Compounding With Chlorinated[1]

8 Compoundingwith ChlorinatedPolyethylene

Ray Laakso

CONTENTS

8.1 Introduction.................................................................................................. 2898.2 Influence of CPE Chemical Structure.......................................................... 290

8.2.1 Saturated Backbone ......................................................................... 2908.2.2 Chlorine Content.............................................................................. 2908.2.3 Viscosity .......................................................................................... 290

8.3 Compounding with CPE.............................................................................. 2928.3.1 Introduction to Compounding ......................................................... 2928.3.2 Compounding Ingredients and Their Function ............................... 293

8.3.2.1 Choosing a CPE ............................................................... 2938.3.2.2 Curatives ........................................................................... 2958.3.2.3 Fillers, Plasticizers, Other Ingredients.............................. 295

8.4 End-Use Applications .................................................................................. 296References ............................................................................................................. 299

8.1 INTRODUCTION

Chlorinated polyethylene (CPE) is a synthetic elastomer produced by the controlledchlorination of polyethylene and has been in commercial production since the late1960s [1–3]. The properties of the CPE product are influenced by a number offactors, which include the molecular weight and molecular weight distribution(MWD) of the starting polyethylene, the chlorine content, and the chlorine distribu-tion. In addition, the chlorination process can be adjusted to produce amorphous, thatis, low- to noncrystalline products, or products that contain higher levels of residualpolyethylene crystallinity. A variety of different CPE grades can be produced in thismanner and thereby offer the compounder numerous opportunities to achieve a widerange of properties for different applications.

The purpose of this overview is to provide the compounder with a basicunderstanding of CPE, how the molecular parameters affect the end-use performancein the compound, and typical formulating techniques that can be used to meetvarious end-use requirements.

Robert C. Klingender/Handbook of Specialty Elastomers DK4127_C008 Final Proof page 289 26.9.2007 2:42pm Compositor Name: BMani

289

8.2 INFLUENCE OF CPE CHEMICAL STRUCTURE

8.2.1 SATURATED BACKBONE

A generalized chemical structure for CPE is shown (Figure 8.1). The ASTM D1418designation for CPE is ‘‘CM’’ where ‘‘C’’ denotes ‘‘chloro’’ and ‘‘M’’ denotes ‘‘asaturated chain of the polymethylene type.’’ CPE and CM are often used interchange-ably in the industry. In this chapter, the term CPE is used.

The saturated backbone of CPE imparts outstanding ozone-, oxidative-, andheat-resistance to a compound’s performance [4]. The inherent nature of the polymerbackbone allows compounds of CPE to be formulated that meet stringent high heatrequirements, for example, up to 1508C for certain automotive applications and 1058Cfor various wire and cable applications using a peroxide cure system [5]. CPE typicallyprovides better heat-aging resistance than polymers containing backbone unsaturation,for example, natural rubber and polychloroprene (CR) (Figure 8.2).

8.2.2 CHLORINE CONTENT

Typical commercial grades of CPE contain from 25 to 42 wt% chlorine (Table 8.1).The addition of chlorine to the backbone creates polarity in the polymer structurethat imparts oil- and chemical-resistance to the polymer and subsequently to thecompounded material. In addition, the chlorine on the backbone can help provideinherent flame retardance by providing a halogen source in a fire situation [6]. This isoften advantageous for the compounder, for example, it may not be necessary to adda costly halogen-containing flame-retardant additive to the formulation if the recipeincludes a CPE that contains a sufficiently high level of chlorine. However, as thecompounder knows, to obtain one property, another is often sacrificed. In the case ofchlorine content, it is necessary to balance the flame-retardant properties with thelow-temperature performance (Figure 8.3).

8.2.3 VISCOSITY

The molecular weight of the polyethylene feedstock plays a key role in determiningthe viscosity of the CPE product. Higher molecular weight feedstocks, that is, thosewith low melt index (I2) values, yield CPE resins with higher Mooney Viscosityvalues. For a given polyethylene I2, other parameters directly affect viscosity, forexample, MWD and comonomer type. The use of broader or narrower MWDpolyethylene resins coupled perhaps with a copolymer of ethylene with, for example,butene, hexene, or octene, can provide a wide range of CPE viscosities. In addition,the chlorine content of the CPE resin can also affect the viscosity of the CPE. For agiven polyethylene feedstock, the CPE viscosity increases with chlorine content.

—CH2—CH—CH2—CH2—CH2—

Cl

—

FIGURE 8.1 Generalized chemical structure of CPE (~36 wt% chlorine).


290 Handbook of Specialty Elastomers

°C °F

H 250 482

G 225 437

F 200 392

E 175 347

D 150 302

C 125 257

B 100 212

A 70 158

Type

No Req. 170 120 100 80 60 40 20 10A B C D E F G H K

Class

Fluoroelastomer

Fluorosilicone

Polyacrylate

EpichlorohydrinNitrileCRButyl

EPDM

CPECSM

Silicone

Styrene butadieneNatural rubber

Increasing heat resistance

Increasing oil resistance

Ethyleneoctene

FIGURE 8.2 Heat and oil resistance of various elastomers (ASTM 2000=SAE J-200Classification).

TABLE 8.1Typical Commercial Grades of CPE for Elastomer Applications

Product

ChlorineContent,a

wt%Crystallinity

Hfa, J=g

Mooney Viscositya

(ML1 1 4 at 1218C),Mooney Units

SpecificGravity Key Properties

TYRINTM CM 0136 36 <2 80 1.16 General purposeelastomer grade

TYRINTM CM 0836 36 <2 94 1.16 General purposeelastomer=highmolecular weight

TYRINTM CM 566 36 <2 80 1.16 Low electrolytegrade

TYRINTM CM 0730 30 <2 65 1.14 Best balance of

low and hightemperatureperformance

TYRINTM 3611P 36 <2 30 1.16 Good for viscosity

modificationTYRINTM 4211P 42 <2 42 1.22 Higher chlorine

viscosity

modification

Note: TM is the Trademark of The Dow Chemical Company. Other product grades are available. Contact thepolymer producers for additional product information. The Dow Chemical Company is the only North

American producer of chlorinated polyethylene. Other producers of chlorinated polyethylene includeShowa Denko (Japan), Osaka Soda (Japan), and Weifang (China).

a Reported values represent typical measurements.


Compounding with Chlorinated Polyethylene 291

Manufacturers of CPE have the ability to use several variables to produce a range ofCPE viscosities for the compounder to use (Table 8.1).

8.3 COMPOUNDING WITH CPE

8.3.1 INTRODUCTION TO COMPOUNDING

CPE, likemost elastomers, needs to be properly ‘‘compounded’’ or ‘‘formulated’’ tomeetthe product performance requirements for any given application. The process of selectingtypes and levels of compounding ingredients can involve a complex combination offactors for the CPE compounder developing a formulation. Factors to consider include:

1. CPE Polymer type. Viscosity. Chlorine content. Residual crystallinity. Additives

2. Performance requirements. Original and aged physical properties. Processing. Electrical properties (where applicable). Applicable standards, for example, automotive, wire and cable

3. Thermoset or thermoplastic application4. Safety

. Environmental issues

. Industrial hygiene issues5. Compounding ingredients

. Black or colorable compound

. Cure system

. Proper selection to meet necessary performance requirements6. Total cost of producing the final article

The consideration of these factors (and others) in the development of a suitablecompound for a particular application can be a difficult task. The effects of various

Increasing chlorine content

Increasingperformance

property

Oil-, solvent-, andflame-resistance

Low-temperatureflexibility

FIGURE 8.3 Effect of increasing chlorine content on various properties.



compounding ingredients on physical properties can usually be easily measured inthe laboratory, but conducting trials at the production level is a critical step of thecompound development process. The production trial reveals factors that may nothave been predicted in the lab, for example, property differences due to scale-up in alarger extruder. The compounder can make modifications and refinements to thecompound based on information from the factory experience.

General references on the subject of ‘‘compounding’’ elastomers can be found inthe literature and usually cover a broad range of polymers [7–9]. In this section, thecompounder is provided with information on factors to be considered in developing aCPE recipe for typical applications. Specific starting-point formulations for variousapplications are included later in this report and in the literature [10].

8.3.2 COMPOUNDING INGREDIENTS AND THEIR FUNCTION

The list of ingredients available to the compounder is quite impressive and cansometimes be overwhelming [11]. Most CPE formulations contain one or moreingredients from each of the following categories:

1. CPE2. Fillers3. Acid acceptors4. Colorants5. Plasticizers6. Flame retardants7. Antioxidants8. Processing aids9. Curatives

10. Coagents

A summary of several of the generic compounding ingredients and their function isincluded (Table 8.2). As noted, certain ingredients are specific to the cure system thatis used. Undesirable chemical reactions can interfere with the curing mechanisms oreven with the stability of the base polymer. For example, zinc-containing com-pounds, for instance, zinc oxide, should be avoided in all CPE compounds. Zincoxide can cause dehydrochlorination of the CPE (regardless of the type of curesystem) resulting in degradation of the polymer structure and a subsequent reductionin physical property performance. In addition, small quantities of zinc can adverselyaffect the cure mechanism in thiadiazole-cured compounds. The CPE manufacturershould be contacted for additional information on interactions=potential interactionsof various compounding ingredients.

8.3.2.1 Choosing a CPE

The initial step in developing a CPE recipe typically involves the selection of theproper base polymer. Some of the most important variables to consider in a CPEproduct are viscosity, chlorine content, and degree of residual crystallinity.



8.3.2.1.1 CPE ViscosityThe viscosity of CPE is typically influenced by a combination of the molecularweight of the starting polyethylene and the level of chlorine added to the polyethy-lene. The combination of these factors contributes to the viscosity of the CPE, asmeasured by such tests as Mooney viscosity or capillary rheology. In general, theviscosity of CPE is controlled by the combination of the polyethylene feedstockmolecular weight and the amount of chlorine added to the polyethylene backbone.However, other factors can affect the viscosity such as the MWD of the polyethy-lene, additives in the final CPE product, and the presence of residual crystallinity.

When developing a new formulation, the compounder may be uncertain aboutwhich viscosity to choose in the initial formulations. A good starting-point for mostgeneral purpose, thermoset CPE compounds is an amorphous product, that is,essentially no residual crystallinity, with a Mooney viscosity (ML1þ 4 at 1218C)of around 75–80 and a chlorine content of 36 wt%. This starting-point CPE productgenerally provides a compound with suitable physicals and good processability.However, the compounder can evaluate the mechanical properties and processabilitycharacteristics to determine if a CPE product with higher or lower viscosity is neededto fulfill the desired application requirements. Blends of different CPE grades canbe used to provide additional processability or physical property advantages. CPEis also compatible with a variety of other elastomers and thereby provides anadditional method of tailoring the processability and physical property characteristicsin polymer blends.

8.3.2.1.2 Chlorine ContentThe chlorine content of commercial grades of CPE typically ranges from 25 to 42wt% chlorine. The chlorine content of the resin is an important choice for thecompounder. CPE resins with ~36% chlorine are most commonly used for thermoset

TABLE 8.2Compounding Ingredients and Their Function

Function Ingredienta

Acid acceptor Magnesium oxide, magnesium hydroxide, calcium hydroxide,epoxy compounds, lead compounds

Coagents or accelerators Allylic, methacrylate

Colorant Carbon black, titanium dioxide, organic pigmentsFiller Carbon black, mineralFlame retardant Antimony oxide, hydrated alumina, halogenated hydrocarbonsPlasticizers Petroleum oils (aromatic and napthenic), esters, chlorinated paraffins,

polymeric polyestersProcessing aids Waxes, stearic acid, low molecular weight polyethylene, EPDM, EVAVulcanizing (curing) agents Peroxide, thiadiazole, electron beam

Antioxidants Variety of oxidative stabilizers are suitable

a Some ingredients are cure-system specific.



elastomeric applications. This level of chlorine in the CPE typically provides avulcanizate that possesses a good balance of chemical and oil resistance, flameretardance, low-temperature performance, processability, and good response to aperoxide cure system. If additional flame-, chemical-, or oil-resistance is desired, itmay be necessary to use a CPE with higher chlorine content, for example, a 42%chlorine product. To achieve a balance between oil-, chemical-, and flame-resistanceand good low- and high-temperature performance, 30% chlorine content amorphousCPE can provide a vulcanizate with suitable performance. CPE resins with evenlower chlorine content (25% chlorine) are also available. Usually, the 25% chlorinegrades contain residual polyethylene crystallinity that improves the compatibilitywhen blended with other polymers such as polyethylene.

8.3.2.1.3 Residual CrystallinityThe parameters in the CPE production process allow the producer to tailor-make thedesired degree of residual crystallinity in the final product. For thermoplastic applica-tions of CPE or for applications requiring higher degrees of compatibility with anotherpolymer such as polyethylene, it is often desirable to use a CPE that contains someportion of the original high-temperature crystallinity (melting point ~1258C–1308C) ofthe polyethylene. This crystallinity imparts stiffness to the CPE and thereby yields ahigher modulus material. The resultant ‘‘polyethylene-type’’ characteristics in thesesemicrystalline CPE products can be used to good advantage when one blends theresin with high-ethylene content polymers to improve compatibilization.

Most CPE products are designed to be amorphous, that is, they contain essen-tially no residual crystallinity from the high-temperature portion of the polyethylene.This yields an elastomer with more rubbery qualities and the resultant products finduse in a wider variety of applications than do the semi-crystalline CPE products.

8.3.2.2 Curatives

Cure agents for CPE compounds are typically based on (1) peroxide cure systemswith coagents; (2) thiadiazole-based chemistries; or (3) irradiation cross-linkingtechniques [12,13]. The choice of cure system depends upon a number of factorssuch as compound cost, processing equipment, and curing equipment.

Peroxide cures are preferred when extra scorch safety, shelf-life, or bin stability,low-permanent set, and high-temperature performance are desired. Thiadiazole cureprovides the ability to cure over a wider range of temperature and pressure conditionswhile generating fewer volatile by-products than do peroxide cures. Irradiation-curable compounds are usually formulated in a similar manner to the peroxide-curablecompounds except that no peroxide is necessary.

8.3.2.3 Fillers, Plasticizers, Other Ingredients

Fillers are used in CPE compounds for the same reasons they are used in most rubbercompounds—fillers provide a means of obtaining a good balance between thenecessary physical property characteristics and the economic requirements of theend-use article. The fillers used with CPE are common to the rubber industry: carbonblack and mineral fillers (clay, whiting, talc, silica, etc.).



A variety of plasticizers are compatible with CPE. The most commonly usedplasticizers include the ester-types. The type of plasticizer that can be used is oftendependent upon the cure system. For example, aromatic plasticizers typically are notused in peroxide-cured recipes (due to hydrogen abstraction of the aromatic protons),whereas the aromatic plasticizers can be used effectively with the thiadiazole-curedcompounds.

The final recipe usually includes a stabilizer, such as MgO or some similar acidacceptor. Other common rubber compounding ingredients are usually added to meetthe physical property and processing requirements of the compound.

8.4 END-USE APPLICATIONS

Starting-point formulations for CPE compounds are available from polymer produ-cers and the open literature [10]. End-use elastomeric applications for CPE are wide-ranging, for example, Wire and Cable, Automotive, Industrial, and General Rubbermarkets. CPE is also widely used in the Impact Modification market segment toimprove the performance of vinyl siding and other vinyl-related products [14].

To aid the user in understanding typical CPE elastomer formulations, examplesfrom different market segments are included (Tables 8.3 through 8.5). A widerange of performance can be achieved using CPE elastomers. The compounder isencouraged to explore the possibilities available with CPE: Oil Resistance, OzoneResistance, Weatherability, Oil and Chemical Resistance, Heat-Aging Resistance,Low-Temperature Flexibility, Processability, Blend Additive, and more.

TABLE 8.3Typical CPE ‘‘HPN Heater Cord’’ Jacket (908C Rating)

Ingredient phr

TYRINTM CM 0136 100Calcium carbonate 50Diisononyl phthalate 25

Amino silane-functionalized hydrated aluminum silicate 60Magnesium oxide 5Polymerized 1,2-dihydro 2,2,4-trimethylquinoline 0.2

a, a0-Bis-(tert-butylperoxy)-diisopropylbenzenedispersed on clay (40% active)

5

85% Antimony oxide on CM binder 6

Trimethylolpropane trimethacrylate 5Total phr 256.2

Specific gravity 1.55

Stock properties

Mooney scorch MSþ 1 at 1218C (ASTM D1646) CPE CompoundMinimum viscosity, Mooney units 30.1

t3 (time to 3-unit rise), minutes >25t5 (time to 5-unit rise), minutes >25



TABLE 8.3 (Continued)Typical CPE ‘‘HPN Heater Cord’’ Jacket (908C Rating)

Ingredient

ODR at 2048C, 0.051 rad, 1.66 Hz, microdie, 6 min (ASTM D2084)

Minimum torque, ML, dN-m 12.2Maximum torque, MH, dN-m 64.1Delta torque, dN-m 55.3

Time to 90% Cure (t90), minutes 1.8

Vulcanizate properties

1.16 mm Insulation on 14 AWG aluminum wireCured 2 min in 1.72 MPa gauge steam

Original stress–strain properties UL 62, 2.5 specification CPE compoundStress at 100% elongation, MPa 4.9Stress at 200% elongation, MPa 9.0

Tensile strength at break, MPa 8.2 minimum 15.8Elongation at break, % 200 minimum 402Air-oven aged 10 days=1108C

Tensile retention, % 50 minimum 105Elongation retention, % 50 minimum 85IRM 902 Oil immersion 18 h at 1218CTensile retention, % 60 minimum 97

Elongation retention, % 60 minimum 78

Note: TM is the trademark of The Dow Chemical Company.

TABLE 8.4Moisture, Flame-Resistant, Lead-Free, Heavy Duty Cable Jacket (908C)

Ingredient phr

TYRINTM CM 566 100

Carbon black N550 5Calcined and surface modified clay 60Dioctyl adipate 15

Dow epoxy resin (D.E.R.TM 331) 5Thiodiethylene bis-(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate 1.5a,a0-Bis-(tert-butylperoxy)-diisopropylbenzenedispersed on clay (40% active)

5

85% Antimony oxide on CM binder 780% Decabromodiphenyl oxide on CM binder 15Trimethylolpropane trimethacrylate 5

Total phr=specific gravity 218.5=1.45

(continued )



TABLE 8.4 (Continued)Moisture, Flame-Resistant, Lead-Free, Heavy Duty Cable Jacket (908C)

Ingredient phr

Stock properties

Mooney scorch MS þ 1 at 1218C (ASTM D1646) CPE compoundMinimum viscosity, Mooney units 26.3t3 (time to 3-unit rise), minutes >25

t5 (time to 5-unit rise), minutes >25


Minimum torque, ML, dN-m 11.1Maximum torque, MH, dN-m 57.3

Delta torque, dN-m 46.2Time to 90% cure (t90), minutes 1.9


1.16 mm Insulation on 14 AWG aluminum wire

Cured 2 min in 1.72 MPa gauge steamOriginal stress–strain properties ICEA S-68–516

4.4.11, ICEA

S-19–81 4.13.11specification

CPE compound

Stress at 100% elongation, MPa 4.1Stress at 200% elongation, MPa 3.45 minimum 8.8

Tensile strength at break, MPa 12.4 minimum 17.4Elongation at break, % 300 minimum 522Air-oven aged 7 days=1008C

Tensile retention, % 85 minimum 103Elongation retention, % 55–65 minimum 83IRM 902 Oil immersion 18 h at 1218C

Tensile retention, % 60 minimum 70Elongation retention, % 60 minimum 81

Note: TM is the trademarks of The Dow Chemical Company.

TABLE 8.5CPE Molded Goods Compound

Ingredient phr

TYRINTM CM 0136 100Carbon black N550 50

Silica 10Trioctyl trimellitate (TOTM) 35Thiadiazole curative 3

Amine accelerator for thiadiazole cure 1Magnesium hydroxide 5



REFERENCES

1. U.S. Patent 3,454,544, Process for the Chlorination of Polyolefins, Issued July 8, 1969 toDow Chemical U.S.A.

2. U.S. Patent 3,429,865, Chlorinated Polyethylene Compositions, Issued February 25,1969 to Dow Chemical U.S.A.

3. U.S. Patent 3,563,974, Linear Polyethylene Chlorination, Issued February 16, 1971 toDow Chemical U.S.A.

TABLE 8.5 (Continued)CPE Molded Goods Compound

Ingredient phr

Styrenated diphenylamines antioxidant 1Hindered phenolic antioxidant=metal deactivator 1Total phr 206

Specific gravity 1.28

Compound properties

Mooney scorch MS þ 1 at 1218C (ASTM D1646)

Minimum viscosity, Mooney units 38t3 (time to 3-unit rise), minutes >25


Minimum torque, ML, dN-m 12.5

Maximum torque, MH, dN-m 52.0Delta torque, dN-m 39.5Time to 90% cure (t90), minutes 13.0


Original stress–strain properties(Cured 20 min at 1608C)

CPE

Stress at 100% elongation, MPa 3.8

Stress at 200% elongation, MPa 7.6Ultimate tensile, MPa 18.0Elongation, % 530

Hardness, shore A 78Die C Tear, ppi at 238C 302Die C Tear, ppi at 1608C 107Low-temperature brittleness, 8C �34

Compression set 22 h=1008C, % 26Ozone resistance, cured 5 min at 1828C72 h at 408C, 100 pphm ozone, 55% humidity Pass—no cracks

Aged in air oven 70 h at 1508CTensile change, % �9Elongation change, % �48

Note: TM is the trademark of The Dow Chemical Company.



4. W.H. Davis, Jr., R.L. Laakso, Jr., L.B. Hutchinson, and S.L. Watson, Peroxide-CuredChlorinated Polyethylene Compounds Having Enhanced Resistance to Ozone-InducedCracking, American Chemical Society Rubber Division,May 29–June 1, 1990, Paper No. 8.

5. R.R. Blanchard, Compounding Chlorinated Polyethylene Elastomers for High TemperatureService, Advances in Synthetic Rubbers and Elastomers Science and Technology, Tech-nomic Publishing Co., Inc., 1973, pp. 1–13.

6. R.M. Aseeva and G.E. Zaikov, Combustion of Polymer Materials, Hanser Publishers,Munich Vienna, New York, 1985, pp. 214–219.

7. F.W. Barlow, Rubber Compounding, Second Edition, Marcel Dekker, Inc., New York,1993.

8. J.E. Mark, B. Erman, and F.R. Eirich, Science and Technology of Rubber, SecondEdition, Academic Press, Inc., San Diego, CA, 1994, Chapter 9.

9. M. Morton, Rubber Technology, Third Edition, Van Nostrand Reinhold, New York,1987.

10. P.A. Ciullo and N. Hewitt, The Rubber Formulary, Noyes Publications, Norwich, NewYork, 1999, pp. 579–597.

11. Rubber World Magazine’s Blue Book 2002, J.H. Lippincott, publisher, Lippincott &Peto Inc.

12. L.E. Sollberger and C.B. Carpenter, ‘‘Chlorinated Polyethylene Elastomers—A Compre-hensive Characterization,’’ presented at a meeting of the Rubber Division, AmericanChemical Society, Toronto, Canada, May 7–10, 1974.

13. J.H. Flynn and W.H. Davis, ‘‘Tyriny Brand CPE Thiadiazole Cure System Studies—Chemistry and Dispersion,’’ presented at a meeting of the Rubber Division, AmericanChemical Society, Los Angeles, California, April 23–26, 1985.

14. Polymeric Materials Encyclopedia, Volume 2=C, CRC Press, 1996, Editor-in-ChiefJ.C. Salamone, chapter on ‘‘Chlorinated Polyethylene,’’ G.R. Marchand.



Compounding With Chlorinated[1]

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