Flammability and mechanical properties of composites fabricated with CaCO3-filled pine flakes and Phenol Formaldehyde resin

Abstract Flammability of wood composites has always been of a concern. To investigate whether CaCO3 particles are efficient fire-retardant fillers for wood composites, wood composites were prepared with Phenol Formaldehyde (PF) resin and pine flakes that were deposited with CaCO3 by the treatments of Na2CO3 and CaCl2. The flammable performance, Limiting Oxygen Index (LOI), simultaneous Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA–DSC), mechanical properties, and water resistance of wood-flake composites deposited with CaCO3 were evaluated. Furthermore, the Scanning Electron Microscopy (SEM) was used to observe the surface morphology of the treated wood flakes, showing that CaCO3 microparticle crystals grew onto the wood flake surfaces. The increase of reactant concentrations from 0.5 M to 1.0 M resulted in an increase in LOI and improvements of the flame-retardant performance of the composites. The TGA–DTG examination showed that the decomposition peak of the treated wood flakes shifted to a lower temperature range. The TGA also demonstrated that the treatment contributed to the accumulation of char layer, which benefited the flame retardancy of the composites. The growth of energy consumed during the sample pyrolysis could be attributed to the insulation of CaCO3 and thicker char layers. After the treatment with reactants (concentration of 0.5 M), although the internal bonding (IB) slightly decreased by 8.3%, the modulus of elasticity (MOE) and the modulus of rupture (MOR) of the composites significantly increased by 182.9% and 63.5%, respectively.