Preparation And Properties Of Flame Retardant Ramie/Phenolic Resin Composites

Ramie is abundant in China and the ramie productions are more than 98% of world productions. The microstructure of ramie fiber exhibites typical characteristics of composite materials; the mechanical properties of ramie fiber are the best in hemp fibers. Ramie has short growth period and can be decomposed naturally. As a result it is used as an ideal reinforcing material of environmental friendly composites. In this research, ramie fabric was used to fabricate flame retardant composite materials with phenolic resin, which were intended to use in aircraft cabin materials.The ramie fabric was treated with two types of flame retardants by padding process, namely phosphate type (CFR-202) and nitrogen-phosphorous type (NEWRAY911), and composed with phenolic resin by laminate molding process to prepare ramie/phenolic resin laminate. The flame retardancy of the laminate treated by nitrogen-phosphorous type flame retardant is better than that of treated by phosphate type flame retardant. The limiting oxygen index (LOI) of the laminate with nitrogen-phosphorous type treatment is increased from 25.2% to 39.1%, and achieves the VO level in UL94 vertical burning test. Cone calorimeter tests show that the laminates with the nitrogen-phosphorous type treatment have increased char residue, extended ignition time, low peak heat release rate, and low average smoke density. It is also found that the mechanical properties of the laminates are not changed because the fiber structure of ramie fabric is destroyed little on this condition of flame retardant treatment.Phenolic resin was treated with ammonium polyphosphate (APP) by mechanical blending method, and composed with flame retarded ramie fabric to prepare ramie/phenolic resin laminate. The LOI of the laminate with APP treatment is increased intensely, from 39.1% to 52.5% with only 1wt% APP loading. Cone calorimeter tests show that the laminates with APP have increased char residue, extended ignition time, and low peak heat release rate. However, the mechanical properties of the laminates deteriorate with the addition of APP. There is an optimal content (3wt%) on APP added to phenolic resin. The montmorillonite (MMT) was added to phenolic resin on the basis of the above, and prepared ramie/phenolic resin laminate. The results show that, the thermal stability and LOI of the laminate with MMT addition are changed a little, and the char residue has increased. The addition of MMT can significantly improve the mechanical properties of phenolic laminate, adding 2.5wt% MMT is able to ensure the flame retardancy of composites, meanwhile the tensile strength and flexural strength are largely improved.