Effect Of The Chemical Modification On The Sructure And Properties Of The Wheat Protein

The shortage of resources and the ever-increasing pollution from non-degraded plastic waste have threatened human being's survival,health and development.Therefore,the natural renewable plant resources have the potential to be used as an alternative to petroleum and become one of the primary chemical materials in the 21st century, which has been one of the fronts of polymer science and material science. As a kind of widespread and abundant natural biopolymer, wheat protein has been a new topic in material science.While the wheat gluten is edible,degraded and has the good thermo-molded properties,film-forming properties and the ability to isolate the CO₂ and O₂, its properties are very sensitive to the environment. The molecular chain of the wheat protein has the unique structure characteristics and interaction. The wheat protein could be physically or chemically modified as there are active groups such as amino,carboxyl,hydroxyl in the side chain. To reduce the sensitivity of the properties to the environment,chemical agent was used to react with the amino acid residues in the protein. So the molecular polarity of the protein decreased; the balance of the charge is broken and hydrophobic interaction increased.The main objectives of this thesis are to study the effects of the chemical modification by caprylic aldehyde on the structure and properties of wheat protein.The effects of the molding temperature on the mechanical properties of the modified wheat protein when caprylic aldehyde content was 2% was studied. The results revealed that Young's modulus,strain at break,tensile strength,crosslink density were increased as the molding temperature increased. At the same molding temperature, Young's modulus was the highest when caprylic aldehyde content was 4%.As the caprylic aldehyde content increased,strain at break and tensile strength were decreased. When caprylic aldehyde content was 4%,crosslink density was the highest. Young's modulus of the modified wheat protein cross-linked with formaldehyde was the highest when caprylic aldehyde content was 2%.As the caprylic aldehyde content increased,train at break,tensile strength,crosslink density were decreased.As the caprylic aldehyde content increased,the initiate fracture of the plasticized wheat protein showed a ductile rupture,and then a brittle fracture when the caprylic aldehyde content was above 6%. When caprylic aldehyde content was 10%,there were not obviously agglomerated particles on the fracture surface but appeared large numbers of microcellular structure, which indicated the molecular interaction of the protein was weakened and the effectof the plasticization with the glycerol was reduced.As the caprylic aldehyde content increased,the water vapor permeability of the modified wheat protein decreased. When caprylic aldehyde content was at the range of 0～4%,the water vapor permeability of the modified wheat protein cross-linked with formaldehyde increased. When the caprylic aldehyde content increased,the water vapor permeability decreased because of the chemical modification.