Tensile strength of polymeric materials

Preparing blends — that is, mixtures — is one of the ways in which researchers try to optimize the properties of polymeric products. Among the principal properties described in patents of such materials are resistance to impact, ease of processing and tensile strength. In an attempt to maximize the tensile strength of blends of poly(vinylidene fluoride), poly(methyl metacrylate) and polystyrene — PVDF, PMMA and PS, respectively — Siqueira et al. (1993) obtained the results in Table 7A.3. The first 16 runs in the table correspond to a simplex centroid design with 9 replicate measurements, whereas in runs 17-20 the PVDF PS proportion is maintained equal to 1, and the quantity of PMMA is varied. 

Proceeding as in the last example, we arrive at the following fitted models y = 44.25x1 + 29.68x2 + 19.65x3  

Design for studying polymeric mixtures of PVDF, PMMA and PS (see text) 

ANOVA results for the models fitted to the data of Table 7A.3  

The analysis of variance shows that the linear model is unsatisfactory, and that the other two models do not show lack of fit (Table 7A.4). This time, however, the special cubic model seems superior. The explained variation is larger, the MS of/MS ratio is smaller, and the cubic term is statistically significant. The contour curves for the cubic model are presented in Fig. 7A.3. The largest tensile strength values are obtained close to the base of the triangle, toward the left vertex, which corresponds to a blend that is predominantly PVDF, with httle or no polystyrene. 

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Clays (such as montmorillonite, laponite etc.) are usually employed as reinforcing filler to improve thermal stability as well as the stiffness and tensile strength of polymeric materials. Montmorillonite and organically modified montmoriUonites -the latter showing an increased interfacial interaction between clay and polymer macromolecules - were incorporated into different polymeric materials such as PU [54], PCL [55], and chitosan/PVA [56], The incorporated clays were well distributed, exfoliated and oriented along the fiber axis. It was reported that, during the... 

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