synopsisThe effects of vinyl acetate content on crystallinity of ethylene-vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystalliiity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene-vinyl alcohol copolymer) was also investigated. 103 98 77 44 112 113 107 110 Calcd by theory 106.2 97.6 72.0 44.0 100.2 97.6 72.0 44.0 12. L.

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A method has been derived whereby the characteristic constants of the rate equation may be derived directly from the thermogravimetric analysis curve. The method described, in contradistinction to previously described methods, does not require transformation to a time scale, nor pointwise graphical differentiation, and no mathematical approximations are made. The method is applicable to any reaction showing one or more successive thermogravimetric inflection points, requiring only that the location of the inflection point and the slope of the curve at that point be determined. It is demonstrated that the constants derived apply to the whole curve as well as the vicinity of the inflection point.

Four composite material systems useful for roofing in the tropics were developed which utilize major percentages of bagasse (sugar cane residue) filler, and minor amounts of phenolic or other resin binders. The various materials were actually manufactured in small quantities in three developing countries and trial exposure roofs installed.