WO1990007409A1

WO1990007409A1 - Extrudable thermoplastic pellet

Info

Publication number: WO1990007409A1
Application number: PCT/US1989/005750
Authority: WO
Inventors: Mark J. Hall; Duane F. Foye; Stephen R. Betso; Kun Sup Hyun; Steven R. Jenkins; Donald E. Kirkpatrick; Paul T. Louks; James A. Stevenson
Original assignee: The Dow Chemical Company
Priority date: 1988-12-23
Filing date: 1989-12-18
Publication date: 1990-07-12
Also published as: JPH04502478A; AU640627B2; AU4802190A; CA2006359A1

Abstract

The extrusion of a vinylidene chloride interpolymer pellets is improved by coating with at least one processing aid. Exemplary, processing aids are fatty acids, esters, fatty alcohols, fatty amides, metallic salts of fatty acids, olefin polymers and polyolefin waxes.

Description

EXTRUDABLE THERMOPLASTIC PELLET

The present invention relates to thermoplastic pellets having improved extrusion properties.

A variety of useful articles may be formed using thermally sensitive polymers, such as vinylidene chloride interpolymers. In the past, the practice generally was to extrude the vinylidene chloride interpolymer directly from the powder form in which it is recovered after polymerization. Because of the convenience of shipping and handling, it is desirable to form the vinylidene chloride interpolymer into pellets prior to final extrusion.

With the increased demand for pellets, the processing conditions to which pellets are exposed has become more demanding. When melt processed, conventional pellets of vinylidene chloride interpolymers have a tendency to generate particulate degradation products (i.e., carbonaceous material, gels, or fish eyes) in the extrudate, particularly when the vinylidene chloride interpolymer is exposed to relatively long residence times in the melt processing equipment. To control the generation of particulate degradation products during melt processing, processing aids such as lubricants (e.g., internal and external types), olefinic waxes and oils, and polyolefins have been blended with the vinylidene chloride interpolymer prior to fabrication into a pellet. However, it has been found that, after exposure to desirable processing temperatures, a certain lag time exists before the blended processing aids function effectively. It is 0 during this lag time in the melt processing equipment that the vinylidene chloride interpolymer is particularly susceptible to decomposition.

It is desirable to produce a pellet of a 5 vinylidene chloride interpolymer which is capable of being extruded without having an unacceptable level of products in the extrudate.

A first aspect of the invention is a pellet of 0 extrudable thermoplastic material comprising vinylidene chloride interpolymer, characterized in that, it is coated with at least one processing aid in an amount effective to improve the extrudability of the vinylidene _- chloride interpolymer.

A second aspect of the invention is a process for improving the extrudability of a pellet of thermoplastic material comprising vinylidene chloride, 0 which process comprises coating the pellet with at least one processing aid.

The inventors have discovered that making a pellet of a vinylidene chloride interpolymer having a -,_- processing aid coated on its surface, improves the extrudability of the vinylidene chloride interpolymer. The pellets of the present invention are considered to possess improved extrudability, i.e., less carbonaceous material contamination on the melt processing equipment, e.g., on an extruder screw heel; and a lower mechanical energy to extrude, i.e., amount of energy expended to extrude the interpolymer due to friction and the viscosity of the polymeric composition, than a pellet formed solely from vinylidene chloride interpolymer.

A large number of experiments were performed to determine the effect of the manner of preparing a pellet upon the extrudability of the resultant pellet. It was very surprisingly discovered that, at essentially constant concentration of ingredients within the final pellet to be extruded, a first pellet prepared by blending in all extrusion aids prior to pelletizing had significantly inferior extrudability to that of a second pellet prepared by coating the preformed pellet (i.e. after pelletizing) with at least one extrusion aid. Thus, in some instances, it appeared that the second pellets could be extruded for 50 times as long as the first pellets, prior to the onset of unacceptable extrudability requiring plant shut down and cleaning of the extrusion equipment.

For the purposes of this invention, it is understood that the term "vinylidene chloride interpolymer" encompasses homopolymers, copolymers, terpolymers, etc. of vinylidene chloride.

The vinylidene chloride may be copolymerized with another monoethylenically unsaturated monomer. Monoethylenically unsaturated comonomers suitable for copolymerization with vinylidene chloride include vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic -it-

acid, methacrylic acid, itaconic acid, acrylonitrile, and methacrylonitrile. The monoethylenically unsaturated comonomers are desirably selected from the group consisting of vinyl chloride, alkyl acrylates, and alkyl methacrylates; the alkyl acrylates and alkyl methacrylates having from about 1 to about 8 carbon atoms per alkyl group, preferably from about 1 to about 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates are most preferably selected from

10 the group consisting of methylacrylate, ethylacrylate, and methyl methacrylate.

The monomer mixture comprises a vinylidene chloride monomer generally in the range of from about 60

15 to about 99 weight percent and the monoethylenically unsaturated comonomer in an amount of from about 40 to about 1 weight percent, said weight percents being based on total weight of the vinylidene chloride interpolymer.

20 The preferred ranges are dependent upon the monoethylenically unsaturated comonomer copolymerized therewith, each are well-known to one skilled in the art.

-j- ^' Methods of forming the vinylidene chloride interpolymers suitable for use in the present invention are well-known in the prior art. The vinylidene chloride interpolymer is generally formed through an emulsion or suspension polymerization process.

30 Exemplary of such processes are U.S. Patents 2,558,728;

3,007,903; 3,642,743; and 3,879,359; and the methods described by R. A. Wessling, in Polyvinylidene Chloride,

Gordon and Breach Science Publishers, New York, 1977,

Chapter 3. 35 Beneficially, in the extrusion of the vinylidene chloride interpolymers, it is frequently advantageous and beneficial to incorporate additives well-known to those skilled in the art. Exemplary of additives which may be incorporated in the package are light stabilizers such as hindered phenol derivatives; pigments such as titanium dioxide and the like, plasticizers, lubricants, extrusion aids and the like. Each of these additives is known and several types of each are commercially available. The additives may be incorporated by methods such as conventional melt blending and dry blending techniques.

Methods of forming the polymeric composition into pellets are well-known to those skilled in the art. Any method capable of forming the polymeric composition into pellets is suitable for use in the present invention. For the purposes of this invention, the terms "pellet" or "pellets" refer to particles having a minimum cross-sectional dimension of at^* least 1/32 inch (0.8 mm), preferably of at least 1/16 inch (-1.6 mm), and most preferably of at least 1/8 inch (3.2 mm); said pellets suitably have a maximum cross-sectional dimension of at least 1/2 inch (13 mm), beneficially of at least 3/8 inch (10 mm), and preferably of at least 1/4 inch (6 mm). An exemplary method of forming the polymeric composition into pellets includes extruding the polymeric composition through a strand die to form an extruded strand, and chopping the extruded strand into pellets. Other methods include under water cutting, dicing, and die face cutting.

Covering at least a portion of the pellet surface is a coating of at least one processing aid. By "processing aid" is meant any component which is employed to improve extrusion performance. These include lubricants (e.g., internal and external types), olefinic waxes and oils, and polyolefins. Although not intended to be bound by theory, it is believed that by applying the processing aid to the surface of the pellet the processing aid will, during melt processing, rapidly migrate to the metal surface of the melt processing equipment. The processing aid will form a film between the polymer and the heated metal surface of the extruder, mill or other equipment used to process the polymer composition. This film significantly reduces the tendency of the molten interpolymer to adhere to these metal surfaces and degrade. In addition, solid state friction is reduced, or can be modified. Friction is a surface phenomena and thus a processing aid on the surface is more effective than in the bulk.

The rapid migration of the processing aid provides relatively fast functioning compared to conventionally compounded processing aids, which require pellet melting prior to functioning. Consequently, a lower amount of the processing aid is necessary to achieve equivalent effects to the same processing aid blended with the vinylidene chloride interpolymer.

The coating is formed by applying the processing aid onto at least a portion of the surface of the vinylidene chloride pellet. Generally, the processing aid will be coated on the vinylidene chloride interpolymer surface in an amount of between about 0.001 weight percent to about 2 weight percent, based on the total weight of the pellet. Preferably, the processing aid will be coated on the vinylidene chloride interpolymer surface in an amount of between about 0.01 weight percent to about 1.5 weight percent, based on the total weight of the pellet. Most preferably, the processing aid will be coated on the vinylidene chloride interpolymer surface in an amount of between about 0.1 weight percent to about 0.7 weight percent, based on the total weight of the pellet. Within the prescribed ranges, the choice of optimum amounts of processing aids will be dependent upon the processing aid selected, the viscosity of the processing aid, the size of the pellet, and the type and size of the equipment through which the pellet is extruded, and other parameters known to those of ordinary skill in the art.

Generally, within the prescribed weight percentage ranges of processing aids which are coated on the vinylidene chloride interpolymer surface, higher levels of processing aid which are coated on the vinylidene chloride interpolymer surface will provide more benefit in terms of decreased particulate degradation in the extrudate. That is to say, when compared to an uncoated pellet, 50 percent coverage of a vinylidene chloride interpolymer surface will produce somewhat decreased particulate degradation of the extrudate. Moreover, 90 percent coverage of the same pellet will produce a still further improvement, as compared with 50 percent coverage of a pellet, in decreasing the particulate degradation in the extrudate.

Preferably, the processing aid will be uniformly coated on the vinylidene chloride interpolymer pellet surface. Similarly, within the ranges discussed above, the thicker the surface coating, the more oenefit one will see in terms of decreasing the particulate degradation in the extrudate. If, however, the processing aid is applied in quantities excessive for the processing aid selected, the viscosity of the processing aid, the size of the pellet, and the type and size of the equipment through which the pellet is extruded, then feeding of the pellet into the melt processing equipment may be impaired because of insufficient friction in the feed zone; or the excess amount of processing aid may form globules on the vinylidene chloride interpolymer surface.

The processing aids coated on the vinylidene 0 chloride interpolymer surface are those generally used for the conventional melt processing of vinylidene chloride interpolymers in either powder or pellet form. The specific processing aid selected will be a matter of choice for the skilled artisan, depending upon a variety

15 of factors. Exemplary factors in selecting a processing aid include melt adhesion requirement.3, fusion delay requirements, viscosity reduction reqjirements, friction reduction, and the rate increase desired for a selected ₀ extruder screw rpm.

Exemplary processing aids include lubricants, and olefin polymers. Preferably, the processing aid should be selected to have a softenir.f point between _- ambient temperatures and below the processing temperature of the plastic in pellet.

Suitable lubricants include :oth internal and external lubricants which improve extrusion performance

-,₀ of the vinylidene chloride interpolyr er. By "internal lubricant" is meant any of the class _f compounds that increase the ease with which the pol:Tier molecules slip past one another, resulting in reduce i melt viscosity, better flow, and a lower energy to e..zrude for melt

35 processing. The lubricants may perfcrm functions in addition to that mechanism referred to as internal lubrication.

By "external lubricant" is meant any of the _- class of compounds that will migrate to the surface of the molten vinylidene chloride interpolymer and form a film between the interpolymer and the heated metal surface of the extruder, mill or other equipment used to process the pellet. This film significantly reduces the 10 tendency of the polymer to adhere to these metal surfaces and degrade. The compositions may perform functions in addition to that mechanism referred to as external lubrication. Although not intended to be bound by theory, the lubricants are classified as "external"

15 because they are believed to be at least partially incompatible with the molten polymer.

Exemplary lubricants include fatty acids (e.g., stearic acid); esters (e.g., fatty esters, wax esters,

20 glycerol esters, glycol esters, fatty alcohol esters, and the like); fatty alcohols (e.g., n-stearyl alcohol); fatty amides (e.g., N,N*- ethylene bis stearamide); metallic salts of fatty acids (e.g., calcium stearate, _2I- magnesium stearate, and sodium stearate, sodium lauryl sulfate, and the like); polyolefin waxes (e.g., paraffinic, nonoxidized and oxidized polyethylene and the like), and mixtures thereof.

The term "olefin polymer" includes homopolymers

30 and copolymers of α-monoolefins and substituted α- monoolefins, particularly α-monoolefins or substituted α-monoolefins having from 4 to 12 carbon atoms.

__c Exemplary α-monoolefins polymers include polyethylene (e.g., ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene); polypropylene; poly(butene-1) , poly(isobutylene) ; poly(1-pentene) ; poly(1-hexene) ; and poly(1-octene) .

Substituted α-monoolefins include those wherein the substituents can be halo, alkyl or haloalkyl having from 1 to 12 carbon atoms; carboxylic acid having from 3 to 8 carbon atoms; alkyl or haloalkyl ester of carboxylic acid wherein alkyl or haloalkyl has from 1 to

12 carbon atoms; α-alkenyl having 2 to 12 atoms; acyl having 1 to 12 carbon atoms; carboxylate having from 1 to 12 carbon atoms; alkoxyl having from 1 to 12 carbon atoms, and aryloxy having from 6 to 12 carbon atoms.

The α-monoolefins and substituted α-monoolefins may also be copoly erized with a variety of suitable comonomers such as carboxylic acids having from 3 to 8 carbon atoms (e.g., ethylene vinyl acetate, and ethylene acrylic acid); alkyl or haloalkyl esters of carboxylic acid wherein alkyl or haloalkyl has from 1 to 12 carbon atoms; α-alkenyls having 2 to 12 atoms; acyls having 1 to 12 carbon atoms; carboxylates having from 1 to 12 carbon atoms; alkoxyls having from 1 to 12 carbon atoms, aryloxys having from 6 to 12 carbon atoms; and α- onoolefin/α-monoolefin copolymers (e.g., ethylene/propylene copolymers).

Preferably, the olefin polymers selected are those which lower the mechanical energy to extrude and the frictional coefficient of the polymeric composition,

Due to friction and the viscosity of the polymeric composition, mechanical energy to extrude is the amount of energy expended when extruding the interpolymer. It defines the amount of energy which has been viscously and frictionally dissipated to the polymer during extrusion. A detailed discussion of mechanical energy to extrude is set forth in Principles 5 of Polymer Processing, Tadmor, Z., and Gogos, C, Chapter 12, Wiley and Sons, (1979).

More preferably, the frictional coefficient of the polymeric composition should be at least about 20 10 percent lower than the frictional coefficient of the polymeric composition without the polyolefin. One method of measuring friction is by impinging a sample of known cross-section on a rotating roll. The ratio of the tangent force to the radial impinging force is

15 defined as the coefficient of friction (C0F). An apparatus called a "screw simulator" is used to allow the measurement of C0F at conditions normally found in an extruder feed section. The apparatus and process is

20 described in detail in the following article which is hereby incorporated by reference: C.I. Chung et al., Poly . Eng. Sci., 17(1), 9 (1977).

Viscosity is the resistance to flow. Viscosity _pc is a function of many variables including molecular weights with higher molecular weight polymers having higher viscosities.

Most preferably, the polyolefins are those

30 selected to have a viscosity in the range of about 200 percent to about 5 percent of the vinylidene chloride interpolymer.

The method of applying the processing aid will, _c obviously, depend upon the physical form of the processing aid. When in powder form, the processing aid may be applied directly to the vinylidene chloride interpolymer surface. Suitable techniques for applying the powder include softening the vinylidene chloride interpolymer surface prior to application of the powder, or by dispersing the powder in a carrier prior to application. When a carrier is employed, the powder may be blended with the carrier and applied concurrently on the vinylidene chloride interpolymer surface, or may be consecutively applied after the carrier is applied on the vinylidene chloride interpolymer surface. Suitable carriers include mineral oil.

When in solid or wax form, the processing aid may be prepared for coating the solid or wax on the vinylidene chloride interpolymer surface by exposing the solid or wax to a temperature sufficient to cause it to soften and become tacky or liquid. The softened solid or wax may then be applied to the vinylidene chloride interpolymer surface by any suitable means. Exemplary means for applying the lubricant to the vinylidene chloride interpolymer surface are by means of spraying, tumble blending, or by high intensity blending.

A particularly preferred technique for applying a processing aid, regardless of its physical form, to the vinylidene chloride interpolymer surface is by using high intensity blending. Typically, the pellets are mixed until they are brought to a temperature at least about 10°C, preferably about 5°C, below the temperature at which the processing aid will soften and fuse. Persons skilled in the art recognize that mixing times will vary with the blending technique, apparatus, and the selected processing aid. The processing aid is then charged in the blender and further mixing of the preheated pellet and processing aid continued until the processing aid fuses on the vinylidene chloride interpolymer surface. Exemplary high intensity blenders include Banbury mixers, Prodex-Henschel mixers, Welex- Papenmeier mixers, and the like.

After being surface coated, the pellet is then melt processed and extruded into any suitable final product. The process of the present invention can be used to form a variety of films or other articles.

The pellet may be fabricated into any suitable final product, e.g., a variety of films or other articles. As is well known in the art, the films and articles are fabricated with conventional coextrusion; e.g, feedblock coextrusion, multimanifold die coextrusion, or combinations of the two; injection molding; coinjection molding; extrusion molding; casting; blowing; blow molding; calendering; and laminating.

Exemplary articles include blown and cast, mono and multilayer, films; rigid and flexible containers; rigid and foam sheet; tubes; pipes; rods; fibers; and various profiles. Lamination techniques are particularly suited to produce multi-ply sheets. As is known in the art, specific laminating techniques include fusion; i.e., whereby self-sustaining lamina are bonded together by applications of heat and pressure; wet combining, i.e., whereby two or more plies are laminated using a tie coat adhesive, which is applied wet, the liquid driven off, and in one continuous process combining the plies by subsequent pressure lamination; or by heat reactivation, i.e., combining a precoated film with another film by heating, and reactivating the precoat adhesive so that it becomes receptive to bonding after subsequent pressure laminating.

Vinylidene chloride interpolymers are particularly suited for fabrication into rigid containers used for the preservation of food, drink, medicine and other perishables. Such containers should have good mechanical properties, as well as low gas permeabilities to, for example, oxygen, carbon dioxide, water vapor, odor bodies or flavor bodies, hydrocarbons or agricultural chemicals. The structures have organic -polymer skin layers laminated on each side of a vinylidene chloride interpolymer barrier layer, with glue layers generally interposed therebetween.

The present invention is illustrated in further detail by the following examples. The examples are for the purposes of illustration only, and are not to be construed as limiting the scope of the present invention. All parts and percentages are by weight unless otherwise specifically noted.

Examples 1-8:

A. Raw Materials

Various components used in the examples are set forth in Table I. TABLE I

Code

PVdC A pellet containing about 96.5 weight percent Pellet of a vinylidene chloride interpolymer; about 1.5 weight percent ethylene vinyl acetate; about 1.2 weight percent tetrasodium, pyrophosphate; and about 0.8 weight percent of epoxidized soybean oil. The vinylidene chloride interpolymer is formed from about 99.8 weight percent of a vinylidene chloride 0 copolymer formed from a monomer mixture comprising 80 weight percent vinylidene chloride and about 20 weight percent vinyl chloride; and about 0.2 weight percent of epoxidized soybean oil. The vinylidene chloride copolymer has a major melting point of 162°C and a weight average molecular weight ₅ of 80,000.

PA-1 Magnesium stearate commercially available from Mallinckrodt, Inc., under the trade designation magnesium stearate RSN 1-1. 0 PA-2 Sodium lauryl sulfate commercially available from Albright and Wilson, Inc., under the trade designation Empicol LZV/E.

PA-3 A poly(ethylene-co-vinyl acetate) containing 28% vinyl acetate, which is commercially available from DuPont de Nemours Chemical Co. c under the trade designation Elvax 3180.

PA-4 An oxidized polyethylene commercially available under the trade designation as Allied 629A from Allied Corp. The oxidized polyethylene has a density (ASTM Test D-1505) of 0.93 grams per cubic centimeter @ 20°C, a 0 drop point of 104°C, and a Brookfield Viscosity of 200 cps (mPa-s) § 140°C.

PA-5 A polyethylene wax commercially available from Allied Corp. under the trade designation Allied 617A. The polyethylene wax has a density (ASTM Test D-1505) of 0.91 grams per 5 cubic centimeter, a drop point of 102°C, and a Brookfield Viscosity of 180 cps (mPa-s) @ 140°C. B. Sample Preparation

Various processing aids are coated on the surface of the PVdC pellets in quantities set forth in Table II. Those processing aids in powder form are coated on the pellet by placing the powder and pellet in a bag and then shaking them. More sophisticated equipment could have been used but was not necessary.

Those processing aids in the form of a wax or solid are coated on the pellet using the following method: the pellets are placed in a high speed blender which is commercially available under the trade designation Welex Model 35 from F. H. Papenmeier K. G. Company. The mixer has a diameter of 35 cm, and a nominal capacity of 1 cubic foot (28 dm^). The baffle of the mixer is adjusted in the radial direction, the impeller is started and maintained at a tip speed of about 2700 feet per minute (fpm) (825 m/min) . When the pellets temperatures reach 75°C, various processing aids, coded in Table I, are charged in the mixer in quantities set forth in Table II. The pellets and processing aids are blended for a period of about eight minutes and then discharged. The coated pellets are cooled to about 65°C by circulating air having a temperature of 20°C.

C. Particulate Degradation Formation Testing

The pellets are extruded through a 2.5 inch (6.3 cm) extruder having a length to diameter ratio of 21/1. The extruder has the following set temperatures: (a) first zone temperature = 174°C; (b) second zone temperature^ 168°C; (b) third zone temperature = 163°C; and (c) die temperature = 165°C. The decomposition of the extruded resin into carbonaceous material is determined by visually inspecting the carbonaceous material on the root of the extruder screw heel. When evaluating the root of the extruder screw heel, pellets are extruded in a continuous process for a period of about 4 hours. After rapid quench cooling of the extruder while still full of extrudate, the extent^* of carbonaceous material formation in the transition section of the extruder screw is qualitatively rated. The carbonaceous material buildup is rated on a scale of 0 to 4 over a continuous range, wherein 0 represents generally no visible carbonaceous material on the surface and 4 represents a layer of carbonaceous material generally completely covering the surface.

D. Test Results

Results of the physical property tests for Examples 1-8 are set forth in Table II, together with the identity and amount of polymer components employed.

Pellet = pellets as set forth in Table I.

Method of Pellet Coating: (a) "Bag" = placing the powdery processing aid and pellet into a bag and shaking; and (b) "Blender" = placing the waxy or solid processing aid and pellet into a high speed blender.

Processing aid: (a) type = processing aid as set forth in Table I; and (b) % = the level of processing aid on the vinylidene chloride interpolymer surface in weight percent.

Particulate Degradation Product = carbonaceous material contamination on the extruder screw heel according to visual inspection, on a scale of 0 to 4.

As can be seen from the above table, the coated pellets generate a relatively low level of particulate degradation product. Examples 9- 16

Examples 1-8 are repeated with the following exceptions. Instead of using the PVdC set forth in Table I, a pellet having the following composition is employed: about 96.5 weight percent of a vinylidene chloride interpolymer; about 1.5 weight percent ethylene vinyl acetate; about 1.2 weight percent tetrasodiuum pyrophosphate; and about 0.8 weight percent of epoxidized soybean oil. The vinylidene chloride interpolymer comprises from about 99.8 weight percent of a vinylidene chloride copolymer and about 0.2 weight percent of epoxidized soybean oil. The vinylidene chloride copolymer is formed from a monomer mixture comprising 94 weight percent vinylidene chloride and about 6 weight percent methyl acrylate and has a major melting point of 165°C and a weight average molecular weight of 90,000.

The coated pellets generate a relatively low level of particulate degradation product.

Claims

1. A pellet of extrudable thermoplastic material, comprising vinylidene chloride interpolymer, characterized in that it is coated with at least one processing aid in an amount effective to improve the extrudability of the vinylidene chloride interpolymer.

2. A pellet as claimed in Claim 1, wherein said pellet has a minimum cross-section dimension of at least 1/8 inch and said interpolymer is formed from a monomer mixture which comprises vinylidene chloride monomer in an amount of from 60 to 99 weight percent and at least one monoethylenically unsaturated comonomer copolymerizable therewith in an amount of from 40 to 1 weight percent, said weight percents being based on the total weight of the monomer mixture.

3. A pellet as claimed in Claim 1 or 2, wherein said interpolymer is a copolymer of vinylidene chloride and a monomer selected from vinyl chloride, methyl aerylate, ethyl acrylates, and methyl methacrylate.

4. A pellet as claimed in any one of the preceding claims wherein the processing aid is coated on the vinylidene chloride interpolymer surface in an amount level of between 0.001 and 2 weight percent, based on the total weight of the pellet.

5. A pellet as claimed in Claim 4, wherein said coating amount is between 0.01 and 1.5 weight percent, based on the total weight of the pellet.

6. A pellet as claimed in Claim 5, wherein said coating amount is between 0.1 and 0.7 weight

10 percent, based on the total weight of the pellet.

7. A pellet as claimed in any one of the preceding claims wherein the processing aid is selected from fatty acids; esters; fatty alcohols; fatty amides;

-,.- metallic salts of fatty acids; olefin polymers, polyolefin waxes, and mixtures thereof.

8. A pellet as claimed in Claim 7, wherein the vinylidene chloride interpolymer surface is coated with

-_n sodium lauryl sulfate and magnesium stearate.

9. A process for making a fabricated article, said process comprising melt processing and extruding a coated pellet as claimed in any one of the preceding

25 claims.

10. A process for improving the extrudability of a pellet of thermoplastic material containing vinylidene chloride, which process comprises coating the 0 pellet with at least one processing aid.

5