Flame retardant finishing of cotton fleece
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In this research, an inorganic phosphorus-containing flame retardant system was developed for cotton fleece. The aluminum hydroxyphosphate (AHP) formed in situ on cotton by the reaction of aluminum sulfate and sodium phosphates was effective in reducing the flammability of cotton fleece from Class III to Class I. The treated cotton fleece retained Class I flammability after one home laundering or the combination of dry-cleaning and hand washing procedure. Non-phosphorus polycarboxylic acid and phosphorus-containing polycarboxylic acid flame retardant finishing systems were developed for cotton fleece and they were the major part of this research. Polycarboxylic acids themselves without esterification were not effective in reducing the flammability of cotton fleece. The esterification of bi-functional carboxylic acids, succinic acid and malic acid, with cotton cellulose, reduced the flammability of cotton fleece from Class III to Class I. The treatment of cotton fleece with bi-functional carboxylic acids was also durable to multiple home laundering cycles. The esterification of multi-functional carboxylic acids, BTCA and citric acid, with cotton cellulose, was more effective than that of bi-functional carboxylic acids in reducing the flammability of cotton fleece, since multi-functional carboxylic acids had higher esterification efficiency with cotton cellulose. The treatment of multi-functional carboxylic acids with cotton cellulose also increased the dimensional stability of cotton fleece, yet, decreased the bursting strength. The treated cotton fleece passed the 45° flammability after 20 home launderings. In the phosphorus-containing polycarboxylic acid system, unsaturated bi-functional carboxylic acid, maleic acid (MA), and sodium hypophosphite were used to flame retardant finish cotton fleece. MA esterified cotton cellulose at relatively low temperatures in the presence of NaH2PO2 as catalyst, and that MA esterified to cotton was able to further react with NaH2PO2 at higher temperatures (150C), whic ph hosphorus bondedto the cotton cellulose. The reactions between MA and NaH2PO2 on cotton also lead to the crosslinking of cotton cellulose. The treatment of MA and NaH2PO2 was effective in reducing the flammability of cotton fleece from Class III to Class I and durable to multiple home laundering cycles. The possible mechanism of polycarboxylic acids flame retardant finishing of cotton fleece was that the esterification of cotton cellulose with polycarboxylic acids reduced the depolymerization reaction, yet, increased the dehydration reaction during the thermal decomposition process.