Industrialization Of Citric Acid Crosslinking System And Preliminary Exploration For Degradation Of Citric Acid

Cross-linking is frequently applied to cotton fabrics for enhanced wrinkle recovery and dimensional stability. The combination of citric acid(CA) and xylitol shows great potential as a non-formaldehyde alternative to the market-dominating N-methylol resins, which are inherently formaldehyde-releasing. This paper focused on analyzing and optimizing the responses of fabric properties to five foremost variables in cross-linking of cotton fabrics by CA/xylitol to gain insight of the system and to promote its industrialization. Response surface methodology(RSM) based on a five-level-five-factor central composite design was employed. The model obtained by RSM suggested that responses to changes in curing temperature were most prominent and the responses to CA and xylitol concentration changes were closely coupled. The optimum operation conditions for curing time, curing temperature, CA concentration, xylitol concentration, and padder-roll pressure were 3 min, 175 °C, 130 g/L, 15 g/L, and 3 kg/cm2 respectively. Pilot-scale experiments were conducted based on the optimum conditions suggested by RSM. The results showed that CA/xylitol cross-linking system presented a comparable performance to the market-dominating dimethyloldihydroxyethyleneurea(DMDHEU) resin. Analysis of cost-effectiveness indicated that CA/xylitol was superior compared to other formaldehyde-free cross-linking agents. Preferable environmental, health, and safety(EHS) attributes of CA/xylitol to the dominating DMDHEU was also recognized. The encouraging results indicate that the CA/xylitol cross-linking system has great potential in replacing N-methylol resins on an industrial scale.The yellowing effect of CA on cotton fabrics can be attributed to the dehydration of CA across vicinal carbon centers, resulting in the formation of unsaturated polycarboxylic acids(PCAs). Decarboxylation is another possible pathway, which yields secondary PCAs of one or two less carbons. Previous study implied that under real curing conditions, the “catalyst” SHP would react with secondary PCA formed from CA decomposition. The cross-linking efficiency of different PCAs presented in the system varied substantially, it is crucial to quantitatively assess the impact of curing conditions on the PCA make-up of the crosslinking system for better understanding its response to processing parameters. Since the reactions between various PCAs and cotton would complicate the quantitative analysis, CA degradation in the absence of cotton fabrics is more suitable to be investigated as a simplified model system. High Performance Liquid Chromatography(HPLC) was used for qualitative and quantitative analysis of different PCAs produced during different degradation state of CA. The effect of sodium hypophosphite(SHP) on the degradation of CA was explored at various temperatures. The results show that SHP can stimulate the degradation of CA, and in this process SHP is not just a catalyst, but involved in the reaction, as a reactant. Rather unexpectedly, as the amount of added SHP increased, the degradation rate of CA decreased. In all cases, heating beyond 12 min would leave no CA in the system. The above findings provide theoretical basis for the kinetics study of CA degradation.