熔融沉积成型加工的结晶性聚合物结构与性能

Hierarchical Structures and Mechanical Performances of Semicrystalline Polymer Parts Fabricated by Means of Fused Deposition Modeling

熔融沉积成型(fused deposition modeling,FDM)作为一种新型的聚合物加工方式,可制备外形复杂、性能可靠、功能集成的聚合物制品,并随着新打印工艺和新材料体系的不断涌现,显示出巨大的应用和发展潜力.但层层堆积的加工方式为FDM成型件引入了薄弱层间结合界面和较大残余内应力,限制了可FDM加工的聚合物材料种类,并制约着FDM成型件的性能和功能.本文结合FDM加工原理分析了可FDM加工的聚合物材料特性,重点关注FDM成型件的微观结构包括多层次聚集态结构、层间结合界面,总结FDM成型件的宏观力学性能及其各向异性,以此构建FDM成型的聚合物结构-性能关系,并展望高性能FDM成型件的发展前景.

Fused deposition modeling(FDM)as the most common additive manufacturing technique,is a revolutionary processing method for polymer materials.FDM technique can build complicated and multifunctional components by selectively depositing one or two kinds of polymer materials layer-by-layer according to the predetermined paths.Further,the recent development of polymer nanocomposites and printing devices has broadened the applicability of FDM technique to fabricate lightweight,customized and multifunctional products for medical,electronics,aerospace and automotive areas.Although the ability to fabricate end-use products is expanding,the evolution of FDM into a fully manufacture tool is limited by several challenges including narrow material selection,weak interlayer bond and poor surface quality.In order to acquire a good knowledge of the processing-structure-performance relationship for polymer parts fabricated by FDM technique,this review firstly analyses the stringent requirements for polymer materials compatible with FDM platform,then provides a comprehensive overview on the crystallization kinetics,hierarchical structures as well as the mechanical performance of FDM-printed parts.For semicrystalline polymer materials,high shear and extension field in the nozzle is found to accelerate the crystallization kinetics and induce oriented structures and shish-kebab morphology.In this sense,FDM-printed parts can achieve mechanical properties superior to their counterparts by means of injection molding.However,the intrinsic layer-wise deposition in conjunction with non-isothermal profile during a typical FDM process tend to introduce weak bond interfaces as well as residual stresses in FDMprinted parts,leading to anisotropic mechanical properties and serious dimensional errors.This in turn puts complicated requirements for polymer materials for FDM platform,including good feeding properties(e.g.elastic modulus E/melt viscosityηlarger than 3.24×10^5 s^−1)and excellent printing properties(e.g.low coefficient of thermal expansion and appropriate melt viscosity).Recent efforts suggest that adding organic/inorganic additives to physically modified polymer materials is a simple and effective way to overcome both limited variety of semicrystalline materials and weak interlayer bond issues for FDM technique.In the near future,polymer composites should be well designed and screened to fit for FDM platform and also the processing-structureproperty relationship for FDM-printed parts should be explored in detail so as to obtain polymer articles with excellent properties and meet the growing requirements from various areas.