Halogen Free and Thermal Stable Novolac Derivatives and Their Properties in Epoxy Composites

Novel cross-linkable polymer has been developed and successfully used in green PCB laminates with good flame retardancy and thermal stability for recently years. The novel hardener was modified by introducing curable functional groups which can react with epoxy resins under processing, to enhance thermal stability and flame retardancy via the increase of cross-linking density. Some merits of high performance laminates as the novel novolac hardener was used, such as higher glass transition (Tg) due to the highly cross-linking density, and the lower coefficient of thermal expansion (CTE), lower water absorbed by introducing more aromatic units to form rigid and tough chemical structures of laminates. Also the increased flame retardancy due to inflammable gas such as N2, CO2 or other volatile compounds released while fire ignition, without using halogen or phosphorus compounds.

Modified novolac resins (highly aromatic and nitrogen content) were used as flame retardant agent in this study. The cured resins exhibited higher glass transition (Tg) than 180oC, and the char yield at 800oC was increased which elaborates the effectiveness of flame retardancy with evaluated LOI value over 35. This is mainly attributed to the increased crosslink densities and highly aromatic content in modified phenol novolac derivative resins which exhibits the higher thermal degradation energies (Ea). Therefore, the more effective flame retardancy would be expected by the loss of nitrogen and hydrocarbon during combustion. By evaluating the cooperative flame retardancy in organic/inorganic hybrid with char yield and LOI increasing percentage, the effects of filler showed the cooperative flame retardancy only in appropriate addition and difference in crosslinking densities.