High Content Of Amorphous Phase Research Articles

Syndiotactic polypropylene as potential material for the preparation of porous membranes via thermally induced phase separation (TIPS) process

This work reports the flat sheet membrane preparation from syndiotactic polypropylene (sPP) by thermally induced phase separation (TIPS) process. sPP obtained by polymerization using metallocene catalysts and isotactic polypropylene (iPP) also obtained via metallocene catalysis with similar molecular weight were used. The phase diagrams of sPP and iPP with diphenylether as diluent were obtained. The properties of three representative membranes from sPP and three from iPP, prepared using different PP concentrations were evaluated with respect to membrane pore structure, gas flow, liquid displacement (bubble point), and water permeability. Two selected membranes, one from sPP and one from iPP were analysed with regard to polypropylene bulk morphology (X-ray diffraction) and mechanical properties (tensile strength). Under the same formation conditions, membranes with less inter-connected pores and less porous surface were obtained from sPP compared with iPP. Overall, lower permeabilities had been found for the sPP membranes, which were attributed to the difference in pore morphology. The differences between sPP and iPP were also discussed in terms of different driving forces for liquid–liquid demixing as deduced from the phase diagrams. The X-ray analysis had shown that the sPP membranes had a higher amorphous phase content than that in iPP, and the mechanical test had revealed a pronounced ductile behaviour for sPP samples. These results helped to explain the lower permeabilities of the sPP membranes, and their pressure-dependency.

Mutant genes at therandrbloci affect the structure and physico-chemical properties of pea seed starches

Mutant genes at two loci, r and rb, known to encode genes affecting the starch biosynthetic pathway, were studied for their effect on the structure and gelatinization of pea seed starches. Comparisons were made using starches from four lines (RRRbRb, rrRbRb, RRrbrb, and rrrbrb), near-isogenic except for genes at these two loci. All the starches had C-type X-ray diffraction patterns, but different contents of 'A' and 'B' polymorphs. The presence of a mutation at either locus increased the 'B' polymorph content in the starches, although the influence of the r mutation was much greater than that of rb. Differences were discovered in the crystalline stucture of the rrRbRb starch which correlated with a high content of amorphous phase as well as with the changes in amylopectin structure. In addition, changes in the crystalline structure of this sample correlated with a lack of co-operative transition during starch gelatinization in excess water. The RRrbrb starch had a greatly increased enthalpy of gelatinization in excess water compared with the wild-type starch. It is proposed that this effect is connected with specific charge interactions between the molecules in the starch granule. The rrrbrb starch had parameters of crystalline structure and gelatinization which reflected the different influences of the two genes. With regard to gelatinization, this starch had relatively wide co-operative transition and low enthalpy and a very high peak temperature of transition.