Patent Publication Number: US-4317765-A

Title: Compatibilization of hydroxyl-containing fillers and thermoplastic polymers

Description:
This application is a continuation of application Ser. No. 643,820, filed Dec. 23, 1975 now U.S. Pat. No. 4,071,494, which was a continuation-in-part of application Ser. No. 66,107, filed Aug. 21, 1970, now U.S. Pat. No. 3,956,230, which was a continuation-in-part of application Ser. No. 702,204, filed Feb. 1, 1968 now U.S. Pat. No. 3,645,939. 
    
    
     This invention relates to the compatibilization of thermoplastic polymers with fillers. More particularly, this invention relates to a technique for coupling a polyolefin and an hydroxyl-containing particulate material such as clay, to provide a composition of improved physical properties, and to the molding of such composites. 
     The modification of the physical and mechanical properties of thermoplastic polymers by the addition of a filler is well known in the art. Greater degrees of property improvement result when the filler is uniformly and highly dispersed throughout the polymer matrix and/or when it chemically reacts with the polymer since the polymer-filler interface provides a possible site of weakness in the composite. Various means of improving the compatibility of the filler with the polymer matrix by providing interaction between the fillter and the polymer are known in the art. For example, when a cellulosic material, such as wood flour or cotton fibers, is used as a filler in polymers containing methylol groups such as phenolic, urea or melamine resins, a reaction occurs between the methylol groups and the hydroxyl groups on the cellulosic filler. Clay particles have been encapsulated in a polymeric material and the resultant encapsulated particles dispersed in a polyolefin in order to obtain improved properties. In such a system, the polymer used to coat the filler should be chemically bonded to the filler in order to obtain optimum properties such as high strength. 
     It is an object of this invention to provide an improved technique for compatibilizing particulate fillers with thermoplastic polymers. 
     It is another object of this invention to provide a two-step process for compatibilizing a hydroxyl containing filler with a thermoplastic polymer whereby the filler is first given a polymer coating and the coated filler is then used as a compatible filler for a thermoplastic polymer. 
     It is another object of this invention to provide a one-step compatibilization process in which a filler is compounded into a matrix thermoplastic polymer with the degree of loading desired in the final composition. 
     It is a further object of this invention to provide molded objects from the compatibilized compositions of this invention. 
     One embodiment of this invention, briefly, comprises providing individual hydroxyl group containing filler particles with a sheath or coating of a thermoplastic filler. This is accomplished by contacting a thermoplastic polymer containing labile atoms which provide sites for the formation of free radicals and filler particles in the presence of an ethylenically unsaturated carboxylic acid or anhydride under conditions which will generate free radicals on the polyolefin. The acid is thereby coupled onto the thermoplastic polymer and is reacted with the hydroxyl groups on the filler particles by means of esterification and hydrogen bonding. Thus, the ethylenically unsaturated acid acts as a coupling agent between the polymer coating and the filler. The resin-coated filler particles which are thereby obtained may then be dispersed in a thermoplastic polymer matrix which may be the same type or a different type as the thermoplastic polymer used to coat the filler particles. Articles molded from the resultant compositions have improved properties (e.g., tensile strength, flexural modulus and impact strength) as compared to compositions prepared in the identical manner except for the omission of the coupling agents. This embodiment is therefore a two-step process for compatibilizing a filler with a matrix polymer. 
     According to another embodiment of this invention, a hydroxyl group containing filler material is compounded into a matrix thermoplastic polymer having labile atoms which provide sites for the formation of free radicals with the desired degree of loading in the presence of an ethylenically unsaturated carboxylic acid or anhydride under conditions which will generate free radicals on the thermoplastic polymer. Therefore, this embodiment is a one-step process for compatibilizing a filler with a matrix polymer. As in the two-step process previously described, the ethylenically unsaturated carboxylic acid acts as a coupling agent between the polymer and the filler. This process results in an improvement in the processability of the original thermoplastic polymer. Thus, the flow properties of polyethylene may be improved by the incorporation of clay filler in the presence of maleic anhydride and a free radical catalyst such as t-butyl perbenzoate. Preferably, the final composition contains from about 30 to 90% by weight of thermoplastic polymer and from about 5 to 70% by weight of filler. 
     As used herein, the term &#34;compatibilizing&#34; is intended to include an interaction such as an actual chemical coupling between the hydroxyl group containing filler and the thermoplastic polymer coating and a physical bonding between the thermoplastic polymer coating and the matrix thermoplastic polymer. 
     The material containing hydroxyl groups used in the practice of this invention may be any of the well known inorganic -OH containing filler materials or reinforcing agents such as siliceous materials (e.g., clay, sand, wollastonite, glass, quartz, diatomaceous earth, mica, silica, asbestos, talc, kaolinite and nepheline syenite); hydrated or partially hydrated metal oxides (e.g., titania, zirconia, vanadia, alumina, chromia, zinc oxide, magnesium oxide and boron oxides); carbonates (e.g., limestone and chalk); etc. The filler material may be either a synthetic or a natural occurring material and, if naturally occurring, may be used in either the purified or unpurified form. 
     The thermoplastic polymers having labile atoms which provide sites for the formation of free radicals include polymers of olefins (e.g., homopolymers and copolymers of ethylene propylene, 1-butene, etc.) including copolymers with polar monomers (e.g., ethylene-vinyl) acetate copolymers); acrylic resins or elastomers (e.g., homopolymers and copolymers with each other or with other monomers of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylic acid and methacrylic acid); polystyrene; copolymers of styrene and other vinyl monomers such as acrylonitrile; vinyl polymers such as homopolymers and copolymers of vinyl acetate, vinyl chloride, alkyl vinyl ether and vinyl butyral; homopolymers and copolymers of dienes such as polybutadiene, polyisoprene, polychloroprene, butadiene-styrene copolymers, isobutylene-isoprene copolymers and other unvulcanized elastomers including natural rubber. Chemical derivatives of such polymers and copolymers of ethylenically unsaturated monomers or dienes (e.g., chlorinated polyethylene, chlorinated polypropylene, chlorinated isoprene copolymers, salts of ethylene-maleic anhydride, ethylene-acrylic acid, ethylene-methacrylic acid, styrene-maleic anhydride, alkyl vinyl ether-maleic anhydride, butadiene-maleic anhydride and isoprene-maleic anhydride copolymers, and completely or partially hydrolyzed ethylene-vinyl acetate copolymers may also be used. Polymers of cyclic monomers may also be used (e.g., homopolymers and copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, propiolactone, caprolactone, caprolactam and ethylene imine). Copolymers of carbon monoxide and sulfur dioxide may also be used (e.g., copolymers of carbon monoxide with ethylene and ethylene imine and copolymers of sulfur dioxide with α-olefins, styrene, vinyl chloride and butadiene). Homopolymers and copolymers of carbonyl compounds may also be used (e.g., homopolymers and copolymers of formaldehyde, acetaldehyde, butyraldehyde, chloral, etc.). Condensation polymers may also be used such as polyesters and alkyd resins which are obtained by the condensation of a polyhydric alcohol and a polycarboxylic acid. Examples of polycarboxylic acids which may be used to form the polyester resin include phthalic acid, phthalic anhydride, succinic acid, adipic acid, isophthalic acid, terephthalic acid, maleic anhydride, etc. The polyhydric alcohols which may be used in the preparation of the polyester or alkyd resin may include the glycols, such as ethylene glycol, propylene glycol, etc. Polyamide resins may also be used (e.g., polymers obtained by the condensation of a polycarboxylic acid such as adipic acid, terephthalic acid and dimer acid with a polyamine such as ethylene diamine, hexamethylene diamine and diethylene triamine). Polyurethanes may also be used (e.g., polymers obtained by reaction of a diisocyanate such as toluene diisocyanate and 4,4&#39;-diphenylmethane diisocyanate with a polyol such as polyethylene oxide, polypropylene oxide, polytetramethylene glycol, hydroxyl-terminated polyesters, hydroxyl-terminated polyisobutylene and hydroxyl-terminated polybutadiene). Other thermoplastic resins based on bisphenol such as polycarbonates, polysulfones and polysulfonates as well as poly-2,5-dimethylphenylene oxide may also be used. Epoxy resins include the condensation products of bisphenol and epichlorohydrin, epoxidized drying oils, the glycidyl ethers of glycerol, epoxylated novolac resins, etc. The thermoplastic resin may be a resin which is capable of being thermoset or cured but which is contacted with the hydroxyl group containing material at temperatures and conditions which will not thermoset or cure the resin. Such resins include silicone resins and elastomers and acrylic resins. The labile atom on the polymer may be, for instance, a hydrogen atom or a halogen atom. 
     The preferred thermoplastic polymers are polyolefins, including homopolymers and copolymers of olefins such as ethylene, propylene, 1-butene, etc. The olefin monomers from which the polyolefin is formed preferably contain from 2 to 20 carbon atoms. The preferred polyolefin is high density polyethylene. Oxidized polyolefins may also be used. 
     Thermoplastic polymers having labile atoms which provide sites for the formation of free radicals, in addition to those previously enumerated, include various nylons, polyesters such as polybutyleneterephthalate, polycarbonates, polystyrene and styrene copolymers such as styrene-acrylonitrile copolymer, polyacetals, cellulose esters such as cellulose acetate and cellulose propionate, polyphenylene oxide and blends thereof with polystyrene and mixtures of polyolefins such as polyethylene and polypropylene. It is also within the scope of this invention to use two different polyolefins in the two-step compatibilization process--e.g., polyethylene may be used as the encapsulating polymer and polypropylene as the matrix polymer. 
     The ethylenically unsaturated carboxylic acid or anhydride coupling agent used in the practice of this invention is preferably dicarboxylic such as maleic acid, maleic anhydride, fumaric acid, citraconic acid, or itaconic acid. Maleic anhydride is the preferred coupling agent. Monocarboxylic acids, such as acrylic acid and methacrylic acid may also be used. 
     Since maleic anhydride has a low melting point and readily sublimes, it is sometimes advantageous to use maleic acid. Maleic acid has a high melting point and little tendency to sublime. Moreover, maleic acid is converted to maleic anhydride at the temperatures at which the compatibilization process is carried out, e.g., temperatures aboved 100° C., preferably 140° C. to 160° C. Therefore, maleic anhydride is formed in situ under the processing conditions from maleic acid. Also poly(maleic anhydride), which is much less volatile than maleic anhydride, may be used. Poly(maleic anhydride) may be prepared, for example, by polymerizing 15 parts by weight of maleic anhydride in 7.5 parts by weight of acetic anhydride at 70° C. for 20 minutes using 5% dicyclohexylperoxydicarbonate as a catalyst. 
     The means for generating free radicals on the thermoplastic polymer is preferably accomplished by using a free radical catalyst such as a peroxide (e.g., t-butyl perbenzoate, dicumyl peroxide, methylethylketone peroxide, benzoyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane. A more detailed compilation of free radical initiators which may be used is set forth at pages II-3 to II-51 of &#34;Polymer Handbook&#34;, Interscience Publishers (1966), the disclosure of which is incorporated herein by reference. 
     The catalyst used is preferably one which will initiate the homopolymerization of maleic anhydride. It is preferred that the catalyst used be one which has a half life up to about 30 minutes at a temperature between the melting point and the decomposition point of the thermoplastic polymer which is used to coat the filler particles. This temperature will vary according to the particular polyolefin used. A catalyst having a half life of up to about 30 minutes at a temperature of between 100°-120° C. is generally adequate for the purpose of this invention. The term &#34;half life&#34; is intended to mean the length of time required for half of the catalyst to decompose. 
     Set forth below are a number of catalysts and the half life of each indicated at various temperatures: 
     
         ______________________________________                                    
                        Temp    Half Life                                 
Catalyst                °C.                                        
                                Minutes                                   
______________________________________                                    
2,5-dimethylhexyl-2,5-di(perbenzoate)                                     
                        130     18                                        
cyclohexanone peroxide  130     20                                        
t-butyl peracetate      130     24                                        
1,1-di-t-butyl peroxy-3,3,5-tri-methyl-                                   
cyclohexane (40%)       130     24                                        
t-butyl di(perphthalate)                                                  
                        130     30                                        
2,5-dimethyl-2,5-di(t-butyl peroxy)hexane                                 
                        150     18                                        
bis(α-t-butyl peroxyisopropylbenzene)(40%)                          
                        150     6                                         
dicumyl peroxide        150     12                                        
dicumyl peroxide        170     1.5                                       
benzoyl peroxide        115     8                                         
benzoyl peroxide        130     1.2                                       
benzoyl peroxide        135     1                                         
t-butyl perbenzoate     130     30                                        
t-butyl perbenzoate     170     2                                         
di-t-butyl peroxide     170     9                                         
di-t-butyl peroxide     180     3                                         
2,4,6-tri-(t-butyl peroxy)triazine                                        
                        170     &lt;1                                        
t-butyl peroxy acid phthalate                                             
                        170     1                                         
bis-(t-butyl peroxy)diphenylsilane                                        
                        170     30                                        
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     Preferably, from about 2 to 30% by weight of ethylenically unsaturated carboxylic acid or anhydride and from about 0.5 to 10% by weight of peroxide, based upon the weight of thermoplastic polymer, are used to couple the thermoplastic polymer to the hydroxyl group containing filler. The use of higher amounts of acid or anhydride results in a decrease in impact strength when the precoated filler is combined with a thermoplastic polymer to prepare a composite. 
     The compatibilized composition may be formed by charging the thermoplastic polymer, the hydroxyl group containing filler, the ethylenically unsaturated carboxylic acid or anhydride and a free radical generating catalyst to a mill and blending the mixture in the mill. In a preferred procedure, the filler and a polyolefin are first blended and maleic anhydride and catalyst are then added and mixing is continued. 
     In the two-step compatibilization process, it is preferred, although not necessary, that the coating thermoplastic polymer be the same chemical species as the matrix polymer but that the two polymers have different properties. Thus, in order to obtain optimum improvement in physical properties of the composites, the matrix polymer preferably has a lower melt index and a higher molecular weight than the coating polymer. It is also preferred that the matrix polymers have impact strength and other properties superior to those of the coating polymer. 
     In preparing the thermoplastic polymer coated filler for subsequent use as a coated filler for the same or a different thermoplastic polymer, the clay should be reacted with sufficient thermoplastic polymer to give a coated filler comprising from about 30 to 80% by weight of clay and preferably about 70% by weight of clay, the remainder being thermoplastic polymer. In order to insure homogeneity of the thermoplastic polymer coating on the filler, a thermoplastic polymer having good wetting and flow properties should be used. Therefore, it is preferred to use a thermoplastic polymer having a melt index of from 5 to 50 as the encapsulating polymer. 
     The thermoplastic polymer coated filler is mixed with sufficient thermoplastic polymer to yield a final composition containing from 5 to 70% by weight of clay and preferably from about 30 to 50% by weight of clay. The resultant composition has mechanical properties such as tensile strength, flexural modulus and impact strength superior to those of uncompatibilized compositions containing the same amount of clay as well as those of unfilled thermoplastic polymer. The normally inert filler is thus converted to a reinforcing agent. 
     When a thermoplastic polymer and a mineral filler containing hydroxyl groups are contacted with, for example, maleic anhydride and a free radical catalyst, the maleic anhydride simultaneously or consecutively adducts or reacts with the thermoplastic polymer and esterifies and forms hydrogen bonds with the filler containing hydroxyl groups. Thus, the maleic anhydride links the thermoplastic polymer and filler together. When polyethylene is used as the thermoplastic polymer and clay as the filler containing hydroxyl groups, the polyethylene and clay are linked together by means of the maleic anhydride forming a block copolymer containing a succinic half acid ester bridge between clay and polyethylene segments. The polyethylene becomes, in this manner, a side chain of the clay. The reaction which occurs may be represented as follows: ##STR1## wherein R. represents the free radical from the catalyst and Y is the residue of a clay molecule. The segment of the block copolymer derived from the maleic anhydride may be polymeric, e.g., polymaleic anhydride, in lieu of or in addition to the single unit shown in the equation. 
     It is essential that the thermoplastic polymer, the filler containing hydroxyl groups and the ethylenically unsaturated carboxylic acid or anhydride be contacted so that reaction may occur between the acid and the other two materials substantially simultaneously. If clay, for example, is first reacted with maleic anhydride to form a clay maleate half ester, the half ester will not subsequently readily react with polyethylene even in the presence of a free radical catalyst. Moreover, if it is attempted to react polyethylene with maleic anhydride at 150° C. in a reaction chamber which is not sealed, reaction does not readily occur in the presence of free radical catalyst and the maleic anhydride sublimes out of the reaction chamber, whereas, when clay is present, sublimation of the maleic anhydride is prevented or minimized and reaction occurs. 
     Ethylenically unsaturated carboxylic acids and anhydrides have long been known to polymerize and/or copolymerize with other monomers under the influence of free radical initiators. However, inorganic salts of these acids are quite resistant to polymerization. Thus, if the acid is allowed to contact the hydroxyl containing filler prior to free radical initiation poor results are obtained. Additionally, if the free radical initiator is allowed to react prior to the addition of the ethylenically unsaturated carboxylic acid or anhydride, cross-linking of the thermoplastic polymer will occur, producing a brittle, non-thermoplastic composite. Thus, it is essential that the thermoplastic polymer and the hydroxyl group containing filler be contacted essentially simultaneously by the ethylenically unsaturated carboxylic acid or anhydride and the free radical initiator. Ideally, this can be best accomplished by first dispersing the filler in the molten polymer and then adding a mixture of acid or anhydride and free radical initiator. Alternatively, the ethylenically unsaturated carboxylic acid or anhydride and the free radical initiator can be added separately in small increments in rapid succession. If necessary, as dictated by the mixing equipment, satisfactory product can also be made by incremental addition of all of the ingredients, i.e., a portion of the polymer, a portion of the filler, a portion of the ethylenically unsaturated carboxylic acid and a portion of the free radical initiator, this sequence being repeated several times. The following table illustrates the criticality of ensuring that the acid and the initiator are added in such a manner so that they can react essentially simultaneously with each other and with the polymer (HDPE is high density polyethylene) and filler: 
     
         ______________________________________                                    
     All products mixed as indicated                                      
     a 70/30 polyethylene/clay ratio                                      
     and subsequently let down to a                                       
                           Notched Izod                                   
Item 50/50 composition by addition of                                     
                           Impact Strength                                
No.  polyethylene.         Ft.-lbs/in.                                    
______________________________________                                    
1    Premix HDPE and clay at 150° C.,                              
                           1.0                                            
     add all maleic acid and then add                                     
     all peroxide while continuing                                        
     mixing.                                                              
2    Premix HDPE and clay at 150° C.,                              
                           Product becomes                                
     add all peroxide while continu-                                      
                           hard and crumbly,                              
     ing mixing.           processing cannot                              
                           be completed.                                  
3    Charge mixer at 150° C. with 1/3                              
                           3.0                                            
     of HDPE, add 1/3 clay slowly,                                        
     add 1/3 of maleic acid and 1/3                                       
     of peroxide, add second 1/3 por-                                     
     tion of HDPE and repeat sequence                                     
     two more times.                                                      
4    Premix HDPE and clay at 150° C.,                              
                           3.8                                            
     add incremental portions of                                          
     maleic acid and peroxide se-                                         
     quentially while continuing                                          
     mixing.                                                              
5    Premix HDPE and clay at 150° C.,                              
                           5.0                                            
     add premixed blend of maleic                                         
     acid and peroxide while continu-                                     
     ing mixing.                                                          
6    Premix clay, maleic acid and                                         
                           1.3                                            
     peroxide at 25° C., add HDPE at                               
     150° C. while mixing.                                         
7    Premix HDPE, maleic acid and                                         
                           1.1                                            
     peroxide at 150° C., add clay                                 
     while continuing mixing.                                             
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     In Item 1, the maleic acid is added to the dispersion of clay in HDPE and apparently reacts with the clay prior to the addition of the free radical initiator (peroxide), producing a product with low impact strength. 
     Item 2 illustrates the cross-linking of the polyethylene which occurs if the peroxide is allowed to react in the absence of the ethylenically unsaturated carboxylic acid. 
     Items 3, 4 and 5 show that products with very good impact strength are produced when the ethylenically unsaturated carboxylic acid and the free radical initiator are added in such a manner so that they can react essentially simultaneously with each other and with both the thermoplastic polymer and the hydroxyl group containing filler. 
     Items 6 and 7 again illustrate the poor impact strength is obtained if the acid and peroxide are allowed to react with either the filler (6) or the polymer (7) alone. 
     As previously discussed, the homogeneous composites of this invention may be molded into articles by various conventional molding techniques. These include injection molding, compression molding, transfer molding, extrusion, blow molding, thermoforming, foam injection molding, foam extrusion and roto molding. The composites may be formed into sheets or films or used as laminating layers. When the hydroxyl group containing material is sand, the composite may be formed into sheets of sand paper in which the sand is integrally bonded. 
     When the homogeneous composites of this invention are formed into sheets or films, the latter may be subjected to subsequent mechanical treatment such as uniaxial or biaxial stretching to enhance the strength. When the hydroxyl group containing filler is fibrous, such as asbestos, the stretching operation will aid in the alignment of the fibers further enhancing the strength of the sheet or film. 
     In the examples which follow, all parts are by weight unless otherwise specified. Examples 1 to 19 and 25 to 31 illustrate the two-step technique described above and Examples 20 to 24 illustrate the one-step compatibilization technique. 
    
    
     EXAMPLE 1 
     To a Brabender Plasticorder there are charged 10 parts of low density polyethylene and 90 parts of clay (Hydrite 10 which is hydrated kaolin with a median particle size of 0.55 microns and a pH of 4.5-5.5 which has been dried at 150° C. for 24 hours in vacuo before use). The composition is mixed for 10 minutes and there are then added 2.0 parts of maleic anhydride and 0.5 part of t-butyl perbenzoate. The composition is mixed at 150° C. for 15 minutes. The pretreated clay thus obtained is mixed at 130° C. with sufficient low density polyethylene to give a filled composition comprising 70 parts of polyethylene and 30 parts of clay. The resultant composition has better tensile yield and break properties and elongation than does a composition prepared in the same manner but omitting the t-butyl perbenzoate and maleic anhydride. 
     The following examples illustrate the effect of varying the amount of clay in the polyolefin encapsulated clay filler: 
     EXAMPLES 2-3 
     The precoating process described in Example 1 is repeated substituting high density polyethylene for low density polyethylene to prepare two samples of precoated clay, one sample containing 90% clay and 10% high density polyethylene and the other sample containing 70% clay and 30% high density polyethylene. Each sample of pretreated clay thus obtained is mixed at 150° C. with sufficient high density polyethylene to give a composition comprising 70 parts of polyethylene and 30 parts of clay. Testing by standard procedures show that the composite prepared from the pretreated clay containing 70% clay gives better tensile properties, including improved yield strength than the composite obtained from the filler containing 90% clay. 
     The following example illustrates the use of poly(maleic anhydride) instead of maleic anhydride. 
     EXAMPLE 4 
     A mixture of 90 parts of Hydrite 10 clay and 10 parts of high density polyethylene are mixed as described in Example 1 in the presence of 20% of poly(maleic anhydride), having a specific viscosity in methyl ethyl ketone at 25° C. of 0.945, and 5% of t-butyl perbenzoate, the percentages being based on the weight of polyethylene. The precoated clay is then mixed with additional high density polyethylene at 150° C. in the presence of 2% of t-butyl perbenzoate, based on the weight of additional polyethylene, to give a composition comprising 70% polyethylene and 30% clay. The resultant composition has good tensile strength. 
     The following example illustrates the substitution of maleic acid for maleic anhydride. 
     EXAMPLE 5 
     A mixture of 70 parts of Hydrite 10 clay and 30 parts of high density polyethylene are premixed in the presence of 20% maleic acid and 5% t-butyl perbenzoate, percentages being based upon the weight of the polyethylene, for 10 minutes at 150° C. The polyethylene encapsulated clay particles are then mixed at 150° C. for 10 minutes with additional high density polyethylene to form a composition comprising 50% polyethylene and 50% clay. The resultant compatibilized composite has good tensile strength, flexural modulus and impact strength. 
     The following examples illustrate the effect of varying the amount of clay in the final composite: 
     EXAMPLES 6-9 
     A high density polyethylene encapsulated clay composition comprising 70% clay and 30% polyethylene is prepared as described in Examples 2-3. A series of filled polyethylene compositions containing varying amounts of clay are prepared by mixing at 150° C. for 10 minutes sufficient of the precoated clay with additional high density polyethylene to give final compositions containing, respectively, 20% clay, 30% clay, 50% clay and 70% clay, the remainder in each composition being high density polyethylene. An identical set of control compositions is prepared except that in the polyethylene pretreatment of the clay, the maleic anhydride and t-butyl perbenzoate are omitted. These compositions are tested according to standard procedures. It is found that all control samples containing untreated clay had no yield strength and the break strength was almost constant, independent of the amount of clay present. The control sample containing 70% of clay has such poor flow properties that a continuous film for testing cannot be obtained. The samples containing pretreated clay in accordance with this invention give considerably improved yield and break strength. As the amount of clay in the final composition is increased, the yield and break strengths of the treated sampled increase up to a maximum value at 50% clay. The impact strength of the compatibilized composition containing 30% clay was improved 30% over the corresponding control and the impact strength of the compatibilized composition containing 50% clay was improved 250% over the corresponding control. 
     The following examples illustrate the improved properties which result from the use of a high melt index polyethylene as the coating or encapsulating material in the coupling reaction of the clay followed by compounding with a low melt index matrix polyethylene. 
     EXAMPLES 10-13 
     A series of compatibilized high density polyethylene clay compositions are prepared by pretreating clay and compounding it with additional polyethylene as described in Example 5. The pretreated clay comprises 70% clay and 30% polyethylene. The pretreated clay is compounded with polyethylenes having varying properties in amounts sufficient to give samples containing 50% clay--50% polyethylene and 30% clay--70% polyethylene. The former composition contains 21% encapsulating polyethylene and 29% matrix polyethylene and the latter composition contains 13% encapsulating polyethylene are 57% matrix polyethylene. Set forth below are the melt indices of both the encapsulating polyethylene and the matrix polyethylene used in each example. An identical set of control compositions are also prepared except that in the polyethylene treatment of the clay, the maleic anhydride and t-butyl perbenzoate are omitted. 
     
         ______________________________________                                    
           Melt Index of  Melt Index of                                   
           Encapsulating  Matrix                                          
Example    Polyethylene   Polyethylene                                    
______________________________________                                    
10         0.7            0.7                                             
11         15.0           0.7                                             
12         22.0           0.7                                             
13         15.0           15.0                                            
______________________________________                                    
 
    
     The impact strength of each of the samples made in Examples 10-13 are compared to the corresponding control and the percent improvement calculated. The results are set forth in the following table. In this table, the designation &#34;50/50&#34; refers to the final sample containing 50% clay and 50% high density polyethylene and the designation &#34;70/30&#34; refers to the final composition containing 70% polyethylene and 30% clay. It will be noted that those examples wherein the encapsulating polyethylene has a higher melt index than the matrix polyethylene result in compositions having much higher impact strength than when the matrix polyethylene and the encapsulating polyethylene are the same. 
     
         ______________________________________                                    
PER CENT IMPROVEMENT OVER                                                 
CORRESPONDING UNCOUPLED CONTROL                                           
Example       Izod Impact                                                 
______________________________________                                    
10        50/50   245                                                     
          70/30   25                                                      
11        50/50   595                                                     
          70/30   260                                                     
12        50/50   715                                                     
          70/30   515                                                     
13        50/50   120                                                     
          70/30   50                                                      
______________________________________                                    
 
    
     The following example illustrates the use of asbestos as the hydroxyl group containing filler. 
     EXAMPLE 14 
     Asbestos fibers having a pH of 9.5 are dried at 150° C. for 24 hours. A mixture comprising 35 parts of asbestos and 15 parts of high density polyethylene having a melt index of 22.0 is mixed in a Brabender Plasticorder at 150° C. for 10 minutes in the presence of 20% maleic anhydride and 5% t-butyl perbenzoate, the percentages being based upon the polyethylene. The polyethylene coated filler is then blended with high density polyethylene having a melt index of 0.5 at 150° C. for 10 minutes to make up a composition comprising 50% polyethylene and 50% asbestos. The resultant composition has better break strength and impact strength than does a composition made up in the same manner except omitting the maleic anhydride and t-butyl perbenzoate from the pretreatment step. 
     The following examples illustrate the use of polypropylene as the polyolefin. 
     EXAMPLE 15 
     A mixture of 70 parts of Hydrite 10 clay and 30 parts of isotactic polypropylene having a melt index of 15.0 is mixed in the presence of 20% maleic anhydride and 5% t-butyl perbenzoate, the percentages being based upon the weight of the polypropylene, at 170° C. for 20 minutes. The pretreated clay is then mixed with sufficient polypropylene having a melt index of 4.0 to give a composite comprising 70% total polypropylene and 30% clay. The resultant composition has considerably better break strength, elongation, flexural modulus and impact strength than does a control composition prepared in the same manner but omitting the peroxide and maleic anhydride. 
     EXAMPLE 16 
     The process of Example 15 is repeated substituting bis-(t-butyl peroxy)diphenyl silane for the t-butyl perbenzoate. The resultant composition has good yield, break and impact strengths, elongation and flexural modulus. 
     The following example illustrates the use of calcium carbonate as the mineral filler in this invention. 
     EXAMPLE 17 
     A mixture of 70 parts of calcium carbonate and 30 parts of high density polyethylene having a melt index of 15.0 are premixed in the presence of 20% of maleic anhydride and 0.56% of t-butyl perbenzoate is 150° C. for 10 minutes. The premix is compounded at 150° C. for 10 minutes with sufficient polyethylene having a melt index of 0.7 to give a composite comprising 50% total polyethylene and 50% calcium carbonate. The impact strength of the compatibilized composition is improved 440% and the break strength is improved 53% over a corresponding control which has been prepared in the same manner but omitting the peroxide catalyst and the maleic anhydride in the pretreatment step. 
     EXAMPLE 18 
     The process of Example 17 is repeated substituting for the calcium carbonate a slurry which is a waste product from paper coating containing clay, calcium carbonate, casein and titanium dioxide. The final composite has a 120% improvement an impact strength and a 54% improvement in break strength over the control. 
     The following example shows the use of asbestos as the filler material and polypropylene as the polyolefin. 
     EXAMPLE 19 
     A mixture of 70 parts of chrysotile asbestos and 30 parts of isotactic polypropylene having a melt index of 15.0 is mixed for 6-8 minutes at 170° C. in the presence of 20% maleic anhydride and 5% t-butyl perbenzoate, the percentages being by weight of the polypropylene. The premix is then compounded with fresh polypropylene having a melt index of 4.0 in an amount sufficient to give a final composition comprising 50% asbestos and 50% polypropylene. The compounding step is carried out at 170° C. for 10 minutes. The physical properties of the resultant composite are considerably improved over a control prepared in the same manner but omitting the peroxide and maleic anhydride in the pretreatment. 
     EXAMPLE 20 
     The following materials are mixed in a Brabender Plasticorder at 130° C. for 15 minutes: 
     
         ______________________________________                                    
Material         Amount                                                   
______________________________________                                    
Clay             50.0%                                                    
Polyethylene     46.4%                                                    
Maleic Anhydride 2.4%                                                     
Dicumyl Peroxide 1.2%                                                     
______________________________________                                    
 
    
     In mixing these ingredients, 1/3 of the clay is charged to the mixing chamber, followed by 1/3 of the maleic anhydride-peroxide mixture and 1/3 of the polyethylene, followed by the same procedure twice repeated. In this manner, the clay adsorbs the maleic anhydride and subsequent reaction with the polyethylene readily occurs under the influence of the peroxide catalyst. When the polyethylene and maleic anhydride are mixed in the absence of the clay, the anhydride tends to sublime out of the heated mixing chamber. The compatibilized mixture may be processed in a manner usual for filled or unfilled thermoplastic resins, e.g., extruded into film or pipe, compression molded into shaped objects, injection molded, etc. 
     EXAMPLES 21-22 
     The process of Example 20 is repeated using varying amounts of materials as indicated in Table 3. Films 5 mil thick are molded from the compatibilized mixture obtained in each example and the water vapor transmission (WVT) is determined according to ASTM E96-63T. The results shown in Table 3 indicate that the practice of this invention results in decreased permeability. 
     
                       TABLE 3                                                     
______________________________________                                    
                            Maleic Anhy-                                  
       Polyethy-                                                          
                Clay   TiO.sub.2                                          
                            dride/Dicumyl                                 
                                       WVT, g/                            
Example                                                                   
       lene %   %      %    Peroxide % m.2/24 hr.                         
______________________________________                                    
Control                                                                   
       100      0      0    0          21.0                               
Control                                                                   
       85.7     0      0    9.5/4.8    7.5                                
21     47.0     45     5    2.0/1.0    10.6                               
22     57.6     35     5    1.6/0.8    8.0                                
______________________________________                                    
 
    
     EXAMPLE 23 
     In a Brabender Plasticorder there are mixed 70 parts of low density polyethylene having a melt index of 2, 30 parts of bentonite clay, 2 parts of maleic anhydride and 0.5 part of dicumyl peroxide. Mixing is continued at 150° C. for 20 minutes. A film 20 mils in thickness is prepared and tensile properties are determined. The composition is found to have higher yield strength and break strength than a corresponding composite prepared in the same manner but omitting the maleic anhydride and peroxide. 
     EXAMPLE 24 
     A mixture of 80 parts of asbestos, 2.4 parts of maleic anhydride, 1.2 parts of dicumyl peroxide and 16.4 parts of low density polyethylene are blended for 20 minutes at about 150° C. The composite is molded into a 1.8 inch thick sheet. The coupled molding is harder, stiffer, smoother, more homogeneous, has better flow and sands more smoothly than a corresponding uncoupled control sheet. The coupled molding is also much denser and has a higher hardness than an uncoupled control. 
     The following example illustrates the improved properties obtained by using the process of this invention in comparison to virgin polyethylene and to composites without the use of a catalyst, coupling agent or both. 
     EXAMPLE 25 
     Thirty parts of high density polyethylene (Fortiflex A60-70R having a melt index of 0.7) are mixed with 70 parts of clay (Hydrite 10) for 10 minutes at 150° C. in a Brabender Plasticorder (roller head No. 6 at 75 rpm). Six parts of coupling agent (maleic acid) and 1.5 parts of catalyst (t-butyl perbenzoate) are added and the mixing is continued for an additional 10 minutes. The resultant cooncentrate is then further blended with 40 parts of additional polyethylene to give a final composite with a 50/50 polyethylene/clay ratio. Table 4 shows physical properties of the composition (Sample E) and illustrates the improvements in mechanical properties obtained by this process in comparison to virgin polyethylene--i.e., polyethylene to which no clay, coupling agent or catalyst has been added (Sample A) and to polyethylene/clay composites prepared as described above, but with the omission of: catalyst and coupling agent (Sample B), coupling agent (Sample C) and catalyst (Sample D). 
     
                                           TABLE 4                                 
__________________________________________________________________________
                 TENSILE.sup.1                                            
                              FLEXURAL                                    
                                      IZOD IMPACT.sup.3                   
                 Yield                                                    
                     Break                                                
                         Elonga-                                          
                               MODULUS.sup.2                              
                                     ft.-lb./in                           
SAMPLE                                                                    
      DESCRIPTION                                                         
                 psi psi tion %                                           
                              psi    NOTCH                                
__________________________________________________________________________
A     Virgin Polyethylene                                                 
                 4410                                                     
                     4070                                                 
                         750  201,000                                     
                                     2.1                                  
B     Polyethylene/Clay                                                   
                 none                                                     
                     4040                                                 
                         2    447,000                                     
                                     0.3                                  
      (no catalyst or                                                     
      coupling agent)                                                     
C     Polyethylene/Clay +                                                 
                 none                                                     
                     4430                                                 
                         2    432,000                                     
                                     0.4                                  
      catalyst (no coupling                                               
      agent)                                                              
D     Polyethylene/Clay +                                                 
                 none                                                     
                     4780                                                 
                         3    434,000                                     
                                     0.5                                  
      coupling agent (no                                                  
      catalyst)                                                           
E     Compatibilized Poly-                                                
                 none                                                     
                     5160                                                 
                         3    499,000                                     
                                     2.8                                  
      ethylene/Clay                                                       
__________________________________________________________________________
 .sup.1 Tensile characteristics by ASTM D88264T                           
 .sup.2 Flexural Modulus by ASTM D79066                                   
 .sup.3 Izod Impact strength by ASTM D25656                               
 
    
     The following examples illustrate the improvements obtained when the two step process is utilized with a combination of high melt index coating polymer and low melt index matrix polymer. 
     EXAMPLE 26 
     Thirty parts of a high melt index, high density polyethylene (Fortiflex A60-1500N having a melt index of 15) are mixed with 70 parts of clay (Hydrite 10 for 10 minutes at 150° C. in a Brabender Plasticorder (roller head No. 6 at 75 rpm). Six parts of coupling agent (maleic anhydride) and 1.5 parts of catalyst (t-butyl perbenzoate) are added and the mixing is continued for an additional 10 minutes. The resultant encapsulated clay is then further blended with the required amount of a low melt index, high density polyethylene (Fortiflex A60-70R having a melt index of 0.7) to give a final composite with the desired polyethylene/clay ratio. Thus, 133 parts of low melt index polyethylene are added to produce a 70/30 composite, while 40 parts are used to produce a 50/50 composite. Table 5 shows physical properties of the final compositions (Samples D and F) and illustrates the improvements in mechanical properties obtained by this process in comparison to the unfilled blends of the same polyethylenes used (Samples A and B) as well as two uncompatibilized polyethylene/clay composites (Samples C and E) processed in the same manner as Samples D and F except that the coupling agent and catalyst are omitted. 
     
                                           TABLE 5                                 
__________________________________________________________________________
                   TENSILE.sup.1                                          
                                FLEXURAL                                  
                                        IZOD IMPACT.sup.3                 
                   Yield                                                  
                       Break                                              
                           Elonga-                                        
                                 MODULUS.sup.2                            
                                       ft.-lb./in                         
SAMPLE                                                                    
      DESCRIPTION  psi psi tion %                                         
                                psi    NOTCH                              
__________________________________________________________________________
A     Virgin Polyethylene*                                                
                   3820                                                   
                       2440                                               
                           140  190,000                                   
                                       2.0                                
B     Virgin Polyethylene*                                                
                   4010                                                   
                       2350                                               
                           63   219,000                                   
                                       1.4                                
C     Polyethylene*/Clay 70/30                                            
                   none                                                   
                       4230                                               
                           4    324,000                                   
                                       0.9                                
      (no catalyst or coupling                                            
      agent)                                                              
D     Compatabilized Polyethy-                                            
                   4780                                                   
                       3830                                               
                           25   349,000                                   
                                       3.1                                
      lene*/Clay 70/30                                                    
E     Polyethylene**/Clay 50/                                             
                   none                                                   
                       2630                                               
                           2    446,000                                   
                                       0.6                                
      50 (no catalyst or                                                  
      coupling agent)                                                     
F     Compatibilized Polyethy-                                            
                   none                                                   
                       5140                                               
                           5    307,000                                   
                                       4.9                                
      lene**/Clay 50/50                                                   
__________________________________________________________________________
 *Fortiflex A601500N plus Fortiflex A6070R in a 30:133 ratio              
 **Fortiflex A601500N plus Fortiflex A6070R in a 30:40 ratio              
 .sup.1 Tensile characteristics by ASTM D88264T                           
 .sup.2 Flexural Modulus by ASTM D79066                                   
 .sup.3 Izod Impact strength by ASTM D25656                               
 
    
     EXAMPLE 27 
     The process described in Example 26, Sample F is followed with the exception that a two-roll mill (61/2×12, friction ratio 1.2, and speed of 20 rpm) is used instead of the Brabender Plasticorder and maleic acid is used instead of maleic anhydride as the coupling agent. In this manner a compatibilized 50/50 polyethylene/clay composite is prepared having the following properties: 
     
         ______________________________________                                    
Tensile Yield Strength:                                                   
                    5200 psi                                              
Tensile Breaking Strength:                                                
                    5180 psi                                              
Tensile Elongation: 8%                                                    
Flexural Modulus:   365,000 psi                                           
Izod Impact:        5.2 ft.-lb/in. notch                                  
______________________________________                                    
 
    
     EXAMPLE 28 
     The process described above in Example 26 is repeated with the exception that Grex DA60-220 (M.I.=22) is used as the high melt index, high density polyethylene and Super Dylan 7004-2 (M.I.=0.5) is used as the low melt index, high density polyethylene. The properties of these compositions (Samples B and D) are set forth in Table 6 and compared to uncompatibilized polyethylene/clay composites (Samples A and C) processed in the same manner as Samples B and D except for the omission of catalyst and coupling agent. 
     
                                           TABLE 6                                 
__________________________________________________________________________
                 TENSILE.sup.1                                            
                              FLEXURAL                                    
                                      IZOD IMPACT.sup.3                   
                 Yield                                                    
                     Break                                                
                         Elonga-                                          
                               MODULUS.sup.2                              
                                     ft.-lb./in                           
SAMPLE                                                                    
      DESCRIPTION                                                         
                 psi psi tion %                                           
                              psi    NOTCH                                
__________________________________________________________________________
A     Polyethylene*/Clay                                                  
                 4820                                                     
                     4900                                                 
                         6    306,000                                     
                                     1.1                                  
      70/30 (no coupling                                                  
      agent or catalyst)                                                  
B     Compatibilized Poly-                                                
                 4710                                                     
                     3510                                                 
                         31   278,000                                     
                                     4.1                                  
      ethylene*/Clay 70/30                                                
C     Polyethylene**/Clay                                                 
                 none                                                     
                     4860                                                 
                         4    453,000                                     
                                     1.7                                  
      50/50 (no coupling                                                  
      agent or catalyst)                                                  
D     Compatibilized Poly-                                                
                 5000                                                     
                     4960                                                 
                         9    406,000                                     
                                     4.3                                  
      ethylene**/Clay 50/50                                               
__________________________________________________________________________
 *Grex DA60220 plus Super Dylan 70042 in a 30:133 ratio                   
 **Grex DA60220 plus Super Dylan 70042 in a 30:40 ratio                   
 .sup.1 Tensile characteristics by ASTM D88264T                           
 .sup.2 Flexural Modulus by ASTM D79066                                   
 .sup.3 Izod Impact strength by ASTM D25656                               
 
    
     The following example illustrates a comparison between the compatibilized compositions of this invention and carboxylated polymers containing fillers: 
     EXAMPLE 29 
     Thirty parts of high melt index, high density polyethylene (Fortiflex A60-1500N) are mixed with 70 parts of clay (Hydrite 10) for 10 minutes at 150° C. in a Brabender Plasticorder in the presence of 20 parts of maleic anhydride and 5 parts of t-butyl perbenzoate. The resultant coated clay is then blended with low melt index, high density polyethylene (Fortiflex A60-70R) at 150° C. for 10 minutes to yield a composite comprising 60% total polyethylene and 40% clay. Table 7 shows the physical properties of the final composition (Sample A). 
     For purpose of comparison, carboxylated polyethylene and ethylene copolymers containing carboxyl groups (Zetafax QX 3623.7, an ethylene-acrylic acid graft copolymer having a melt index of 5,, Surlyn A 1650, an ethylene-acrylic acid copolymer containing zinc ions; and DQDA 2300, a carboxylated polyethylene having a melt index of 7) are substituted for the Fortiflex A60-1500N polyethylene in the above process except that the coupling agent and catalyst are omitted. The carboxylated ethylene polymer treated clay is blended with Fortiflex A60-70R polyethylene as described above. The properties of these compositions are set forth in Table 7. The results indicate that the composite prepared by the maleic acid-peroxide coupling technique gives superior physical properties. 
     
                                           TABLE 7                                 
__________________________________________________________________________
                 TENSILE.sup.1                                            
                              FLEXURAL                                    
                                      IZOD IMPACT.sup.3                   
       DESCRIPTION                                                        
                 Yield                                                    
                     Break                                                
                         Elonga-                                          
                               MODULUS.sup.2                              
                                     ft.-lb./in                           
SAMPLE                                                                    
      Clay-Coating Polymer                                                
                 psi psi tion %                                           
                              psi    NOTCH                                
__________________________________________________________________________
A     Fortiflex  4940                                                     
                     4910                                                 
                         7    289,000                                     
                                     3.90                                 
      A60-1500N                                                           
B     Zetafax QX --  3900                                                 
                         12   234,000                                     
                                     1.20                                 
      3623.7                                                              
C     Surlyn A   --  4100                                                 
                         9    257,000                                     
                                     0.78                                 
      1650                                                                
D     DQDA       --  3860                                                 
                         9    257,000                                     
                                     1.03                                 
      2300                                                                
__________________________________________________________________________
 
    
     The following example illustrates the use of a copolymer of butylacrylate and acrylonitrile in the process of this invention: 
     EXAMPLE 30 
     Thirty parts of an acrylic elastomer obtained by the copolymerization of butyl acrylate and acrylonitrile is charged into a Brabender Plasticorder set at 150° C. Seventy parts of clay (Hydrite 10) is added and the composition is mixed at a 150° C. for 10 minutes. Thirty parts of the clay-polymer premix and 12.0 parts of additional acrylic copolymer are blended for 10 minutes in the mixer at 150° C. to yield a composite containing 50% acrylic elastomer and 50% clay. 
     In the manner described in the preceding paragraph, 18.6 parts of the same acrylic elastomer and 43.4 parts of clay are blended in a Brabender Plasticorder at 150° C. There are then added 3.72 parts of maleic anhydride and 0.93 parts of t-butyl perbenzoate and the composition is blended for 10 minutes at 150° C. This permix, comprising 70% clay and 30% acrylic elastomer, is blended with 11.1 parts of additional acrylic elastomer for 10 minutes at 150° C. to yield a compatibilized composite comprising 50% acrylic elastomer and 50% clay. 
     A comparison of the mechanical properties of the uncompatibilized composite prepared as described in paragraph 1 and the compatibilized composite prepared as described in paragraph 2 show that the properties of the compatibilized composite are superior to those of the uncompatibilized composite. The results are as follows: 
     
         ______________________________________                                    
                          COMPAT-                                         
                          IBILIZED                                        
           UNCOMPATIBILIZED                                               
                          COM-                                            
           COMPOSITE      POSITE                                          
______________________________________                                    
Tensile Strength, psi                                                     
Yield        221              318                                         
Break        95               163                                         
Elongation, %                                                             
             1090             940                                         
Flexural Modulus, psi                                                     
             320              350                                         
______________________________________                                    
 
    
     EXAMPLE 31 
     When the process described in Example 1 is repeated substituting for the polyethylene equivalent amounts of, respectively, a copolymer of ethylene and ethylacrylate; polystyrene; polubutadiene; a hydrolyzed ethylene-vinyl acetate copolymer originally containing 18% vinyl acetate; a polyamide obtained by the condensation of terephthalic acid and ethylene diamine; a polyurethane obtained by the reaction of toluene diisocyanate and polyethylene glycol; and an epoxy resin obtained by the condensation of Bisphenol-A and epichlorohydrin, compatibilized clay composites are obtained. 
     In the following discussion of molding techniques the composite used comprised 50 parts by weight clay coupled to 50 parts by weight of polyethylene by reaction with maleic anhydride and also the composite with a 30/70 clay/polyethylene ratio. The polyethylene-clay composites have a low melt index which is not normally associated with an injection molding grade of material. This melt index has been found to have a much greater than normal dependency on pressure. Thus, at high injection pressures this material behaves like a material having a higher melt index. 
     Filling of the mold cavity is greatly enhanced if the pressure drop in the cavity is minimized. This is achieved by utilizing full round runners and open gates with a vented mold, a design that is frequently used with filled plastics. 
     The polyethylene-clay composites have a fast freeze-off, i.e., they solidify rapidly in the mold cavity allowing the molded part to be ejected without distortion or sticking after a minimal cool-down period. 
     Various injection molded objects have been made on various molds and on a variety of machines. With optimum mold design and high injection pressure, molding of even complex shapes is very easy. Quite satisfactory results are also obtained under less than optimum conditions. The fast freeze-off, mentioned above, allowed molding cycles to be reduced by 25%, providing increased machine productivity. 
     At high pressures, the polyethylene-clay composites may be injection molded at relatively low temperatures, e.g., 325° F. while higher temperatures, e.g., 450° F. are required at lower injection pressures. Bath tub spouts were injection molded and these were subsequently chrome plated. The peel strength of the plating varied from 3 to 4 pounds in some cases, to 16 to 18 pounds in others. The plated tub spouts survived two thermal cycles of from 185° F. to -35° F. without failure whereas spouts molded from acrylonitrile-butadienestyrene rubber failed during the first cycle. 
     Other objects which were injection molded using polyethylene-clay composites include meter boxes weighing about 7 pounds each, pipe couplings ranging from 3-4 inches in diameter and tennis rackets. 
     The incorporation of about 0.1 to 0.5% of a lubricant such as zinc stearate can be utilized to improve flow during molding. 
     Generally, it has been found that flow rates during the injection molding process increase rapidly with pressure. It is preferred to use a relatively high injection pressure and a molding temperature of from 320° to 475° F. Only minimum cool-down times are required, resulting in significant decreases in the overall molding cycle times. Different types of machines measure pressure in different places, thus gauge readings are not comparable. Also, required pressure is dependent on die design, i.e., pressure drop in sprues and runners. 
     The low melt index of the polyethylene-clay composite makes it particularly well suited to extrusion. By extrusion at a melt temperature between 325° and 400° F., there were produced sheets 35 mil thick and 60 mil thick; tubing 3/4-inch in diameter and 1 inch in diameter; a 20 mil thick coating on a 10 mil diameter wire; 3 mil and 1 mil blown film; 1 inch conduit; and 2 inch pipe. The incorporation of about 0.1 to 0.5% of a lubricant such as zinc stearate greatly enhances extrudability. 
     The composites of this invention may be formed into foamed or porous objects by methods known in the art for manufacturing foamed plastic articles. For example, a foamed molding strip with a specific gravity of about 0.8 may be formed by extruding a dry blend of the polyethylene-clay composite, a chemical blowing agent such as Celogen A2 and a dry lubricant such as zinc stearate. Foamed sheets 3/8 and 1/2 inch thick having a specific gravity from 0.8 to 1.0 were molded by the Union Carbide process utilizing nitrogen gas as the blowing agent, producing products with an excellent stiffness to weight ratio. Again, a significant reduction in molding cycle time was realized. 
     Four ounce bottles with 60 mil and 30 mil wall thickness were manually blown from extruded straight parisons. 
     The 60 mil extruded sheet previously described was thermoformed to produce 2 inch deep receptacles having an outer diameter of 41/2 inches.