Division of plastics

BRIEF CHARACTERISTICS OF INDIVIDUAL PLASTICS

POLYETHYLENE

We distinguish the following types of PE:

• LDPE - low density (0.915 - 0.935 g/cm³)

• LLDPE - linear low density

• mLLDPE - linear low density, produced using metallocene catalysts

• HDPE - linear high density (0.442 - 0.465 g/cm³)

• HDHMWPE - high molecular PE

• HDUHMWPE - ultra high molecular PE

Semicrystalline plastic, soft and flexible. The properties are dependent on the polymerization method, which affects molecular density, structure and crystallinity.

Generally, PE has low absorbency, very good chemical resistance (resistant to acids, alkalis, alcohols, gasoline, up to 60 °C, resistant to all organic solvents).

It swells under the action of aliphatic and aromatic hydrocarbons, but surfactants induce stress corrosion. Good stress corrosion resistance is shown by LLDPE, while for other types, low density and low melt index give better corrosion resistance.

PE has low UV radiation resistance. UV stabilization for higher durability is necessary.

It is highly flammable, physiologically harmless; properties can be modified by copolymerization.

The influence of structure on the PE properties is given in the following table:

	Density (g/cm3) 0.410 - 0.470		The shape of the molecular chains of expansions -> linear.		The length of the molecular chain low -> high
Degree of crystallinity	L/H	H	L	H	L	H
Processability	H	L	H	L	H	L
Fluidity	No effect		No effect	H	L
Tensile and bending strength	L	H	L	H	L	H
Stiffness and hardness	L	H	L	H	No effect
Corrosion resistance	L/H	L/H	L/H	L/H	L	H
Heat resistance	L	H	L	H	L	H
Resistance to low temperatures	L	H	L	H	L	H
Chemical resistance	L	H	L	H	L	H
Transparency	H	L	H	L	No effect

L = low
H = high

POLYETHYLENES - COPOLYMERS

a) EVA - ethylene - vinyl acetate (with 9-40% content)
It is a flexible polymer; the flexibility increases with the increasing VA content, so does the transparency and ductility. It is suitable as a replacement for PVC.

b) IM - ionomers
They are not crystalline; they have good ductility and transparency in the area of use (-40 to 40 °C)
The chemical resistance is lower than in conventional PE types (for example, they are not resistant to oxidizing acids, alcohols, acetones and chlorinated hydrocarbons). The weather resistance is weaker; the stress corrosion resistance is very good.

POLYPROPYLENE – PP

Compared to PE, it is harder, glossier and can withstand higher temperatures, but is more brittle at low temperatures below 0 °C. Stiffness and strength lie between the values of PE and some structural plastics (PA, ABS). The permeability to gases and vapors is low, but CO₂ and chlorinated hydrocarbons are permeable. Chemically, it is very resistant, up to 120°C it resists salt solutions, strong alcohols and acids; strong oxidizing acids and chlorinated hydrocarbons attack it. PP breaks down oxygen.

Although the out-door exposure resistance is better than in PE, UV stabilization is necessary. The PP transparency can be increased by the addition of nucleophilic reagents that increase the crystalline share.

Copolymerization with ethylene (PPC) increases some physical and mechanical properties, especially impact and notch toughness at low temperatures.

PP-CR (with controlled rheology), high flow index, use for weak-walled PP-R parts, the so-called random copolymers, they have good transparency, use for packaging in food industry, cosmetics, etc.

POLYSTYRENE – PS

STANDARD PS

Amorphous plastic, clear, hard, brittle, high surface gloss. The heat resistance is low; short-term resistance max. 90 °C. Due to its low moisture content, it has very good insulating properties.

The chemical resistance is low. Resists alkalis, non-oxidizing acids, salt solutions; does not resist esters, aromatic and chlorinated hydrocarbons. Gasoline, chemical oils and aromatic substances induce stress corrosion.

PS is not suitable for outdoor applications and is not used for filling with fillers and stiffening additives.

HIGH IMPACT POLYSTYRENE S/B (also called HIPS)

Removes the brittleness of PS by copolymerization with butadiene. It has higher impact strength even at lower temperatures. Also, the stress corrosion resistance is higher. It is not transparent and has reduced weather resistance.

STYRENE-ACRYLONITRILE / SAN COPOLYMER

Hard, brittle (higher impact strength compared to PS), transparent, good optical properties, absorbency is higher than in PS. Since it does not contain butadiene, it has a higher UV radiation resistance than HIPS and ABS.

By substituting α-methylstyrene for styrene, types with a higher glass transition temperature can be obtained (with resulting higher heat resistance and impact strength).

ACRYLONITRILE-BUTADIENE-STYRENE / ABS TERPOLYMER

Unlike PS, it is tough, rigid, with higher chemical resistance. It is not harmful to health and has low absorbency. As there is a considerable number of different types of ABS, the variability of properties is also considerable.

ABS is also used for the following blends: PC/ABS, PBT/ABS, M/ABS, ABS/PA

ACRYLONITRILE-STYRENE-ACRYLATE / ASA

Unlike the ABS material, the butadiene component in ASA is replaced with acrylate rubber, which improves the weather resistance as this component is less sensitive to UV radiation and oxygen in outdoor applications. The ASA material is used alone or as a blend - PC/ASA and PBT/ASA.

MABS - METHYL METHACRYLATE / STYRENE - BUTADIENE / ABS

This combination allows this material to have good transparency, high impact strength, higher heat resistance and also better weather resistance than ABS

POLYMETHYL METHACRYLATE - PMMA

It is brittle, rigid, has a high E-modulus, excellent surface hardness, excellent optical properties (refractive index). It has good ageing resistance even without UV stabilization.

Resists weak acids and alkaline oils, fats and non-polar solvents. Strong acids and alkalis attack it, as do chlorinated hydrocarbons. It is not resistant to stress corrosion.

Copolymers are mainly used to increase hot shape stability, impact strength and stress corrosion resistance. (A/MMA) MBS (methyl methacrylate-butadiene-styrene) copolymer is used to increase impact strength at low temperatures.

POLYACETATE, POLYOXYMETHYLENE - POM

It is a partially crystalline material, either in the form of a homopolymer or a copolymer (the latter exhibiting higher alkali resistance and heat resistance). The copolymer has higher heat resistance, better aging resistance, higher thermal stability in processing.

It is one of the plastics with the highest stiffness and strength values and has good dimensional stability. It has good heat resistance and also resistance to low temperatures (up to -40 °C). Due to its excellent abrasion resistance and high surface hardness, it is used for the production of sliding components.

Strong acids and oxidizing agents attack it; the resistance to all solvents is excellent. It is not resistant to ageing; UV stabilization is required.

Various modifications are possible, e.g. to reduce friction (modification with graphite, MoS₂, Teflon, silicone).

POLYAMID - PA

Basic types of PA: PA 6, PA 66, PA 6/66, PA 610 (612), PA 46, PA 11, PA 12

PAT (transparent), PPA (polyphthalamide).

It is characterized by hardness and brittleness in dry state, toughness in wet state. The wettability and absorbency are the highest of the commonly processed plastics (the maximum absorbency in PA 6 is up to 10 % while the minimum absorbency in PA 11 is 2 %). The wettability and absorbency are determined by the PA structure, which also applies to physical and mechanical properties, for PA6 it is 2.8 %, for PA 66 it is 2.5 % of the moisture content at 50% relative humidity / 23C

PAs with a strong polar character (containing CONH groups, e.g. PA 6.6) have higher E-modulus, heat resistance, ductility. PAs with an increasing proportion of groups – CH₂ (e.g. PA6) exhibit higher wettability and E-modulus.

The PA crystallinity is dependent on the cooling rate of injection in the tool and ranges from 10 % (fast cooling  fine structure) to 60 % (slow cooling, larger spherulites, higher E-modulus, higher strength, high abrasion resistance). Thus, the tool temperature is a very important factor in PA affecting the properties of injections.

Unlike other plastics, PA does not have a sharp melting point, so it does not affect the flow into the tool by increasing the melt temperature.

PA resists most chemicals well (chlorinated hydrocarbons, alkalis, aromatic hydrocarbons, gasoline, etc.), but does not resist strong alcoholic solutions and strong acids. Some natural substances (tea, coffee, fruit juices) color PA. UV stabilization is required for prolonged exposure to higher temperatures.

PA 6.6

From the special types of PA and copolymers, it is necessary to highlight the following:

PA 46 - has the highest heat resistance of the PA series
PA 6-T- transparent PA - has a low wettability compared to PA 6 and PA 6.6. They have low shrinking, good workability.
PAMXD6 - containing 30-60 % of glass, has the highest strength and stiffness of the PA series, has good heat resistance.

Plus the following blends:

- PA 66/PA6, PA 66/6 (copolyamides)
- PA 6/PA 12
- PA 6 + polyolefins (PP, PE)
- PA 66 + polyolefins (PP, PE)
- PA / TPE
- PA / ABS
- PA / PPE

POLYBUTYLENE TEREPHTHALATE - PBT

Partly crystalline plastic, opaque thermoplastic. It has excellent strength and stiffness (but slightly lower than PETP), good ductility at low temperatures, excellent sliding properties and abrasion resistance, high hot shape stability (especially in glass-reinforced types).

It has minimal absorbency and is therefore suitable for electrical engineering. Chemical resistance is good; it resists weak acids and alkalis, alcohols, chlorinated hydrocarbons, gasoline, solvents, but does not resist strong acids, alkalis and ketones. It has good resistance to hot water.

Blends: PBT/ASA, PBT/ABS, PBT/PC, PBT/PET

POLYETHYLENE TEREPHTHALATE - PET

Amorphous, transparent thermoplastic. Most applications in packaging, PET bottles, foils, fibers

POLYPHENYLENOXIDE (modified PS) - PPO (also polyphenylene ether) / PPE

It is a compound polymer; it is tough, rigid, excellent dimensional stability, good heat resistance (short term up to 130 °C), excellent electrical insulation properties (but not against creeping currents). Due to its PS content, it exhibits susceptibility to stress corrosion. The chemical resistance is good; does not resist halogen hydrocarbons, gasoline.

Blends: PPE+PE, PPE+PA, PPE+SB

POLYCARBONATE - PC

It is clear, rigid, highly tough (at temperatures of 150 °C to 135 °C) with high surface gloss, good weather resistance, very good electrical insulation properties that are not affected by moisture.

The chemical resistance is lower; it does not resist strong acids, gasoline and alkalis; some substances cause stress corrosion (5% caustic soda, tetrachloride, n-propanol). PC can be sterilized; it is self-extinguishing.

However, the given excellent properties of PC are conditioned by optimum processing technology. It is absolutely necessary to process PC with a humidity of max. 0.02 %; it is necessary to observe the melt temperatures, holding pressure and especially the tool temperature, because PC is very susceptible to stress corrosion. An admixture of 10-40% short fibreglass increases corrosion resistance.

PC-HT - polycarbonate with increased temperature resistance.

Blends: PC/ABS, PC/ASA, PC/PBT, PC/PET, PC/PEI

THERMOPLASTIC ELASTOMERS - TPE

a) TPE-O

Polyolefin modified EPDM, hardness range 40 Sh A to 50 Sh D

b) TPE-S

SEBS (styrene-ethylene-butylene-styrene)
SBS (styrene-butadiene-styrene)
Hardness range 42 Sh A to 94 Sh A. Not hydroscopic.

c) TPE-U (thermoplastic polyurethane)

Hardness range 80 Sh A to 98 Sh A, 30 Sh D to 95 Sh D.

d) TPE-E

Thermoplastic elastomer based on polyether ester and polyester, with increased heat resistance.
Hardness range 40 Sh A to 74 Sh D

e) TPE-A

Polyether block amide composed of rigid polyamide segments and flexible polyether segments.
Hardness range 75 Sh A to 90 Sh A, 25 Sh D to 63 Sh D.

HIGH–TECH POLYMERS

POLYESTERCARBONATE - FURNACE

It is PC/aromatic terephthalate that is characterized by high heat resistance compared to polycarbonate (according to VICAT, 159 °C to 182 °C). Furthermore, the material has very good impact resistance and can be modified with flame retardants including glass filling. It is most often used in automotive as parts for headlights and other applications where good heat resistance is required.

POLYETERIMD – PEI

It has high resistance at high temperatures and electrical breakdown load, good electrical properties, excellent flame resistance, chemical resistance. High injection pressures (up to 2,000 bar) and temperatures (up to 425 °C) are required for processing.

POLYETHERSULPHONE - PES

Amorphous, transparent, high heat resistant thermoplastic. It is available unfilled as well as filled with fibreglass.

POLYSULPHONE - PSU

Amorphous, transparent thermoplastic with very good heat resistance but lower than PES. Also available as filled with fibreglass; needs to be dried below 0.05 %; UV radiation resistance is insufficient; additional stabilization is required; melt processing temperatures app. 350-390 °C, good hydrolysis and hot steam resistance, chemical and gamma radiation resistance, good electrical and dielectric properties. Used for car parts and also in medicine. These properties for PSUs can also be used in the case of PES.

POLYPHENYLENE SULFIDE - PPS

It is a partially crystalline polymer, suitable for injection and extrusion, and can also be filled with glass and carbon fibers or minerals. It is highly crystalline, has excellent heat resistance (up to 300 °C in the short term). It has excellent chemical resistance (at low temperatures, it resists basically all solvents, only at elevated temperatures it swells. Oxidizing agents and concentrated nitric and sulfuric acid attack it. UV stabilization must be used against the effects of light. When filled with carbon fibers, surface resistance of 10² – 10³ Ώ, excellent electrical and insulation and self-extinguishing properties can be achieved, must be dried before processing because it is humid. Used in lighting technology and electrical applications and car parts.

POLYPHENYLENESULFONE - PPSU

Amorphous, transparent thermoplastic, formerly known as polyarylsulfone. It has exceptionally good impact and notch toughness, excellent hydrolysis resistance, chemical resistance, permanent thermal load app. 207 °C, must be dried (at 150 °C for 3 hours) before processing, melt temperature app. 380 °C, mold temperature app. 150 °C, processing by injection, extrusion and vacuum forming.

POLYIMIDE - PI

It has excellent heat resistance, but processing is very difficult; pressing and sintering are used. It is a linear aromatic polyimide. Products are usually made by machining from blanks or by pressing. The material has a wide heat resistance range from -271 °C to +290 °C.

POLYAMIDEIMIDE - PAI

Aromatic, amorphous thermoplastic suitable for processing by both injection and extrusion. It has excellent oxidation and chemical resistance, also excellent electrical properties, resistance to burning without the use of retardant, permanent heat resistance up to 220 °C. It is also available with the content of 30% GF or carbon fibers including PTFE modification. Mainly used in electrical engineering and demanding automotive applications.

POLYETHERIMIDE - PEI

Aromatic, amorphous thermoplastic, transparent - yellow-brown color; can be processed by both injection and extrusion technology. Material with excellent physical and mechanical properties (resistance to creep under load at high temperatures), non-flammability (only fluoroplastics have higher non-flammability).

The chemical resistance is very good; it is soluble only in methylene chloride or trichloroethylene. It has low stress corrosion. Excellent resistance to hydrolysis. Wettability app. 1 %; it is necessary to dry to a level below 0.05 %. Materials can be unfilled, but also including fillers, such as fibreglass, carbon fiber. Demanding processing, melt temperature about 400°C and mold temperature app. 140 °C. Used for lamp reflector parts and in other applications requiring excellent temperature resistance.

POLYETHERKETONE - PEK

Linear aromatic thermoplastic, semi-crystalline, excellent mechanical properties that can be maintained up to 330 °C, high chemical resistance, permanent use temperature up to 260 °C, also possible with V0 flame retardant design, melt temperature app. 400 °C, mold temperature app. 190 °C. Used in aviation and cosmonautics.

POLYETHERETHERKETONE - PEEK

Semi-crystalline thermoplastic, containing aromatic polyketone; due to its properties, it is suitable for modification with fillers such as fibreglass or carbon fibers, PTFE, graphite, MoS ₂; for modification with carbon fibers or fibreglass, it is possible to achieve high modulus of flexibility and permanent heat resistance above 300 °C; excellent chemical resistance including very good electrical properties and exceptional abrasion resistance, which is useful for applications such as bearing housings or in medical applications. It is often supplied in the PTFE+MoS₂ modification or as a PEEK/PEI blend.

POLYARYLETHERKETONE - PEKEKK

Semi-crystalline thermoplastic is usually supplied in modification with fibreglass and carbon fibers, especially for applications where there is a risk of explosion (mines, gas plants), because when filled with carbon fibers, a surface resistance at the level of 10⁵ – 10³ Ώ is achieved. The melt temperature is above 400 °C and the mold temperature app. 200 °C. The material can also be used for extrusion. It is used for similar applications as PEEK. The material can also be supplied in a flame retardant design.

The problem is the processing, where the melt temperature is 370-430 °C and the tool temperature is up to 150 °C.

POLYBENZIMIDAZOLES - PBI

A material with excellent temperature resistance, mainly used for fibers, e.g. flame retardant overalls, braking parachutes, astronaut cabins.

ALIPHATIC POLYKETONE - PK

A semi-crystalline plastic, whose properties are classified among PA and POM. Low wettability; it is also supplied filled with fibreglass (30 %), good chemical resistance including resistance to hydrolysis, for filled GF 30%, HDT/A is - 215 °C; it is sensitive to UV radiation, therefore not suitable for outdoor applications. Processing temperatures of 240-270 °C.

LC POLYMERS – LCP

Polymers with liquid crystal structure (Liquid - Cristal - Polymer), semi-crystalline thermoplastic. In practice, mainly liquid-crystalline polymers based on aromatic polyesters are used. LC polymers are characterized by high fluidity, strongly influenced by the melt temperature. The long-term temperature of use is in the range of 210-240 °C while the short-term is app. 300 °C. They have a high heat resistance and is used in electrical and automotive industries; they are also supplied as glass or mineral filled. With a fibreglass content of 30 %, an E-modulus of up to app. 20,000 MPa is achieved. The shape stability of HDT/A is 260-290 °C, depending on the nature of the filling. The melt temperature is app. 360 °C; mold temperature app. 70-110 °C; drying to 0.01% of moisture must be provided before processing. They are also available as a PC/LCP blend. Mostly used in electrical engineering in the automotive industry for headlight parts, ignition systems, connector sockets, etc.

BIOPLASTICS

Currently, the focus is mainly on PLA-based biopolymers - polylactide or polyactic acid derived from sugarcane, corn, potatoes and other plants.

It is an affordable product, has excellent clarity, but on the other hand, low heat resistance and poor barrier properties.

PHA - polyhydroxyalkanoates - linear polyester.

It is produced by a selected strain of bacteria and stored as "fat" that is used for the production of polymers.

PHA has limited availability, is relatively expensive, but offers better properties than PLA, and is suitable for injection.

LONG FIBER FILLED POLYMERS / LVRT OR LFT

The most commonly used thermoplastic matrices are PP, PA, PC/ABS, PBT, POM, PPS, TPE-U.

Filler content up to 60 % of long fibreglass. Glass, carbon, aramid fiber is used as a fibrous filler.

It is a material that has the fastest growth in new applications, particularly in the automotive industry.

Compared to short fibreglass, increased mechanical properties, increased notch toughness and very good stability at higher temperatures are achieved.

POLYMER MIXES (blends)

They are widely used because they affect some of the negative properties of individual plastics. Blends are not mere arithmetic averages of the properties of the plastics used, but significantly increase many properties.

From the many blends used, we list the following:

• PP + EPDM (significant effect on the impact strength

• SAN + PSU

• ASA + PC (higher heat resistance than ASA)

• ABS + PA

• ABS + TPU

• ABS + PVC

• ABS + PC (higher toughness and stiffness than ABS)

• M + ABS

• PMMA + ABS (better stiffness and weather resistance than ABS)

• PMMA+ ASA (better weather resistance than PMMA/ABS)

• PA 6 and PA 6.6 (electrical insulating varnishes with good adhesion to metal, glass, wood)

• PC + ASA

• PC + PBT

• PC + PP

• PC + PMMA

• PPE + PA 6.6

• PBT/PET

• PBT/ASA

TABLE OF PROPERTIES OF SELECTED PLASTICS

The values relate to conditioned bodies

TABLE OF PROCESSING PROPERTIES