Sizing agents and their effect on the water absorption behaviour of GF/acrylic composites
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Machar DEVINE (UNITED KINGDOM), Duncan HORNSBY , Conchúr M Ó BRÁDAIGH (UNITED KINGDOM), Dipa RAYAbstract :
Thermoset materials such as glass-fibre reinforced polyester or epoxy have been used in the marine environment for decades in applications from tidal turbines to minehunters. However, since these materials are not recyclable, they are typically incinerated or sent to landfill at the end of their useful lives. A recyclable alternative may be found in liquid acrylic resins (Elium®) which, with their promising mechanical properties and room temperature processing, have been shown in recent years to be a near drop-in replacement for traditional thermoset resins.
Since the performance of composite materials decreases upon water absorption, the water absorption behaviour and resulting changes in mechanical properties are important to understand for new recyclable matrices such as acrylic. The performance of GF/acrylic saturated with seawater has previously been shown to be comparable to equivalent thermoset composites, but it has been suggested that a sizing agent tailored for acrylic could improve the water absorption performance even further.
In this study, GF/acrylic composites, alongside neat acrylic resin coupons, are subjected to repeated absorption-desorption cycles to induce damage to the resin and fibre-matrix interface. The composites’ reinforcement fibres were treated with either an acrylic-tailored sizing agent or a multicompatible sizing agent. The effects of this damage are characterised by monitoring changes in the absorption rate and the water uptake of the three materials, as well as the mechanical properties (tension, flexure, and short beam strength) of the composites. By comparing the performance of both composites, the effect of the tailored sizing agent on resistance to water absorption and the damage caused by it can be determined.
Permanent damage caused by water absorption was detected in the resin and the composites as increases in the diffusion coefficients with each wet-dry cycle. Diffusion was initially dominated by the matrix as the water content and diffusion coefficient of the neat resin was higher than the composites. However, in subsequent wet-dry cycles, the diffusion coefficients of the composites were higher than that of the resin. The importance of wicking along the fibre-matrix interface therefore increases as interfacial damage is introduced.
Perhaps surprisingly, the effect of the sizing agent on water absorption behaviour was found to be much less significant than other factors such the fibre volume fraction and the presence of voids. By the third wet-dry cycle, both composites manufactured with multicompatible-sized and acrylic-tailored reinforcements experienced similar degrees of interfacial loosening. In addition, neither reinforcement was found to cause consistently greater retention of mechanical properties than the other. The reasons for this overall similarity in performance are explored using fractography, and through discussion of the nature of interfacial damage.
Since the performance of composite materials decreases upon water absorption, the water absorption behaviour and resulting changes in mechanical properties are important to understand for new recyclable matrices such as acrylic. The performance of GF/acrylic saturated with seawater has previously been shown to be comparable to equivalent thermoset composites, but it has been suggested that a sizing agent tailored for acrylic could improve the water absorption performance even further.
In this study, GF/acrylic composites, alongside neat acrylic resin coupons, are subjected to repeated absorption-desorption cycles to induce damage to the resin and fibre-matrix interface. The composites’ reinforcement fibres were treated with either an acrylic-tailored sizing agent or a multicompatible sizing agent. The effects of this damage are characterised by monitoring changes in the absorption rate and the water uptake of the three materials, as well as the mechanical properties (tension, flexure, and short beam strength) of the composites. By comparing the performance of both composites, the effect of the tailored sizing agent on resistance to water absorption and the damage caused by it can be determined.
Permanent damage caused by water absorption was detected in the resin and the composites as increases in the diffusion coefficients with each wet-dry cycle. Diffusion was initially dominated by the matrix as the water content and diffusion coefficient of the neat resin was higher than the composites. However, in subsequent wet-dry cycles, the diffusion coefficients of the composites were higher than that of the resin. The importance of wicking along the fibre-matrix interface therefore increases as interfacial damage is introduced.
Perhaps surprisingly, the effect of the sizing agent on water absorption behaviour was found to be much less significant than other factors such the fibre volume fraction and the presence of voids. By the third wet-dry cycle, both composites manufactured with multicompatible-sized and acrylic-tailored reinforcements experienced similar degrees of interfacial loosening. In addition, neither reinforcement was found to cause consistently greater retention of mechanical properties than the other. The reasons for this overall similarity in performance are explored using fractography, and through discussion of the nature of interfacial damage.