Mechanical Properties, Heat Resistance and Flame Retardancy of Glass Fiber-Reinforced PLA-PC Alloys Based on Aluminum Hypophosphite

Abstract

Poly(lactic acid) (PLA) and polycarbonate (PC) alloy (the wt. ratio of PLA and PC was 70/30) was modified by blending with glass fiber (GF), and then aluminum hypophosphite (AP) was applied to improve the flame retardancy of GF-reinforced PLA-PC alloys. The mechanical properties of the alloys were investigated by tensile, flexural and impact tests. The heat resistance was surveyed via HDT test. The flame retardancy, combustion and thermal behavior of the alloys were evaluated by LOI and UL-94 tests, cone calorimeter and thermogravimetric analyzer, respectively. The results showed that the addition of GF enhanced the mechanical properties and heat resistance of PLA-PC alloy significantly; and the flame retardancy of GF-reinforced alloys could be improved obviously through adding AP, resulting in UL-94 V-0 rating (1.6 mm). Interestingly, the PLA-PC/AP alloys could reach the UL-94 V-0 rating at a lower loading of AP in the presence of GF. Meanwhile, the mechanical properties still retained in a high level, and were higher than 77% of the corresponding alloys filled only by GF. The thermogravimetric analysis and cone calorimetric test results revealed that AP could slow down the decomposition rate of PLA-PC matrix and increase its melt viscosity; meanwhile, it was found that GF played several roles on the flame retardancy, mainly including stabilizing the char residue formed during the combustion process, insulating heat and mass, and improving the compactness of the char residue via increasing the residual mass.

Keywords:

• Aluminum hypophosphite
• Flame retardancy
• Glass fiber
• Poly(lactic acid)/polycarbonate alloy
• Reinforcement

Notes

^a Results were reported as the average value of 7 test bars.

^b The char layer formed was falling down rather than dripping.

^c The results of 7 test bars were 6 V-0 s and 1 V-1.

^a Injection molding after drying without extruding in the twin-screw extruder, and the barrel temperature was set at 170–210°C.

^b Injection molding after drying without extruding in the twin-screw extruder, and the barrel temperature was set at 220–260°C.

^a Annealed at 120°C for 6 h.

^a FIGRA was calculated using PHRR divided by time to PHRR.

^b MAHRE, defined as the cumulative heat emission divided by time, was the peak value of the average rate of heat emission.

^c It was calculated on the basis of the matrix without glass fiber.

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