Fabrication processes and characterization of short fiber-reinforced thermoplastic composites

Abstract

Various reinforcing fibers have been used as heat-resistant and strength-enhancement material components, ranging from inorganic ceramic fibers to synthesized organic fibers. In recent years, basalt fiber (BF), a natural fiber, has gained much attention as a potential reinforcing material. Basalt is a common volcanic rock formed from the rapid cooling of basaltic lava and is made of fibrous material in a melting process at temperatures approaching $1450^\circ C$. BF is ideally suited for material applications requiring mechanical strength, high temperature resistance, durability, and chemical resistance, and is environmentally sound. Due to its outstanding properties, BF is emerging as an alternative to traditional materials in the automotive industry for the production of heat-resistant parts.

BF-reinforced plastic composites (BFRPs) have been studied extensively and provide numerous advantages and possibilities. However, most previous work has focused on BF incorporation into the resin matrix. The performance of composites is determined by the properties of the fiber and the matrix, as well as the interface compatibility between them

excellent adhesion properties promote efficient load transfer across the matrix–fiber boundary. In general, there are several methods used to improve interfacial bonding strength, including silane coupling and plasma treatment for fiber surface modification and blending of the compatibilizer with resin for compatibility enhancement.

In this study, to improve the interfacial bonding strength between BF and matrix resin, functionalization processes were designed as described below.

Firstly, amino-silane coupling agents were applied to BF-reinforced polyamide 6,6 composites. The effects of their molecular structures, especially the number of amino groups and the corresponding chain lengths, on the mechanical properties of basalt fiber-reinforced PA6,6 composites (BFRP) were then investigated.

Secondly, to improve the interfacial strength between BFs and PA6,6, plasma polymerization of a 3-aminopropyltriethoxysilane (APTES) were applied to BF-reinforced polyamide 6,6 composites. we investigated the complex reaction mechanism in plasma polymerization using argon gas and APTES.

Additionally, there was an effort to apply this compounding techniques to three-dimensional (3D) printing. 3D printing, one of the latest manufacturing processes for creating advanced composites, has recently attracted a great deal of attention. 3D printing uses various methods to build a desired geometry based on a digital model. The most widely used type of 3D printing is fused deposition modeling (FDM), in which a thermoplastic can deform when heated, and then returns to a rigid state when cooled. The unique nature of 3D printing allow it ideally make complex structural materials that form different microstructure than those prepared by conventional manufacturing processes. However, because only a few materials have been used as a feedstock for 3D printing, the resulting products exhibit limited mechanical properties. Therefore, this technology is rapidly advancing to make it suitable for the manufacturing of composite products.

Fiberous reinforcement can significantly improve the mechanical properties of 3D-printed polymeric materials. Although continuous fiber are great for increasing the mechanical strength of composites, but their processing makes it difficult to apply in 3D printing. More commonly used for 3D printing fabrication are the short fiber-reinforced thermoplastic (SFRTPs). SFRTPs have typically been fabricated by extrusion and molding processes and ensure moderately increased strength. The mechanical properties of SFRTPs are highly determined by the contribution of each component, such as the fiber length, fiber orientation and voids distribution.

Here, for improving our understanding of the microstructure inside 3D-printed BFRPs, the microstructural characteristics of these composites were identified through advanced technical measurement method, and their effects on the strength were examined in more analytical ways through a theoretical approach. This study will allow us to accurately predict the effects of various microstructural features on the final mechanical properties of 3D-printed BFRPs composites. A systematic study was also performed to examine the anisotropic microstructure dependent mechanical properties of 3D-printed BFRPs. In terms of interfacial improvement between the fiber and the matrix, a hyper-physical material made of highly controlled surfaces, highly assembled structures, and highly compatible components, which was not possible with conventional processing routes, was prepared along with the inherent properties of 3D printing, and its mechanical properties were characterized.