Search

The degradative activities of neutral protease against chitosan samples with different molecular parameters were characterized. The effects of the degree of deacetylation (DD) and molecular weight (MW) of chitosan on its susceptibility to degradation were investigated. The DD and MW of the chitosans were determined using potentiometric titration and viscometry, respectively. The molecular weight distribution of initial and degraded commercial chitosan was investigated by gel permeation chromatography. Initial degradation rates (r) were determined from the plots of viscosity decrease against time of degradation. The time courses of degradation of chitosans with neutral protease were non-linear and the enzymatic hydrolysis was an endo-action. Classical Michaelis–Menten kinetic parameters were measured by analyzing the amount of reducing sugars and Eadie–Hofstee plots established that hydrolysis of chitosan by neutral protease obeyed Michaelis–Menten kinetics. Michaelis–Menten parameters and initial degradation rates were calculated and compared to determine the influences of DD and MW on hydrolysis. The results showed that higher DD and higher MW chitosans possessed a lower affinity for the enzyme and a slower degradation rate. Those samples with a lower DD and lower MW were more susceptible substrates.

Tri(acryloyloxyethyl) phosphate (TAEP) was blended with methacrylated phenolic melamine (MAPM) in different ratios to obtain a series of UV curable intumescent flame retardant resins. The cured TAEP/MAPM samples greatly expanded when burning. Their expansion behaviour and flame retardance of the cured resins were characterized by the volume ratio after and before combustion, and by limiting oxygen index. A distinct synergistic effect was found between TAEP and MAPM. TAEP–0.30MAPM sample showed the highest expansion degree (104) and the highest LOI value (41) among all resins. The degradation was monitored by thermogravimetric analysis and in-situ Fourier-transform infrared spectroscopy. A degradation mechanism is suggested in which the phosphate group in TAEP first degraded to form poly(phosphoric acid)s, which further catalysed the degradation of the material to form char with emission of nitrogen volatiles from MAPM, leading to the formation of expanding char. The morphologic structures of crusts of the formed chars were observed by scanning electron microscopy, demonstrating the synergistic effect between TAEP and MAPM.

Methacrylated phenolic melamine (MAPM) was synthesized as a flame retardant multifunctional oligomer for UV curable systems, and characterized by FTIR, 1 H NMR and elemental analysis. A series of formulations was prepared based on MAPM and a commercial UV curable epoxy acrylate EB600. Their thermal behaviours were investigated by thermogravimetric analysis, indicating that MAPM had no effect on the char formation of EB600. The flammability was monitored by the limiting oxygen index (LOI); the LOI value of EB600 increased from 21.5 for pure EB600 to 26.5 for the blend containing 50% MAPM addition. The “composite bar test” result showed that the vapour phase action flame retardant mechanism was the dominant mode for MAPM. The thermal degradation mechanism of MAPM was investigated by in situ FTIR, DP–MS and elemental analysis. The results showed that MAPM first degraded to form melamine at around 300 °C, which would further undergo condensation on heating with elimination of ammonia. Nitrogen underwent about 19% conversion to the residue and 81% had vapourized below 500 °C.

Tri(acryloyloxyethyl)phosphate (TAEP) was blended in different ratios with a commercial epoxy acrylate to obtain a series of UV curable flame retardant resins. The thermal oxidative degradation mechanism of their cured films in air was studied by thermogravimetric analysis and in situ Fourier-transform infrared spectroscopy. The cured film with TAEP addition showed improved thermal stability at elevated temperature with higher char yield. The kinetics of their thermal decomposition were evaluated by Kissinger, Friedman and Vachuska–Voboril methods. The results showed that the activation energies of the blends were lower than that of pure epoxy acrylate at lower degree of degradation, whereas higher activation energies were obtained at higher degree of degradation.

Tri(acryloyloxyethyl) phosphate (TAEP) and di(acryloyloxyethyl)ethyl phosphate (DAEEP) were synthesized from phosphorus oxychloride and hydroxylethyl acrylate and used as flame retardant multifunctional monomers for UV curable systems. The UV cured TAEP and DAEEP films have limiting oxygen indexes of 36 and 29, respectively. Their thermal behaviours were studied by thermogravimetric analysis, and they show three characteristic degradation temperature regions, attributed to the decomposition of phosphate, thermal pyrolysis of acrylate side chains, and decomposition of unstable structures in char, respectively. This was further demonstrated by in situ Fourier-transform infrared and direct pyrolysis/mass spectrometry measurements, and monitored by inductively coupled plasma-atomic emission spectrometry. As flame-retardant mechanism it is proposed that the degraded products of phosphate form poly(phosphoric acid), which further catalyses the breakage of carbonyl groups to form an intumescent char, preventing the samples from further burning.