Metallocene-catalyzed copolymers of ethylene and α-olefins were investigated by X-ray scattering and differential scanning calorimetry. Evaluated α-olefin comonomers consisted of 8, 12, 18, or 26 carbons. As indicated from the small-angle X-ray scattering, ethylene–hexacosene copolymer with comonomer content of 3 mol % may contain second crystallites. Because no other reflections were observed in the wide-angle X-ray scattering patterns, the side-chain crystallites should have the same crystal lattice dimensions as the prevailing main-chain crystallites. Since this potential side chains crystallization can only be found in the ethylene–hexacosene copolymer with 3 mol % of comonomer, a critical concentration of long-chain comonomer should be reached for this secondary crystallite formation. It was also found that the thickness of the interlamellar amorphous layer stays virtually constant regardless of the changes in comonomer content and side-chain length.
Cellulose powders hydrophobized by surface esterification with carboxylic acids with different chain lengths (3, 10 and 18 carbons) were dispersed in a polypropylene matrix. Quality of the dispersion and nucleation activity of the filler were investigated by means of differential scanning calorimetry and optical microscopy. The results showed that the esterification decreases the crystallization rate in case of cellulose esterified with propionic or decanoic acid. On the other hand, the oleic acid ester demonstrated slightly higher crystallization rates than the unmodified cellulose, which was ascribed primarily to the newly arisen non-esterified surface after disintegration of the filler. Optical microscopy with hot stage showed the high nucleation ability of the natural cellulose fiber and its suppression in case of esterified surfaces. A complete inability to nucleate polypropylene crystallization was observed in case of decanoyl ester, while the other two retained some activity, but lower than that of the natural fiber. Finally, analysis of the filler dispersion and distribution revealed that the decanoyl and octadecanoyl esters disintegrate during melt mixing, while both dispersion and distribution of the fibers modified with propionic acid are poor.
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