Since PVC has a high polarity and high compatibility with a variety ofother high-performance plastics, it is possible to mix these easily to form polymeralloys. By polymer alloying techniques some of the shortcomings of rigid PVCproducts can be modified. Fig.1 shows the outline of property modificationthrough polymer alloying.

In addition to the polymer alloying technique, modifications of heat resistanceetc.

Impact resistance

Generally,in order to improve the impact resistance of PVC products, impact modifiers(toughening agents) which have rubber-like properties such as ABS, MBS, acrylicrubber, chlorinated polyethylene or EVA, are mixed with PVC. Sufficient impactresistance for practical use can be obtained by blending 5~20 weight parts ofthese impact modifiers to 100 weight parts of PVC. The impact modifier in theform of micro particles is dispersed within the molecular structure of PVC.When the PVC products receive an impact, these micro particles in the molecularstructure absorb the impact energy and prevent damage to the PVC product. PVCwhose impact resistance is modified is used in a wide range of applicationsincluding exterior construction materials (window frames, siding), industrialboards, impact resistant water pipes, rigid PVC packaging (blister packs, caps,casings), surface protecting films, or electrical parts (connectors).

Heat distortion temperature (softening temperature)

Inorder to enhance the heat resistance, heat distortion temperature or softeningtemperature of PVC products, heat resistant resins such as ABS resins, α-methylstyrene copolymers, or afterchlorinated PVC are usually blended in.Fig.3 and Fig.4 show the improvement of the softening temperature by blendingABS as an example, and the improvement of thermal deformation temperature byblending after chlorinatedPVC,respectively.

PVC with enhanced heat resistance is used for heat resistant rigid PVC pipes,such as hot water supply pipes or electric cable protecting tubes, andinstrument panels of vehicles. On the other hand, soft PVC products withmodified heat resistance can be manufactured by blending with a high-polymerplasticizer. Such products are used for heat resistant cable covering and otherapplications.

Prevention of plasticiser bleed and volatilisation
In order to prevent bleeding, volatilisation or migration of plasticisers toother materials from soft PVC products, plasticizers with high molecular weightor high compatibility with PVC are adopted. Fig.5 shows an example where apolyester plasticiser with a molecular weight of 1,500 is used to replace DOP,which is a general-purpose plasticiser with a molecular weight of 390. Testpieces are placed in an oven of 160 °C and rates of weight loss are measured torepresent volatilisation of plasticisers as time elapses.

On the other hand, plasticiser freeflexible PVC products are manufactured as in the case of graft polymerised EVA(ethylene vinyl-acetate copolymer) and PVC, or a terpolymer composed ofethylene-vinyl acetate-carbon monoxide. PVC including plasticisers which do notmigrate or bleed at high temperatures is used for electric/electronic parts andheat resistant cables. Some of the non-migrating type plasticizers are used formedical bags/tubes or industrial hoses.