| With the wide use of non-degraded polymer-based materials, environmental pollution caused by the waste is increasing and the petroleum-based resource is gradually exhausting. Therefore, it is necessary to develop novel polymeric material mainly derived from natural polymer. Chemical grafting and physical blending is a handy and important way to exploit high performance polymeric materials, which has become a new branch in polymer material science and engineering. It can optimize mechanical properties or bring out new functions. Chitosan, chitin, starch, alginate and cellulose have attracted wide attention because of their good biodegradability, renew-ability and plentiful resource. Meanwhile, hydroxyl groups and amino groups in chitosan, hydroxyl groups and acetyl groups in chitin, hydroxyl groups in starch, hydroxyl groups and carboxyl groups in alginate, hydroxyl groups in cellulose facilitate the forming of new grafting segment of copolymer or inter-molecular hydrogen bonds with other polymers, which usually leads to good miscibility, and even high performances and new function.The creative points in this thesis are as follows: (1) A series of chitosan-g-polycaprolactone (CP), chitin whisker-g-polycaprolactone (CWP) and starch-g-polycarprolactone (SP) were prepared by initiating ring-open polymerization ofε-caprolactone (ε-CL) onto chitosan, chitin whisker and starch assisted with microwave, and then provided high-performance materials as precursor. (2) A series of biodegradable composites with enhanced mechanical properties, based on various cellulose derivatives and soy protein isolate (SPI), have been produced. The effect of side groups and content of cellulose derivatives have been concluded. (3) The complex microspheres based on alginate (AL) and SPI were prepared by solution blending and then Ca2+ crosslinking, and their function as pH sensitivity drug carrier was explored as well. (4) The self-assembled rigid supramolecular nanoplatelets (SN) from Pluronic polymers with various lengths of polyethylene oxide (PEO) andβ-cyclodextrin have reinforced the soy protein isolate (SPI)-based biodegradable plastics in terms of strength and modulus but at the expense of elongation. Meanwhile, the nanoplatelets with moderate length of free PEO segments showed optimal water resistance.The main contents in this thesis are as follows:1. Biodegradable and biocompatible composites based on SPI and various cellulose derivatives have been prepared, and the effects of the content and species of cellulose derivatives on the structures and mechanical properties for the composites were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscope and tensile test. The selected cellulose derivatives, such as methyl cellulose (MC), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC), were miscible with SPI when the content of cellulose derivatives was low, and then the isolated crystalline domains, shown as the structures of network and great aggregate, formed with an increase of cellulose derivative content. The miscible blends could produce the higher strength, and even result in the simultaneous enhancement of strength and elongation for the HEC/SPI and MC/SPI blends. Meanwhile, the moderate content of great MC domains also reinforced the materials.2. Chitosan-g-polycaprolactone (CP) was prepared via microwave assisted ring-open polymerization, and their structures and compositions were measured by FTIR and elemental analysis. The CP was compounded into PCL to produce simultaneous reinforced and toughed materials, i.e. over 2-fold of tensile strength and ca. 3-fold of elongation in contrast to neat PCL. The dependence of structures and mechanical properties on the content and structure of CP for the composites was investigated by XRD, DSC, dynamic mechanical thermal analysis and tensile test. The rigidity of chitosan contributed to high strength, while the co-continuous interfacial structure and miscibility between two components mediated grafted PCL obviously enhanced the elongation of composite materials.3. Chitin whisker-g-polycaprolactone (CWP) was also prepared via microwave assisted ring-open polymerization, and then directly injection molded as the sheets. The structure and composition of CWP were measured by FTIR, transmission electron microscope and elemental analysis, and the structures and mechanical properties for the molded plastics were investigated by XRD, DSC, DMTA, contact angle and tensile tests. With an increase of weight ratio ofε-caprolactone monomer vs. chitin whisker, the weight fraction of PCL increased, resulting in the obvious improvement of mechanical properties. When the PCL content was the highest, the tensile strength and elongation reached 29.7MPa and 1148.37%, respectively. Herein, the rigidity of chitin whisker contributed to high strength, while the co-continuous interfacial structure and miscibility between two components mediated with grafted PCL segment enhanced the elongation.4. Starch-g-polycaprolactone (SP) was prepared by grafting polycaprolactone (PCL) onto starch via microwave assisted ring-open polymerization, and then directly injection molded as the sheets. The structure and composition of SP were measured by FTIR and elemental analysis, and the structures and mechanical properties for the sheets were also investigated by XRD, DSC, DMTA and tensile tests. With an increase of weight ratio ofε-caprolactone monomer vs. starch, the weight fraction of starch increased. When the starch content was the highest, the tensile strength and elongation ratio reached 20.94MPa and 11.39% respectively, which were over 2-fold of tensile strength and ca. 3-fold of elongation of the composites with the lowest starch content. Herein, the starch component contributed to high strength, while the co-continuous interfacial structure and miscibility between two components mediated with grafted PCL segment favored the enhancement in the elongation.5. The complex microspheres based on alginate (AL) and soy protein isolate (SPI) were prepared by solution blending and then Ca2+ crosslinking, and their function as drug carrier was explored as well. The effects of composition on the structures of microspheres were studied, and the XRD results proved the miscibility between components. Meanwhile, FTIR results suggested that such miscibility was driven by strong hydrogen bonding. Especially, the complex microsphere with equal content of AL and SPI had the best miscibility by morphological analysis, shown as a smooth and uniform surface in SEM images. The controlled release function of the complex microspheres were verified using theophylline as a drug model, that is, the swelling and drug release were affected by pH conditions and showed obvious differences under given pH of stomach, intestine, and colon. Moreover, the intestine and colon may be optimal site for prompt release of drugs. Except for the attribution of AL component to pH sensitivity, the complex microspheres also inherited the bioactivity of SPI component, which may lower irritants of drug to the tissues.6. The self-assembled rigid supramolecular nanoplatelets (SN) from Pluronic polymers with various lengths of polyethylene oxide (PEO) andβ-cyclodextrin (β-CD) have reinforced the SPI-based biodegradable plastics in terms of strength and modulus but at the expense of elongation. Meanwhile, the water resistance, which limited the application of the SPI plastics, was also enhanced. The low loading of nanoplatelets was able to disperse into SPI matrix homogeneously, which resulted in reinforcement in nanocomposites. With an increase of nanoplatelets loading, the repulsion between nanoplatelets and SPI matrix occurred, accompanying with the formation of rectangle objects, resulted in a decrease of mechanical performance of the nanocomposites. The nanoplatelets with longest free PEO segments produced highest strength with least loss of elongation by virtue of enhanced association with SPI matrix mediated by PEO segments. Meanwhile, the nanoplatelets with moderate length of free PEO segments showed optimal water resistance. Herein, the reinforcing function of a supramolecular nanoplatelet, similar to the structure of layered silicate, was verified.The result of the above foundation researches dealing with the composite materials based on grafted and physical modified poly- and oligo-saccharide have provided important scientific data for the further development and application. As a result, this thesis shows a scientific significance and the prospects of applications, which is well consistent with the target of environmental protection and the strategy of sustainable development.
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