Studies on the ambient temperature crosslinking of latex films based on natural rubber grafted with poly(diacetone acrylamide) using DMTA

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.