Introduction:
Epoxy resin represents some of the highest performance resin due to the mechanical properties and resistance to environmental degradation, which leads to their exclusive use in aircraft components. Epoxy resins are the most commonly used thermoset plastic in polymer matrix composites and do not give off reaction products when they cure and so have low cure shrinkage. They also have high thermo stability, high abrasion resistance, and high impact strength.(Chow2007&Singla 2010)
Because of the need to materials that are non- toxic to the human body and have appropriate characteristics for specific purposes is ever increasing due to the lack of resources and increasing levels of environmental pollution, in these days various synthetic polymers are being prepared combined with various reinforcing particles in order to improve the mechanical properties and to obtain the characteristics demanded in actual application. (Premalal 2002)
These natural particles are especially being sought since the production of composites using natural substances as reinforcing materials is not only inexpensive but also able to minimize the environmental pollution caused by the characteristic biodegradability, decreasing the wear of the machinery part, making the final product light ,so these composites will play an important role in resolving future environmental problems.(Yang 2004)
Poly (ethylene glycol) (PEG) hydrogel based polymers are among the most widely used synthetic materials for biomedical applications. Because of their biocompatibility, and ease of fabrication, hydrogels are highly suitable for use as constructs to engineer tissues as well as for cell transplantation. A critical parameter of importance for PEG hydrogels is their mechanical properties which are highly dependent on the environmental conditions. Properties of PEG-based hydrogels can be engineered to resemble scaffolds composed of extracellular matrix molecules, which provide structural support, adhesive sites and mechanical as well as biomechanical signals to most cells. The molecular structure of PEG 4000 is HO-CH2-(CH2-O-CH2-)n-CH2-OH (Drira,2006)