Study On The Grafting Modification Of Protein Onto Surface Of Polyacrylonitrile Fiber

In recent years, more and more researchers have focused on the modification of the chemical fiber with natural protein. Polyacrylonitrile fiber, for its relatively cheap price and other important characteristics, such as soft, wool-like hand, good antibacterial property and excellent resistance to sunlight, is widely used in the textile industry. But Polyacrylonitrile fiber is hydrophobic and exhibits some obvious disadvantages, such as low moisture-absorbency and electrostatic tendency, which greatly limits its further applications.For the first time, the mechanism of grafting of protein onto the Polyacrylonitrile fiber was proposed. The grafting modification consists of three parts: (1) hydrolysis of the original Polyacrylonitrile fiber; (2) chlorination of the hydrolyzed Polyacrylonitrile fiber; (3) grafting of protein onto the chlorinated Polyacrylonitrile fiber. The nitrile group–C≡N in Polyacrylonitrile fiber is converted to carboxyl group–COOH after hydrolysis in NaOH aqueous solution.Afterwards, chloroformyl group–COCl is obtained when carboxyl group is treated with SOCl2. Finally, nitrogen acylation and esterification are carried out when chloroformyl group reacts with amino group–NH2 and hydroxyl group–OH of the protein which provides the chemical fiber with protein on its surface. A novel chemical modification method of Polyacrylonitrile fiber was first introduced by grafting of natural protein-soy protein and soybean milk, separately, onto the surface of Polyacrylonitrile fiber. The effects of the production procedures on grafing efficiency were systematically investigated and the grafting conditions were optimized. The structures and morphologies of the protein grafted fiber, such as moisture absorption, water retention, specific electric resistance, mechanical properties and thermal tolerance were characterized.Using the bean dregs as the raw material, the technological condition of extracting soy protein isolate was optimized through alkali extraction and acid precipitation technique with the leaching solution pH value, 10.0; extraction temperature 50℃; feed-liquid ratio, 1:10 and leaching time, 50min. At this condition, protein extraction rate was 79.36%. The hydrolysis of Polyacrylonitrile fiber was affected by hydrolysis time, hydrolysis temperature and concentration of NaOH. To make the protein modified Polyacrylonitrile fiber in this study, the best hydrolysis conditions were: NaOH concentration 14%, hydrolysis temperature 80℃and hydrolysis time 15 min. Grafting modification could make up the decrease of the mechanical properties due to the surface erosion during the hydrolysis reaction.Chlorination reaction made the grafting of protein onto Polyacrylonitrile fiber possible by providing the active chloroformyl group. In this study, ten gram of hydrolyzed Polyacrylonitrile fiber was first treated with 1.0 mL of SOCl2 at 110℃for 30 min during the chlorination reactions and then put into 1.0 mL of 10wt % NaOH aqueous solution at 80℃for 3min for the grafting of protein onto the surface of the Polyacrylonitrile fiber. After these procedures, the protein was grafted onto the Polyacrylonitrile fiber with a proper grafting efficiency.FT-IR spectra have presented that some new amide group I andⅡband peaks appeared at 1530 cm-1and 1630cm-1 respectively. Meanwhile, new carboxyl group appeared at 3400cm-1. The intensity of these new peaks increased with the increasing grafting efficiency while the intensity of the original nitrile group at 2243 cm-1 decreased greatly, which indicated the presence of protein in the modified fiber through the reactions of nitrile group. X-ray diffraction showed that the protein-modified Polyacrylonitrile fiber showed an intense reflection at about 16.8? and another sharp peak at about 29.5? and a broad diffuse reflection between the two sharp peaks. The characteristic feature of the XRD pattern of protein-modified Polyacrylonitrile could be described by the classical crystalline and amorphous structure model for semi crystalline polymers. SEM micrographs have confirmed that the surface of protein modified fiber was covered by integrated and compact protein film.With protein grafting modification, the moisture absorption was increased from the original 2.0% up to 5.2%. This grafting modification leaded the water retention from 12.5% of the ungrafted Polyacrylonitrile fiber up to 23.6%. The specific electric resistance was decreased from 1.91×109?·g/cm2 to 4.63×108?·g/cm2. Compared with ungrafted fiber, the protein modified Polyacrylonitrile fiber showed much better moisture absorption, water retention and antistatic property which resulted from the fact that plenty of polar groups, such as carboxyl group, amino group and hydroxyl group, etc. Though there was a little decrease of the breaking strength, breaking elongation, stating weight loss temperature and residual mass after surface grafting modification, generally speaking, the modified fiber still exhibited good mechanical properties and thermal stability which could meet the requirement of textile production and wearing.