| Traditional petroleum-based plastic has brought convenience to our lives, at the same time it caused serious environmental pollution. Besides, it is not sustainable as petroleum is non-renewable. Starch-based biodegradable plastics was regarded as one of the most promising biodegradable plastics, and usually prepared by blending of TPS and degradable resin. Its mechanical properties could be enhanced by addition of inorganic component. As commonly used inorganic filler, nanometer calcium carbonate(NCC) could improve the impact resistance and toughness of the material while reducing the cost. Since inorganinc NCC has low interface compatibility with organic phase, we systhesized hyperbranched polyester(HBP) with terminal carboxyl groups to modify NCC, which was supposed to improve interaction between NCC and organic phase, also dispersion and stability of NCC in the organic matrix. And modified NCC was expected to enhance comprehensive mechanical properties of starch-based biodegrable plastic.Ten kinds of HBP were synthesized and their intrinsic viscosity [η] were determined. [η] of HBP synthesized from citric acid and PEG-6000 was the highest. Reaction conditions were optimized to improve [η] of HBP. The optimized conditions were as follows: reaction temperature was 160℃, the amount of catalyst was 3.0% of the total mass of reactants, the time of the first period was 3h at atmospheric pressure and 1h under vacuum, the time of the second period was 3h at atmospheric pressure and 3h under vacuum. The pressure was 0.6k Pa. The optimized product was characterized by FTIR, GPC, TGA and DSC. The result showed that its esterification ratio reached 58.8%, [η] was 37.6 ml/g. Mn was 37.1×103, Mw was 77.6×103. There is only 3.0% weight loss below 269.1℃. Tm, Tc, Tg were 51.0℃, 22.6℃,-21.8℃, respectively.The HBP were used to modify NCC. Effect of modified solvent, the amount of the modifier, stirring speed on the modification effects was tested. The results showed that HBP had better modification effect than stearic acid. Due to a stronger shearing force, modification with high speed mixer had better effect than ordinary mechanical stirring. The lowest oil absorption value was 36.0, indicating the best modification effect, when DMF was modified solvent, the amount of HBP was equivalent of stearic acid of 3.0wt% NCC, and reaction was stirred by high-speed mixer. FTIR and TEM results showed that NCC and HBP modifier have effective surface combination, and dispersion of the NCC in organic matrix was improved.TPS was prepared with glycerol by twin-screw extruder. Addition amount of the plasticizer, processing temperature, and screw speed were optimized to enhance comprehensive mechanical properties. The best processing parameters were as follows: glycerol was 50wt% of native starch, the processing temperature was 175℃, and screw speed was 120r/min. Tensile strength σ of the TPS was 11.3MPa, elongation at break ε was 130.9%, elastic modulus E was 202.6MPa. TPS and PLA were blended with modified NCC to increase ε. Increasing range of ε was the highest when NCC modified by HBP from citric acid and PEG-6000 condensation was added. And σ of blending was 22.7MPa, ε was 20.2%; E was 262.2MPa. While adding NCC modified by HBP from citric acid and 12-hydroxy stearic acid condensation, as well as amphiphilic compatibilizer, σ of the blending was 12.5MPa, ε increased to 27.3%. This confirmed certain toughening effect of modified NCC on starch-based plastics. |
PDF Full Text Request