Effect of silicone processing aids on the mechanical properties of flame retardant polyolefin compounds

摘要

Flame retardant polyolefin compounds have been used in a growing number of wire and cable markets, such as transportation, electrical & electronic, building & construction and appliance applications. In the flame retardant polyolefin compounds, halogen free flame retardants such as alumina trihydrate (ATH) or magnesium hydroxide (MDH) become really effective when used at high loadings, such as more than 40% by weight, yet deeply affecting the mechanical and rheological properties. Normally, traditional formulations of flame retardant polyolefin compounds use silicone processing aids to improve rheological properties, yet very little attention was paid to the influence of silicone processing aids on the mechanical properties of polyolefin compounds. Influence of the addition of small (0 to 10% by weight) amounts of silicone processing aids on the mechanical properties of flame retardant polyolefin compounds for wire and cable was systematically investigated. The composites were prepared in a twin-screw extruder, using linear low density polyethylene (LLDPE) and ethylene vinyl acetate (EVA) as matrix materials. Alumina trihydrate (ATH) was added a lot in composites as halogen free flame retardants. The results shows that the increase of silicone processing aids content in composites can lead to high scratch resistance and elongation at break but lower tensile strength. With the content of silicone processing aids increase to 10% by weight, the mass loss of scratch damage decreased by 42%, comparing to the sample without silicone processing aids. The elongation at break increased by 12%, and tensile strength decreased by 26%. Besides, the silicone additives acted as very efficient processing aids, reducing processing torque and dramatically by 26%. While, influence of silicone processing aids on the mechanical properties of flame retardant polyolefin compounds varies from one formulation to another. Therefore, optimum content of silicone processing aids depends on application requirement to obtain the best integrated properties of the composites.