Polymer blends with chlorinated polyethylene

The effect of the amorphous component on the crystallization ability of the crystallizable polymer has been examined for some miscible blends. An improvement of poly( -caprolactone) (PCL) crystallization has been observed in blends with chlorinated polyethylene (CPE) [20], while for poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) [21], PCL/SAN [22], and poly(butylene therephthalate)/polyarylate (PBT/ PAr) [23] blends, the crystallization ability is markedly reduced. 

Dimercapto-l,3,4-thiadiazole derivatives, accelerated by amines, are used to cross-link chlorinated polyethylene. Polyisobutylene containing brominated i ra-methylstyrene cure functionahty can be cross-linked in polymer blends with dimercapto-1,3,4-thiadiazole derivatives accelerated with thiuram disulfides. Trithiocyanuric acid is suggested for use in polyacrylates containing a chlorine cure site and in epichlorohydrin mbbers. 

FIGURE 11,1 Ultrasonic velocity versus acrylonitrile-butadiene mbber/ethylene-propylene-diene monomer (NBR-EPDM) blend composition (a) no compatibiUzer, (b) with chloro-sulfonated polyethylene (CSM), and (c) with chlorinated polyethylene (CM). (From Pandey, K.N., Setua, D.K., and Mathur, G.N., Polym. Eng. Set, 45, 1265, 2005.)... 

When two polymers interact or react with each other, they are likely to provide a compatible, even a miscible, blend. Epoxidized natural rubber (ENR) interacts with chloro-sulfonated polyethylene (Hypalon) and polyvinyl chloride (PVC) forming partially miscible and miscible blends, respectively, due to the reaction between chlorosulfonic acid group and chlorine with epoxy group of ENR. Chiu et al. have studied the blends of chlorinated polyethylene (CR) with ENR at blend ratios of 75 25, 50 50, and 25 75, as well as pure rubbers using sulfur (Sg), 2-mercapto-benzothiazole, and 2-benzothiazole disulfide as vulcanizing agents [32]. They have studied Mooney viscosity, scorch... 

Fig. 7a-c. Phase contrast microscope pictures of a blend of ethylene-vinyl acetate copolymer (40% vinyl acetate) with chlorinated polyethylene (43 % chlorine) before and after phase separation. Since both polymers are elastomers the mobility is quite high. The original pictures are coloured red and green. These black and white pictures have enhanced contrast to make the phase separation clear... 

One example in this category is the case of one polymer in two stereoregular forms Other examples are of two polymers which are chemically very similar such as poly(methyl acrylate) with poly(vinyl acetate) A series of systems which have been studied in some detail are various mixtures of chlorine containing polymers. Blends of chlorinated PVC with PVC have been studied It has been suggested that at 65.2 % wt.- % chlorine they are miscible and at 67.5 wt.- % they are not. Chlorinated polyethylene with 45 wt.- % chlorine has also been found to be miscible with PVC In this case it was suggested that phase separation occurs on heating. 

Figure 2.14 Miscibility map for blends of chlorinated polyethylene (CPE) and a-methyl styrene/acryloni-trile (MSAN) copolymer (reproduced (replotted) from reference Cowie,J.M.G.,Elexpuru,E.M. and McEwen,. y,J.Polym.Sci. Part B Polym.Phys.,( 99 ) 29, p. 407, with permission of John Wiley Sons, Inc.)...

Thermoplastic chlorinated polyethylenes are seldom used on their own but primarily in blends with other polymers, particularly PVC. If chlorination is taken to a level at which the polymer is only semi-compatible with the PVC, a blend with high impact strength may be obtained. In these circumstances the material is classified as an impact modifier. 

Blending of polymers is an attractive method of producing new materials with better properties. Blends of aliphatic polyesters, especially of poly(e-CL), have been investigated extensively and have been the subject of a recent review paper [170]. Poly(e-CL) has been reported to be miscible with several polymers such as PVC, chlorinated polyethylene, SAN, bisphenol A polycarbonate, random copolymers of Vdc and VC, Vdc and AN, and Vdc/VAc, etc. A single composition-dependent Tg was obtained in the blends of each of these polymers with poly(e-CL). This is of interest as a polymeric plasticizer in these polymers. Blends of PVC and poly(e-CL) with less than 50 wt % of poly(e-CL) were homogeneous and exhibited a single Tg. These blends were soft and pliable because the inherent crystallinity of poly(e-CL) was destroyed and PVC was plasticized... 

On the other hand, some mechanically compatible blends as well as some dispersed two-phase systems have made respectable inroads into the commercial scene. Many of these are blends of low-impact resins with high-impact elastomeric polymers examples are polystyrene/rubber, poly (styrene-co-acrylonitrile) /rubber, poly (methyl methacrylate) /rubber, poly (ethylene propylene)/propylene rubber, and bis-A polycarbonate/ ABS as well as blends of polyvinyl chloride with ABS or PMMA or chlorinated polyethylene. 

In situ polymerisation does not however guarantee homogeneous blends as two phase regions can exist within the polymer/polymer/monomer three component phase diagram. In the case of vinyl chloride polymerisation with solution chlorinated polyethylene, the vinyl chloride has limited solubility in both poly(vinyl chloride) and chlorinated polyethylene. The phase diagram has the form shown in Fig. 3 The limit of swelling of vinyl chloride in the chlorinated polyethylene is A and the highest concentration of PVC prepared by a one-shot polymerisation is B. 

As reported by Diehl et al. [58], interpolymers are also compatible with a broader range of polymers, including styrene block copolymers [59], poly(vinyl chloride) (PVC)-based polymers [60], poly(phenylene ethers) [61] and olefinic polymers such as ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer and chlorinated polyethylene. Owing to their unique molecular structure, specific ESI have been demonstrated as effective blend compatibilizers for polystyrene-polyethylene blends [62,63]. The development of the miscibility/ compatibility behavior of ESI-ESI blends differing in styrene content will be highlighted below. 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

In addition to ABS, with polybutadiene as the elastifying component, there is another forerunner among the polymer products formulated for low-temperature impact resistance, PVC-U. Elastifying ligands include EVAC, EVAC/VC graft polymer, PAEA C (polyacrylic acid ester/vinyl chloride copolymer), ACE (acrylic ester/MMA graft polymer) as well as the chlorinated low-pressure polyethylene PE-C in use for over 35 years. All of the polymer blends listed here are suitable for outdoor applications since they contain no unsaturated components. Polybutadiene-modified products are better suited to interior applications, for example MBS, a methylmethacrylate/butadiene/styrene graft polymer [55]. 

The major polymers with whieh PVC ean be alloyed are aerylonitrile-butadiene eopolymers, aerylonitrile-butadiene-styrene terpolymer, ethylene-vinylacetate copolymers, chlorinated polyethylene, chlorosulfonated polyethylene, thermoplastic polyurethanes, acrylics and methacrylics, and polycaprolactone. Table 18 lists the property enhancements achieved by blending these polymers with PVC. 

The significant advantages of products produced from chlorinated polyethylene are their improved resistance to chemical extraction, plasticizer volatility, and weathering. Products made from chlorinated polyethylene do not fog at higher use temperatures and can be made completely flame retardant. They do, however, exhibit chemical instability similar to that of polyvinyl chloride (PVC). They may be used as primary compounding materials or as blending resins with PVC, high- and low-density polyethylene, and other polymers. They are cross-linkable by irradiation or chemical means. 

A more positive aspect of the chemical functionality of PHB is that the polymer can act as a processing acid for other polymers such as PVC and polyacrylonitrile. Both PHB homopolymer and the HB-HV copolymers reduce the gelation time and improve the surface finish of extrudates when blended with unplasticized PVC at the 1% level prior to processing. They function in much the same way as high molecular weight polyacrylates and chlorinated polyethylene, which are already used commercially in this application. In addition, the power required to melt-extrude polyacrylonitrile-based resins, such as the Barex range from Lonza AG, is much reduced by the addition of 1% PHB to the polymer. 

---