range of thermoplastic elastomers. As can be seen, TPUs and TPOs have higher hardness than TPVs.

2.3 Abrasion Resistance

Abrasion resistance is important in performance of thermoplastic elastomers where pulling, rough surface, industrial applications, and contact friction matters. The hard type of these polymer materials usually has better abrasion resistance. TPU and COPA have the highest abrasion resistance.

2.4 Transparency

Most thermoplastic elastomers are opaque. Only some grades are transparent like TPU.

2.5 Tensile and Tear Resistance

Tensile strength and tear resistance are the most important properties in some applications. Typically, hard thermoplastic elastomers have better tear resistance and tensile strength. TPU, COPA and COPE also have the highest tensile and tear resistance.

2.6 permeability Resistance

Resistance to oxygen permeability of most thermoplastic elastomers is almost good. Most of them contain gases such as oxygen and nitrogen for several days or even weeks (depending on local thickness).

2.7 Adhesion and Bonding

When thermoplastic elastomers are bonded onto a substrate or assemble, adhesion and bonding become important functional properties. In general, polar TPEs have very good bendability. For compounds containing polar polymers, polar TPEs are compatible and can create a strong bond. For non-polar substrates such as polypropylene or polyethylene, EPDM/PP TPV, TPOs, IIR/PP TPV and NBR/PP TPV excellent compatibility can be seen.

2.8 Elasticity

An important performance range for TPEs is elasticity. TPVs have a continuous thermoplastic network containing dispersed rubber, their elasticity mechanism is very similar to rubbers.

2.9 Bending Fatigue Resistance

The ability of elastomers to stretch or repeatedly bend, return to its original state and resist crack growth, is bending fatigue resistance. While thermoset rubber compounds are recognized as the best bending fatigue resistant materials, EPDM/PP TPVs have greater bending fatigue resistance.
The following table briefly shows some properties of TPU, TPV and TPO.

Table 2.  Some properties of TPU, TPV, and TPO

Author: Javad Moftakharian/ Emad Izadi

References
[1] “Thermoplastic elastomer.” [Online]. Available: https://en.wikipedia.org/wiki/Thermoplastic_elastomer.
[2] “TPE Alphabet Soup: TPO, TPV, SBC, TPU, COPE, COPA.” [Online]. Available: https://www.teknorapex.com/compare-thermoplastic-elastomers-tpe-sbc-tpv-tpo-tpr-rubber.
[3] “TPU.” [Online]. Available: http://www.bpf.co.uk/Plastipedia/Polymers/Thermoplastic_Elastomers.aspx.

Adhesives have been used by humans for a long time, so that today they are an inseparable part of various industries. Today, with the growth of technology, polymer adhesives replace other sources of fasteners in various cases. In this article, different types of adhesives are introduced, the amount of adhesive consumption in different industries and in the world is stated, and its applications in different industries are examined [1].

Adhesive

Adhesive is a material which is used for keeping two surfaces together. Before, use an adhesive surface preparation must be done. For surface preparation, first of all adhesive must wet the surface, then after applying the adhesive on the surface, it must lead to strength between surfaces and remain stable. Most of the times the raw materials which are used for adhesives, are polymeric materials. These polymers can be categorized as below [2]:

1. Thermoset Adhesives:

• Epoxy resins
• Phenolic resins
• Amine resins
• Polyurethanes
• Silicone resins [3]

2. Thermoplastic Adhesives:

• Poly vinyl acetate
• Poly vinyl acetal
• Poly acrylate
• Cyanoacrylate
• Cellulose derivatives
• Melt thermoplastic adhesives (Thermal adhesives) [4]

3. Rubber Adhesives:

• Nitryl rubber
• Neoprene
• Polysulfides [5]

4. Natural Adhesives:

• Herbal
• Animal glue [6]
Applications of adhesives in different industries
Adhesives are extremely used in the most of industries such as: food packing, drug packing, construction, automotive, and medical. As it can be seen in figure1, most of the use of adhesives belongs to packing industry [7].

In the whole world, Asia due to its massive countries such as China and India, is the biggest user which had almost 34.4% at 2011. After Asia. America with 32.9% and Europe with 25.3% respectively, had the second and third place.

Uses of adhesives in the packing industry includes: Multilayers films, Labeling, and food packing

 

 

Uses of adhesive in automotive industry

As it can be seen in the figure 5 to link different parts such as: roof, windshield and, side panels are sued adhesives.

Adhesives applications in transportation industry

Nowadays, in transportation industry especially in marine transportation is adhesives are widely used because, in marine industry the low weight of products and improving the quality of products is crucial. In figure 6 and 7 use of different adhesives in the ships and aircrafts has shown.

 

 

Adhesives in Construction

It can be used for:
• Gluing ceramics and tiles
• Gluing flooring
• Gluing prefabricated and concrete roofs

Among the types of adhesives, acrylic ones have the largest part of the market, so that the amount of this consumption in 2013 was 36.9% compared to all existing adhesives. After that, polyvinyl acetate (PVA) adhesives with a consumption of about 28.1% and silicone adhesives with a consumption of 18% are among the most widely used adhesives.
Another way to classify adhesives is based on their curing method, based on which adhesives can be divided into two categories:
1. curing adhesives without the need for an initiator:
• Dry adhesives
• Hot melt adhesives
• Pressure-sensitive adhesives
• Interlayer adhesives
2. curing adhesives with the help of initiator:
• Adhesive curing under UV
• Adhesive curing by heat
• Adhesive curing by humidity

 

Emulsion Adhesives

There are adhesives that are cured and hardened by drying. These adhesives are classified into two categories: water-based and solvent-based, which are called emulsion adhesives.
Solvent-based adhesives are divided into two categories:
1- Wet bonding adhesives
2- Contact adhesives
Water-based adhesives are adhesives that use water as an active component, and the connection is made by water evaporation or water absorption by the base material. Water-based adhesives, like solvent-based adhesives, are divided into two categories: contact and wet bonding. It is expected that water-based adhesives will replace solvent-based adhesives in the last decade.

 

Fig. 9. Application of emulsion adhesives in the field of wooden joints, flooring installation, parquet, and packaging industry [14]

Hot-melt Adhesives: There are in the thermoplastic resins family, they melt and flow under heat and create a strong adhesion and connection with the existing substance as a result of quenching.
It is expected that in 2018, Hot-melt adhesives will have the largest proportion of consumption among all types of adhesives in various industries, including the packaging industry and non-woven textiles.
There are different types of hot-melt adhesives that are used in different fields, such as: Hot-melt adhesives based on polyolefin (polyethylene and polypropylene) in the packaging industry. Hot- melt adhesives based on polyvinyl acetate in the field of binding. Hot-melt pressure sensitive adhesives used in the field of health and medical products. Hot-melt adhesives in the automotive and filter industry.

 

 

Fig. 10. Applications of hot-melt adhesives [15]

Pressure Sensitive Adhesives (PSA)

Pressure-sensitive adhesive is an adhesive that adherence the adhesive with the substrate by applying a small amount of pressure. Pressure-sensitive adhesives can be solvent-based, water-based, or hot-melt.

 

Fig. 11. PSA Adhesives [16]

These adhesives have a widely range of applications from automotive and medicine industry to basic industries.
Polymers which are used as PSA adhesives: Polyester, Polyurethane, Silicone, and Acrylic.

 

UV Adhesives

Adhesives that are cured with UV rays, this curing method requires less time than the thermal method and reduces the side products, so that UV adhesives have replaced thermal adhesives in most fields. UV adhesives are used for medical purposes such as making syringes, tweezers, and dental fillers. These adhesives are also used in the wood industry, making decorations, and other industries.

 

Fig. 14. Medical applications of UV adhesives [19]

Some adhesive manufacturers world-renowned companies:
 Henkel of Germany
 3M of USA
 HB Fuller of USA
 Bayer of Germany
 Mactac of USA

 

Author: Emad Izadi Vasafi

References:

[1] https://polymerdatabase.com/Adhesives/Adhesives.html
[2] https://www.britannica.com/technology/adhesive
[3] https://fastenerengineering.com/what-are-thermoset-adhesives/#:~:text=Thermoset%20adhesives%20are%20thermosetting%20polymers,such%20as%20heat%20or%20light.
[4] https://www.labelplanet.co.uk/glossary/adhesive-thermoplastic/
[5] Pocius, A. V. “Adhesives and sealants.” (2012): 305-324.
[6] https://blog.lddavis.com/natural-glues-for-industrial-applications
[7] https://www.masterbond.com/industries/adhesives-sealants-and-coatings-variety-industries
[8] https://www.fortunebusinessinsights.com/industry-reports/adhesives-and-sealants-market-101715
[9] Gadhave, Ravindra Vilas Indubai, and Chaitali Ravindra Gadhave. “Adhesives for the Paper Packaging Industry: An Overview.” Open Journal of Polymer Chemistry 12.2 (2022): 55-79.‏
[10] https://www.globenewswire.com/en/news-release/2018/01/11/1287163/0/en/Automotive-Adhesives-and-Sealants-Bonding-for-Betterment-of-Automobile-Industry-to-Witness-a-CAGR-of-7-9-during-2017-2023.html#:~:text=Automotive%20adhesives%20and%20sealants%20are,mechanical%20bolts%2C%20welds%20and%20rivets.
[11] https://www.adhesivesmag.com/articles/97993-marine-applications-for-adhesives-and-sealants
[12] https://market.us/report/aerospace-adhesives-and-sealants-market/
[13] https://mccoymart.com/post/what-are-the-applications-of-adhesives-in-the-construction-industry/
[14] https://www.fcimag.com/articles/92241-all-about-flooring-adhesives-chemistries-and-applications
[15] https://www.asahimelt.com/eng/hm/
[16] https://onlytrainings.com/psa-pressure-sensitive-adhesives-formulation-optimization-and-key-ingredients-selection-for-high-performance-applications
[17] https://kmsmedsurg.com/3M-Micropore-Surgical-Tapes-with-Dispenser?language=en&currency=USD
[18] Sanai, Yasuyuki, and Kouzou Kubota. “Effect of UV-curing conditions on the polymer structures: A comparison between coating and adhesive.” Polymer Journal 52.9 (2020): 1153-1163.‏
[19] https://www.heraeus.com/en/hng/industries_and_applications/uv_technology/curing_of_uv_adhesives_and_uv_paints_in_medical_engineering.html

Polyamide (nylon) thermoplastic resins are widely used due to a very suitable balance between process-ability and desired properties. The most commonly used nylons are nylon 6 (PA6), and nylon 6 and 6 (PA6,6). Some final applications of this resin require high impact properties at low temperatures, so different methods are used to increase the impact properties of these polymers. For example, for some applications, toughened nylon grades are used. But the most common method to overcome this problem is the combination of polymer with elastomers or thermoplastic elastomers grafted with maleic anhydride, such as ethylene-propylene grafted with maleic anhydride (EPR-g-MAH), or a thermoplastic elastomer such as styrene-ethylene-butadiene-styrene or SEBS-g-MAH which is grafted by maleic anhydride.

In many cases, due to the high price, lack of dimensional stability against water absorption, and lack of proper process-ability, the use of polyamide has been limited. Usually, PA6/PP compounds instead of pure polyamide are used in the industry to solve this problem.

In this article, to investigate  POE is a relatively new polyolefin elastomer and has better processability than EPR with PP, which is investigated in this article in its two pure and grafted states.

Table1. The percentage composition of nanocomposites [1]

In compound prototyping, the effect of different percentages of POE and POE-g-MA from 5 to 20 weight percentage has been investigated.

As it is shown in figure1, adding pure POE to PA6/PP nanocomposites with 70/30 ratio causes to a slight increase of impact strength. This enhance has some limitations due to incompatibility between PA6, and POE. Thus, use of POE-g-MA in comparison to pure POE dramatically influences on impact strength of the polymer. So that with addition the amount of impact modifier, the properties due to the presence of POE-g-MA are increased compared to POE. For example, the compound containing 20% POE-g-MAH has an impact strength of about 6 times that of pure PA6/PP/Organoclay.

In Figures 2 and 3, the changes of K_c (fracture toughness) and G_c (fracture energy) of all nanocomposites at two temperatures of -40°C and 25°C (RT: room temperature) are specified. As expected, Kc and Gc increase linearly with increasing POE value in a similar process. Also, it can be seen in both figures that all nanocomposites at room temperature show a higher value of Kc and Gc than at -40°C. In addition, the improvement of the impact property of POE-g-MAH compared to POE can be seen in the figure.

The improvement of toughness in the compound can be explained as follows: When PP-g-MAH adds to PA6/PP, the interfacial adhesion between PA6 and PP is enhanced by the formation of PA6-g-PP copolymer. Also, because of physical similarity, intermolecular adsorption (physical entanglement) may occur between PP and POE. These two factors promote compatibility between PA6 and POE. The interaction between POE and PA-g-MAH and the mechanism of compound toughness improvement can be seen in Figure 4.

As seen in Figure 5, the anhydride group of POE-g-MAH reacts with the terminal amine group of PA6 and finally PA6-g-POE copolymer is formed, which strengthens the surface energy between PA6 and PP. Figure 6 shows the interaction between POE-g-MAH, PA6-g-PP, PP and clay, which indicates the final compound and improves the desired properties.

In Figure 7, morphology of PA6/PP/Organoclay/PP-g-MAH in the presence of POE and POE-g-MAH can be seen. As it has shown, the presence of POE compatibilizers in comparison to pure one, especially in high consumptions of POE-g-MAH shows a remarkable effect.

Author: Emad Izadi Vasafi

References:

[1] Wahit, M. U., et al. “Ethylene-octene copolymer (POE) toughened polyamide 6/polypropylene nanocomposites: Effect of POE maleation.” Express Polym Lett 3.5 (2009): 309-319.

Injection molding efficiency is more focused on multiple process and machine parameters that dictate the quality of the final product in terms of multiple output responses. It is important to state that precise optimization of various input parameters is very important to achieve the desired quality indicators. Five of the most common defects of the injection molding process were reviewed in the first part of the article. Five more of the most common quality defects related to injection molding, the factors that cause them, and the actions that can be taken to fix them, will be investigated in this article.

Introduction

Injection molding is one of the most widely used methods of producing parts and products. The method is fast, works with a variety of plastics, and can result in a prototype or finished product that is both durable and highly detailed. But this process is complex and full of challenges. Fortunately, many of them are easily solvable [1]. Injection molding defects are often caused by process problems. Some molding defects may be difficult or expensive to fix, but most of these defects can be prevented without having to redesign the mold tool or replace other production equipment by adjusting the molding process. Usually, these defects can be avoided relatively easily by adjusting the flow rate, temperature or pressure of mold.

Common defects in injection molding

6. Flash

This means that there is excess plastic on the part of the mold separator or ejector. Flash, also called spew or burrs, is a large amount of molding material that appears as a thin edge or ridge on the edge of a component. A flash defect occurs when material has flowed out of the intended flow channels and into the space between the tool plates or into the injector pin. An injection molding flash defect is usually subtle, but if it is particularly evident in a product, it may be considered a major defect. The process of reworking a flash-molded product often involves cutting off excess material.

Reasons:

 

• Insufficient clamping force
• Mold defect (not locking the mold)
• Improper design
• Excessive injection pressure and temperature

Solutions:

• Proper design of the template
• Cleaning the mold surface
• Increasing the time and reducing the injection speed
• Reducing the temperature of the nozzle
• Reduction of injection pressure

7. Delamination

If the thin layers on the surface of a molded part easily separate the underlying material, leading to peeling of the underlying material, it is a molding defect called delamination. This defect is considered as a relatively serious defect because it reduces the strength of the part.

Reasons:

 

• Mixing incompatible polymers
• Excessive humidity
• Valve and flow path have sharp angles.

Solutions:

• Not using a lot of recycled materials
• Try to avoid the impurities in the materials
• Chamfering sharp corners
• Increasing the mold temperature
• Dry the material properly.

8. Short Shot

It is a phenomenon in which mold cavities cannot be completely filled. Short shot occurs when the flow of molten material does not completely fill the cavities of a mold. The result is that the molded part is incomplete after cooling. A short shot may appear as incomplete compartments on plastic display shelves or missing prongs on a plastic fork. Short shots are usually classified as a major defect that can affect the performance or appearance of the molded manufacture.

Reasons:

 

• Mold temperature, material temperature or pressure and injection speed are too low.
• Uneven plasticization of raw materials
• The part is too thin or the valve size is too small.
• Premature curing of molten polymer due to improper structure design

Solutions:

• Choosing plastics with lower viscosity or higher MFI
• Increasing the temperature of the mold and materials to increase flowability
• Changing mold design so that the gas is not trapped inside the mold and is properly discharged.
• If the maximum material feed is reached, increase the material feed in the molding machine or use a machine with a higher material feed capacity.

9. Weld Lines

There are seams that appear in the place where two areas of molten plastic meet. Weld lines can appear on the surface of a molded part where the molten material has converged after being split in two or more directions in the mold. A hairline-like weld is the result of poor material bonding, which reduces the strength of the product.

Reasons:

 

• If there are holes, inserts, or multi-gate injection molding methods in the manufactured parts, or if the wall thickness of the parts is uneven, weld lines may occur.

Solutions:

• Rising mold or molten plastic temperature
• Increasing injection speed
• Using polymers with lower viscosity or melt temperature

10. Vacuum Voids

Vacuum voids are air bubbles that are trapped in or near the surface of an injection molded part. Quality control professionals usually consider voids to be a minor defect, but larger or more voids can in some cases weaken the molded part because air exists below the surface of the part where the molded material should be.

Reasons:

 

• Not filling the form completely
• Poor mold ventilation, especially around ridges
• Improper location of the port
• Very fast filling speed (trapped air creates short shots)
• Improper mold temperature
• Excessive part thickness (more than 6.3 mm (1.4 in))
• Trapped moisture
• Air entrapped through porous or ultrafine air-absorbing additive powders

Solutions:

• Placing the port in the thickest part of the mold
• Using plastics with lower viscosity. This ensures that less gas is trapped because the air can exit faster.
• Increasing maintenance pressure as well as maintenance time
• Ensuring that the mold parts are perfectly aligned [2].

Final Word

If injection molding is not done correctly, costly errors can occur. Quality problems in finished products can range from some minor surface issues to some serious defects that may even compromise user safety. Also, such defects can affect the performance and quality of the product. As a result, customers may stop buying from a particular brand. Therefore, it is very important for plastic mold makers to ensure that the process is done without any errors. In this article, we discussed some of the most common problems and common solutions of advanced injection molding.

In order to investigate the defects of the injection process in the polymer industry, contact the experts of Aria Polymer Pishgam company.

 

Author: Emad Izadi Vasafi

References:

1. Kashyap S, Datta D. Process parameter optimization of plastic injection molding: a review. International Journal of Plastics Technology. 2015 Jun;19(1):1-8.
2. https://www.creativemechanisms.com/blog/what-cause-injection-molding-defects-and-how-to-fix-them
3. https://waykenrm.com/blogs/plastic-injection-molding-problems-and-solutions/
4. https://www.plasticmoulds.net/troubleshooting-product-defects.html

Despite the numerous advantages of injection molding, there is always the possibility of high-cost defects. These problems in injection molding products range from minor surface defects to more serious defects in product quality, which can adversely affect the safety and performance of products [1]. The created defects can be caused by problems with the molding process, material use, tool design, or a combination of all three. Therefore, as with any quality issue, knowing how defects occur is half the solution. As an importer or manufacturer of injection molding products, being aware of common molding defects and how to avoid them can help you reduce costs related to unsalable goods and product returns [2].

Most Common Defects of Injection Molding Process

1. Flow Lines

Flow lines are among the cases of molding defects that create a wavy state on the surface of the product, which is known as a frog jump caused by the slow flow of the melt [3]. The flow lines appear as a wavy pattern, often a slightly different color than the surrounding area and generally in the narrower sections of the molded part. They may also appear as ring-shaped bands on the surface of the product near mold entry points or ports, through which the molten material passes. Flow lines usually do not affect the integrity of the component. But if they are found in some sensitive consumer products such as sunglasses, they can be unpleasant and unacceptable.

Causes:

 

This defect is caused by the variable speed rates that the molten plastic creates as it changes direction through the lines and bends inside the mold tool. Also, when the melt flow flows in parts with different thicknesses or when the injection speed is very low, which causes the melt to solidify at different speeds, this defect can be seen as in Figure 1.

Remedies:

• Increasing the injection speed, pressure and temperature of the material to ensure that the material fills the mold before it cools.
• Rounding the corners of the mold is where the wall thickness increases to help keep the melt flow rate constant and prevent flow lines.
• Placing the mold vents where there is more clearance between them and the cooling mold to help prevent premature cooling during flow.
• Increasing the diameter of the nozzle to increase the flow rate and prevent rapid cooling

2. Burn Marks

This defect happens when the gas in the cavity is not released at the right time, resulting in blackening at the end of the flow. Burn marks usually appear as black or brown discoloration on the edge or surface of a molded plastic piece. In plastic injection molded parts, burn marks usually do not affect the integrity of the part unless the plastic is burned to the point of destruction.

Causes:

 

• Trapped air
• Overheating of the plastic inside the mold cavity
• Excessive injection speed

Remedies:

• Reducing mold temperature
• Minimizing the rate of injection
• Enlarging the exits of the valves so that the trapped air is removed from the mold [5].
• Using antioxidant masterbatches to delay burns

3. Warping

It is called distortion of molded parts. Warp is a deformation that can occur in injection molded products when different parts of a component contract unevenly. Just as wood can warp unevenly as it dries, so can plastic and other materials warp during the cooling process, when uneven shrinkage puts undue stress on different areas of the molded part. This unwanted stress causes the final product to bend or twist as it cools. This is especially evident in the part where the part is supposed to be flat.

Causes:

 

• The removed part is very hot.
• Improper temperature balance between core and cavity temperature
• Excessive condensation in valves due to high injection pressure
• Improper design of the part
• The current is too long [6]

Remedies:

• Ensure adequate cooling time
• Lowering the temperature of the material or mold.
• Use of anti-warpage masterbatch for polymer injection products

4. Jetting

It is a kind of snake-like deformation occurs when the gate size is very small and thus the filling speed is very fast [7]. Jetting refers to a type of deformation in a molded component that can occur when an initial jet of molten material is injected into a mold cavity that begins to solidify before the cavity is filled. Jetting often appears as a curved line on the surface of the final component, usually leading from the initial injection gate. This visible flow pattern can lead to partial weakness of the part of product.

Remedies:

 

• Increasing mold and material temperatures
• Reducing the size of the channel to reduce the injection speed
• Ensuring the proper amount of contact between the molten plastic and the mold
• Use of masterbatch to lubricate the surface

5. Sink Marks

Another defect that leads to a decrease in the beauty of the piece on the surface of the mold (as in Figure 5), is in the form of depressions, usually in the thicker parts of the mold. The main cause is usually shrinkage of the polypropylene material during the crystallization process.

Causes:

 

• Inadequate injection pressure
• Inadequate storage time
• Inadequate quantity of materials
• Too high injection speed
• Short cooling time
• High melting or mold temperature
• Improper valve design or valve location
• Poor part design, non-uniform walls or excessive wall thickness

Remedies:

• Increasing the pressure and holding time to cool the material near the surface of the manufacture.
• Increase cooling time to reduce indentation
• Design your mold with thinner component walls to allow for faster cooling near the surface.
• Reducing the speed of injection

 

In the second part of the article, five other common defects of injection molding will be investigated.

Author: Emad Izadi Vasafi

References

1. Khosravani MR, Nasiri S. Injection molding manufacturing process: Review of case-based reasoning applications. Journal of Intelligent Manufacturing. 2020 Apr;31(4):847-64.
2. https://www.intouch-quality.com/blog/injection-molding-defects-and-how-to-prevent
3. https://waykenrm.com/blogs/plastic-injection-molding-problems-and-solutions/
4. https://www.creativemechanisms.com/blog/what-cause-injection-molding-defects-and-how-to-fix-them
5. http://www.veejayplastic.com/blog/troubleshooting-injection-molding-defects/
6. https://www.hmcpolymers.com/troubleshooting-new
7. https://www.immould.com/common-injection-molding-problems-and-solutions/
8. Kashyap S, Datta D. Process parameter optimization of plastic injection molding: a review. International Journal of Plastics Technology. 2015 Jun;19(1):1-8.