Composite-resin systems for direct digital additive manufacturing

直接数字相加制造(DDAM)，又称实体自由曲面制造，是一种通过逐层打印来制造三维物体的生产方法。预计一旦达到转折点，DDAM将呈指数级增长。由聚合物复合材料制成的3D打印结构可能会有广泛的应用，如原型、医疗和牙科产品、体育用品和零部件。熔融沉积成型(FDM)、立体成形(SL)和选择性激光烧结(SLS)是目前用于制造结构和成分可控的零件的DDAM方法。其中，SL是基于紫外光在可固化单体浴中的光聚合。SLS是基于喷墨打印和通过红外激光在选定区域熔融聚合物粉末。FDM是基于热塑性熔融细丝的微挤出和它们的逐层沉积。SL和SLS的优点是速度快、分辨率高。Fdm技术的主要优势是它能够创建几乎任何形状或几何特征。另一方面，SL和SLS在清洗未固化或未熔化的管段时都会产生废物。力学性能差是所有这些方法(SL、SLS和FDM)的缺点，限制了它们的应用。无论是固化层还是熔融层，它们都限制了聚合物颗粒和层之间互穿聚合物网络的形成。因此，它们会产生较弱的颗粒(层)间结合和熔接痕。此外，流模口水、凹陷和膨胀是熔融成型的其他问题，这些问题是从传统塑料挤出工艺中继承下来的。我的计划的目标是通过发现反应挤压沉积(RED)过程来解决这些问题。纤维素纳米晶(CNC)-聚氨酯复合材料将被用作材料。选定的二异氰酸酯将在微型混合室中与CNC分散的多元醇和延迟时间控制的催化剂混合。然后，在聚合开始之前，由计算机控制的微毛细管将混合物沉淀。一旦连续的层被沉积，分子在层间扩散，就会发生延迟聚合。选择聚氨酯是因为它们的机械性能和生物相容性可调，适合于它们的广泛应用。另一方面，数控颗粒将扮演两个角色：首先，沉积和沉降阶段的流变性将由数控颗粒控制。其次，具有高弹性模数(134 Gpa)的棒状纳米颗粒将在低浓度渗流的情况下提供所需的机械性能。该程序将包括五个部分：1)单体的制备；2)接枝数控并分散在多元醇中；3)微观混合和微通道流动；4)催化聚合和焊缝成形的流变性；5)层状沉积的力学性能。

Direct Digital Additive Manufacturing (DDAM) which is also called as Solid Freeform Fabrication is a production method of making three-dimensional (3D) objects by layer by layer printing. The growth of DDAM is expected to be exponential once it reaches to its turning point. 3D printed structures made of polymeric composites may find broad range of applications such as prototypes, medical and dental products, sporting goods, and spare parts. Fused deposition modelling (FDM), stereolithography (SL) and selective laser sintering (SLS) are current DDAM methods to create parts with controlled architecture and composition. Among them, SL is based on photopolymerization in a curable monomer bath by UV laser beam. SLS is based on inkjet printing and melt fusion of polymer powder on selected areas by infrared laser beam. FDM is based on micro extrusion of thermoplastic molten filaments and their deposition layer by layer. Advantages of SL and SLS are speed and high resolution. The primary advantage of FDM technology is its ability to create almost any shape or geometric feature. On the other hand both SL and SLS generate waste from the cleaning of uncured or unmolten segments. Weak mechanical properties are the disadvantages of all of those methods (SL, SLS and FDM) and limit their applications. Whether cured or fused layers, they have limited formation of interpenetrating polymer networks among polymer particles and layers . Thus they generate weak interparticle (layer) bonding and weld lines. In addition die drool, sag and swell are other problems of FDM which are inherited from conventional plastic extrusion processes. The goal of my program is to address those problems by the discovery of Reactive Extruded Deposition (RED) process. Cellulose nanocrystal (CNC)-polyurethane composites will be used as materials. Selected diisocyanates will be mixed with CNC dispersed polyols and delayed time controlled catalysts in a micromixing chamber. Then, the mixture will be deposited before polymerization starts by the computer controlled micro capillary. Delayed polymerization will take place, once successive layers are deposited and diffusion of molecules among layers takes place. Polyurethanes are selected because of their tunable mechanical and biocompatible properties, suitable for their wide range of applications. On other side, CNC particles will play two roles: First of all, the rheology of the deposition and settling stages will be controlled by CNC particles. Secondly, rod-shaped CNC particles with high modulus of elasticity (134 GPa) will give the desired mechanical properties to finished products at low concentrations with percolation. The program will have five parts: 1) Preparation of monomers; 2) Grafting CNC and dispersing in polyols; 3) Micro mixing and microchannel flow; 4) Rheokinetics of catalytic polymerization and weld formation; 5) Mechanical properties of layered deposition.