Hot-end co-extrusion of multiple thermoplastic filaments for unblended composite additive manufacturing

Additive manufacturing (AM) techniques can print multiple materials to realise three-dimensional products with increased complexity not only in their shapes but also in their mechanical behaviour. Here, we study hot-end co-extrusion printing of multiple thermoplastic filaments. By co-extrusion printing of different filaments in bi- and tri-material configurations from a single printing platform, we demonstrate that versatile material behaviours and functionalities can be realised. In particular, rigid thermoplastic filaments can be mechanically boosted to exhibit fracture-free elongation via co-extrusion with a soft elastomer. For example, the widely used polylactic acid (PLA) and acrylonitrile butadiene-styrene (ABS) filaments can be co-axially extruded with thermoplastic polyurethane (TPU) filaments to enhance their toughness by 34-fold and 30-fold, respectively. During hot-end co-extrusion, the two materials do not mix but are still coupled by strong hydrogen bonds at their interface, thereby enabling mechanical behaviour not observed in conventional blended composites. We further utilise our hot-end co-extrusion 3D printer to manufacture and demonstrate customised products, such as fracture-free mechanical structures, personalised functionally graded body protection gears, and highly repeatable and rapidly actuatable soft actuators. The unblended, locally tuned pneumatic actuator can lift an object that weighs 12.6 times heavier than its own weight at 17.7% contraction ratio.

增材制造（Additive Manufacturing，AM）技术可实现多材料打印，制造出不仅形状复杂度提升、且力学行为更丰富的三维产品。本研究聚焦单打印平台下的热端共挤出打印工艺，采用双材料与三材料构型对多种热塑性丝材开展共挤出加工。研究表明，该工艺可实现多样化的材料力学行为与功能特性。具体而言，刚性热塑性丝材可通过与柔性弹性体共挤出，获得无断裂伸长的性能提升：例如，广泛使用的聚乳酸（PLA）与丙烯腈-丁二烯-苯乙烯共聚物（ABS）丝材，分别与热塑性聚氨酯（TPU）丝材进行同轴共挤出后，其韧性可分别提升34倍与30倍。在热端共挤出过程中，两种材料并未发生混合，但界面处通过强氢键实现牢固结合，因此可呈现传统共混复合材料无法实现的独特力学行为。本团队进一步利用自研的热端共挤出3D打印机，制备并验证了多款定制化产品，包括无断裂力学结构件、个性化功能梯度防护齿轮，以及高重复性、快速响应的柔性驱动器。其中，未发生材料混合的局部可调气动驱动器，可在17.7%的收缩率下，举起自重12.6倍的负载物体。