Study Of Preparation And Properties Of Starch-based Biodegradable Plastics

Starch-based biodegradable plastics are considered as one of the most promising biodegradable plastics.Generally it is prepared by blending thermoplastic starch(TPS)with degradable resin,such as Polylactic Acid(PLA),Polycaprolactone(PCL),Polybutylene Succinate(PBS)etc.Compared with pure degradation resin,it has good processing performance and lower cost,but TPS has inferior mechanical properties,which limits the application of degradable plastics.Currently,by adding some inorganic nanoparticles during nanocomposite preparations,starch-based biodegradable materials can be strengthened and toughened.Nano calcium carbonate(NCC)is a commonly used inorganic nanoparticle,which is widely supplied,with low price,non-toxic and odorless,as well as with good rigidity and thermal stability.It is extensively used as an enhancement and toughening agent to prepare polymer/NCC composites.However,NCC has a high surface energy and is prone to agglomeration,which affects the two-phase combination effect with organic phase.Therefore,modification is required before use.In this work,the rosin derivative Maleopimaric anhydride(MPAD)was synthesized from rosin and maleic anhydride.And a series of hyperbranched polyesters were synthesized with MPAD as the"core"and polyol or hydroxy acid as the"arm",with 1,1,1-trimethylolethane,1,1,1-trimethylolpropane,glycerol,polyethylene glycol 1000,and 2,2-dimethylolpropionic acid respectively by one-step method.Through the test of intrinsic viscosity[?]and esterification percentage,the hyperbranched polyester synthesized from MPAD and 2,2-dimethylpropionic acid was selected as the modifier for the next step modification of NCC,and the synthetic conditions were optimized.For the best synthetic conditions,reaction temperature was 220?and atmospheric pressure stage reaction time was 5 h,vacuum reaction stage was 3 h,the catalyst was 3%of the molar amount of 2,2-dimethylpropionic acid.The inherent viscosity under the optimum conditions was4.13 mL/g,and the esterification rate was 33.2%.The hyperbranched polyester was further characterized by Fourier transform infrared spectroscopy(FTIR),gel permeation chromatography,thermogravimetric analysis and nuclear magnetic resonance.The M_n was 2.4×10~3,the M_w was 21.0×10~3,the polydispersity index was9.0,the temperature with thermal weight loss of 3%,10%and 50%were 288?,338?and 383?,respectively,showing good thermal stability.The hyperbranched polyester synthesized under the optimal reaction conditions was used as a modifier,and the NCC was modified by a high-speed disperser to prepare modified nano calcium carbonate(MNCC).The Modified conditions were optimized by testing the oil absorption value,activation degree and particle size of MNCC.The optimum modification conditions of MNCC were as follows:the addition of modifier was 8%of the total mass of original calcium carbonate,the modification time was 1 h,and the modification temperature was 75?.Under the optimal conditions,the oil absorption value,activation degree and particle size of MNCC were 41.6,74.4%and 1.393?m,respectively.MNCC was further characterized by FTIR,contact angle test and transmission electron microscope(TEM).The static contact angle of MNCC with water was 108°.FTIR and TEM showed that the hyperbranched polyester successfully modified NCC and improved the dispersibility of MNCC.MNCC prepared under the optimal modification conditions was used as a reinforcing agent,and three kinds of starch-based biodegradable plastics TPS/PLA/MNCC,TPS/PBS/MNCC and TPS/PCL/MNCC were prepared by melt blending of TPS with PLA,PBS or PCL through a twin-screw extruder.In order to improve the mechanical properties,the ratio of TPS/degradable polyester,the addition amount of MNCC and extrusion temperature were optimized respectively.(1)The optimum preparation conditions for TPS/PLA/MNCC composites were as follows:the ratio of TPS/PLA was 3:7,the addition of MNCC was 5%of the total weight of TPS/PLA,and the extrusion temperature was 175?.Under the optimal conditions,tensile strength,elongation at break and modulus of elasticity of the composite material were 31.2 MPa,66.7%and 176.8 MPa,respectively.(2)The optimum preparation conditions for TPS/PBS/MNCC composites were as follows:the ratio of TPS/PBS was 4:6,the addition of MNCC was 5%of the total weight of TPS/PBS,and the extrusion temperature was 160?.Under the optimal conditions,tensile strength,elongation at break and modulus of elasticity of the composite material were 15.3 MPa,34.5%and 56.0 MPa,respectively.(3)The optimum preparation conditions for TPS/PCL/MNCC composites were as follows:the ratio of TPS/PCL was 4:6,the addition of MNCC was 5%of the total weight of TPS/PCL,and the extrusion temperature was 140?.Under the optimal conditions,tensile strength,elongation at break and modulus of elasticity of the composite material were 15.4 MPa,670.1%and 33.7 MPa,respectively.Mechanical properties,thermal properties and morphology of starch-based degradable plastics prepared under optimal conditions were compared and analyzed by tensile test,thermogravimetric analysis,differential scanning calorimetry and scanning electron microscope.The results showed that the addition of MNCC improved the elongation at break and thermal stability of starch-based biodegradable plastics to a certain extent,and reduced the glass transition temperature of TPS/PLA blends and the melting temperature of TPS/PBS and TPS/PCL,as well as increased the process temperature range of the composite.MNCC could be uniformly dispersed in TPS/PLA/MNCC,TPS/PBS/MNCC and TPS/PCL/MNCC composites,and had a good interface interaction with the matrix.