Preparation plastic/rubber blends

For the purpose of this discussion, the basic processes for the preparation ofblends prepared by polymer melt-mixing will be considered. The procedures discussed here are applicable to most commercially produced plastic/rubber blends. 

One can use a roll mill to prepare the plastic/rubber blends, using heated rolls, in the laboratory. However, for production this may be very cumbersome and, since the polymers are melt-mixed at high temperature in the atmosphere, handling of the molten polymer and degradation by heat could be an issue. Quality consistency could be another issue with this process. 

An open mill is a short name for an open plastic mixing mill. It is a roller exposed rubber machine used in a rubber factory to prepare plasticated rubber and rubber compounds, or to conduct heat refining, and it is part of the basic equipment in the rubber industry. An open mill mainly relies on two relative rotary rollers to extrude and shear rubber material and cut the macromolecule chains inside rubber through multiple kneading and associated chemical reactions in the process of kneading, which evenly blends all kinds of components inside rubber and finally achieves the purpose of milling. 

TPEs prepared from rubber-plastic blends usually show poor high-temperature properties. This problem could be solved by using high-melting plastics like polyamides and polyesters. But, often they impart processing problems to the blends. Jha and Bhowmick [49] and Jha et al. [50] have reported the development and properties of novel heat and oil-resistant TPEs from reactive blends of nylon-6 and acrylate rubber (ACM). The properties of various thermoplastic compositions are shown in Table 5.4. In this kind of blend, the plastic phase forms the continuous phase, whereas... 

Preparation of the Blends of Plastics and Crosslinked Rubbers 137 Table 3.3 Attributes of different crosslinking systems for unsaturated polymers. 

Preparation of Plastic and Crosslinked Rubber Blends (TPVs) by a Batch Process... 

The process for the batoh preparation of TPVs is very similar to the one described above. The process layout for a crosslinked rubber/plastic blend preparation is the same as that for non-crosslinked blends (Figure 3.6). The prcxress steps involved in a plastic-crosslinked rubber blend prcxluction by a batch process are ... 

Plastic/mbber blends offer a way to combine the best of both worlds - the softness and elasticity of rubber and the processability of thermoplastic. As discussed in this chapter, there are several methods for the preparation of plastic/mbber blends. Physical melt mixing of the plastics and mbbers provides a simple, quick, and most economical way of producing such blends. One can also prepare multicomponent and specialty blends by this procedure. Both Banbury batch mixers and twin-screw mixers are used to produce these blends. Most physical blends are now prepared by this melt-mbdng process. 

Furthermore, the C=C bonds in the natural rubber structure might induce poor thermal and oxidative resistance in the natural rubber blends. Thus, Thawornwisit and coworkersproposed the preparation of hydrogenated natural rubber, which is one of the chemical modifications available to improve the oxidation and thermal resistance of diene-based natural rubber before blending with poly(methyl methacrylate-co-styrene). The poly(methyl methacrylate-co-styrene) was resistant to the outdoor environment and had excellent optical properties with a high refractive index, but it was extremely brittle and had low impact strength. Hydrogenated natural rubber could, however, be used as an impact modifier, as well as to improve its thermal and oxidative resistance for these acrylic plastics. 

Iron oxides, which were undoubtedly components of these prehistoric paints, still find application today as low-cost, low-toxicity pigments in paint, plastics, rubbers and cosmetics. The three main colours available are red (haematite-, Fe203), yellow (goethite FeO.OH) and black (magnetite-, Fe304), and other colours can be produced by blending these three. The oxides are generally prepared by precipitation from aqueous solution ... 

Elastomer-plastic blends without vulcanization were prepared either in a two roll mill or Banbury mixer. Depending on the nature of plastic and rubber the mixing temperature was changed. Usually the plastic was fed into the two roll mill or an internal mixer after preheating the mixer to a temperature above the melting temperature of the plastic phase. The plastic phase was then added and the required melt viscosity was attained by applying a mechanical shear. The rubber phase was then added and the mixture was then melt mixed for an additional 1 to 3 min when other rubber additives, such as filler, activator, and lubricants or softeners, were added. Mixing was then carried out with controlled shear rate... 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

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