Composite-resin systems for direct digital additive manufacturing

直接数字增材制造（DDAM），也称为固体自由形状制造，是一种通过逐层打印制造三维（3D）物体的生产方法。一旦达到拐点，DDAM的增长预计将呈指数级增长。由聚合物复合材料制成的3D打印结构可以找到广泛的应用，例如原型，医疗和牙科产品，体育用品和备件。熔融沉积建模（FDM）、立体光刻（SL）和选择性激光烧结（SLS）是目前用于制造结构和成分可控零件的DDAM方法。其中，SL是在可固化单体浴中用紫外激光束进行光聚合的。SLS是一种基于喷墨打印和红外激光束在选定区域上熔融熔融聚合物粉末的技术。FDM是基于热塑性熔融长丝的微挤压及其逐层沉积。SL和SLS的优点是速度快、分辨率高。FDM技术的主要优点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部分时会产生废物。所有这些方法（SL、SLS和FDM）的缺点是机械性能弱，限制了它们的应用。无论是固化层还是熔融层，它们在聚合物颗粒和层之间形成互穿聚合物网络的能力有限。因此，它们产生弱的颗粒间（层）键合和焊缝。此外，模具流口水、凹陷和膨胀也是传统挤出工艺遗留下来的问题。我的计划的目标是通过发现反应挤压沉积（RED）工艺来解决这些问题。将采用纤维素纳米晶(CNC)-聚氨酯复合材料。所选的二异氰酸酯将与CNC分散多元醇和延迟时间控制的催化剂在微混合室中混合。然后，在计算机控制的微毛细管开始聚合之前，混合物将被沉积。一旦连续的层沉积下来，分子在层之间扩散，就会发生延迟聚合。选择聚氨酯是因为其可调的机械和生物相容性，适合其广泛的应用。另一方面，CNC颗粒将起到两个作用：首先，沉积和沉淀阶段的流变性将由CNC颗粒控制。其次，具有高弹性模量（134 GPa）的棒状CNC颗粒将在低浓度的渗透下为成品提供所需的机械性能。该计划将分为五个部分：1)单体的制备；2)接枝CNC并分散在多元醇中；3)微混合和微通道流动；催化聚合和焊缝形成的流变动力学；5)层状沉积力学性能。

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.