Effects of Gamma Radiation on the Physicochemical Properties of Polyester Resin and Its Use in Composite Materials

In this chapter is discussed the importance of using gamma radiation as a novel technology for recycling of polyester resin, and their applications in composite materials. In the introduction section, some aspects of the environmental problems related with waste polyester resins are discussed. As it is known, novel strategies are required for diminishing the environmental pollution. They are based in no more consumption of non-renewable sources, more use of waste and recycled materials, and the manufacturing of more environmental friendly products, with improved physicochemical properties. The next section is focused on the methods for recycling or reusing of polyester resins. It is well known that mechanical, chemical, and thermal are the most current recycling processes. The mechanical follows the shredding and grinding processes and a method for separation. This has been used for to obtain thermostable polymers, which are used as fillers in different materials. The others processes also are discussed. In the second section, some concepts of gamma radiation are discussed. Such electromagnetic energy, has been used during decades for modifications of the physicochemical properties of different materials. In the case of polymeric materials, the physicochemical changes happen through the processes: scission or cross-linking of polymer chains, and grafting. Each process is produced according to the physicochemical properties of the polymers and the applied dose rate. In the next section, the effects of gamma radiation in polyester resin are mentioned. The polyester resin is usually in the liquid state; once the reaction temperature is reached, this changes from liquid to gel state. Is to say, the gamma radiation produce cross-linking of polymers chains and complete the polymerization process. Gamma radiation shows several advantages, for example it does not require any activation energy for its initiation; and the final reaction can be controlled. The total polymerization depends of the gamma radiation dose and the type of polymer. In the final section, some studies about gamma radiation as modifier of composites elaborated with polyester resins and different polymers, are discussed. The polymers act as reinforcements or fillers. The irradiated composites show high degree of cross-linking and morphological changes on their surface as well as high improvements on the physical and mechanical properties.