Research On 3D Printing Materials Of Poly (Lactic Acid) Based Biomass Composites

In fused deposition molding?FDM?,the factors that affect and restrict the performance of FDM products mainly include 3D printer,FDM processing,software controlling and printing materials.Due to high requirements of mechanical strength,heat resistance temperature,surface quality and printing speed,a few varieties of FDM printing materials are available in recent China.Mainly used as arts and crafts,3D printing products cannot meet the requirements of engineering application.Therefore,it is urgent to develop printing materials applied in different fields,improve the performance of existing materials in such aspects as heat resistance,mechanical strength and antistatic performance,rich the variety of printing materials,reduce the cost of materials and construct the mechanism of FDM processing.As the raw material of PLA,poplar fibre,coffee grounds,graphene and carbon nanotube,this paper introduces the preparation of PLA based 3D printing wire and also researches the influence of FDM processing,organic fibre and carbon nano fillers on mechanical properties,thermal properties,electric conductivity and rheological properties of products.It can be concluded that:?1?The optimal FDM processing of PLA is that:deposition angle is 45°,layer thickness is0.3 mm,filling density is 100%and printing temperature is 210?.The structure of printing products affect its mechanical properties to some extent.For instance,the tensile strength of products is lower than that of pure PLA but the elongation rate of products increases by 186%.FDM processing impacts little on glass transition temperature,crystallization temperature and melting temperature of PLA but does affect the crystallinity of PLA significantly,which drops from 35.8%to 3.6%.PLA is likely to crystallize within 90?-120?.The crystallinity of PLA products can reach as high as 40.7%under 120-min heat treatment in 100?.?2?No significant thermal degradation emerges in PLA/poplar fibre composite wire through the preparation of wire materials and FDM processing.Slight thermal degradation?mainly is the degradation of hemicellulose in poplar fiber?of the composite wire emerges at 210?.The composite materials indicate the best comprehensive mechanical performance when the addition amount of 250 meshes poplar fibre is 3%.The preparation processing of PLA/poplar fibre composite wire have small impacts on the crystallinity,but FDM processing affects the crystallinity of PLA/poplar fibre composite wire significantly,which leads to the crystallinity of FDM products is relatively low.However,crystallinity of FDM products rockets under 100?thermal treatment.?3?Using“materials studio”to predict the compatibility of PLA and poplar fibre,the modification of acetic anhydride or KH550 on poplar can promote the compatibility of fiber and PLA,but the effect is not significant.Therefore,the poplar fiber is not suitable to be grafting modified by using coupling agent or acetic anhydride in industrial production.?4?Using“materials studio”to predict the compatibility of PLA and coffee grounds,Coffee grounds have relatively good compatibility with PLA.When the addition amount of coffee grounds is 3%,the bending strength of the composite materials is as high as 109MPa,which increases 33.24%compared to pure PLA.Thermal treatment can increase the mechanical properties of materials significantly.The crystallinity of PLA/coffee grounds composite materials is relatively low,which is less than 10%.The crystallinity of PLA/3%coffee grounds composite materials under 100?thermal treatment for 30 minutes experience a significant growth,which is 50.18%.?5?The viscosity of PLA/carbon nanotube composite materials is significantly dependent on the temperature and the shear rate.PLA and its composite materials do not degrade significantly in the processing of wire preparation and FDM.Moreover,it is effective to reduce the impacts of graphene and carbon nanotubes on the rheological properties of the composite materials by decreasing the temperature.Carbon nanotubes and graphene can induce the crystallization of PLA,which can help to improve the crystallinity of PLA,so as to improve mechanical properties.When graphene addition amount is 2%,the bending modulus of the composites reach the peak of 3199 Mpa,which is 21.63%higher than that of pure PLA.Graphene and carbon nanotubes show little impact on the melting temperature,while the glass transition temperature drops approximately 5?,which is not conducive to the application and popularization of FDM products.The electric conductivity of graphene or carbon nanotube modified PLA composite materials increases exponentially,which can reach the peak of 100 S/m.In addition,the electric conductivity of the PLA/carbon nanotube composites could be represented by?=e^aw-b.?6?Maleic anhydride?MAH?,maleic anhydride grafted ethylene/octene copolymer?POE-g-MAH?and maleic anhydride grafted polystyrene?PS-g-MAH?present a positive effect on improving the strength and toughness of PLA/graphene composites to some extent.When the graphene addition amount is 3%,the mechanical properties and electrical conductivity of the composite are relatively good to meet the market requirements.