Blending with Elastomers

Rubber matrices have commonly been used as a second phase to improve the toughness of brittle thermoplastic materials, such as polypropylene and polyethylene. These systems, commonly referred to as polyolefin thermoplastic elastomers (TPOs), are a special class of thermoplastic elastomers that combine the processing characteristic of plastics at elevated temperatures with the physical properties of conventional elastomers at service temperature, playing an increasingly important role in the polymer material industry. Polyolefin blends attract additional interest due to the possibility of recycling plastic wastes, avoiding the complex and expensive processes of separation of the different components. 

Several elastomer matrices have been used to improve the mechanical properties of PLA, but special attention has been paid to polyurethane elastomer (PU) ° and natural rubber (NR). Lt is well known that thermoplastic polyurethane elastomers are widely used in a diverse range of implantable medical devices due to a unique combination of toughness, durability, flexibility, biocompatibility and biostability. Ln addition, it 

Ishida et reported melt blending of PLA with four types of common rubbers, ethylene-propylene copolymer (EPM), ethylene-acrylic rubber (EAM), acrylonitrile-butadiene rubber (NBR) and isoprene rubber (IR), to toughen PLA. All blends showed separated phase morphology where the elastomer phase was homogeneously distributed in the form of small droplets in the continuous PLA phase. Izod impact testing showed that toughening was achieved only when PLA was blended with NBR, which showed the smallest rubber particle size in the blends. In addition, the interfacial tension between both phases, PLA and NBR, was the lowest. 

---

PVC is flexibilized by addition of plasticizers as already noted. It is also made more flexible through blending with elastomers that act as impact modifiers. These blends are used when impact resistance is essential. 

Generally, the impact resistance of a polymeric material can be improved by blending with elastomers or other resilient polymers. However, owing to the poor miscibility often occurring among blend constituents, a suitable compati-bilizer must be added to the formulation. 

Piccodiene . [Hercules] Aliphatic hy-drocarbmi resin thermoplastic with balanced tack, adhesive, and cohesive props, when blended with elastomers. 

PP blends with PE have already been discussed. PP blends with elastomers will be discussed in the following parts. In Table 1.48 few examples of PP blends with other PO s are given. 

Mixtures of polar polymers, such as PVC, PC, PMMA, TPU, PA, PEST, PGI, SAN, or ABS could be compatibilized by incorporation of two copolymers, the first containing vinyl alcohol, the second an anhydride. For example, blends of TPU with Phenoxy, EVAl, COPO, modified cellulose, and/or polyalkylene oxide, had attractive physical, optical and barrier properties, and were melt-processable without degradation. They could be transformed into films, sheets, or bottles with good barrier properties. Blends containing PA were used for films, tubes, toys, gears, bearings, shafts, curtain sliders, door rollers, etc. The blends with elastomers were reported suitable for improved wiper blades [La Fleur et al., 1994]. 

PiBj, PiB and EPDM are able to act as diluents for iPP at lower concentration. In blends with elastomer content larger than 20%, the mutual solubility of the two components in the melt, decreases with the increase of the elastomer content ... 

PP is often made using two reactors in series the first reactor makes isotactic PP, while the second reactor makes a random copolymer of PP and PE. The copolymer is amorphous, and it is blended with the PP homopolymer to enhance impact resistance (Tan et al. 2005). PP blends with elastomers will be discussed in the following parts. In Table 1.47 few examples of PP blends with other POs are given. 

Duraloy PBT blended with elastomers or POM Hoechst Celanese Corp. 

In Section 6.8, CNIS data are compared with measurements of strain energy release rates G/ obtained under the well-defined criteria of linear elastic fracture mechanics of materials under the conditions of small-scale yielding. A variety of polypropylene resins, their blends with elastomers, rigid fillers, or both are included in this study. 

PP blends with elastomers and those with engineering resins are discussed in separate chapters. 

To improve low-temperature impact performance of PP, it has been blended with elastomers, viz. TPU or nitrile-butadiene rubber (NBR). Addition of wfTPU) < 15 wt.% improved impact and other mechanical properties. Significant improvements of the tensile strength, as well as the tensile strain and strength at break, were obtained by adding to PP 2 wt% of di-methylol-p-octyl phenol, than blending it with NBR. 

---