Polypropylene blends with commodity resins

Blending also addressed two aspects of PP processability high viscosity and poor melt strength. Several external lubricants were incorporated into the resin, viz. s 5 wt.% of either polydimethylsiloxane (PDMS), fluorinated polymers or elastomers. Usually, these blends also showed improved impact strength and elasticity. Another modification involved either copolymerization or grafting with acidic monomers, thus forming a transient crosslinking by the ion clusters. The presence of 

Modification of the PP chain was also used as a preliminary step for improving the weatherability by blending with resins that have good resistance to ultraviolet (UV) irradiation, viz. acrylics, vinyls and/or vinylidenes [2, 3]. 

Almost all PP blends are immiscible the only miscible ones are those with aPP, some sPP, EPR containing la s 10% of ethylene, and atactic polybutene-1 (PB-1) [4]. However, the isotactic PB-1 was reported immiscible with PP [5]. In immiscible blends, the interfacial adhesion in both molten and solid states is usually poor, thus compatibilization is advisable. However, as for any immiscible polymer pair, there are three cases where acceptable product is obtained without compatibilization (1) at low concentration of either component, i.e., at ) = 1 - j s 0.1 (2) blends with phase co-continuity, e.g., = inversion/ (3) for applications not requiring high strength. 

Compatibilization of PP blends is based on either copolymerization or grafting [3, 4]. In both cases, one part of the resulting compatibilizer should be miscible with the PP phase, the other with the second component. For example, EPR is used in PP/PE blends the propylene part of EPR provides miscibility with PP and the ethylene part does so with PE. For the purpose of compatibilization, the block-type EPR is more desirable than random. Acid or anhydride modified PP is used for blends with PA, PC or PEST. Here, the PP part provides miscibility with the PP phase, while the acidic or anhydride groups usually react with chain-end groups of the other poljmier to form a compatibilizing block copolymer. 

Three types of blend crystallization are distinguished (1) simultaneous of both components (2) in the presence of molten second component and (3) in the presence of solid second component. The case (1) takes place when ranges of the crystallization temperatures, T, of the two polymers overlap and their crystallization rates are similar their mixed spherulites usually have additive physical properties. For the case (2), Paul and Barlow predicted five crystallization patterns (i) no effect (ii) retardation (iii) delay (iv) acceleration and (v) crystallization of a 

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Blending with LLDPE is used to upgrade the properties and improve the processing of conventional LDPE. For example, by adding 25% of ethylene—1-butene LLDPE resin with I2 of 0.5 to conventional LDPE resin, the dart impact strength of 75 p.m film is increased from 490 to 560 g, the puncture strength from 41 to 49 J /mm (770-920 ft-lbf/in.), and the tear strength from 43 to 63 N /mm (246—360 ppi). CompositionaHy uniform VLDPE resins are used in blends with HDPE, commodity LLDPE, and polypropylene (PP) (70,71,89). 

The blends described in the EDCPB provide a cross section of commercial alloys available in Asia, Europe, and North America. The focus is on blends with the five principal engineering resins polyamides, thermoplastic polyesters, polycarbonates, polyoxymethylenes (acetals), and polyphenylene ethers. There are but few examples of the commodity (and these mainly with polypropylene) as well as with high performance specialty resin blends. This may leave a wrong impression of the global blend industry. 

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