Study Of Irradiation Modified Soy Protein Isolate/Starch Biodegradable Material

Since the20th century, research of synthesis high polymer plastic progresses hasadvanced by leaps and bounds which brings the huge convenience for people’s life. However,with the growing production of plastic, it also brought lots of serious environmental pollutionall over the world. As a result of increasing concerns of environmental pollution caused bynon-biodegradable petroleum-based plastics and exhausting of petroleum resources,researchers are interested in making natural degradable and environmentally-friendly plasticsfrom renewable resources as alternatives to non-biodegradable petroleum-based plastics.Therefore, the research on preparation and properties of materials from SPI/starch areimportant in terms of both academic field and social applications.In this paper, a kind of biodegradable material was made of soy protein isolate (SPI) andstarch of irradiation modification, also its relevant processes and parameters were studiedsystematically. The best pressing conditions of preparing the SPI/starch biodegradablematerial were as follows: pressing temperature of130℃, hot pressure of15MPa, pressingtime of15min. So in the best pressing conditions, using five-factor orthogonal rotationexperiment, the modified conditions of SPI/starch biodegradable material were optimized.The optimum conditions were as follows: the addition of irradiation dose of30kGy,12%ofthe starch content,12%of succinic anhydride content,23.33%of glycerol content,16.67%ofwater content. Under these conditions, the properties of the obtained SPI/starch biodegradablematerial were as follows: elongation of300.86%，tensile strength of7.62MPa，waterabsorption of40.5%，light transmittance of37.5%.In thermodynamic performance test, the results showed that: In the SPI/starchbiodegradable materials of irradiation modification, the thermal weight loss process could bedivided into three processes: water volatilized when the temperature was44.97-89.33℃;glycerol volatilized when the temperature was155.76-248.38℃; the degradation ofSPI/starch molecules was happened when the temperature followed by303℃. FTIR resultsshowed that: as the increase of irradiation dose, the reaction intensify between SPI and thestarch molecules with the increased NH bond. In the secondary structure of SPI/starchbiodegradable material,As the increase of irradiation dose, the content of α-helical and thecontent of unordered structure remarkable reduced，the content of β-sheet did not changeobviously，β-turn increased.The results of X-ray diffraction analysis showed that: the hot-press process contribute to SPI molecules arrangement，the formation of hydrogen bond，the emergency of new crystalline region，the enhancement of material’s order. The results ofamino acid analysis showed that: irradiation technique promoted the composite reactionbetween SPI and the starch molecules.the content of every amino acid of the SPI/starchbiodegradable material was decreased and the contents of arginine and lysine was reducedmore.The results of SEM analysis showed that: irradiation treatment enhance cross-linkingdensity of the material and minished air bubble of raw materials，thereby the surface of thematerial become more smooth and was glossy. Compared with the raw material，the contentof sulfydryl reduced and the content of disulfide bond increased in the raw material ofirradiation modification.The results of color difference analysis showed that：after the rawmaterial was modified by irradiation，Hunter b value increased，Hunter a value decreased，L value was not notable to vary. The viscosity of the raw material of irradiation modificationshowed a result that as the increase of irradiation dose, the viscosity of the raw material wentdown firstly, then up.When the SPI/starch biodegradable material was buried in49days, in the aqueous soilsolution environment, the rate of weight loss was60.74%weight; while in the natural soilenvironment, the rate of weight loss was64.57%. The results meet the country’s requirementsthat the rate of weight loss must be more than60%., Technical and health physics andchemistry index parameters of the disposable tableware had been tested and were in line withnational requirements, so disposable tableware can be applied.