Toughness of PVC

The 8 values of both PVC and TPU are available. The selection of TPU should also be based on the application itself. For example, in the case of modifying PVC, if TPU is used as the substituent of liquid plasticizer, then it must have a good compatibility with PVC in order to make a homogeneouslike system. If TPU is just used to improve the toughness of PVC, then the amount of TPU in the blends is usually less than 15 parts (PVC as 100 parts), therefore, partial compatibility is enough. 

Two independent groups have reported that polypyrrole can be formed within a swollen film of poly(vinyl chloride) attached to an electrode surface 296 297). Niwa etal. 298 299) have described the properties of these composites, which, they claim, can combine the toughness of PVC with the conductivity of polypyrrole. 

Fig. 11. Effect of local loading rate on fracture toughness of PVC using various specimen configurations and data reduction schemes.

Figure 10.15. Toughness of PVC plastificates containing diesters of sebaoic acid of different alcohols (methyl, ethyl, butyl, and octyl). [Data from Gibbons W S Kusy R V, Polymer, 39, No.26, 1998, p.6755-65.]...

FIGURE 14.17 Variation of toughness of PVC-PMMA blends with variation of PVC-PMMA blend ratio (w/w) (Higashida et al., 1992)... 

The toughness values are obtained from the stress-strain curves and not from the conventional Charpy or Izod impact tests. Hence their units are obtained in MPa as observed. The variation in ultimate tensile strength and toughness of PVC-PEA blends have been shown in Figures 14.18 and 14.19. 

A major deficiency of PVC for many applications (for example in the building industry) is its poor resistance to impact. Consequently it became a common practice during the 1970s to incorporate rubber-based modifiers such as ABS, MRS, and MARS to improve the toughness of PVC. In this particular respect, they were very successful and much higher levels of initial impact resistance were achieved. However, PVC impact modifiers all contain butadiene segments which are oxidatively very unstable, particularly at high temperatures and in... 

The valuable characteristics of polyblends, two-phase mixtures of polymers in different states of aggregation, were also discussed in the previous chapter. This technique has been widely used to improve the toughness of rigid amorphous polymers such as PVC, polystyrene, and styrene-acrylonitrile copolymers. 

There are a number of applieations such as bottle and film where tough materials of high elarity are desired. The advent of MBS material has been a significant advance to meet the requirements. It has been found possible here to produce an additive with sufficiently different solubility parameters from the PVC for it to exist in the disperse phase but with a very similar refractive index to the PVC so that light scattering at the interface between the two phases is at a minimum. However, owing to differences in the formulation of PVC compounds, a particular MBS modifier may not have exactly the same refractive index as the PVC eompound. 

Bromine compounds are often used as flame retardant additives but 15-20ptsphr may be required. This is not only expensive but such large levels lead to a serious loss of toughness. Of the bromine compounds, octabromo-diphenyl ether has been particularly widely used. However, recent concern about the possibility of toxic decomposition products and the difficulty of finding alternative flame retarders for ABS has led to the loss of ABS in some markets where fire retardance is important. Some of this market has been taken up by ABS/PVC and ASA/PVC blends and some by systems based on ABS or ASA (see Section 16.9) with polycarbonates. Better levels of toughness may be achieved by the use of ABS/PVC blends but the presence of the PVC lowers the processing stability. 

This is used most often in process plants. It is a tough, low-cost material with probably the widest range of chemical resistance of any of the low-cost plastics. On a volume basis, PVC is more favorable than polypropylene because the modulus of PVC is considerably higher than that of polypropylene, so it will form more rigid structures when used at the same thickness. On a weight basis it is not as favorable as PVC because it has a specific gravity of 1.4 compared with 0.92 for polypropylene. 

Low-density polyethylene (polythene) is a relatively cheap, tough, flexible plastic. It has a low softening point and is not suitable for use above about 60°C. The higher density polymer (950 kg/m3) is stiffer, and can be used at higher temperatures. Polypropylene is a stronger material than the polyethylenes and can be used at temperatures up to 120°C. The chemical resistance of the polyolefines is similar to that of PVC. 

The toughness of brittle polymers, such as rigid PVC, may be improved by the addition of a semicompatible elastomer such as a polyethyl acrylate graft copolymer. Such composites are harder than polymers plasticized with liquid plasticizers. 

Another important addition polymer is polyvinylchloride (PVC), which is tough and easily molded. Floor tiles, shower curtains, and pipes are most often made of PVC, shown in Figure 12.30. The addition polymer polyvinylidene chloride (trade name Saran), shown in Figure 12.31, is used as plastic wrap for food. The large chlorine atoms in this polymer help it stick to surfaces such as glass by dipole—induced dipole attractions, as we saw in Section 7.1. 

Lucovyl H 4010 is used in all applications of PVC where the material must be transparent, rigid, tough, and must satisfy food legislation. 

The possibility of fracture on impact can be reduced by dispersing an elastomeric phase uniformly through the rigid material, as it is done in polyblends or better in grafting vinyl monomer upon rubber. H. Bartl and D. Hardt describe the manufacture of a tough rigid PVC by grafting vinyl chloride upon an elastomeric ethylene—vinyl acetate copolymer. 

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