Mechanochemical synthesis and evaluation of rubber-thermoplastic polymer blends

Abstract

Natural rubber-polypropylene (NR/PP)blends have been studied under dif ferent conditions vis. processing parameters, mixer and at different ratios. It has been found that the requirement of a typical thermo­ plastic rubber can be achieved at a ratio of NR to PP of 60:40. It was found that chemical interaction between the two phases, which may take place as a result of mechanochemical reaction, could not be achieved, and the thermoplastic rubber produced was essentially a physical blend. The role of free-radical initiators such as benzoyl and dicumyl peroxide, on the behaviour of NR/PP(60/40) blends was investigated. It was shown that dicumyl peroxide was more effective than benzoyl peroxide in im­ proving mechanical properties of blends. Again no chemical reaction between the two phases could be achieved. Crosslinking reaction in the rubber phase may be responsible for the improvement in tensile properties in the presence of dicumyl peroxide. Ethylene-propylene terpolymer (EPDM)was also used in an attempt to improve the adhesion between the two phases. However, the results shown in this work con­ firm that no such interaction takes place in the presence of EPDM and the overall properties of the blend is lower than in the case of dicumyl peroxide. The performance of different ratios of natural rubber-polypropylene (60/40) composition as a solid phase dispersant (SPD)in polypropylene-polyeth­ ylene (1:1) blends was investigated. The behaviour of the above system was compared with that of EPDM when used as SPD in the same blends; NR/ PP offers better tensile properties while EPDM contributes mainly to impact performance of the PP/PE blends. Photo-oxidative stability of these blends in the presence of NR/PP and EPDM was also investigated. In general, EPDM system offered better overall stability. However, in both cases (i.e., NR/PP and EPDM systems), a synergistic system based on a combination of peroxide decomposer, UV-absorber/screen and free-radical scavenger e.g., HOBP/Cyasorb 1084/Irganox 1076, was shown to be the best photo-antioxidant system. The effect of partial replacement of fresh natural rubber by reclaim rubber (RR)on the properties of NR/PP (60/40) blends was studied. It was found that properties of natural rubber-polypropylene (60/40) blend could be maintained by replacing up to half of the fresh rubber by re­ claim rubber. The behaviour of this composition (i.e.,(NR/RR)/PP at a ratio of 30:30:40)as a solid phase dispersant in PP/PE(1:1) blend was investigated. It was shown that although this system offers a better photo-oxidative stability than a blend which is based entirely on fresh rubber, its impact performance is inferior to blends containing either NR/PP (i.e., no RR) or EPDM as SPD's.