Acrylic-Polyurethane Based Graft-Interpenetrating Polymer Networks for High- Performance Applications

Abstract

In this research, interpenetrating polymer networks (IPNs) based on polyurethane (PU) and acrylic copolymer were synthesized for high-performance applications. Two different polymers with different mechanical and thermal properties were utilized to take advantage of the synergy of the networks. Chemical bonds between the two phases were utilized to minimize the phase separation between two polymers and enhance the final properties. The use of synthesized IPNs in transparent high fracture toughness and impact structural applications, fiber-reinforced composite, and thermal energy storage devices were studied. The stress relaxation behavior of the synthesized IPNs was also modeled. In chapter 2, graft-interpenetrating polymer networks were synthesized for transparent protection applications. Excellent transparency was observed in IPN samples with a high percentage of styrene. Fracture toughness results indicated more than 100% improvement compared to poly(methyl methacrylate) (PMMA) and polystyrene as traditional transparent impact resistant polymers. Novel graft-IPN synthesized in this chapter has huge potential in transparent high fracture toughness applications. In chapter 3, graft-interpenetrating polymer networks containing commercial vinyl ester were employed in carbon fiber reinforced polymer matrix composites. Enhancement in damping properties was observed in IPN structure compared to pure acrylic copolymer due to the presence of PU. No phase separation was observed in the IPN matrix, and composite samples showed good adhesion between fibers and matrix without any debonding or fiber pull-out. The composites' flexural and tensile properties were also obtained and showed enhancement compared to composite samples prepared in the literature. The results obtained in this chapter, combined with simple manufacturing method of composites, indicate the potential of graft-IPN carbon fiber composite in different high-performance applications. In chapter 4, the application of graft-IPNs was broadened by increasing the percentage of PU in the system. The effect of changing the monomer of the acrylic copolymer from styrene to MMA was also studied. Temperature ramp test and tensile results showed broad properties for elastomeric to more ductile applications. Excellent transparency and impact resistance for sandwich structure of pure polycarbonate (PC) sheets with novel graft-IPNs between them were also obtained. The strength of materials as an adhesive was also determined using a lap shear test. The flexible graft-IPN has vast potential to be used in transparent high impact resistance applications. In chapter 5, the stress relaxation behavior of the IPN samples with different percentages of PU and different styrene ratios were studied using dynamic mechanical analysis under tensile and flexural tests. Synthesized glassy IPNs showed excellent compatibility between two phases with comparable resistance against relaxation to COP samples in the stress relaxation test. Rubbery samples also exhibited excellent resistance against relaxation, which shows their potential in damping applications. These experimental results were used to simulate the numerical model for the stress relaxation behavior of the samples. For this purpose, a three-dimensional FEM model was utilized with the Generalized Maxwell model and four-term Prony series constants. Good overlap between experimental and simulated stress relaxation data was observed for all samples, which shows the potential of the generated model in predicting the stress relaxation behavior of IPNs. In the final chapter, semi-interpenetrating polymer networks were synthesized out of polyethylene glycol (PEG)-based PU and MMA-based acrylic copolymer. PU was utilized to act as a thermal energy storage material. At the same time, acrylic copolymer was used to act as a skeleton to keep the whole system together at a higher temperature. The synthesized sample showed excellent thermal properties with cycling and shape stability. Such material has tremendous potential to be used in thermal energy storage applications such as electronics and solar cells.