Influence of Nanofiber Loading and Moulding Conditions on the Joining Strength of Thermoplastic Composites Fabricated by Injection Over-Moulding Process

Abstract

An over-moulding process has promised a novel technology for joining lightweight thermoplastic composites with metal or polymer composite parts. Specifically, the substrate parts (metal or textile composites) are put into a mould of the injection moulding machine and melt polymer is injected onto substrate parts. This over-moulding process provides great benefits in terms of fast welding and moulding at the same time. However, the interfacial joining strength of over-moulded parts is still unreliable, and it has a strong dependence on surface treatment of substrate and moulding conditions. The key topic of this joining process is to achieve a reliable joining strength. In this study, we focused on using cellulose nanofiber (CNF) to interconnect between substrate and injection part by purpose of mechanical interlocking in nanoscale. Furthermore, joining strength was determined by single-lap shear test to examine the effect of presence of nanofiber. The single-lap joint consists of plain weave carbon fibre (CF) reinforced polypropylene (PP) composites (CFRPP) as substrate part and pure PP as overinjection polymer. To place the cellulose nanofiber at the interface, CF wovens and PP sheets were stacked alternately, and CNF contained PP sheet was placed at outer layer. The CFRPP substrate was obtained by heating press, pure PP was injected onto the substrate at the side of presence of CNF. This study was investigated on the influence of process conditions (i.e., injection temperature and runner route) and CNF content ratio (up to 3.0 wt%) on the shear strength as joining strength. Furthermore, the fracture morphology was observed through scanning electron microscope (SEM).

Selective Reinforcement of Joining Interface Using Nanofibers in Single-Lap Joints of Thermoplastic Composites Fabricated by the Injection Overmolding Process: Creep Deformation Behaviour

“…In the influence of the CNF content, the addition of 1.0 wt% CNF to the PP nanocomposite film increased the joining strength under all process conditions. Furthermore, the addition of 2.0 wt% CNF deteriorated the lap shear strength compared with the 1.0 wt% CNF-filled single lap joint, as reported in our previous work [13], [14]. Thus, these results showed that the optimum content of CNFs existed.…”

“…The details of the fabrication process of a single lap joint reinforced by CNFs at the joining area are described in the literature [14]. The fabrication processes are divided into two steps: (A) fabrication of CFRTP laminate and (B) overmolding of PP onto the CFRTP substrate.…”

“…Other nanofillers have been incorporated into adhesives to improve interfacial interactions [7]. Thus, we previously attempted to use nanofillers to reinforce the joining interface in the overmolding process [13], [14]. By interleaving the optimum loading of nanofiller-filled polymer films between the CoFRTP laminate substrate and injected polymer, the interfacial laminar shear strength increased by 52% [13], and the lap shear strength increased by 32% [14].…”

“…Thus, we previously attempted to use nanofillers to reinforce the joining interface in the overmolding process [13], [14]. By interleaving the optimum loading of nanofiller-filled polymer films between the CoFRTP laminate substrate and injected polymer, the interfacial laminar shear strength increased by 52% [13], and the lap shear strength increased by 32% [14]. However, for the long-term use of overmolded hybrid composites, the fatigue and creep properties should be considered to ensure the reliability of the joining strength.…”