One of the most important features of high-consumption polymers such as polyethylene (PE) and polypropylene (PP) is their ability to adjust different properties with different additives in the formulation. So, most of the properties of polymers can be changed by adding different fillers. In general, fillers increase stiffness, abrasion resistance, and decrease the shrinkage parameter of manufactured parts with the injection process. Despite the benefits achieved by  various additives, some of their disadvantages such as changes in the degree of toughness or problems in the processability. can be also mentioned.  In particular, polyolefins such as PE and PP as the most widely used polymers  are non-polar in nature and also they are incompatible with most fillers, which are often hydrophilic materials. For this reason, the proper connection between the interface of the fillers and the polymer matrix is weak. However, achieving properties such as the ones in color polymers, conductivity in the polymer material, or flame retardancy ,usually requires the use of suitable fillers in large quantities [1]. For example, to achieve the desired flame retardant properties in polymers, it is necessary to add about 60% by weight of Halogen Free Flame Retardant Fillers (HFFR), including aluminum hydroxide (ATH) or magnesium hydroxide (Mg (OH)). The mechanism of modification of such fillers can be improved by using various methods such as coating the filler surface and thus increasing the adhesion at the interface between the filler and the polymer matrix. Common coatings that are often applied to the surface of fillers; Common coatings that are often applied to the surface of fillers; Contains hydroxyl groups such as stearic acid and other suitable organic substances[2].

Figure 1. Application of Filler Compounds in HFFR Products.

The advantages of using these solutions include improving the dispersion of the filler in the polymer matrix, which in turn improves the mechanical properties, increases the chain mobility, and also reduces the viscosity of the molten polymer during the polymer blending process. Hydrophobic polyolefins usually are non-polar but they will be hydrophilic by applying copolymerization processes or reactive extrusions [3]. In the presence of compatibilizer, a stable bond is made between the filler and the polymer matrix. Small molecules, such as stearic acid, are too small to have entangled with polymer chains. But they are quite able to reduce the interfacial stress at the interface between the polymer and the filler. However, these materials cannot be very effective as a coupling agent/compatibilizer in all polymer blends [4]. It should be noted that various polymer coupling agent/compatibilizer have been used in scientific papers and industrial applications contating polypropylene functionalized with acrylic acid (PP-g-MA), functionalized Polyethylene with maleic anhydride (PE-g-MA), functionalized polypropylene with maleic anhydride (PP-g-MA) and also the ethylene-propylene rubber grafted maleic anhydride (EPR-g-MAH).

Figure 2 – Polymer Coating With Flame Retardant Properties In The Outer Layer Of Power Cables.

Figure 3. The Mechanism of Compatibilizer In A Polymer Matrix.

Figure (4) – Some Properties of Polymer Flame Retardant Compounds (HFFR).

This paper investigates the effect of polyethylene functionalized by maleic anhydride (PE-g-MA) as a compatibilizer in the PE/HFFR Filler blend to improve the mechanical properties of these blend by increasing the amount of connection between the filler and the polymer matrix.

Figure 5 – Diagram of Changes in The Elastic Modulus and Tensile Modulus Of PE/ HFFR Filler in The Presence Of PE-G-MA as A Compatibilizer At A Rate Of 10% By Weight [5].

As shown in Figure (5), the presence of the flame retardant filler, FR Filler, increases the elastic modulus (Young’s modulus) and decreases the tensile strength of the compound. Obviously, these changes are due to the presence of a polar filler increases the stiffness of the polymer compound and consequently, the amount of its elastic modulus increases significantly. It is also observed that the use of a suitable compatibilizer in the PE/Mg (OH) polymer blend has significantly increased the amount of elastic modulus and at the same time the tensile modulus has been relatively  increased. The reason for the significant improvement in the mechanical properties of the desired mixtures is due to the creation of interfacial interaction (at the interfacial boundary) of the two phases in the mixture, namely HFFR Filler particles in the PE polymer matrix. The presence of the coupling agent in this mixture, in addition to helping the homogeneous and uniform distribution of filler particles during the extrusion process, also prevents the agglomeration of the particles after the compounding process.

Figure 6 – Diagram Of Elongation At Break And Impact Resistance Of Blend Compatibilized With  PE-G-MA And Non- Compatibilized Compound [6].

As shown in Figure (6), the use of PE-g-MA as a coupling agent increases the amount of elongation at break and also significantly increases the impact strength. The reason for improving the mechanical properties, as described earlier, is due to the improved dispersion of magnesium hydroxide particles as a flame retardant additive in the polymer matrix (which in this case is the blend of polyethylene).

Aria Polymer Pishgam Company has presented its coupling agent  product based on functionalized linear low density polyethylene (LLDPE-g-MA), especially for use in HFFR compounds. For more information about this product and other related products, please contact the business unit of Aria Polymer Company.

Author: Ali Moshkriz

As an engineering polymer, polycarbonate (PC) is the hardest transparent material used in a wide range of polymer industries. This polymer can be used in various processes equipment such as injection molding and extrusion. In addition to transparency and according to polarity of PC, it also shows good paintability properties. The most important properties of polycarbonate are high chemical resistance, high impact and scratch resistance, high weather resistance, self-extinguishing and non-flammability, etc. Compared to polyolefins, these distinctive properties of polycarbonate have made this polymer a good candidate in various industries such as transportation, construction, production of safety glass, production of various electronic components and computer hardware equipment and compact discs, etc.

Figure (1) – High transparency of polycarbonate as another benefit in the production of different types.

One of the main problems of polycarbonate is its low impact strength, especially in recycled grades; Because in the industry, due to the high price of this polymer, there is usually a greater tendency to use its recycled grade, and due to the low mechanical properties of such grades, the need to use suitable impact modifiers are necessary. However, in some special grades, PC  has a good impact strength, which often has a low melt flow index (MFI), and as a result, due to the high viscosity of the melt, these grades are not suitable for the production of some polymer parts, especially in injection process. The most suitable method used to improve the impact strength of polycarbonate is to use impact modifiers with a core-shell structure for this polymer. Impact modifiers can include modified polymers and some suitable additives. It is worth mentioning that in some references, special chemical and polymerization processes are used in order to produce transparent polycarbonate with high impact strength.

Figure (2) – Some applications of polycarbonate in various industries.

If the desired mechanism to improve the impact properties of polycarbonate is done with elastomers or rubber toughening method, the dispersion of the droplets (dispersed phase) in the polymer matrix, should follow the pattern of the matrix-dispersed as shown in the figure below.

Figure (3) –homogeneous distribution of impact-modified particles dispersed in the polycarbonate matrix.

Figure (4) – Impact transfer mechanism of polycarbonate containing impact modifier.

Figure (5) – TEM images related to the dispersion of impact modifier particles in the PC matrix.

a) Sample modified with 5% impact modifier. b, c) Injected specimen containing 5% impact modifier.

As shown in Figure (5), the samples compounded by means of a double screw extruder has had a more uniform mixing and distribution than the ones produced by injection machine, and of course sample C has higher rheological and mechanical properties.

An analysis on properties of polycarbonate samples with different impact modifiers: 

PC containing different amounts of impact modifiers from 1 to 11% and also at different temperatures such as -25℃ and -50 ℃ has been studied in order to evaluate the effect of impact modifiers at different loading level in low or high temperature range.

Figure (6) – Investigation the effect of different impact modifiers (type A and B) at difference loading levels.

In the figure 6, the impact modification of polycarbonate using impact modifiers in different ratios and temperatures is investigated. As it is shown, at low temperatures (negative or zero temp), the impact strength of polycarbonate is weak, while at high temperatures (positive temp), its impact is higher. Increasing the percentage of impact modifier has a positive effect on PC impact strength. This point is important from the perspective that achieving the desired percentage of impact strength occurs at optimal value, and after this point the impact strength increases significantly.

Aria Polymer Pishgam Company has presented its impact modifier product based on functionalized thermoplastic elastomers, especially for use in recycled polycarbonates. The impact properties of recycled polycarbonate using Aria couple 1947 as an impact modifiers is examined in the following diagram.

For more information about this product and other related products, please contact the Sales Department of Aria Polymer Company.

Author:Ali Moshkriz

In the first part of the series, we got acquainted with ordinary polymer fibers; then, in the second part, we examined high-performance polymer fibers. In the third and final part, we introduce the methods of producing polymer fibers.

Properties required for fiber-forming polymers

Despite the wide range of natural and synthetic polymers, only a few can be used as useful fibers. This is because a polymer must meet certain requirements before it can be successfully and efficiently converted into a fibrous product. Some of these important requirements are:

• It must have long, linear and flexible chains.
• Side groups of its chains should be polar and small in size.
• It must be soluble in a common organic solvent or can be melted for extrusion.
• Chains must be able to orient or crystallize under tensile and shear flow conditions during the extrusion process.
• Molecular weight of it must be high enough to achieve proper mechanical and thermal stability, and at the same time low enough to dissolve or melt in extrusion process.

Suitable polymers for fiber production can be converted into fibers by melt spinning, solution spinning, gel spinning, liquid crystal and dispersion spinning. [1, 2]

In the following, we will examine each of these methods.

Methods of producing polymer fibers

1) Melt Spinning

This method is commonly used to make fibers from polyolefin, nylon and polyester. The melt spinning process involves melting and extruding the polymer through a spinneret (i.e., a die with capillary holes), followed by cooling and solidifying it to form filaments. The polymer used is usually in the form of granules or dry pellets. First, the material enters the extruder through a hopper. The extruder melts and transfers it to a metering pump which delivers molten polymer into the spinning chamber at a very controlled speed, then the polymer is pushed into the holes in the spinneret and passes through them into a filament. These filaments pass through a cooling chamber to solidify. The amount of cooling and solidification in cooling chamber is usually controlled by passage of air. In some cases, heated cells and liquid baths may also be used. During the solidification process, a take-up device is used to draw filaments and turn them into small diameters. In order to improve the physical structure and mechanical properties of resulting fibers, they are often transferred directly to tensile process.

Important and influential parameters in this process are:

• Shape of the hole, the dimensions and the number of spinneret
• Extrusion temperature
• Flow rate of the mass within each hole of spinneret
• Speed ​​of drawing
• Length of spinning path
• Cooling conditions

During spinning, these parameters must be carefully controlled to obtain the desired structure and characteristics for fibers. To understand how to control these parameters, we need to analyze the engineering of melt spinning process, which includes molten polymer flow, balance of forces and energies, and growth of molecular orientation and crystal structure. The great advantage of melt spinning is no requirement to treatment step, as no solvent is used. Another one is its very high production speed, which varies from a few hundred meters per minute to several thousand meters per minute. [1]

2) Solution Spinning

This method is used to produce fiber from polymers that do not form a stable melt, but can be dissolved in solvents. The two most important methods of spinning solution are dry and wet spinning. Dry spinning is commonly used for polymers that are soluble in volatile solvents, and wet spinning is often used for polymers that dissolve in non-volatile solvents or unstable heat.

2- a) Dry Spinning

Here, the solution is transferred to filament by a metering pump with controlled speed. Often for solvent recovery, filaments are placed in an enclosed drying tower. After leaving filaments, polymer solution comes in contact with a stream of hot inert gas (usually air) and the solvent evaporates. Hot gas carries all or most of solvent evaporated from solution and exits drying tower. During this process, polymer concentration in filaments increases and they become solid. Dry spinning (800-100 m / min) is faster than wet spinning and slower than melt spinning. Examples of products are dry-spinning, polyacrylic nitrile, polyvinyl chloride and cellulose acetate fibers. The solvents used in this method usually have a boiling point and low evaporation heat. Solvents should also be easily recoverable, non-toxic and non-explosive in terms of stable heat. Examples of these solvents include alcohols, acetone, ether, and tetrahydrofuran. For efficient evaporation and recovery of solvent, the drying gas is often heated (the inlet gas temperature varies from 100 to 250°C depending on the nature of polymer and solvent). If possible, concentrated polymer solutions are preferred to reduce the amount of solvent used. The range of polymer concentrations in dry spinning is usually between 15 and 40%. Figure 2 shows a schematic of this process. [1]

2-b) Wet Spinning

Figure 3 shows the process of wet spinning. First, spinneret is placed in a spinning bath that contains an anti-solvent (a liquid that is soluble in a polymer solution but cannot dissolve the polymer). During spinning, polymer solution is extruded from spinneret into the bath and is deposited to form solid filaments. Then, the solvent in solution is removed by anti-diffusion mechanism. There are many different designs of wet spinning systems; Spinning baths can be placed horizontally or vertically. In a vertical spinning bath, filaments can move up or down. In addition to the spinning bath shown in Figure 3, more coagulation baths may be needed to remove the solvent, and sometimes the next steps of production (e.g., traction, washing, drying, heat regulation) with the process. Tricyclic is combined. Wet spinning is often used to process polyacrylonitrile fibers, polyvinyl chloride, polyvinyl alcohol and cellulose. The concentration of polymer used in wet spraying varies from 5 to 30%, which is usually lower than dry spray. Compared to spinning and dry spinning molds, the spinning process has a much lower spinning speed (from 50 to 300 meters per minute). This is mainly because the filaments in the liquid baths withstand much greater tensile forces. [1]

3) Gel Spinning

Gel spinning, also known as dry-wet spinning, can be used to produce high-performance polymer fibers. There are several forms of this process. First, polymer solution is pumped into spinneret, which is located above the spinning bath, to create a short air gap. Extruded filaments pass through the air gap, which is similar to a dry spinning process, and then, like wet spinning, go into a spinning bath. This process allows the formation of gel filaments by reversible thermal coagulation. They have sufficient mechanical stability and are transferred into the oven to be stretched into high-performance fibers.

In melt and solution spinning processes, the tensile step is necessary to achieve high molecular orientation and good mechanical properties. However, the stretch in gel spinning process is unique and outstanding. In general, gel filaments still contain large amounts of solvent and form swollen networks that are attached to small crystalline regions (Figure 4). Such gel filaments are usually pulled under high temperature in the oven. Although pulling is also possible after complete removal of solvent, the presence of solvent during extraction can help facilitate movement of polymer chains and lead to a very high molecular orientation in fibers. (Figure 5)

Gel spinning makes it possible to produce high-performance fibers from polymers with flexible chains such as very high molecular weight polyethylene (UHMW-PE). Usually for formation of gel filaments, the concentration of solution is low, for example, 1-2% for UHMW-PE.

4) Liquid Crystal Spinning

High-performance fibers can also be obtained by liquid crystalline polymers. Liquid crystals are highly structured liquids with nematic, cholesteric, esmetic molecular arrangement (Figure 7). Liquid crystallization in polymers may be achieved by dissolving polymer in a solvent, such as lyotropic liquid crystal polymers, or by heating polymer to the top of glass transfer or melting temperature, such as thermotropic liquid crystal polymers. Liquid crystal polymer chains in the form of rods can create high-performance fibers, because these chains can easily be oriented in the longitudinal direction of fiber without bending. Figure 8 shows unusual dependence of viscosity concentration of lyotropic liquid crystal polymer solution. As polymer concentration increases, viscosity increases. However, after concentration reaches a critical value, viscosity decreases rapidly. This is because without regular distribution of chains, at low concentrations, the liquid crystal phase is not formed and polymer solution becomes isotropic. When concentration reaches a critical value, a liquid crystal phase is formed and the alignment of polymer chains reduces the resistance to flow, resulting in lower viscosity. For thermotropic liquid crystal polymers, the molten viscosity of polymer also decreases rapidly at the temperature at which the liquid crystal phase appears. While thermotropic liquid crystals can be converted to fiber by melt spinning, lyotropics can use a gel or wet spinning process, although both lyotropics and thermotropic can be converted into fibers, the most successful liquid crystal fibers in this field are based on lyotropic polymers. A prime example is polyphenyl terephthalate (PPTA) or Kevlar^®, first produced in 1972 by DuPont. Kevlar^® can be produced in a manner similar to gel spinning (Figure 9). However, unlike UHMW-PE fiber gel, in which low-concentration solutions are used, Kevlar^® is spun from concentrated solutions, for example, 20% PPTA in 80% sulfuric acid. In addition, molecular orientation above Kevlar^® is obtained directly from liquid crystal phase. [1]

5) Dispersion Spinning

Spinning is used to produce fibers from polymers that are not soluble and only melt at very high temperatures. For example, polytetrafluoroethylene (T_m=327°C) cannot be converted to fiber by usual melt or solution spinning. In order to form fibers, fine-grained PTFE particles are dispersed in a polymer aqueous solution (e.g., polyvinyl alcohol) and then fibers are made using dry or wet spinning to create homogeneous dispersion. After spinning process, polyethylene is heated to break down the polymer, and the PTFE particles are deposited on the fibers. [1]

6) Reaction Spinning

Reactive spinning of monomers or prepolymers can be used to form fibers from reactive starting materials. A good example of reactive spinning is the formation of Spandex^® fibers that are made using two types of prepolymers: one is flexible macro glycol and the other is rigid diisocyanate. Macro glycol is a long-chain polymer with hydroxyl groups at both ends. This part of Spandex^® macro glycol is flexible and responsible for its tensile properties. Diisocyanate is a shorter-chain polymer and isocyanate groups at both ends which is rigid and strong. During fiber formation process, two prepolymers, in solution, are mixed with some additives and transferred to spinneret. After leaving, filamnets are heated with presence of nitrogen and solvent, react with prepolymers, and form solid Spandex^® fibers. [1]

7) Electrospinning

The idea of ​​electrospinning is based on an external electric field that is used for fluids or melted polymer. This field leads to creation of an electric charge on the surface of polymer and overcomes surface tension, resulting in a rapid flow or jet production. This method is only valid for charged polymer solutions or melts with sufficient molecular interactions. In electrospinning, a small drop of loaded solution at the end of a capillary is transformed into a cone. At a critical voltage, as load increases, a stable jet is discharged from tip of the cone. Low molecular weight jet of liquid is broken down into tiny droplets, a phenomenon called electrical spraying, while a polymer solution does not break with sufficient chain overlap and fusion, but so-called flexural instability. This causes a whip-like movement between the tip of capillary and the ground. Figure 10 shows a schematic of the electrospinning process.

Non-woven mats produced in this way have a special surface with high porosity and small pores that typically produces fibers with a nanometer diameter to below the micrometer. It is very difficult to obtain fibers with a diameter range of less than 1000 nm from other common methods. Nanofibers obtained by electrospinning can be used for many applications such as purifiers, membranes, optics, vascular grafts, protective clothing, molecular molds and woven frames.

In this method, properties of fiber depend on uniformity of electric field, viscosity of polymer, strength of the electric field and distance between nozzle and collector. [2]

Sources

1. Xiangwu Zhang, Fundamentals of fiber science, DEStech Publications, Inc., 2014
2. S. Eichhorn, J.W. S. Hearle, M. Jaffe, T. Kikutani, Handbook of Textile Fibre Structure, Volume 1: Fundamentals and Manufactured Polymer Fibres, Woodhead Publishing Limited, 2009
3. https://www.ec21.com/product-details/Polyester-Staple-Fiber-Production-Line–8443999.html

Compiled by: Hamidreza Tayari

Fibers are part of our daily lives. Reflecting on their surroundings can understand their full impact on society, from everyday uses such as clothing and carpets to artificial grass, fiber-reinforced composites in sporting goods (rackets, golf clubs, etc.), boats, civil engineering, aerospace and military applications such as aircraft and rocket.
There are many different types of fibers; most of them have diameters greater than one micrometer, and they can be divided into polymer fibers and non-polymer fibers. Polymer fibers include synthetic polymer fibers and natural polymer fibers. Synthetic polymer fibers are made from polymers synthesized from raw materials, such as petroleum-based chemicals or petrochemicals. Generally, synthetic polymer fibers are created by forcing, usually through extrusion, polymers through small holes (called spinnerets) into air or other mediums to form filaments. Natural polymer fibers include those produced by plants and animals. They are typically biodegradable and can be classified as natural cellulose fibers and natural protein fibers. Non-polymer fibers are those that are not made from polymers, and include carbon, glass, ceramic, metal, and composite fibers, etc. [1]

We first define some terms commonly used in the field of fibrous materials. We should add that some of these definitions are expanded upon later in here . However, before one can define the term fiber, one needs to define the most important attribute of the fiber that serves to define a fiber, namely the fiber aspect ratio. The aspect ratio of a fiber is the ratio of its length to diameter (or thickness). A fiber can be defined as an elongated material having a more or less uniform diameter or thickness less than 250 µm and an aspect ratio greater than a hundred. This is an operational definition of fiber. This geometrical and useful definition of fiber applies to any material, and we can define other common terms related to fibers. These are in alphabetical order:

• Aspect ratio: The ratio of length to diameter of a fiber.
• Bicomponent fibers: A fiber made by spinning two compositions concurrently in each capillary of the spinneret.
• Continuous fibers: Continuous strands of fibers, generally, available as wound fiber spools.
• Cord: A relatively thick fibrous product made by twisting together two or more plies of yarn.
• Crimp: Waviness along the fiber length. Some natural fibers, e.g. wool, have a natural crimp. In synthetic polymeric fibers crimp can be introduced by passing the filament between rollers having teeth. Crimp can also be introduced by chemical means. This is done by controlling the coagulation of the filament to produce an asymmetrical cross-section.
• Denier: A unit of linear density. It is the weight in grams of 9000 m long yarn. This unit is commonly used in the US textile industry.
• Filament: Continuous fiber, i.e. fiber with aspect ratio approaching infinity.
• Monofilament: A large diameter continuous fiber, generally, with a diameter greater than 100 µm.
• Nonwovens: Randomly arranged fibers without making fiber yarns. Nonwovens can be formed by spunbonding, resin bonding, or needle punching. A planar sheet-like fabric is produced from fibers without going through the yarn spinning step. Chemical bonding and/or mechanical interlocking is achieved. Fibers (continuous or staple) are dispersed in a fluid (i.e. a liquid or air) and laid in a sheet-like planar form on a support and then chemically bonded or mechanically interlocked.
• Spinneret: A vessel with numerous shaped holes at the bottom through which a material in molten state is forced out in the form of fine filaments or threads.
• Spunbonding: Process of producing a bond between nonwoven fibers by heating the fibers to near their melting point.
• Staple fiber: Fibers having short, discrete lengths (10-400 mm long) that can be spun into a yarn are called staple fibers.
• Tenacity: A measure of fiber strength that is commonly used in the textile industry. Commonly, the units are gram-force per denier, gram-force per tex, or newtons per tex. It is a specific strength unit, i.e. there is a factor of density involved. Thus, although the tensile strength of glass fiber is more than double that of nylon fiber, both glass and nylon fiber have a tenacity of about 6 g/den. This is because the density of glass is about twice that of nylon.
• Tex: A unit of linear density. It is the weight in grams of 1000 m of yarn. Tex is commonly used in Europe. [2]

A wide range of polymers can be transformed into fibers (we will address this in later articles). These fibers have many important applications that make them simple to use in everyday and everyday applications to various industries and sophisticated and high-tech applications. The most important of these fibers are polyester, polyamide or nylon, polyolefin, acrylic, aramid and vinyl.
Polymer fibers are classified according to their performance into conventional and high performance fibers. In this article, we look at ordinary performance fibers and in the following article we look at high performance fibers.

1) Polyester Fibers

Polyester fibers, which mainly consist of polyethylene terephthalate (PET), make up a large volume of the world’s synthetic fiber industry products and somehow dominate the industry. These fibers are inexpensive and are easily obtained from petrochemical sources and have a good range of physical properties. They are durable, lightweight, easily paintable and resistant to wrinkles and have excellent washability. These fibers are used in both continuous and discrete fashion in textile and furniture fabrics, carpets, tires, car seat belts, filters, tents, sails and more.
Although the dominant polymer in these fibers is PET, other polyesters also have their place. Polybutylene terephthalate (PBT) and more recently polyethylene terephthalate (PTT) are used in carpet fibers due to their superior fiber resistance. [3]

Dacron was the first polyester introduced in 1953. It is a long chain polymer composed of 85% by weight an ester of dihydric alcohol and terephtalic acid.

2) Polyamide or Nylon Fibers

Due to their properties, these fibers are widely used in many fields and industries, especially the textile industry. We deal with each of these areas separately.

A) textiles

Nylon fibers have properties that make them one of the most popular synthetic fibers. These include high strength as a textile fiber; abrasion, luster, chemicals and oils resistance, water washability, dyeability in a wide range of colors, good elasticity and resilience, smooth, soft, long-lasting fabrics of filament yarns. Because of these properties of nylon fibers are widely used in clothing such as knitwear, socks, underwear, raincoat, ski clothing, windsurfing, swimming and cycling clothing, as well as for home furnishings such as furniture, Upholstery, rugs and curtains are used. A combination of excellent abrasion resistance, appearance and economic agents puts polyamide fibers in a great position in the carpet fibers market and it can be expected that these nylons will still be the most used fibers for carpets.

B) Industrial Applications

Excellent mechanical properties, fatigue resistance and good tensile strength are the reasons for the superiority of polyamide fibers for industrial applications and for use in truck and aircraft tires. Other uses of these fibers are upholstery fabrics, seat belts, parachutes, ropes, fishing line, nets, sleeping bags, tarpaulins, tents. In addition, high strength, toughness and wear resistance are key factors in the choice of polyamide fibers for a wide range of military applications.

C) Nonwovens

Nylon, like polyester fibers (PET), has a high melting point that works well at high temperatures. Nylon fiber is more sensitive to water than PET. In some cases it is used as a blend fiber because it has excellent tear strength. Overall, the resiliency and wrinkle recovery of a non-woven nylon product is not as good as PET fiber. Because of its toughness, nylon fibers are suitable for flooring.
Also used in Ni-H and Ni-Cd batteries as separators, synthetic suede, thermal insulation, special paper, automotive products, sportswear and conveyor belts.

3) Polyolefin Fibers (Polyethylene and Polypropylene)

With the exception of carbon, glass, metal and ceramic fibers, most natural or synthetic fibers in general commercial use are organic structures with a carbon-carbon chain backbone. Basically polyolefin polymers have high molecular mass, aliphatic and saturated hydrocarbons, some of which can be easily fused.

A typical polyolefin fiber density range is from 0.90 to 0.96 gr/cm³ and shows extremely low moisture regain. Polyolefin fibers, thus, are suitable choices for applications requiring aquatic buoyancy and negligible moisture regain, such as mooring ropes, oil spill booms, and fishing nets, etc.
Polyolefin fibers have good tensile properties, good abrasion resistance and excellent resistance to chemicals, mildew, micro-organisms, and insects. Polyolefin textile structures show good wicking action, high insulation and are comfortable to the skin, which are significant factors for active sportswear and protective clothing.

However, polyolefins have problematic properties for specific applications. For example, due to the low melting point, polyethylene C125-120 ° C and polypropylene C165-160 ° C cannot be used at high temperatures. These fibers are not usable on exterior surfaces; since polyolefins are susceptible to photosynthetic degradation, they have low resistance to dehydration at temperatures above 100 ° C, are difficult to dye and have limited shade of color. The olefins also have high flammability, low resilience, and stress-induced creep.

Use of polyolefin fibers in medical textiles

Polyolefin, PP in particular, exhibits excellent chemical resistance and chemical inertness. These properties are prerequisites for medical and surgical applications. Fibrous structures for medical applications also require a combination of strength, flexibility, and controlled moisture and air permeability. Materials for these applications can be classified into four specialized areas:

• non-implantable materials – wound dressing, bandages, plasters, etc.
• extracorporeal device – artificial kidney, liver and lung
• implantable materials – sutures, surgery meshes, vascular grafts, artificial joints, artificial ligaments
• healthcare/hygiene products – bedding, diaper, surgical gowns, wipes, etc.

For non-implantable material applications, knitted, woven or nonwoven polyethylene fabrics are used in wound contact areas and wound care products. In some orthopaedic bandages, woven or nonwoven fabrics made of polypropylene fibers are used. Knitted, woven, or nonwoven polypropylene fabrics can serve as reinforcements for plasters.
For implantable applications, non-bioabsorbable sutures are typically made of PP fibers by braiding. Surgery meshes, for example hernia meshes.

Healthcare/hygiene products are mainly based on PP nonwovens. The largest single fiber application for PP is nonwoven fabrics. There are three different types of nonwoven structures of PP for this application: spunbonded (SB), melt-blown (MB) and thermal-bonded carded webs. The latter is mainly used for diaper linings in a similar fashion to SB nonwovens. Disposable diaper and incontinence control applications are the largest single PP nonwoven fabrics market.

Hospital gowns, uniforms, and surgical gowns are mainly disposable because of the high cost of laundering and sterilization. Thus, PP nonwovens are ideal for this application. Many hospital garments are made of SMS PP nonwoven composites, in which the added barrier membranes are incorporated in the middle layer to prevent the passage of blood-borne pathogens or disease-causing microbes [16]. In addition, PP nonwovens are a major component of wipes and beddings used in healthcare facilities. Hollow PP fibers are used in mechanical lungs to remove carbon dioxide from patients’ blood and supply fresh blood.

Use of polyolefin fibers in filtration

A wide variety of industrial processes requires the separation of solids from
liquids (suspension) or gas (aerosol) for purifying products, saving energy raising process efficiency, recovering precious materials, and improving pollution control system, etc. For example, air filters are used for separating suspended solid particles (soot) or liquid droplets (aerosol) in air. Filter media fabric design must be based on the performance properties such as the length of service life, physical and chemical condition of the operation. The design criteria cannot be overemphasized because filter fabric failure during service could result in lost production cost, loss of product,
heavy maintenance cost and added environmental pollution. The fibrous filter media are fabricated in woven, knitted, nonwovens or their combinations to meet the performance criteria. Filtration mechanisms are: interception, inertial deposition, Brownian motion, electrostatic, and gravitational. One of the earliest applications for polyethylene yarns was in the production of industrial filtration fabrics. The range of properties offered by polyethylene is particularly suitable for this application, and PE fiber is being used increasingly for this purpose. The polyethylene yarns are used for industrial filtration fabrics owing to the following features:

• The high wet strength of PE fibers and PE fabrics are not weakened during the filtration of water solutions.
• The excellent resistance of polyethylene to a wide range of chemicals and solvents used for filtration of industrial liquids.
• The high abrasion resistance of polyethylene enables the fabrics to withstand considerable abrasion during filtration.
• Polyethylene is particularly good in cake release. Solid particles are built up into cakes between the layers of filters during the filtration of industrial liquids. These cakes are removed perhaps many times a day by opening the filter presses, and it is important that the solid material should come away cleanly and easily from the filter fabric.
• The complete resistance of polyethylene to attack by micro-organisms is of great value in many filtration applications, such as the filtration of sewage.
• Dimensional stability.
• Low cost. [5]

4) Acrylic Fibers

Most of the growth in the use of acrylic fibers is due to its replacement with wool. Acrylic has many of the desired properties of wool, yet it is superior in many areas where wool is deficient. Acrylic fibers such as wool are valuable because of their warmth, softness of hand, generous bulk and pile qualities, and ability to recover from stretching. Acrylics, meanwhile, are less expensive, more resistant to abrasion and chemical attack, and more stable toward degradation from light and heat. In addition, acrylics are not attacked by moths and biological agents and show very little of wool’s tendency to felt. [4]

Acrylics, in stiff competition with nylon, polyester and polyolefin, have penetrated only markets where they have a clear advantage in critical properties. For example, acrylics are clearly superior in resistance to sunlight. This makes continuous filament acrylics valuable in outdoor applications, such as convertible tops, tents, and awnings. Pigmented acrylics can be used in applications where maximum resistance to fading and loss of strength is needed. [4]

In applications such as awnings that require high flame resistance, modacrylic fibers are used. Acrylics with low comonomer content are highly resistant to chemical attack and thermal degradation. These properties make acrylics suitable for industrial filters and battery separators. [4]

In the general apparel market, acrylic and modacrylic fibers are used as artificial fur or fur-like fabrics. These fibers are made in coarse deniers with special cross sections and surface modifications (e.g., surface inclusions or roughening) to simulate natural animal hairs. Uniform fabrics and silky fabrics are also produced from continuous filament acrylic and modacrylic yarns. [4]

5) Vinyl Fibers

A) Polyvinyl Alcohol (PVA) or Vinylon Fibers

One of the characteristic properties of PVA fiber is its high affinity to water. Its strength, modulus and toughness are not much different from those of conventional fibers. However, the main weaknesses of vinylon fiber are that it is not thermoplastic and exhibits little elastic recovery, although it is superior in these areas to cotton and rayon.
In the industrial fields, the vinylon spun yarns prepared by the perlok spinning system are used for various purposes such as ropes, fishery materials, industrial sewing threads, bicycle tire cords, hoses (fire hose, braided hose), sheets, industrial heavy fabrics, agricultural materials, etc. The vinylon spun yarns prepared by cotton-spinning systems are used typically in the manufacture of sheets, tents, sporting goods, rubbery soled cloth shoes, coated fabrics with polyvinyl chloride, fertilizer bags, warp yarns of tatami mats, and so on.
The industrial uses of vinylon filament yarn include laver cultivating nets, conveyor belts, radial tire cords, sewing threads for tatami mats, canvas and duck, base cloths, reinforcing fibers, hoses and so on. Its new applications are in the field of civil engineering industry as reinforcing materials (geotextiles). [4]

B) Polyvinyl Choloride or Vinyon Fibers

The most characteristic property of PVC fiber is its non-flammability, which leads to its many applications. The PVC fiber is thermoplastic, highly resistant to water, and shows insulating properties to electricity and heat. Its disadvantages are its low softening temperature and low tenacity. [4]

Finally, the physical and mechanical properties of polymer fibers are presented in the table below:

Table 1. Physical and Mechanical Properties of Polymer Fibers

Sources

[1]. Xiangwu Zhang, Fundamentals of fiber science, DEStech Publications, Inc., 2014
[2]. K.K.Chawla, Fibrous Materials, Cambridge University Press, 2005
[3]. J. E. McIntyre, Synthetic fibres: Nylon, polyester, acrylic, polyolefin, Woodhead Publishing Limited, 2005
[4]. Menachem Levin, Handbook of Fiber Chemistry, Taylor & Francis Group, LLC, 2007
[5]. Samuel C. O. Ugbolue, Polyolefin Fibres, Industrial and medical applications, Woodhead Publishing Limited, 2009
[6]. https://www.researchgate.net/figure/World-fiber-production-distribution-FY2013-Fiber-Handbook_fig3_321906085
[7]. https://www.alibaba.com/product-detail/PET-bottles-recycled-polyester-staple-fiber_60287036235.html
[8]. https://zjhaili.en.alibaba.com/product/60633459443-803693685/333dtex_72f_Bright_Recycle_Polyester_Yarn_POY.html
[9]. https://www.geotextile-fabrics.com/products/geotextile-fabric/short-fiber-geotextile-fabric.html
[10]. http://www.str-ucture.com/en/what/construction-projects/reference/car-park-roofing-bochum-germany-2009/
[11]. https://ariapolymer.co/polymer-fibers-part-2-high-performance-fibers/
[12]. https://www.alibaba.com/product-detail/Nylon-triangle-fiber_268111882.html
[13]. http://syntechfibres.com/application-areas/
[14]. https://www.usbiodesign.com/biomedical-textile-specialties/general-surgery
[15]. https://4.imimg.com/data4/LV/JT/MY-598948/polypropylene-fibers-500×500.jpg
[16]. https://sc02.alicdn.com/kf/HTB1sltCdVGWBuNjy0Fbq6z4sXXaw/polyethylene-fibers-for-concrete.jpg_350x350.jpg
[17]. https://www.alibaba.com/product-detail/Stock-Lot-of-Loose-Acrylic-Fiber_50029846015.html
[18]. https://www.extremeterrain.com/bestop-trektop-nx-glide-softtop-blktwill-0717-2door-jeep.html#product_pics-0
[19]. https://www.amazon.com/Awntech-Maui-LX-Retractable-Projection-Burgundy/dp/B00GDLS24G
[20]. https://ariapolymer.co/polymer-fibers-part-1-introduction-and-common-fibers/
[21]. https://www.ebay.com/itm/Vintage-TISSAVEL-France-Pile-100-Acrylic-Faux-Fur-Jacket-Women-s-Medium-/264365038428
[22]. https://apexnewsroom.com/global-polyvinyl-alcohol-fiber-vinylon-fiber-market-xiangwei-ningxia-dadi-stw-minifibers/4565/
[23]. https://www.ecplaza.net/products/pvc-fibre-reinforced-hose_373193
[24]. https://teletype.in/@meera/SJu3VlesS

Compiled by: Hamidreza Tayari

Key words: polymer fiber, polyester, acrylic, polyolefin, vinyl, vinylon, vinyon, polyamide, nylon, synthetic fiber, man-made fiber

In the first part of the article Blow Molding and its types of processes were introduced. In other words, blow molding is the forming of a parison, which is embedded in the mold, by blowing air, and is performed by three extrusion, injection and injection stretch.
In the second part, we first discuss the plastics that are suitable for this type of molding, and then discuss the advantages and disadvantages of it.

Choosing the Right Plastic for Blow Molding Process

What features does a plastic need to be suitable for this type of molding?

To answer this question, we first need to know the two concepts of thermoplastic and thermoset. Polymers are divided into thermoplastic and thermosets, based on their type of heat behaviour. Thermoplastics are types that soften, melt, and return to solid state if they are cold (this can be done repeatedly), if they are heated. But in thermosets due to heat, a chemical reaction occurs that causes cross-links between the polymer chains and the hardened material to lose their ability to melt and thus their processability. That is why thermoplastics are used in plastic molding processes, such as blow molding, injection molding, compression molding, and so on. For example, nylon, polycarbonate, polyethylene, polypropylene and polybutylene, are thermoplastic and epoxy, polyimide and alkyd, are thermoset.

Figure 1. thermoplastic and thermoset polymer [4]

Among the large family of thermoplastics, polyolefins, due to their properties, are used in a variety of molding processes, including injection molding, sheet extrusion, coating extrusion, and in particular blow molding. The advantages of polyolefin resins include their processability, toughness and good chemical resistance, light weight and relatively lower price than other plastics. In addition, the basic properties of polyolefins can be converted to a wide range of desired properties. These materials can be extruded with various other polymers. For example, ethylene vinyl alcohol (EVOH) and nylon are used to produce multilayer containers with gas permeability. Polyolefins used in blow molding are LDPE, LLDPE, MDPE, HDPE, ethylene copolymer such as ethylene vinyl acetate (EVA), polypropylene and propylene copolymer. [2]

The major areas of application of polyolefins in the blow molding process are as follows:

• Food packaging, detergents, cosmetics and personal care
• Vehicle parts, such as fuel tank, oil bottle, air duct and seat
• Consumer products, such as toys, home appliances and sports goods

To answer this question, we will examine the concept of grade.

Grade

Plastics are classified by type of application by grade. In fact, grade shows what properties a plastic has and what it’s good for. For example, Table 1 shows the differences between the properties and application of several grades of polyethylene:

Table 1. Difference between properties and applications of somme grades of high density polyethylene [2]

The physical and mechanical properties of some grades of high density polyethylene and polypropylene are also presented in the following two tables.

Table 2. Physical and mechanical properties of different high density polyethylene grades [2]

Table 3. Physical and mechanical properties of different polypropylene grades [3]

Figure 6. Application of different grades of polypropylene [9]

Advantages and Disadvantages of Blow Molding

Blow molding like other forms of plastic molding, has its own advantages and disadvantages. some of which have been briefly mentioned in the previous article. The following table examines this in more detail:

Table 4. Advantages and disadvantages of blow molding processes [1]

Sources

1. Samuel L.Belcher, practical guide to injection blow molding, CRC publication, 2007
2. http://v1.petrochem-ir.net/en/product/polymers?page=hdpe.htm
3. http://www.jppc.ir/
4. https://qph.fs.quoracdn.net/main-qimg-4985d7dfe92871d093accbcd60477942
5.https://www.prnewswire.com/news-releases/santa-barbara-additive-manufacturing-company-alt-llc-announces-upcoming-indiegogo-campaign-recycled-3d-printing-filament-from-everyday-plastic-waste-300375308.html
6.https://www.alibaba.com/product-detail/L501-virgin-hdpe-plastic-granules-pellets_62043686813.html spm=a2700.7724857.main07.33.3e531f9e92BLXT
8. https://shoraimandiri.wordpress.com/
9. http://chemical.milliken.com/blog-posts/reduce-reuse-recycle-the-core-of-milliken-s-sustainability-and-innovation

Compiled by: Hamidreza Tayari

Blow molding is one of the most economical and fastest processes of manufacturing plastic products used to produce various types of plastics including polyethylene, polyethylene terephthalate, polyvinyl chloride, polypropylene, polycarbonate, nylon and many more. A wide range of products, contains fuel tanks, bottles, pots and toys, are made using this process.

In simple terms, blow molding is a thermoplastic molding process of parison (molten tube) in which the parison or preform is placed in a mold cavity and pressured air is blown in it to take the shape of the mold. Blow molding processes are divided into three categories: extrusion, injection and injection stretch. Below we explain them.

Extrusion Blow Molding (EBM)

Extrusion is the simplest and most common blow molding process. In this process, the molten plastic first is extruded, then after closing the molds, compressed air is injected through the top, causing it to swell and to form the mold. Finally, after the mold has cooled enough, it opens and the part is removed. The important thing to note here is that before removing the part, the extra parts are removed or so-called polished.

Injection Blow Molding (IBM)

In this process the preformance is first made by the injection molding, placed in another mold, and then compressed air is blown into it, and finally removed. Most thermoplastics can be made by injection molding process. In the early use of this method mainly crystalline polystyrene was used in the packaging of non-prescription headache drugs due to its good transparency. Nowadays, other resins such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), high-density polyethylene, low-density polyethylene, polysulfone, polycarbonate, acetal, nylon, acrylic, polyamide and many more are used to make components by this process. [3]

Injection Stretch Blow Molding (ISBM)

This process is exactly the same as the injection blow molding process, with the preform being slightly heated and stretched in the longitudinal and radial direction before blowing the air and forming the final piece. In fact, this will stretch and orient the amorphous polymer chains, resulting in a different type of crystallinity. The chains are aligned, and apply a linear arrangement throughout the stress region. This expanded chain, or “stress-induced crystallization”, gives the product mechanical strength. [1]

Injection stretchblow molding was identified by the introduction of non-alcoholic beverage bottles. The thermoplastics used in this process include polyethylene terephthalate (PET), polyvinyl chloride (PVC), acrylonitrile-methyl acrylate copolymer (Barex®), polypropylene, crystalline polystyrene and polyamide (nylon). PET, meanwhile, is characterized by its high transparency, good strength, the ability to apply color additives, the availability and acceptance of the packaging industry (from cosmetics packaging to beverages, pharmaceuticals and so on), has the most use and application. [3]

The most widely used injection molding and injection stretchmolding processes are in the production of various types of bottles (usually PET), such as detergent, carbonated beverage, sauce, cosmetic, shampoo, pharmaceutical product, personal care, car wax, spice, honey, beer, vinegar, syrup, soft and still mineral water, tea (hot fill), milk, edible oil, fruit juice (with pulps and fibers), and many more. [2]

The important issue in this regard is acetaldehyde. Acetaldehyde is a natural sweetener found in all citrus fruits and is often used in beverages. It is a by-product of PET production and its importance in the PET industry is related to the production of water bottles. Of course it is harmless to the consumer, but should be kept in a very low level and controlled so that it does not taste. For this reason, in some cases, oriented polypropylene (OPP) is used for production of bottles of water, pharmaceuticals, household cleaners and hot fill beverages (up to 90°C). OPP, unlike PET, does not produce any acetaldehyde. It has significant weaknesses, as compared to PET, such as much weaker impermeability to O₂ and CO₂ gases, lower stress-strain strength, and a longer injection molding cycle, which increases the cost of production. [1]

Table 1. Properties of polymers suitable for ISBM

Sources

[1]. Ottmar Brandau, Stretch Blow Molding, second edition, Elsevier Inc., 2012
[2]. https://www.sipasolutions.com/en/catalog/bottle-production-systems/ecs-fx-integrated-systems#13_ppp_description_count
[4]. https://www.oberk.com/packaging-crash-course/what-is-extrusion-blow-molding
[3]. https://connectusfund.org/11-advantages-and-disadvantages-of-blow-moulding
[5]. https://www.milacron.com/mblog/2018/02/28/what-is-blow-molding/
[6]. http://nebula.wsimg.com/1041c53bcca959a5f721af7c3fd51ada?AccessKeyId=566BD8E34B7EC1CB5AFE&disposition=0&alloworigin=1
[7]. https://ariapolymer.co/blow-molding/
[8]. https://www.indiamart.com/proddetail/extrusion-blow-moulding-machine-11911192773.html
[9]. https://ariapolymer.co/blow-molding/
[10]. https://www.powerjet-machinery.com/injection-blow-molding-machine/
[11]. https://robinsonpackaging.com/wp-content/uploads/2016/02/infographic-stretch-blow-moulding.jpg
[12]. https://www.directindustry.com/prod/nissei-asb-machine-co-ltd/product-74412-1433739.html
[13]. https://www.myplasticmold.com/blow-molding

compiled by: Hamidreza Tayari

Using compatibilizers is a common approach to intensify the effect of reinforcing fillers such as glass fiber in plastic (esp. PE or PP) compounds to improve the properties. But how?

Polypropylene is an important polymer in plastic industry. Recently it has been applied in many applications such as electronic, construction and automotive products due to its proper process characteristics, high chemical stability and electrical insulation. However low mechanical and thermal properties of PP can cause limitation to be used in some applications. Numerous researches have been done to increase the mechanical properties of PP by adding reinforcing fillers. Among the reinforcing materials, glass fiber has an important position to enhance the mechanical strength of PP. This approach can be completed by using compatibilizer in compounds by eliminating the poor interfacial adhesion between components.

But which compatibilizer can be used in PP/GF more effectively? The simple comparison between the common compatibilizers, SEBS-g-MA, POE-g-MA or PP-g-MA, has been reviewed in this article. The impact strength and tensile strength are considered as criteria for mechanical properties.

1.PP-g-MA or SEBS-g-MA?

Based on Fig.1, the opposite effect is resulted by comparing the tensile and impact strength of PP/SGF in different amounts of compatibilizers. The results show that the addition of a PP-g-MA and SEBS-g-MA improves the impact strength with different intense. However the SEBS-g-MA has negative effect on tensile strength of the PP/GF compounds due to the nature of the SEBS as a thermoplastic elastomer. Thus the PP-g-MA in optimum content is more effective than SEBS-g-MA in mechanical strength since it has no rubbery manner and also better compatibility in PP/GF compounds.

2- PP-g-MA or POE-g-MA?

Based on Fig.2, both compatibilizers are effective in enhancing the impact properties. However, unlike the PP-g-MA, POE-g-MA increases the impact strength with drastic reduction in the tensile strength.  Similarly, the PP-g-MA in optimum content is more effective than POE-g-MAH with the same reason.

Therefore, it seems that PP-g-MA is a good option to be applied as compatibilizer or coupling agent in PP/GF compounds. The PP-g-MA is able to make covalent bonds with function groups of GF and also leads to strong interphase due to its compatibility with matrix. Chemical reaction between PP-g-MA and GF is shown in Fig.3. This compatibility at the interphase can absorb the energy and show well impact resistance. Also the resulted interphase improve toughness without sacrificing rigidity and stability of their shape.

Thus PP/PP-g-MAH/GF can be very useful compounds using in automotive and electronic parts. Aria Polymer company is manufacturer of various compatibilizers applying in engineering plastic such as filled PE or PP compounds like PP/GF. For more information, contact us by ariapolymer.co.