Thermoplastic hybrid-matrix composites prepared by a room-temperature vacuum infusion and in-situ polymerisation process

This work explores a novel route for the fabrication of hybrid-matrix composites based on a recently developed liquid thermoplastic acrylic resin. This resin was modified using a poly(phenylene ether) (PPE) oligomer with vinyl functionality. Glass fibre-reinforced laminates based on acrylic and PPE-modified acrylic matrices were produced by a room-temperature vacuum infusion and in-situ polymerisation process. Comparative assessments of their mechanical performance and mode-I interlaminar fracture behaviour revealed enhanced matrix ductility, transverse flexural properties and initiation fracture toughness. Crazing was identified as the dominant mechanism for improved resistance to crack initiation

Novel epoxy powder for manufacturing thick-section composite parts under vacuum-bag-only conditions. Part II: Experimental validation and process investigations

Validations of a one-dimensional process model are carried out by manufacturing thick-section glass-fibre reinforced composite laminates with a low-exotherm epoxy powder. An experimental apparatus is developed which heats the laminates from one side while insulating the remaining sides (i.e. approximating one-dimensional heat transfer conditions). The experimental results are analysed and used to validate process models for the epoxy powder system. Process simulations are performed to analyse the influence of material format, laminate thickness change, and heating methods (i.e. one-sided heating vs two-sided heating, and heated tooling vs oven heating). It is shown that epoxy powder eliminates the risk of ‘thermal runaway’, but thermal and cure gradients persist for a conventional processing cycle. Methods to inhibit the evolution of these gradients are explored using process simulations. These methods include modifying the temperature cycle and using multiple epoxy powders with varied latent curing properties

Continuous fibre-reinforced thermoplastic acrylic-matrix composites prepared by liquid resin infusion – a review

Increasing demand for lightweight materials is a major driving force for the steady growth of the continuous fibre-reinforced polymer composite industry. In recent years, strict global targets demanding greater environmental responsibility have led to a shift in research focus to address the end-of-life challenges posed by the use of thermoset matrices. Thermosets offer lower-cost processibility than thermoplastics, which historically required cost- and energy-intensive production methodologies. Consequently, despite their well-demonstrated recyclability, thermoformability and weldability, thermoplastics are yet to attain the same technological maturity as thermosets. In situ polymerisable thermoplastic resins have been identified as attractive emerging solutions for improving the processibility of thermoplastics. Thus, are essential materials in meeting the demand for fibre-reinforced thermoplastic composites. This review presents a comprehensive summary of recent works on room-temperature-processible liquid thermoplastic acrylic resins and their composites. Moreover, open problems and research opportunities are identified and discussed

3D printing and epoxy-infusion treatment of curved continuous carbon fibre reinforced dual-polymer composites

A manufacturing technique was developed to fabricate curved continuous carbon fibre reinforced composites based on 3D printing and epoxy-infusion treatment. Composite preforms were first manufactured by material-extrusion based 3D printing of continuous carbon fibre reinforced thermoplastic polyamide-6 (PA-6) filaments. Powder thermoset epoxy was added to the preforms to fill up the gaps, remove air voids and enhance the interfacial bonding through a traditional vacuum bagging and oven curing process. Uniaxial tensile tests showed that the stiffness and strength of the printed composites were increased by 29.3% and 22.1%, respectively, compared to the thermoplastic-only composite specimens. The epoxy-infusion treatment technique was also adopted to manufacture composites with curved fibre alignment and investigate the performance of 3D printed notched specimens under uniaxial tension. It was shown that the placement of continuous carbon fibres along the principal stress trajectories increased the failure strength and the fracture toughness of the composites by 81% and 157% respectively, compared to the unidirectional and concentric placement methods

‘Resin welding’: A novel route to joining acrylic composite components at room temperature

The solubility of acrylic polymer in its own liquid monomer creates the opportunity to ‘weld’ acrylic-matrix (Elium®) composites without the application of heat. In this method, termed resin welding, acrylic monomeric resin is infused between acrylic-matrix composite parts. The resin dissolves and diffuses into the acrylic matrix and creates a continuous material, and a strong bond, when it polymerises, without the sensitivities of traditional welding methods to adherend or bondline thickness. Single lap shear testing was conducted on resin-welded and adhesively-bonded coupons with varying bondline thicknesses and filling fibres, and the bonding and fracture mechanisms were investigated using SEM and the diffusion of dyed acrylic resin. The highest bond strength of resin-welded coupons reached 27.9 MPa, which is 24 % higher than the strongest weld reported in the literature, indicating that resin welding is a promising alternative to traditional bonding and welding methods for acrylic-matrix composites