Wood Plastic Composites Based On LiCl-Modified Polyamide 6 And Its Plastic Alloy

In recent decades,wood plastic composites(WPC)based on natural fiber and general purpose plastics such as polyethylene(HDPE),polypropylene(PP),and polyvinyl chloride(PVC)were applied in decoration field.However,deficiency of the strength has restricted the further application.Due to the conflict between low thermal stability of natural fiber and high melting point of engineering plastics,such as polyamide 6(PA6),polyamide 66(PA66),and polyethylene terephthalate(PET),it is difficult to prepare the composites based on engineering plastics with higher mechanical properties.In this paper,the melting point of PA6 was reduced by lithium chloride(LiCl),and then WPC based on PA6,PA6/PP,and PA6/HDPE blends were prepared,respectively.The main contents and results are as follows:(1)LiCl could reduce the melting point and processing temperature of PA6,and was used to prepare WPC.The chain extender(PBO)could improve the molecular of PA6,and then enhance the mechanical properties of the composites.Due to the complexation between PA6 and LiCl in a Haake torque rheometre,the melting point and crystallinity of PA6 were decreased,and the crystallographic form was changed from a-phase with small grain size to ?-phase with large grain size.As a result,the processing temperature of the composites was decreased,and the composites was prepared via hot pressing.From the color and FTIR analyses,the phenomena that the composites became dark with carbonized surface has been avoided.The complexation is similar to pseudo-crosslinking,so the mechanical performances of the composites were increased,especially the impact strength.In order to improve the strength of the composites,the molecular weight of PA6 was increased by the addition of PBO.Due to the formation of hydrogen bond between PBO and wood flour,the compatibility and mechanical properties of the composites could be improved.(2)The melting point and processing temperature of PA6/PP blends were decreased by LiCl.Both LiCl and MAPP could improve the compatibility and mechanical properties of the composites.In this paper,PA6,PP,LiCl,and MAPP were mixed in a Haake torque rheometre,and then the composites based on PA6/PP blends were prepared under low processing temperature.From the color and FTIR analyses,the composites could essentially maintain the color of wood flour.The complexation between LiCl and PA6,anhydride groups of MAPP could improve the compatibility and mechanical properties of the composites.The condensation of MAPP and PA6,as well as the esterification between MAPP and wood flour could improve the compatibility and mechanical properties of the composites.With the increasing of PA6 content,the flexural strength and modulus of the composites were increased,but the impact strength was decreased.However,due to the formation of large spherulite promoted by more PP,the impact strength of the composites with 40%PA6 was lower than that with 50%PA6.(3)The melting point and processing temperature of PA6/HDPE blends were decreased by LiCl.Both LiCl and MAPE could improve the compatibility and mechanical properties of the composites.In this paper,PA6,HDPE,LiCl,and MAPE were mixed in a Haake torque rheometre,and then the composites based on PA6/HDPE blends were prepared under low processing temperature.From the color and FTIR analyses,the composites could essentially maintain the color of wood flour under the processing temperature of 200?.The complexation between LiCl and PA6,anhydride groups of MAPE could improve the compatibility and mechanical properties of the composites.The condensation of MAPE and PA6,as well as the esterification between MAPE and wood flour could improve the compatibility and mechanical properties of the composites.With the increasing of PA6 content,the flexural strength and modulus of the composites were increased,but the impact strength was decreased.(4)The modification of LiCl and in-situ grafting(one-step method)were applied to prepare PA6/HDPE/MCC Composites with high mechanical properties.Dicumyl peroxide(DCP)and maleic anhydride(MAH)were dissolved in acetone,then the solution was sprayed onto PA6/HDPE blends.After the acetone was evaporated in the fuming cupboard,LiCl was incorporated to the plastic blends in a Haake torque rheometer.MCC was compounded with the aforementioned blends via hot pressing.MAH was grafted to PA6 and HDPE molecular chains when DCP was initiated under high temperature.The condensation of MAH and amino end groups of PA6,as well as the esterification between MAH and hydroxyl groups of MCC could improve the compatibility and mechanical properties of the composites.LiCl could complexed with PA6,MAH,and MCC.So LiCl could improve the mechanical performances of the composites.LiCl could improve the glass transition temperature(Tg)of the composites,and could increase the temperature range of the application.In conclusion,LiCl could obviously decrease the melting point and processing temperature of PA6,and then was applied to prepare WPC based on PA6,PA6/PP,and PA6/HDPE,respectively.The serious degradation and surface darkening were avoided.Moderate LiCl could increase the compatibility and mechanical properties of the composites,and then could widen the application fields,especially engineering fields with high demanding.As a result,the composites has extensive market prospect.