Application Of Novel Sliding Graft Copolymer

Recently, increasing concerns over the environmental impact and sustainability of conventional polymer materials have motivated academia and industry to devote considerable efforts to the development of polymers from renewable resources. In the past studies, our groups and Ito’s research team have jointly developed this sliding copolymer (SGC) with novel structure.SGC is a kind of special PR derivatives, in which many linear poly-ε-caprolactone (PCL) side chains are bound to cyclodextrin rings of a polyrotaxane, was prepared by ring-opening polymerization of ε-caprolactone. Recently, there is no report about the effect of the nolvel PR as a functional additive to polymer. Therefore, to satisfy the sustainable development of engineering materials, it is of great strategic significance to synthesize this polyner from biomass resources.In this paper, the SGC that jointly developed by our laboratory and Ito’s research team was used as tougner to toughen PLA and DGEBA respectively. In addition, SGC and PLA were chosen as the two components to prepare a new-typed biobased thermoplastic vulcanizate (TPV) via dynamic vulcanization process. The main conclusions are listed as follows.(1)In the first part of this thesis (Chapter2), The "sliding graft copolymer"(SGC) was employed to toughen brittle polylactide (PLA) by simple melt blending. All PLA/SGC blends exhibited good processability, toughness and biocompatibility. It is found that the blends showed a typical "sea-island" morphology by SEM and TEM. The particle size is from0.8μm to4.1μm. Differential scanning calorimeter (DSC) indicated that SGC improved the cold crystallization capability of PLA.Because SGC has a dilution effect on the PLA matrix, i.e., SGC is in a highly elastomeric state at the cold crystallization temperature of PLA since it is already melted. Therefore, SGC improves the mobility of PLA segment and the crystallization ability of PLA. The tensile and impact properties have been increased due to the addition of SGC.The elongation at break of PLA/SGC/MDI(40/10/2) increased from13%(for neat PLA) to36%, at the same time the notched Izod impact strength was increased from2.4kJ/m2to5.2kJ/m2. SEM micrographs of tensile-fractured surface and impact-fractured surface revealed that the toughness improvement is caused by SGC domains acted stress concentrations which would absorb much energy.(2) In the second part of present thesis (Chapter3), based on the prior research work the SGC was employed to toughen brittle polylactide (PLA) with methylene diphenyl diisocyanate (MDI) by reactive blending. According to content in the first part of this thesis, the toughness of PLA/SGC blends have not improved markedly due to the incompatibility between PLA and SGC phase and weak interface adhesion. In order to increase the compatibility of PLA and SGC,adding MDI as reactive agent during the melt blending. Notched Izod impact strength of PLA/SGC/MDI (40/10/2) blend increases to48.6kJ/m2,20times as compared to unmodified PLA, which is much higher than those reported in most literatures. The obtained improved compatibility and high toughening effect of PLA by SGC has been attributed principally to following factors:(i) formation of PLA-co-SGC copolymer,(ii) in situ crosslinking of SGC and (iii) the chain extension of PLA.The crosslinked SGC (c-SGC) elastomeric particles with slide crosslinking points performed as stress concentrators and absorbed considerable energy under impact and tensile process. Moreover, the crosslinked SGC particles have the advantages of moving crosslinking points compared with traditional crosslinking network, i.e., the crosslinking points can slide along the linear chains to the optimum points when crosslinked SGC particles under external loading, thereby resulting in absorbing more fracture energy.(3) In the third part of present thesis (Chapter4), SGC and PLA were chosen as the two components to prepare a new-typed biobased TPV via dynamic vulcanization process. The dynamic vulcanization technology of SGC/PLA TPVs was confirmed by the experiments. The effects of dynamic vulcanizating time, dynamic vulcanizating temperature, blending ratio of elastomer to plastic and the content of curing agent (HMDI) on SGC/PLA TPVs performances have been studied. The curing behavior, morphology and mechanical properties were investigated. The optimal dynamic vulcanizating time, dynamic vulcanizating temperature, blending ratio of elastomer to plastic and the content of curing agent are15min,170℃,70/30and16%,respectively. TEM micrographs of SGC/PLA TPV prepared under the optimum curing conditions revealed that the crosslinked SGC elastomers were broken up into micron-sized particles and homogeneous dispersed in PLA matrix, which exhibited good elasticity and mechanical properties. The tensile strength and elongation at break of SGC/PLA TPVs ranged from7to17MPa and80%to180%, respectively. The in vitro cytotoxicity tests showed that the cytotoxicity of SGC/PLA TPVs belonged to grade1, indicating good cytocompatibility. The hydrolysis test proved that SGC/PLA TPVs have degradability.(4) In the fourth part of present thesis (Chapter5), SGC was chosen as toughener, diethyl methyl benzene diamine (E100) was curing agent to toughen diglycidyl ether of bisphenol A (DGEBA). This chapter mainly studied the effects of content of SGC on the morphology, thermal behavior, curing reaction and mechanical performance of the cured systems. In the DSC curves of DGEBA/SGC blends, the single glass transition temperatures were observed, indicating the miscibility of epoxy with the SGC. The miscibility of the DGEBA/SGC thermosetting blends could be the intermolecular specific interactions (viz. hydrogen bonding) between amine-cured epoxy and SGC, which is readily to detect by means of fourier transform infrared spectroscopy (FTIR). The compatibility between DGEBA and SGC is good as evidenced by the SEM of cryo-fractured surfaces of DGEBA/SGC blends. It shows that with the content of SGC increasing, the flexural strength, tensile strength and tensile modulus decreased,while the impact strength and elongation at break distinctly inereased, which demonstrates that the toughness of the epoxy resin system could be improved effectively by adding SGC. When the amount of SGC was20wt%,the impact strength was four times than that of neat DGEBA. It is indicated SGC is good toughner for DGEBA. The toughening mechanism can be proposed by the impact-fractured surface of samples. The neat DGEBA is smooth,indicating the brittle fracture. After the additon of SGC, the fractured surface is rough. There are mountain-like stripes and radial stripes in the DGEBA/SGC blend illustrated tough fracture has taken place. The toughening mechanism of DGEBA/SGC/E100system was that the sliding graft copolymer may be having an effect on constraints and closure of crack. Therefore, the sliding graft copolymer can toughen epoxy resins effectively by simple melting blend.