Applications of Starch Based Biodegradable Polymer Blends Modified By Radiation and Chemical Treatments

Abstract

In recent years, Biodegradable starch-based polymers have recently been proposed as having great potential for several applications in the biomedical field. Preparation and characterization of plasticized starch/ cellulose acetate/ carboxymethyl cellulose blend hydrogels formed by electron beam irradiation In this part, films from plasticized starch and different ratios of cellulose acetate (CA) and carboxymethyl cellulose (CMC) were prepared by solution casting and then exposed to electron beam irradiation (EB) at different doses. The blends before and after EB irradiation were characterized by determining the gel content, swelling characters, thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and surface morphology by scanning electron microscopy (SEM). The structure property of the polymer blends before and after electron beam irradiation was investigated ,and the results can be summarized in the following points - We found that the gel content was increased by increasing the CA ratio. However, the gel content was found to increase by increasing EB dose up to 30 kGy and then tends to decrease at high doses. The effect of EB irradiation doses on the gel fraction of PLST/CA/CMC blends, containing a constant ratio of CMC (5%) is clear. This can be attributed to higher tendency of CMC to form crosslinking than CA polymer. - Swelling degree decrease with increase the ratios of CA but by small amount and then decrease at high concentration of CA these due to structure of CA have high branched side chain than starch which make little amount of water to be absorbed by polymer blend . the effect of EB irradiation dose and introducing CMC on the swelling in water is clear. Further decrease in the swelling (%) can be observed due to higher tendency of CMC to form crosslinking than CA polymer. - It is clear that both IR spectra for pure PLST/CA or PLST/CA/CMC blend hydrogels showed the existence of extensive hydrogen bonding in the range 3000–3500 cm-1. However, it seems that the PLST/CA/CMC blend hydrogel possess relatively higher extents of hydrogen bonding than PLST/CA hydrogel. - It can be seen that the stress at break was slightly increased by increasing CA ratio in PLAS/CA blends. However, stress at break was increased by increasing EB dose up to 10 kGy and tends to level off at higher doses specially in presence of CMC. On the other hand, the strain at break was found to decrease with increasing EB dose. - The TGA thermograms indicate that the thermal stability of unirradiated PLST/CA and PLST/CA/CMC blends is higher than the unirradiated PLST. This is due to the blending with CA and CMC polymers with higher dissociation energies. - DSC thermograms for unirradiated and irradiated blends of PLST and (PLST/CA) and( PLST/CA/CMC) were investigated The effect of electron beam irradiation at 30 kGy on the DSC thermograms for PLST and PLST/CA blends it can be concluded that the blending of CA results in increasing the Tm of PLST. This increase in Tm may be due to that the CA and CMC polymers would prevent the amylopectin from retrogradation. - The SEM micrographs of the fracture surfaces of unirradiated films of PLST and PLST/CA films showed that the starch granules are disrupted and form a continuous phases. Also, the increase of CA content is a companied by a decrease in the compatibility, in which the fracture surface is rough and the micrograph shows two phases. These micrographs were changed after exposure to 30 kGy of electron beam irradiation. The roughness in PLST/CA/CMC blends are decreased than in case of unirradiated samples.