Chlorinated PVC blends with improved processability

#Chlorinated polyvinyl chloride (CPVC) is a rigid thermoplastic material that was introduced in 1960 for water distribution piping that can operate at 100 psi and 180.degree. F. These conditions are safely above typical temperatures and pressures of domestic water heaters. Because CPVC retains physical properties at temperatures well above other thermoplastics, it has been specified for a variety of other extruded and custom-molded products. In view of its inertness in the presence of many corrosive fluids, CPVC has been used widely in electroplating, metal finishing, in other corrosive fluid systems, in pipe and fittings, in pumps, tanks and other products.

#The post-chlorinated polyvinyl chloride resins can be processed and formed by conventional techniques such as milling, calendering, extruding, laminating, compression molding, and transfer molding. One major disadvantage that is experienced with CPVC resins is their poor processability. This is exemplified by milling CPVC on a roll mill which results in high torque and high temperatures accompanied by its decomposition. Softening additives or plasticizers have been added to CPVC in order to improve its processability, however, although its processability is thus improved, these additives produce undesirable effects. Some of the more significant detrimental effects produced by inclusion of the additives are heat sensitivity, softness and weakness in terms of lower tensile strength and less desirable chemical and electrical properties than exhibited by CPVC alone. These negative attributes of the additives on CPVC limit usefulness of the modified CPVC in the manufacture of rigid plastic articles.

#Poor processability of CPVC has been recognized and attempts have been made to ameliorate this problem. U.S. Pat. No. 3,268,626 to Jennings describes a thermoplastic composition which has substantially the same properties as CPVC resin but which also possesses improved processability and shock resistance. This composition comprises CPVC resin containing small amounts of two copolymers, i.e., a first copolymer of styrene and acrylonitrile containing 20 to 35% by weight of polymerized acrylonitrile units having a dilute solution viscosity of 0.3 to 0.7; and a second rubbery, cross-linked copolymer of butadiene and acrylonitrile containing 20 to 30% by weight of polymerized acrylonitrile units. On the basis of 100 parts by weight of CPVC, amount of styrene-acrylonitrile copolymer can vary from 1 to 15 parts by weight and amount of butadiene-acrylonitrile copolymer can vary from 3 to 15 parts by weight.

#The attached drawing represents tests that were performed on CPVC resins alone and blends thereof with unmodified and modified terpolymers with molecular weight modifiers. These tests were performed on a Brabender milling apparatus to evaluate processability of CPVC resins and blends thereof with the terpolymers pursuant to the invention defined herein.

#The invention described herein relates to a thermoplastic composition which is a blend of unplasticized CPVC resin and a terpolymer of a ring substituted or unsubstituted alkylstyrene, ring substituted or unsubstituted vinyl benzene or an alkyl acrylate, and a nitrile. Dilute solution viscosity (DSV) in methyl ethyl ketone of suitable terpolymers is less than 2, preferably 0.1 to 1.5, and more preferably 0.5 to 1. Amount of the terpolymers blended with the CPVC resin can vary from a minimum amount sufficient to improve processability of the resulting blend without adversely affecting other properties thereof, to a maximum amount which does not adversely affect the improved processability nor substantially adversely affect the other properties.

#Blends of CPVC with the terpolymers are yellowish, transparent, and have only one glass transition temperature. Such CPVC blends have improved heat deflection temperature, tensile strength, as well as processability.

#As is well known, one major drawback of CPVC resins is their poor processability. Since it is known that polystyrene and low molecular weight poly alpha methylstyrene are often used as processing aids for plastics, attemps were made to blend these processing aids and copolymers thereof with other monomers in order to improve processability of CPVC without adversely affecting other properties thereof. When CPVC was first blended with a terpolymer of alpha methylstyrene, styrene and acrylonitrile, processability of such blends was as poor as that of CPVC alone. After evaluating results of these blends, it was decided to try lower molecular weight terpolymers. The use of the terpolymers of lower molecular weight falling within the herein defined DSV ranges, produced the desired results.