Preparation And Low-Temperature Sizing Properties Of Diblock Grafted Starch

Starch has been widely used in textile warp sizing.However,its adhesion to fibers is poor,and starch paste is prone to ageing at low temperature.It leads to poorer adhesion to fibers and it is difficult to meet the requirements of low temperature sizing of warp yarns.In order to improve the application effect of starch size in low temperature warp sizing,Fe²⁺-H₂O₂ redox initiator system as initiator and two-step graft polymerization technology were used to successively initiate the graft copolymerization of acrylic acid（AA）and methyl acrylate（MA）with starch in aqueous medium to prepare diblock grafted starch（PAA-g-S-g-PMA）.The paste properties（viscosity,viscosity stability and adhesion to fiber）of PAA-g-S-g-PMA at low temperature were investigated,and its low temperature sizing properties were evaluated.Firstly,PAA-g-S-g-PMA with total grafting ratio of 6.51%was prepared using Fe²⁺-H₂O₂ as initiator.The paste properties of PAA-g-S-g-PMA at different temperatures were evaluated by comparing acid-thinned starch（ATS）.The results showed that,compared with ATS paste,the viscosity,the viscosity stability and the adhesion to cotton,polylactic acid and polyester fiber of PAA-g-S-g-PMA paste were improved at the same temperature.As the temperature decreased from 95°C to 35°C,the viscosity of PAA-g-S-g-PMA rose from 34 m Pa·s to 82 m Pa·s,and the viscosity of ATS rose from 13 m Pa·s to 72 m Pa·s.The viscosity stability of PAA-g-S-g-PMA paste was higher.The adhesion of PAA-g-S-g-PMA paste to cotton,polylactic acid and polyester fiber decreased by 8.4N,1.4N and 13.8N respectively,and ATS paste decreased by 12.9N,2.8N and 21.8N respectively.These results indicated that the starch could alleviate the downward trend of viscosity stability and adhesion due to the decrease of paste temperature after two steps of grafting polymerization.When the paste temperature was as low as 55℃,PAA-g-S-g-PMA paste still had good paste properties.Secondly,on the basis of the above results,a series of PAA-g-S-g-PMA with different total grafting ratio were prepared,and the effect of total grafting ratio on the paste properties of PAA-g-S-g-PMA at 95℃and 55℃was evaluated.The results showed that at the same temperature,the total grafting ratio increased from 3.7%to 8.04%,the viscosity of PAA-g-S-g-PMA paste also increased,and the adhesion to cotton,polylactic acid and polyester fiber was enhanced.With the increase of total grafting ratio,compared with the results at 95℃and 55℃,the adhesion of PAA-g-S-g-PMA paste to cotton,polylactic acid and polyester fibers decreased by 7.5N,1.3N and 9.3N respectively when the grafting ratio was 3.7%,and 4.4N,0.8N and 8N respectively when the grafting ratio was 8.04%.It showed that the increase of the degree of graft polymerization had a better effect on alleviating the downward trend of the adhesion of the above three fibers at low temperature.Comprehensive analysis of results showed that the relatively suitable total grafting ratio of PAA-g-S-g-PMA was 8.04%.Finally,in order to verify the feasibility of two-step graft polymerization of starch in warp sizing at low temperature.ATS and PAA-g-S-g-PMA（total grafting ratio was 8.04%）were selected to conduct respectively sizing of cotton yarn and polylactic acid yarn at95℃and 55℃,and the sizing properties were measured.The results showed that,compared with ATS sizing,loss in elongation of PAA-g-S-g-PMA sizing decreased,increase in tensile strength,abrasion resistance and decrease in hairiness of PAA-g-S-g-PMA sizing increased at the same temperature.Compared with the results at 95°C and 55°C,the loss in elongation of PAA-g-S-g-PMA sizing increased,increase in tensile strength,abrasion resistance and decrease in hairiness of PAA-g-S-g-PMA sizing decreased.However,compared with the sizing after using ATS,the sizing properties decreased less and the sizing effect was better at low temperature.