Decrease In Degree Of Crystallinity Research Articles

The compatibilization of SBR/EVA by mercapto-modified EVA

Styrene–butadiene copolymer/ethylene–vinyl acetate copolymer (SBR/EVA) blends with different ratios were prepared by using a Haake internal mixer. These blends were compatibilized with mercapto-modified EVA (EVALSH), which promotes bonding between the SBR phase and the EVALSH through a chemical reaction between the mercapto groups of the reactive compatibilizing agent and the double bond of the unsaturated rubber. The presence of EVALSH resulted in an improvement of the tensile strength of the unvulcanized SBR/EVA blends and also a more uniform dispersion of the EVA phase inside the SBR matrix for blends containing higher amount of the rubber phase. The formation of insoluble material in the blends containing EVALSH indicates reactive compatibilization, which was confirmed by Fourier transform infrared analysis and also by dynamic mechanical analysis. In this case, a decrease in damping properties of the SBR phase was observed as a consequence of decreasing chain mobility. EVALSH also caused a decrease in degree of crystallinity of the EVA phase as observed by differential scanning calorimetry analysis.

Variation in crystalline type with amylose content in maize starch granules: an X-ray powder diffraction study

Abstract Comparative studies of native maize starches with different amylose contents were carried out using X-ray powder diffraction. The results show a transition of crystalline type from A through C to B, accompanying a decrease in degree of crystallinity from 41.8% to 17.2% across a range of apparent amylose content from 0% to 84%. Hydration induces an increase in degree of granule crystallinity, but does not change the transition of crystal type. Progressively from A-type to C-type, crystallinity decreases rapidly with an increase in amylose content. From C-type to B-type, overall crystallinity decreases more slowly. The crystal type is strongly dependent on amylose content and on average chain length of the respective amylopectin. Waxy A-types have an average chain length of about 20, while in high amylose B-types this rises to ≈35. The proportion of short chains (∼10–13 glucose units) appears to affect crystal type significantly. Some V-type material was detected at high amylose levels. The proportion of this increased after prolonged exposure of the granules to iodine vapour. Implications for the arrangement of starch components in the granule are discussed.

Diacetylene-Containing Polymers VII. Synthesis and Characterization of New Diacetylene-Containing Polyesters and Copolyesters Derived from Dipropargyl-1,10-decanate, Dipropargyl Terephthalate, 4,4′-Dipropargyloxy Diphenyl, and 4,4′-Bis[(5-carbopropargyloxy)pentoxy] diphenyl

A series of new thermoplastic diacetylene containing polyesters and copolyesters was synthesized and characterized. The copolyesters had melting points as low as 50°C and were topochemically cross-linkable on electron beam irradiation. One of the copolymers was found to form a nematic melt in the region of 48—67°C and was cross-polymerizable in the liquid-crystalline state to form a polydiacetylene network. The tensile strength and Young’s moduli of the polymers reached as high as 145 MPa (1 Mrad) and 535 MPa (5 Mrad) respectively. The values decreased with decrease in degree of crystallinity or melting point of the crystallites and the tensile strength went through a maximum on irradiation with an electron beam. Electron beam irradiation brought about a decrease in elongation at the break and increase in Young’s modulus.

Differential scanning calorimetry in the saccharification of cellulose

The kinetics of the acid hydrolysis of cellulosic materials were studied by differential scanning calorimetry, particularly regarding the dependence of the kinetic parameters and the enthalpy change on the crystallinity and moisture content of the cellulose samples. The rate constant of the acid hydrolytic reaction increased with decreasing degree of crystallinity and increased with increasing moisture content of the sample. The heat of reaction increased with decreasing degree of crystallinity and with increasing initial moisture content of the sample.

Effect of tabletting on the degree of crystallinity and on the dehydration and decomposition points of cephalexin crystalline powder.

Changes in the degree of crystallinity and in the dehydration and decomposition points of cephalexin (CEX) crystalline powder caused by tabletting were studied by means of X-ray diffraction analysis, infrared (IR) spectroscopy and differential thermal analysis (DTA). The degree of crystallinity of the compressed phase IV CEX was determined by the X-ray diffraction and IR-spectral methods, and the results agreed reasonably well. The maximum compression stress (MP) and the compression loss energy (LE) of phase IV CEX powder during tabletting compression were measured during compression in a single-punch tabletting machine. The degree of crystallinity of the compressed phase IV CEX decreased with increasing values of MP and LE, and was about 40% at LE=1.75 kcal/mol. The dehydration and decomposition points of the compressed phase IV CEX fell with decreasing degree of crystallinity. The plot of log (LE) against the degree of crystallinity showed a good straight line. The value of LE estimated by extrapolating the plot to zero crystallinity was 14.0 kcal/mol.