Modified PVC

RigidPoly(vinylchloride) Foam. The techniques that have been used to produce rigid vinyl foams are similar to those for the manufacture of flexible PVC foams. The two processes that have reached commercial importance for the manufacture of rigid vinyl foams (246) are the Dynamit-Nobel extmsion process and the Kleber-Colombes Polyplastique process for producing cross-linked grafted PVC foams from isocyanate-modified PVC in a two-stage mol ding process. 

Fig. 10. Preparation and morphology of toughened PVC (a) secondary PVC grain (50—250 flm) (b) modified PVC with coherent primary grain (ca 1 -lm) (220). CPE = chlorinated polyethylene EVA = ethylene—vinyl acetate copolymers ABS = acrylonitrile—butadiene—styrene MBS = methyl...

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. 

A series of polyester-based TPU (566TPU series) were synthesized in our lab and used to blend with PVC to manufacture a modified PVC material for medical uses [14]. Morphological studies showed that 566TPU has very good compatibility with PVC. Detailed mechanical and electronic property tests were also conducted. Some of the data are provided in Tables 3 and 4. 

These results showed that TPU, represented here by 566TPU, has the best overall results in modifying PVC among those tested. It has good compatibility with PVC, and the resulting polymeric blends have good mechanical properties suitable for various processing methods. 

It may not be appropriate to compare the thermal stability characteristics of VC/VAc copolymer to that of a VC homopolymer (PVC). The copolymerization would involve different kinetics and mechanism as compared to homopolymerization resulting structurally in quite different polymers. Hence, copolymerization of VC with VAc cannot be regarded as a substitution of chlorines in PVC by acetate groups. To eliminate the possibility of these differences Naqvi [45] substituted chlorines in PVC by acetate groups, using crown ethers (18-crown-6) to solubilize potassium acetate in organic solvents, and studied the thermal stability of the modified PVC. Following is the mechanism of the substitution reaction ... 

Thermal stabilities of modified PVC samples acet-oxylated to varying degrees (reaction temperature 46°C) were determined [45]. Rate of thermal dehydrochlorination at 1% degradation was taken as a measure of thermal stability. The log of the degradation rate is plotted against the acetate content of the polymer in Fig. 2. 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

There are various requirements for impact-modified PVC. The most demanding is for outdoor sidings and window frames, where lifetimes of 20 years are expected. Because butadiene polymers or copolymers (e.g., acrylonitrile/butadiene/styrene (ABS), methyl methacrylate/butadiene/styrene (MBS)) are susceptible to UV degradation these polymers are usually not employed instead acrylate polymers are used for these applications. 

Polyvinyl Chloride. Biswas and Moitra [102] observed substantial increase in conductivity for metal modified PVC (Fig. 29). Table 1 presents the electrical conductivity data of the PVC-DMG-M(II) complexes. Interestingly, conductivities appreciably increase relative to PVC in the order PVC < PVC-DMG-Cu(II) < PVC-DMG-Ni(II) < PVC-DMG-Co(II). The enhancement in the conductivity is readily ascribable to the varying extents of charge transfer between the 3d metal ion centers and the electron-rich heteroatoms in DMG. Apparently, ease of such charge transfer will depend upon the availability of M vacant orbitals which follows the order Co2 + (3d1) > Ni2+(3d8) > Cu2 + (3d9). 

Since the objective was the preparation of a modified PVC containing a relatively few appended chains of polybutadiene, the reaction was carried out heterogeneously by suspending the PVC in chlorobenzene. The suspension was cooled to 5°-10°C, butadiene, a cobalt compound, and Et2AlCl were added, and the mixture was stirred at 5°-10°C for 30-60 minutes before the addition of methanol to terminate the reaction. 

Discoloration. When PVC, free of plasticizer or stabilizer, is compression molded in air at 200°C under adequate pressure (c.g., 500-6000 psig), thermal degradation results in discoloration to a pink to brown colored film. When the modified PVC containing as little as 3% of grafted cis-1,4-polybutadiene was pressed under the same conditions, the resultant film was essentially colorless or no more than faintly discolored. 

To improve the thermal stability of PVC, it is common to add stabilizers, generally metalloorganic compounds, in concentrations of 1-5 parts per 100 parts of PVC. Although the cis-1,4-polybutadiene grafted PVC, in the absence of an added stabilizer, yielded essentially colorless or only faintly discolored films, completely colorless films were obtained when the conventional stabilizers were added in concentrations of 0.1-0.3 parts per 100 parts of modified PVC. Organotin stabilizers were not necessary and, in some cases, actually resulted in greater color development than when they were absent. 

Polybutene has also been shown to improve impact resistance and dynamic thermal stability in impact modified PVC-U formulations (433). 

Calcium carbonate nanoparticles are commercially available and are claimed to give a cost effective way of increasing impact strength (113). Their use in impact modified PVC has improved mechanical properties (57). 

Silane modified PVC films have been proposed for selective absorption of chloro-organics in the... 

Plasticised PVC was surface modified by nucleophilic substitution of the chlorine atoms of PVC by sulphide ions in aqueous media in the presence of a phase-transfer catalyst. The modified PVC was sterilised by steam autoclaving and gamma irradiation and subjected to plasticiser extraction. Surfaces were evaluated by contact angle measurements, SEM, cell culture studies, haemolysis assay and whole-blood clotting time measurements. Mechanical properties were examined. 31 refs. 

Gas transport coefficients of PVC and PVC modified with pyridine groups were studied. It was found that there is a strong time dependence of the permeability and diffusivity of oxygen, nitrogen, carbon dioxide and methane in membranes prepared by solvent casting of PVC and pyridine modified PVC. There is a two-fold reduction for PVC of the diffusion coefficients during the first two days,... 

Toronto, 27th April-2nd May 1997, p.1902-6. 012 ENHANCED PROPERTIES OF IMPACT MODIFIED PVC WITH POLYBUTENE... 

The addition of polybutene to impact modified PVC formulations reveals improved impact resistance and increased dynamic thermal stability in the PVC formulation. Polybutene added at levels up to 10% of the total impact modifier gives a significant increase in the Izod impact and increase in dynamic thermal stability by as much as 25%. 6 refs. 

Brighton, 23rd-25th April 1996, p.391-405. 42C382 TEMPERATURE AND IMPACT RATE DEPENDENCE OF THE DUCTILE/BRITTLE TRANSITION OF IMPACT MODIFIED PVC Gervat L Disson J P Bianchi C Marvalin C Morel P Elf Atochem S A... 

The impact behaviour of pure and impact modified PVC is studied in terms of the ductile-brittle transition. These transitions show an Arrhenius dependence on temperature related to the beta motions of the PVC matrix. A model based on Eyring theory is proposed. Beyond its theoretical interest, the model predicts the impact performance of PVC at various temperature and impact modifier contents. 6 refs. 

Organotin derivatives of maleic acid may have an additional stabilizer function with the Diels-Alder reaction (Figure 3.3.3) by scavenging function. Their performance is good in all types of vinyl chloride polymerization, i.e. suspension, emulsion, and bulk. Optimum results are obtained when they are combined with small amounts of phenolic antioxidants particularly in plasticized PVC, impact-modified PVC, and PVC copolymers. 

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