Preparation and properties of a novel flame retardant polyurethane quasi-prepolymer for toughening phenolic foam

Lignin-Based Phenolic Foam Reinforced by Poplar Fiber and Isocyanate-Terminated Polyurethane Prepolymer

Phenolic foams (PFs) are lightweight (<200 kg/m³), high-quality, and inexpensive thermal insulation materials whose heat and fire resistance are much better than those of foam plastics such as polyurethane and polystyrene. They are especially suitable for use as insulation in chemical, petroleum, construction, and other fields that are prone to fires. However, PFs have poor mechanical properties, poor abrasion resistance, and easy pulverization. In this paper, a polyurethane prepolymer was treated with an isocyanate, and then the isocyanate-terminated polyurethane prepolymer and poplar powder were used to prepare modified lignin-based phenolic foams (PUPFs), which improved the abrasion resistance and decreased the pulverization of the foam. The foam composites were comprehensively evaluated by characterizing their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame-retardant properties. The pulverization ratio was reduced by 43.5%, and the thermal insulation performance and flame-retardancy (LOI) were improved. Compared with other methods to obtain lignin-based phenolic foam composites with anti-pulverization and flame-retardant properties, the hybrid reinforcement of foam composites with an isocyanate-terminated polyurethane prepolymer and poplar powder offers a novel strategy for an environmentally friendly alternative to the use of woody fibers.

Synthesis of a novel modified chitosan as an intumescent flame retardant for epoxy resin

According to the concept of fire life cycle assessment (LCA), a new type of intumescent flame retardant was designed and synthesized by chemically bonding chitosan, phosphorus pentoxide and melamine. The resultant compound, chitosan ethoxyl melamine phosphate (CEMP), was characterized by FTIR, 1H NMR, 31P NMR, XRD and SEM. The performance of CEMP and organic montmorillonite (OMMT) was evaluated in the substrate of epoxy resin (EP) with limited oxygen index (LOI), UL-94, cone calorimetric test (CCT), TGA and TG-IR. As a result, intumescent flame retardant EP (EP3) containing 30.6% LOI and V-0 rating was prepared by adding 3 wt% OMMT and 15 wt% CEMP. The CCT results indicated that CEMP and OMMT reduced the peak of heat release rate (PHRR) to about one fourth that of pure EP and total heat release (THR), 1/2. Decomposition of EP and EP3 was traced from 100 to 600°C by TG-IR.

Preparation and properties of melamine-formaldehyde rigid closed-cell foam toughened by ethylene glycol/carbon fiber

Toughing melamine-formaldehyde (MF) rigid closed-cell foams were prepared by using ethylene glycol (EG) and carbon fiber (CF) as composite toughening agents. The pulverization rate, compressive strength, bending strength, cellular structure, closed-cell ratio, water absorption ratio, thermal conductivity, thermal stability, limiting oxygen index (LOI), and char yield were characterized to study the morphology, mechanical, thermal, and fire-retardant properties of as-prepared toughing MF rigid foams. The pulverization rate result showed that introduction of composite modifier can obviously improve the toughness of MF rigid foams. The cellular structure, closed-cell ratio, and water absorption results showed that the addition of EG/CF can increase the closed-cell ratio and control the cell size of MF rigid foams. The compressive strength and bending strength results showed that the incorporation of composite modifier of MF rigid foams dramatically improved the mechanical properties. The LOI, char yield, and thermal stability results showed that the toughing MF rigid foams remained more intact char skeleton with flame-retardant effect, thus reducing the fire hazards. The as-prepared toughing MF rigid foams showed the best comprehensive performance with pulverization rate of 5.21%, compressive strength of 355.3 kPa, bending strength of 0.44 MPa, closed-cell ratio of 79.1%, water absorption of 9%, thermal conductivity of 0.031 W m−1 K−1, and LOI of 39.6%. Compared with unmodified MF rigid foams, toughing rigid closed-cell MF foams possess excellent pulverization rate, compressive strength, bending strength, cellular structure, thermal insulation, and flame retardancy.