P h y s i c a l

a n d

S o m e

M e c h a n i c a l I m p o r t a n t

P r o p e r t i e s

o f

P o l y m e r s

P h i l l i p T. DeLassus, N i c o l e F. W h i t e m a n The Dow Chemical Company Freeport, TX 77541, USA

A. Introduction B. Narrative Descriptions 1. Multipurpose Polymers 2. Polyolefins and Barrier Polymers 3. Styrenics and Engineering Thermoplastics 4. Elastomers C. Properties of Commercial Polymers Table 1. Multipurpose Thermoplastics Table 2. Polyolefins and Barrier Polymers Table 3. Styrenics and Engineering Thermoplastics Table 4. Elastomers A.

V-159 V-159 V-159 V-160 V-160 V-161 V-162 V-162 V-164

ranges or subclassifications. Often the sources of data on polymer properties disagree. We have assumed that the disagreements were honest results of subtle differences in the polymer or the test. In some cases we report averages, in some cases we report the "best" value, and in other cases we report ranges. The reader is advised to refer to the specific product literature and to consult the technical service representatives of the suppliers. Standard or typical abbreviations for each polymer are also included.

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B.

INTRODUCTION

This section of Polymer Handbook focuses on critical polymers in the commercial world. The polymers were chosen because they already have a large economic impact or are likely to have an economic impact during the lifetime of this Handbook. Hundreds of polymers are the subjects of study and application in the world. Many of these have commercial status. However, including all of them would compromise the utility of this chapter. Properties for all the polymers of this section plus many others are included with more details in various chapters of this Handbook. Because of their cost and properties, polymers in this section often get first consideration for applications, or are the benchmarks against which alternative materials are compared. The data in the tables of this section can be used for rapid comparison against performance requirements. Brief narrative descriptions of the polymers are given in the next section. More complete descriptions can be found in other places; the Handbook of Plastic Materials and Technology (I. I. Rubin (Ed.), Wiley Interscience, 1990) is an excellent resource. A common set of properties are given in Section C. In many cases, the data are not available or are not relevant. In some cases, we have chosen to highlight a specific example of a family of polymers. However, in some cases, selecting a single member of a family did not represent the range of applications and properties available, so we included the

NARRATIVE DESCRIPTIONS

1. Multipurpose Polymers

Poly(ethylene terephthalate) (PET) This polymer is usually made by a two-step condensation polymerization of the dimethyl ester of terephthalic acid and ethylene glycol. Articles made with this polymer can be either semicrystalline or amorphous. Applications include fibers for carpeting and clothing, bottles (especially for soft drinks), and films for food packaging and magnetic tapes. Poly(ethylene terephthalate, 1,4~cyclohexane dimethanol) (PETG) This polymer substitutes enough 1,4-cyclohexane dimethanol for ethylene glycol in the backbone (to prohibit crystallization). Applications include food packaging and injection molded parts. Poly(vinyl chloride) (PVC) Applications for this polymer fall into two broad categories depending upon formulation. The name for this polymer is often freely abbreviated as "vinyl". Flexible poly(vinyl chloride) This type typically contains 30-40 wt.% additives, especially plasticizers, to lower the glass-transition temperature. Applications include hoses, films, flooring, and automotive interiors. Rigid poly (vinyl chloride) This glassy polymer is used for molding and profile extrusions with less additives. Typical applications include pipe, house siding, window frames, and bottles. Ethylene-methacrylic acid copolymers, partially neutralized with sodium or zinc (lonomer) The most important applications are for food packaging as films or sheets. They adhere to nylon in coextrusion, and they heat seal well.

Ethylene-acrylic acid copolymers (EAA) These adhesive copolymers typically have between 3 and 20wt.% acrylic acid. They are often used in extrusion coating to provide a heat seal layer for packaging, especially when good flavor/ aroma retention is needed. Ethylene-vinyl acetate copolymers (EVA) The range of compositions can be from 2-50 wt.% vinyl acetate. Tough, clear films are made with copolymers having low levels of vinyl acetate (2-7 wt.%). Hot melt adhesives are an application for higher levels of vinyl acetate (18-40 wt.%). Polytetrafluoroethylene (PTFE) This homopolymer of tetrafluoroethene has a wide range of valuable properties. Applications often rely on the very low surface energy (useful for non-stick coatings), the chemical resistance to many liquids (useful for gaskets and liners), and the wide range of service temperatures. Ethylene-styrene interpolymers (ESI) These copolymers exhibit a very wide range of properties depending on composition. At low levels of styrene, the copolymers are crystalline, flexible, thermoplastics. At intermediate levels of styrene, the copolymers are amorphous and highly elastomeric. At high levels of styrene, the copolymers have a mixture of glassy and rubbery properties with a glasstransition temperature ranging to above room temperature. Applications vary as widely as the properties, including new areas for thermoplastics. PolyOactic acid) (PLA) This compostible polymer is synthesized from renewable resources. The properties vary according to the composition (D- and L- conformations). Applications include food packaging as film or molded cups. 2. Polyolefins and Barrier Polymers

Polyethylene familyThe total usage of all members of this family is the greatest of all thermoplastics. Most members of the family are easy to fabricate and have low cost. The properties vary widely across the family. Food packaging is a frequent application. High density polyethylene (HDPE): This set of highly crystalline polymers is used in molding and film applications, with milk jugs being a prime example. These polymers are less flexible than other polyethylenes. Low density polyethylene (LDPE): This set of branched polymers is less crystalline than HDPE. Members are flexible and clear, with moderate toughness. Linear low density polyethylene (LLDPE): These are copolymers of ethylene with modest amounts of butene, hexene, or octene linear oc-olefins. Grades are available for films and for molding. Films typically show good toughness. Some grades are suitable for fibers. Very low density polyethylene or ultra-low density polyethylene (VLDPE or ULDPE): These are also copolymers of ethylene and linear a-olefins; however, they have densities less than 0.915 g/cm3. They have improved toughness and sealability compared to LLDPE. Polyolefin plastomer (POP): New catalyst technologies allow synthesis of these materials which include these with

lower densities. Copolymers over a wide range of composition yield a wide range of properties for films, fibers, and molding applications. Polypropylene (PP) Most applications use the isotactic form. Oriented (OPP) and unoriented films are used often for food packaging, sometimes in combination with vinylidene chloride copolymers. Polypropylene fibers are used for webbing in outdoor furniture, carpets, and both woven and non-woven fabrics. Polypropylene is also an important engineering thermoplastic. Vinylidene chloride copolymers (PVDC) This set of polymers includes resins for extrusion and molding, resins for solution coating, and latexes for coating. A variety of comonomers are used to achieve different properties. The barrier properties are important for food packaging. Typically, these polymers are used with other polymers such as polyethylene or polypropylene in multi-layer structures. Ethylene-vinyl alcohol copolymers (EVOH) These polymers are actually hydrolyzed copolymers of ethylene and vinyl acetate. They are excellent barriers to mass transport, especially when dry. They find applications in both flexible and rigid packaging for food, typically as part of a multi-layer structure. 3. Styrenics and Engineering Thermoplastics

Polystyrene family These inexpensive polymers span the range of engineering thermoplastics. They are easy to fabricate by either extrusion or molding. Typically, small amounts of additives are used, including extrusion aids, mold releases, FR agents, UV stabilizers, and plasticizers. General purpose polystyrene (GPPS): This homopolymer is transparent and glossy. It quickly sets after molding to give stiff parts. Polystyrene can be made into foam articles such as insulating board or cups, using extrusion techniques or by expanding beads. Other applications include food packaging and molded parts in appliances. High impact polystyrene (HIPS): This rubber-modified composite typically contains 1-10 wt.% rubber, generally polybutadiene, to give added toughness. It is also used in many applications including food packaging and molded parts. Styrene-Acrylonitrile copolymers (SAN): A typical copolymer has 70 wt.% styrene and 30 wt.% acrylonitrile. These clear polymers have excellent dimensional stability and long-term toughness. Furthermore they are resistant to a wide range of solvents. Rubber-modified styrene-acrylonitrile copolymers (ABS): This material has a continuous SAN phase with about 15 wt.% rubber modification, generally polybutadiene. In most applications, impact resistance is the reason for the selection of ABS. Applications include housings and covers for appliances and tools, plus a variety of automotive moldings. Syndiotactic polystyrene (SPS): This semi-crystalline polymer can be used at higher temperatures. Applica-

tions include molded parts that must maintain close tolerances. Polycarbonate (PC) This polymer is usually made in large scale by the condensation of phosgene and bisphenol A. It has great impact strength and excellent optical properties; hence, it is used for lenses, compact discs, glazing, instrument panels, and high-volume food services wares. It can be modified with reinforcing fibers, FR agents, and stabilizers. Development of new applications is intense. Nylon family These are polyamides resulting from the condensation reaction of an amine function and an acid function. As a family, they are tough and hard. They are resistant to many liquids and have low coefficients of thermal expansion. They can be reinforced with glass fibers, carbon, and minerals. Applications include molded parts for electrical power transmission, molded parts for a wide range of automotive functions, pulleys, bearings and items which need good abrasion resistance and toughness. Nylon 6: This homopolymer of caprolactam is in the middle of the range of nylons for toughness, hardness, and heat distortion. Nylon 6,6: This copolymer of hexamethylene diamine and adipic acid has the greatest hardness and highest resistance to heat deformation and lowest toughness of the nylon family. Polyfmethyl methacrylate) (PMMA) This important member of the acrylate family is often freely abbreviated "acrylate". It has moderate toughness and excellent optical properties. It is hard. Hence, applications include glazing, fibers for transporting light, instrument panels, and packaging. Polyoxymethylene (Acetal) Acetal resins are derived primarily from formaldehyde although copolymers are common. Endcapping is done to reduce the rate of degradation. These polymers are strong, tough, and stiff, and they have a low coefficient of friction against many materials. They are creep resistant and are extremely resistant to

fatigue. Applications are often based upon dimensional stability and solvent resistance. 4. Elastomers

Poly(organosiloxanes) (silicone polymers) Most silicone polymers are either homopolymers or copolymers of dimethylsiloxane. They have high flexibility over a wide range of temperatures. They "repel" water strongly. Membranes are an important application for elastomeric grades. Other applications include stopcock grease, car polishes, and anti-stick formulations. Chlorinated polyethylene (CPE) After a starting polyethylene has been chlorinated, the resulting material is typically 25-50 wt.% chlorine. The properties range from thermoplastic to elastomeric. Applications for CPE include automotive hoses, tubing, and wire jacketing plus extensive membranes for roofing. It can be an impact modifier for PVC. Polyolefin elastomers (POE) These copolymers of ethylene and an a-olefin are made with single-site catalysts. They have very low densities. Materials can be designed for a wide range of applications. Polyurethane elastomers (some TUP, thermoplastic polyurethane) These terpolymers can be used uncured for most applications; however, selected grades can be cross-linked to enhance properties. As a family these elastomers are tough and wear resistant. They have excellent chemical resistance and flexibility. They can have excellent clearity. Applications include cable jackets, Automotive fascia, connectors, fittings, and many, many more. Ethylene-Propylene-Diene Terpolymers (EPDM) These terpolymers typically contain a few percent of a diene such as hexadiene. This material is easy to fabricate and then is usually heat-treated at 125°C to 175°C to induce crosslinking. The physical properties are much different after crosslinking. Commonly, they are heavily formulated for applications which include wire jacketing systems, automotive hoses, and roof sheeting.

C.

PROPERTIES OF COMMERCIAL POLYMERS

TABLE 1. MULTIPURPOSE THERMOPLASTICS

PETfl

PETG

Rigid PVC

Flexible PVC*

1.4 Hoop-172 axial-69 Hoop-4275 axial-2206

1.27 50

1.39 55

1.18-1.70 5.5-26.2

1724

2800

4.8-12.4

D638 D638

2000 180

40-80

150-450

D256 D785

90 R105

Shore D 65-85

D648

63

Property

Unit

Test method

MECHANICAL Density Tensile strength

g/cm3 MPa

D792 D638

Tensile modulus

MPa

D638

Flexural modulus Elongation to break Notched Izod at room temp. Hardness

MPa % J/m

THERMAL 0 Deflection C T @ 264 psi 0 Deflection T @ 66 psi C 0 Vicat softening point C 0 UL temp. Index C UL flammability code rating Linear coefficient mm/mm/°C of thermal expansion ENVIRONMENTAL Water absorption 24 h Clarity

D648 D1525 UL746B UL94

79

D696

71 180

66-77 63-82

HB

V-O

Varies Varies Varies

9.1 x 10" 5

9-18 x 10~ 6

13-45 xlO" 6