Bio-sourced epoxy matrix composites with natural fibre reinforcement

Abstract

The increasing concern about environment and pollution issues caused by disposal of petroleum-based waste lead to requirement for green composite which is sustainable and eco-friendly. Fibre reinforced composite with natural fibre reinforcement or bio-sourced resin matrix may be a feasible answer to the demand of green material. To fabricate fully-green composite, this work selected ramie fabric (RF) and rosin-sourced epoxy (rEP) resin as reinforcement and matrix respectively. To improve the fire safety performance of the rEP/RF composite, ammonium polyphosphate (APP) and organic phosphate (OP) were applied to modify the rEP and RF respectively, and the combined effect of simultaneously modification to fibre and matrix on inflammability of composite was investigated. Secondly, to furtherly study the combined flame retardant effect, different flame retardant (FR) additives including APP, aluminum trihydrate (ATH), zinc borate (ZnB) and expandable graphite (EG) were applied to modify rEP respectively and then reinforced by OP modified ramie fabric (OP@RF). Furthermore, a concept-proof study of liquid composite molding (LCM) process was carried out to fabricate RF/rEP composite, this section is to solve the high viscosity problem of rEP system in resin transfer molding (RTM) process. At last, a preliminary study about bio-sourced itaconic acid based epoxy (IABE) resin was carried out, the mechanical performance of glass fibre (GF) reinforced IABE (IABE/GF) composite and carbon fibre (CF) reinforced IABE (IABE/CF) composite was characterized. The specific information of each part of work was as follows.
To begin with, a fully-green composite composed of RF and rEP was developed. The RF and rEP were modified by OP and APP, respectively. Correspondingly, four groups of samples (rEP/RF, APP@rEP/RF, rEP/OP@RF and APP@rEP/OP@RF) were manufactured via vacuum bag assisted compression molding process. Thermal properties, flammability, heat release behavior, and mechanical properties of the samples were characterized. The preliminary results shows that both the FR modification to the fabric and the resin improved the fire safety performance of the composite. The APP@rEP/OP@RF composite achieved self-extinguishing in vertical burning test and a limit oxygen index of 33.2%, the peak heat release rate (PHRR) and average heat release rate (HRR) were reduced by 79% and 57% respectively than those of rEP/RF composite. However, the mechanical properties of the samples with FR modified matrix or FR modified ramie fabric behaved unfortunately inverse.
Secondly, on the basis of first part of work, to furtherly investigate the combined effect of OP@RF with rEP modified by different FR additives, the RF was still modified by OP and rEP was modified by APP, ATH, ZnB, and EG, respectively. Six formulations of composite groups: control (rEP/RF), rEP/OP@RF, APP@rEP/OP@RF, ATH@rEP/OP@RF, ZnB@rEP/OP@RF and EG@rEP/OP@RF, were fabricated. Thermal gravimetric analysis (TGA), flexural and tensile tests, UL-94 vertical burning and limit oxygen index (LOI) tests, and scanning electron microscope (SEM) were carried out to evaluate the influence of different FR additives on composite performance. The results proved that the combination of OP@RF with rEP modified by different FR additives improved the inflammability of composite with different extent. The APP@rEP/OP@RF and EG@rEP/OP@RF composites achieved V0, V0 inflammability in UL-94 category, 71.4% and 42.7% reduction in peak heat releasing rate, 46.6% and 21.1% reduction in heat releasing rate compared with rEP/OP@RF composite and 35.0%, 41.5% in limiting oxygen index test, respectively. However, the introduction of OP@RF into composites showed obviously negative influence on composite mechanical performance.
Furthermore, in a concept-proof study, a preform-based resin transfer molding (RTM) process was presented that was characterized by first pre-loading the solid curing agent onto the preform, and then injecting the liquid nonreactive resin with an intrinsically low viscosity into the mold to infiltrate and wet the pre-loaded preform. The separation of resin and hardener helped to process inherently high viscosity resins in a convenient way. Rosin-sourced, anhydrite-cured epoxies that would normally be regarded as unsuited to liquid composite molding, were thus processed. Rheological tests revealed that by separating the anhydrite curing agent from a formulated RTM resin system, the remaining epoxy liquid had its flowtime extended. C-scan and glass transition temperature tests showed that the preform pre-loaded with anhydrite was fully infiltrated and wetted by the liquid epoxy, and the two components were diffused and dissolved with each other, and finally, well reacted and cured. Composite laminates made via this approach exhibited roughly comparable quality and mechanical properties with prepreg controls via autoclave or compression molding, respectively. These findings were verified for both CF and RF composites.
Finally, itaconic acid, as a natural-sourced product with enough production and acceptable price, its unsaturated double bond and carboxyl group endows it potential as precursor of epoxy monomer, some IABE systems was designed and synthesized. To furtherly extend the application of IABE resin, GF and CF were applied to reinforced the IABE resin respectively. The IABE/GF and IABE/CF composites were fabricated via compression molding process and the mechanical performance was characterized. The current work was preliminary and the aim was to provide some fundamental information about mechanical properties of IABE/GF and IABE/CF composites.
The current work tried the possibility of combining natural fibre and bio-sourced epoxy to form fully-green composite. The influence of FR treated RF on flame retardancy of fibre reinforced composite was investigated. The combined effect of fibre treated by OP with matrix treated by different FR additives was discussed. This work also tried to find a solution for RTM process for high viscous rosin-sourced resin. In addition, the mechanical performance of IABE/GF and IABE/CF composites were evaluated as the extension of future work about bio-sourced epoxy resin composite.

Date of Award	1 Jul 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Xiaosu Yi (Supervisor), Xiaoling Liu (Supervisor) & Chris Rudd (Supervisor)