The Synthesis And Application Of Polyaspartic Acid Hydrogrl

Poly aspartic acid (PASP), a type of soluble polyamino acid with a large carboxyl group at its side chains, has excellent biodegradability and biocompatibility. A network-like microstructure can be obtained through the crosslinking of the molecular chains of PASP. This cross-linked PASP is called PASP hydrogel. With the interaction of the hydrophilism of the amide bond on the PASP main molecular chain, the hydrogen bond of the carboxyl group on the side molecular chain, and the absorbability of the crosslinking, PASP hydrogel shows an excellent water absorbing and retaining capacity. Thanks to this characteristic, PASP hydrogel can be widely used in the production of water-retaining agents for agriculture and forestry, daily chemical products, medicine carriers, and other fields such as electronics, construction, and packaging materials, etc. At present, although there has already large scale production and wide application of PASP in China and all over the world, the development of PASP hydrogel remains restricted to R & D in laboratories, due to the limit of production process and high cost. Therefore, it is important to develop a synthesis process to make it feasible for industrialized production of PASP hydrogel, and to make it possible for large scale production through pilot project. This will strongly push forward the production and application of PASP hydrogel and lay a good foundation for the development of PASP industry.The main work of this paper has five aspects:First, the development and research on the heterogeneous hydrolysis/ crosslinking one-step synthesis process of PASP hydrogel, using diamine compound as the cross-linking agent. By optimizing the process conditions, it shows that the optimum parameters of the reaction conditions are:reaction temperature,0 ℃; reaction time,12 hours; Molar ratio of the PSI loop to NaOH,10:9; Molar ratio of the PSI loop to hydrazine,10:5; the maximum swelling ratio of PASP hydrogel,593g/g. The significant factor that affects the reaction is the reaction temperature. The study of the degradation of PASP hydrogel shows that longtime simple mechanical vibration can affect the crosslinking structure, which can break and collapse at the cross-linking point; while the main chain of PASP can be broken and degraded by enzymic action.Second, the research on the homogeneous synthesis process of PASP hydrogel, using epoxy compounds as the cross-linking agent, hydrolysis followed with crosslinking. The optimum parameters of the reaction conditions are:reaction temperature,50℃; pH= 4.8; the quantity of the dissolvent,6 ml/g PSI; crosslinking agent quantity,0.16 M/M PSI (EGDGE), or 0.2 M/M PSI (PEGDGE). The maximum swelling ratio of PASP hydrogel is respectively,590 g/g (EGDGE), and 445 g/g (PEGDGE). The significant factor that affects the swelling ratio is the reaction temperature.Third, PASP hydrogel pilot experiments using two processes, at optimized test process conditions. A number of experiments in succession have proved the stability of the pilot process and equipment. Besides, on the basis of the pilot production, a ten thousand-tonnage level PASP hydrogel production line was designed, using epoxy crosslinking production process. The materials and heat balance of the whole production line were calculated; equipments were designed and selected based on the pilot experiment and the flux of materials at each process; the total cost and unit costs including raw materials, power, staff wages and depreciation of fixed assets were calculated. Furthermore, trial production was done on two processes:PSI solid-phase polymerization and hydrolysis, on the pre-installed production line. The results of trial production showed that the production capacity on such production line could reach 12491 t/y PASP hydrogel.Fourth, PASP hydrogel was used as water retaining agent in agriculture and forestry. Festuca elata, fraxinus seedlings, and xanthoceras sorbifolia tree seedings were used as experiment objects to study the effect of PASP hydrogel to promote the growth of plants under drought stress. After applying PASP hydrogel to the festuca elata under drought stress, the root length, the number of roots and moisture content exceeded those of objects at the comparison area by respectively 117.50%,25.00% and 46.08%, leaving very little difference from those of the plants in non-drought conditions. Applying PASP hydrogel to the fraxinus seedlings, not only increased their growth, but also reduced their mortality ratio by about 68.4%. The experiment of transplanting xanthoceras sorbifolia trees in drought area showed a more distinctive effect of PASP hydrogel promoting the growth of the plants. The survival rates and leaves moisture contents of three transplanting methods turned to be respectively 10-20% and 20-140% higher than those done without PASP hydrogel; physiological index such as chlorophyll fluorescence parameters including QY, Mo, ABS/RC, TRO/RC, ETO/RC and DIO/RC were also distinctively different.Finally, a multi-generation PASP dendrimer was synthesized by solid-phase method, using cross-linked PS microspheres grafted respectively by o-phthalic acid and succinic acid as carrier and the synthesis processes were optimized. The structure was proved through methods such as FTIR, NMR, and Elemental Analysis, in connection with carboxyl titration. Besides, a preliminary research was done using PASP dendrimer as a carrier in immobilized lipase, with adsorption method and covalent method respectively. The results showed that, the specific lipase activity of G3 was 25.0% and 42.8% higher than G1 with adsorbent and covalent immobilized methods respectively; for the molecules of the same generation, the lipase activity immobilized with covalent method was 16.7%-33.3% higher than using adsorbent method.