ABSTRACT
Simultaneously regulating the crystallizing and combustion behaviors of poly(lactic acid) (PLA) will be conducive to its further development in the fields of electronic appliances, automotive and rail transit materials. To achieve this goal, a novel bifunctional additive triethylamine phenylphosphonate (TEAP) was synthesized through acid-base neutralization reaction between trimethylamine and phenylphosphonic acid. When TEAP was added into PLA, the crystallization behaviors of PLA/TEAP assessed by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) suggested that TEAP acted as a nucleating agent and plasticizer for PLA, which effectively increased the crystallization rate of PLA. However, PLA with 3 wt% TEAP showed a slower crystallization rate than that of PLA with 1 wt% TEAP due to the filler aggregation of TEAP. Thus, the crystallization rate increased first and then slightly decreased with increasing content of TEAP. Compared with the variation of the crystallization rate, the long period (L) and amorphous layer thickness (L a) resulting from SAXS showed opposite trends, while the average crystal thickness (L c) changed slightly; the reason may relate to the variation of the number of lamellae with increasing the content of TEAP. Meanwhile, the results of WAXD and Raman spectra showed the crystal structure of PLA was not affected by the addition of TEAP. The combustion behaviors of PLA and PLA/TEAP were evaluated by the limiting oxygen index (LOI), UL-94 test, cone calorimetry test (CCT) and thermal gravimetric analyses coupled to Fourier transform infrared spectroscopy (TGA-FTIR). According to the results, TEAP mainly promotes the removal of melt dripping, hence brings away heat and delays the combustion. Besides, the production of phosphorus-containing free radicals can quench hydrogen or oxygen free radicals in the fire. Thus, the fire safety of PLA is significantly improved by adding a very low content of TEAP (1-3 wt%). Only 1 wt% loading of TEAP can increase the LOI value of PLA from 19.5 vol% to 28.6 vol%, pass the UL-94 V-0 rating and have a low peak heat release rate of 404 kW m-2.
ABSTRACT
A hydroponic experiment was conducted to study the effects of applying 100% NO3- -N, 100% NH4+ -N, and 75% NO3- -N+25% NH4+ -N on the nitrogen metabolism and the nitrate reductase (NR) and glutamine synthetase (GS) gene expression of cherry tomato during its fruit development. Applying 75% NO3- -N+25% NH4+ -N slightly increased the single fruit mass, and increased the fruit NH4+ -N, total amino acid, and total N contents and N accumulation significantly, compared with applying 100% NO3- -N. In treatments 100% NO3- -N and 75% NO3- -N + 25% NH4+ -N, the fruit NR activity and its gene expression had no significant difference, but were higher than those in treatment 100% NH4+ -N. The fruit GS activity was significantly higher in treatment 75% NO3--N+25% NH4+ -N than in treatment 100% NO3- -N. In the three treatments, isozyme GS1 (Cytosolic type GS) and GS2 (Chloroplast type GS) expression was inconsistent with GS activity, suggesting that the effects of applied N on GS activity could be mainly reflected at posttranscriptional level.
