Catalytic and ionic cross-linking actions of l-glutamate salt for the modification of cellulose by 1,2,3,4-butanetetracarboxylic acid

The sodium l-glutamate is reported as an efficient catalyst for the cross-linking between 1,2,3,4-butanetetracarboxylic acid (BTCA) and cellulose. Results presented ester absorbance of the treated fabrics strongly increased in the presence of the homemade l-glutamate salt, a mixture of l-glutamic acid (LGA) and NaOH at a specific ratio. Importantly, anti-wrinkle properties of the treated fabrics were significantly improved. Based on the relative concentration calculation, l-glutamate promoted the reaction of BTCA with cellulose by accelerating the formation of BTCA anhydrides and the esterification of anhydrides with cellulose. Besides, the improved anti-wrinkle property was partially attributed to the fact that the generated LGA reacted with cellulose and formed ionic cross-linking networks through amino groups with carboxyl groups in BTCA, which was confirmed by the Fourier transform infrared spectra and the computational calculations. Through detailed comparisons, l-glutamate catalyzed fabrics showed as good durability as sodium hypophosphite, indicating a possible alternative for phosphorus-containing catalysts.

Effects of divalent anionic catalysts on cross-linking of cellulose with 1,2,3,4-butanetetracarboxylic acid

1,2,3,4-Butanetetracarboxylic acid (BTCA) can efficiently esterify cellulose with pyrophosphoric acid (PPA) as a catalyst to remove protons of reaction intermediates. However, valence and relative concentration ratio (RCR) of catalyst anions correlating to pH of finishing bath played a critical role in the reactions. Results here indicated that wrinkle recovery angle, tensile strength retention and ester absorbance of fabrics treated at pH of 2.8 showed higher values. It was a competing reaction for BTCA molecules to esterify or depolymerize cellulose. Importantly, divalent PPA anions were more efficient than monovalent ones in catalyzing the esterification between anhydrides and cellulose, which was confirmed by FTIR results and two-dimensional correlation spectroscopy analyses and by the RCRs of PPA anions and their changing rates versus pH. Furthermore, the higher catalytic efficiency of divalent anions was proved by the selected model catalysts. Meaningfully, the fabrics treated at pH≤3.2 presented good durability.

Effects of acid diffusibility and affinity to cellulose on strength loss of polycarboxylic acid crosslinked fabrics

1,2,3,4-Butanetetracarboxylic acid (BTCA) imparts good anti-wrinkle property to cotton fabrics and results in significant strength loss due to cross-linking and acid degradation of cellulose simultaneously. However, benzophenone-3,3',4,4'- tetracarboxylic acid (BPTCA), an aromatic acid, crosslinks cellulose effectively but causes less strength loss to the products under similar conditions. The difference in damages to cellulose fibers was analyzed by using diffusibility and corresponding affinity of the acids to cellulose fibers, which were estimated by their molecular sizes and Hansen solubility parameters (HSP). Both experimental results and theoretical speculations revealed consistent agreement, indicating that smaller acid molecules could diffuse into cellulose fiber more rapidly and deeply, resulting in more acid degradation. Besides, the aliphatic acid such as BTCA has higher molecular affinity than BPTCA to cellulose, causing additional more degradation of cellulose. Both factors are potential reasons of the observed more severe tensile strength loss of the BTCA treated cotton fabrics.

Catalytic actions of alkaline salts in reactions between 1,2,3,4-butanetetracarboxylic acid and cellulose: II. Esterification

1,2,3,4-Butanetetracarboxylic acid (BTCA) reacts with cellulose in two steps with catalysis of alkaline salts such as sodium hypophosphite: anhydride formation and esterification of anhydride with cellulose. The alkali metal ions were found effective in catalyzing formation of BTCA anhydride in a previous report. In this work, catalytic functions of the alkaline salts in the esterification reaction between BTCA anhydride and cellulose were investigated. Results revealed that acid anions play an important role in the esterification reaction by assisting removal of protons on intermediates and completion of the esterification between cellulose and BTCA. Besides, alkaline salts with lower pKa1 values of the corresponding acids are more effective ones for the reaction since addition of these salts could lead to lower pH values and higher acid anion concentrations in finishing baths. The mechanism explains the results of FTIR and wrinkle recovery angles of the fabrics cured under different temperatures and times.