The main objective of the present work was to develop intumescent fire-retardant coating (IFRC) for wood based on modified natural rubber (NR). A newly modified form of NR, namely graft copolymers of NR and poly(methacrylic acid) (PMAA), NR-g-PMAA, was first synthesized by a solution polymerization technique. The IFRC was then prepared by compounding the synthesized NR-g-PMAA with a curing agent and an intumescent additive to form a compound coating. Cross-linking of the NR-g-PMAA coating was achieved by reactions with polyisocyanate based on hexamethylene diisocyanate (poly‐HDI) under ambient conditions. Interactions of NR-g-PMAA with poly‐HDI were also studied using X-ray photoelectron spectroscopy. Expandable graphite (EG) was employed as intumescent filler in the present study. The thermal stability of the NR-g-PMAA coating films was first studied by thermogravimetric analysis. The fire-retardant properties of wood, with or without the NR-g-PMAA coating, were then examined using the limiting oxygen index and cone calorimetry test. The flammability tests indicate that the flame-retardant properties of wood were greatly improved by treatment with the NR-g-PMAA-based IFRC. Hence, it can be stated that this new form of modified NR has shown to possess potential application in the IFRC when used in combination with EG.
The concept of crosslinking natural rubber (NR) latex particles bearing diacetone acrylamide (DAAM) functional groups with a hydrazide crosslinker during film formation has been investigated using dynamic mechanical thermal analysis (DMTA). First, graft copolymers of NR and poly(diacetone acrylamide) prepared using 5 and 10 wt% of DAAM (abbreviated as NR-g-PDAAM5 and NR-g-PDAAM10, respectively) were synthesized. Then the dynamic mechanical properties of the cast NR-g-PDAAM latex films were measured. Two separate peaks were observed in tan δ versus temperature. The first peak appeared at −62°C, which corresponds to glass transition of the NR phase. The second peak at −23°C for NR-g-PDAAM5 (-18°C for NR-g-PDAAM10) was tentatively attributed to the characteristics of NR-g-PDAAM phase. Furthermore, a shift to higher temperature of the tan δ peak corresponding to the NR-g-PDAAM phase was observed in the NR-g-PDAAM latex films, when adipic acid dihydrazide (ADH) was added prior to film casting. The added ADH increased the thermal energy required for molecular mobility in the NR-g-PDAAM phase of the cast film, providing evidence of crosslinking between the DAAM functional groups and the ADH during film formation.
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