مجله ایرانی پلیمر
سال:1387 | دوره: | شماره: |تعداد مقالات:5

Melt blending of poly (lactic acid) (PLA) and biodegradable hyper branched poly (ester amide) (HBP) has been performed in order to toughen PLA without compromising its biodegradability and biocompatibility. The FTIR spectra, thermal properties, disperse phase morphology, and mechanical properties of the blends with different HBP contents were investigated. A reasonable toughening mechanism is also given. The presence of intermolecular hydrogen bonds between PLA and HBP is confirmed by FTIR spectroscopy technique. Addition of HBP not only reduced the crystallinity of PLA from 30.99% to 18.58%, but also has toughened it as well. By an increase in HBP content from 2.5% to 10%, the blend showed a slight increase in tensile strength but a significant increase in elongation-at-break values. Meanwhile the scanning electron micrographs showed an evenly dispersed HBP in PLA. The hydrogen bond interactions and the energy-dissipation process led to a tough biodegradable polymer blend.

A two-step preparation and the characterization of composite gel beads of tamarind gum (2.0 wt%) and sodium alginate (0.6 wt%) as spherically well shaped forms are reported. In the first step, the prepared solution containing tamarind gum and sodium alginate was extruded as small drops by means of syringe into a stirred calcium chloride (CaCl2, 3.0 wt%) at 4oC and then in the second step the beads were soaked in solidified agent solution (Na2B4O7, 2.0 wt%). Thus, we obtained composite gel beads with diameter range between 2 and 3 mm. We have demonstrated the properties of the composite beads, such as morphological, thermal stability and functional groups characterized by different techniques (i.e., SEM, DSC, and FTIR). The swelling behavior in response to pH variation as well as the mechanical strength of the composite gel beads are examined and reported. The results have demonstrated that the composite gel beads not only have the advantages of rather rough surface, three-dimensionally network structure, and high anti-acid and anti-alkali properties, they are not prone to breakage under load. The composite gel beads prepared are potentially useful as polymeric carriers or supports in biotechnology and biochemistry applications.

In modern synthetic organic chemistry laboratories protocols for convenient and rapid transformations are highly desired. Microwave activation has received considerable attention in recent years and it is a subject of intense debate in the scientific community. This technique as an alternative to conventional energy sources for introduction of energy into reactions has become a very well-known and practical method in various fields of chemistry. Microwave-assisted organic synthesis is known for the spectacular accelerations produced in many reactions as a consequence of the heating rate, a phenomenon that cannot be easily reproduced by classical heating methods. As a result, higher yields, milder reaction conditions, and shorter reaction times can often be attained. Microwave is now extensively accepted as an efficient and non-ionized electromagnetic energy source in several different fields of polymerization reactions such as step-growth, ring-opening and radical polymerizations. Its specific heating method attracts extensive interest because of rapid volumetric heating, suppressed side reactions, energy saving, direct heating, decreased environmental pollutions, and safe operations. This review introduces the application of microwave irradiation in step-growth polymerization in details up to 2008. In order to demonstrate the effectiveness of microwave-assisted reactions, some comparisons are made with the classical heated polycondensations.

The effects of hot mercerization on open-end and ring spun yarns in slack and under tension conditions were compared. It was found that hot mercerizing at optimum temperature had different effects on cotton yarns of different structures. The results indicated more pronounced effect of treatment temperature on physical properties of ring yarn, while the mercerized open-end spun yarns showed higher dye uptake and tensile strength compared to the ring spun yarns. The degree of mercerization of ring and open-end spun yarns was obtained by measuring the barium activity number. X-ray and infrared spectroscopic analyses (the ratio of a 1372 cm-1/a 2900 cm -1) were used to measure the crystallinity of cotton yarns mercerized at various temperatures. Results showed that mercerization treatments lead to a decrease in cellulose crystallinity as assessed by determining the increase of the reactivity of cellulose towards dye sorption. The decrease in crystallinity was varied with experimental conditions. It was also revealed that the higher the mercerizing temperature, the more shrinkage occurred on both yarns, where ring spun yarns have shown higher shrinkage.

Poly (lactic acid) (PLA) is one of the most promising biodegradable materials with excellent mechanical properties, but the disadvantages of stiffness, poor thermal stability, and high costs limit its applications in general use plastics such as industrial packaging and agriculture films. In present work, biodegradable PLA/starch composites are prepared from PLA and etherified starch (EST) by extrusion and uniaxial orientation processing with a pretreated mixing procedure under a programmed temperature. The products are examined using Fourier transform infrared (FTIR) spectroscopy technique. The results revealed that small amount of PLA molecules have strong interaction with EST which may be ascribed to the esterification between the terminal carboxyl groups of PLA and hydroxyl groups in EST. The morphological properties observed by scanning electron microscopy (SEM) technique confirmed that the composites with a pretreatment procedure had much better dispersion and homogeneity of starch in the PLA matrix than the composites without the pretreatment procedure. Consequently, an improvement in mechanical properties has been achieved. Comparing with the samples without the pretreatment procedure, the mechanical performances such as tensile strength, elongation-at-break and modulus of the composites with a pretreatment procedure were significantly improved. This approach is identified as a reasonable method to produce commercial PLA/starch composites with economical feasibility.