Design, production and fire characterization of flax fiber reinforced shape memory polymer composites with flame retardant property

Natural fibre reinforced polymer composites have been widely used instead of synthetic fibre reinforced composite applications in recent years due to their environmentally friendliness, low cost and ease of availability. It is highly preferred especially in the automotive, marine and aviation sectors. The material used in these areas must be flame retardant as well as having superior mechanical and chemical properties. In this study, it is aimed to increase the flame retardancy of the shape memory polymer matrix composites produced with natural flax fibre by using polydopamine and titanium dioxide nano powders. Dopamine hydrochloride was polymerized in tris - hydrochloride acid buffer solution and flax fibres were coated with dipping and blending method with polydopamine. 1.5 percent titanium dioxide was used to increase the flame retardancy of the polymer matrix. The coating and nano powder distribution were characterized by scanning electron microscopy. The fire behaviours of composites were examined by horizontal and vertical burning and limiting oxygen index tests. Thermal analyses were carried out by thermogravimetric method. Both vacuum assisted oven and hot press process were studied for curing and hot press was chosen as feasible application resulting homogenous and fully saturated wet fibre surface. As a result of this study, the polydopamine coating reduced the flame spread rate about 54 percent. When titanium dioxide combined with polydopamine was used, the flame spread rate decreased about 74 percent. According to the limiting oxygen index test result, it was observed that the polydopamine coating increased the minimum amount of oxygen required for combustion to 23 percent, and when using polydopamine together with titanium dioxide to 24 percent from non-coated flax fibre value 20 percent.