Testing PVAC

Another attractive quality of the PVA is its outstanding chemical stability. Peter and Stefan ( ) investigated the chemical stability of PVA vis a vis a series of solvents and reagents and some of their results are summarized in Table I. This table presents a comparison between the chemical resistances of PVA, polyvinyl butyral(PVB), polyvinyl acetate(PVAc), and cellulose acetate(CA). It is evident from this table that the PVA is considerably more stable than the rest of the tested materials. 

The newer type of colloidal catalysts have been prepared containing palladium (4), platinum (4), rhodium (5), and iridium (6). A variety of synthetic polymers has been applied. Among those tested were polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polymethyl methacrylate (PMMA), and polymethyl acrylate (PAMA). In general, polyvinyl alcohol (4a) has been found most satisfactory. 

Figure 3.5 shows the temperature variation of H for the four above mentioned polymers, namely PMMA, PVAc, PET and PEEK. In the case of the two amorphous polymers (PMMA and PVAc) H decreases with T and the Tg value can he clearly identified with a hend in the 7/ vs T plot. However, the two semicrystalline materials quenched into the amorphous state (PET and PEEK) show an apparent maximum just before the glass transition takes place. Also, in the case of PET tested immediately after quenching it is observed that H increases with T above room temperature. These phenomena will be discussed in Section 3.3 in the light of the physical ageing undergone by the above polymers. It is seen that H follows an exponential decrease as a function of T given by (see eq. (2.5))... 

These equations have not stood the test of predicting viscosities in filled systems and polymer blends. For calculating the viscosities of PVC-PVAc polymer blends (filled and unfilled) used as record moulding compounds, we have analysed from systematic investigations [40] the influence of... 

Under long-term outdoor exposure, involving frost action and car-bonation, latex-modified mortar shows increased resistance to weathering in comparison with conventional mortar and concrete. The weatherability of the latex-modified mortars is shown in Fig. 4.69The exposure test was done at the Building Research Institute Outdoor Exposure Site in Ibaraki Prefecture, Japan. Except for PVAC-modified mortars, the flexural and compressive strengths of most latex-modified mortars under outdoor exposure conditions tend to become nearly constant at one year or more, and a weatherability factor is greater or similar to that of unmodified mortar. 

In the present contribution an investigation on the biodegradation of blends and graft copolymers of PHB of both natural and synthetic origin and PVA/PVAc blends is reported. The evaluation of the effects of each component in blends and copolymers on both the overall extent of biodegradation and the biodegradation of counterparts, was investigated in aqueous media and in soil by means of respirometric tests. 

Three different films obtained by a hot pressing procedure of powder mixtures containing plasticized PVA, PVAc with and without bactmal PHB were submitted to the biological degradation of soil microorganisms in a respirometric test aimed at simulating soil burial conditions. The compositions of the blend films are summarized in Table 1. 

PVAc-based commercial wood adhesives are evaluated using standard tests for non-structural applications, as reported in EN 205 [8], and they are classified in agreement with the standard EN-204 [9]. This standard allows to classify wood adhesives in 4 categories from D1 to D4. D1 adhesives show a good resistance only in dry conditions D2 adhesives should withstand a rather low water presence, such as in occasional exposure in kitchens and bathrooms D3 adhesives are suitable to come in contact with cold water, such as for outside windows and doors, kitchen and bathrooms furniture D4 adhesives are suitable to be used in extreme conditions (resistance to hot water). Vinyl acetate homopolymer can be used to formulate D1 or D2 adhesives. Vinyl acetate based adhesives cross-Unked with hardeners and urea-formaldehyde (UF) adhesives belong to class D3. Only the phenol-formaldehyde (PE), resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF) adhesives, some special 2-component polyurethanes (PUs), and cross-linking vinyl adhesives belong to class D4. 

The PVAc homopolymer (1) and the VAc/Unseed oil (10%) copolymer (2) obtained in organic solvent were tested using the EN205-D3 test. In agreement with this test the adhesive strength can be measured in dry conditions (D3-1) or in wet conditions (D3-3). The presence of ethyl acetate as solvent (solid content 50%)... 

For the two conditions described above, samples were taken out of the cold water and subjected to the tension test as described above. Ten replicates were made for each condition and compared to PVAc controls (total 80 specimens). 

Most of the glued components produced in Europe for non-structural purposes such as joinery use urea-formaldehyde (UF), poly (vinyl acetate) (PVAc) or polyurethane (PUR) adhesives. These adhesives must meet the performance requirements specified in EN 204 (2002) [15] for thermoplastic adhesives or EN 12765 (2002) [16] for thermosetting adhesives when tested in accordance with the following test methods ... 

FIGURE 3.6 Effect of molecular weight on the viscosity of PVAC solutions. PVAC polymers (Cairn) (Table 7.1) were dissolved in cyclohexanone to form 40% solutions (by weight). These were dyed to aid visibility. The test tubes were tipped over and photographed after 2seconds. The low-molecular-weight polymer solutions flowed faster (a) S2. (b) SI. (c) S27. 

Recent decades have seen major amalgamations and restructuring of the PVAC Industry. Many firms have merged with losses of trade names traditionally used In conservation. As part of the general Improvements In quality control, the standard of many PVACs has risen, as demonstrated by the increasing water whiteness of the products. However, few of these new products (even If still traded under old names) will have been tested for conservation purposes. 

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