Mechanism And Mechanical Properties Of Cellulose Graft Copolymers

Cellulose is the most important skeletal component in plants and the most abundant renewable material in nature. Recently, owing to the rapid increase in petroleum price and the compelling requirement of sustainable development, biodegradable and environmentally friendly cellulose materials have become a main topics of research and development. However, the application of cellulose materials is restricted by the some properties such as insolubility in general solvents, poor chemical resistance, and low strength, which are attributed to the structure of cellulose. Thus, the modification of the cellulose materials is required.The grafting reaction of cellulose has been the focus of the research of this kind. A large number of hydroxyl groups in cellulose macromolecules attribute to chemical modification of cellulose, thereby obtaining the cellulose materials with bifunctional properties and various chemical structure for different proposes. Therefore, the application of cellulose materials is broadened.The copolymerization of caprolactam(CPL) onto cellulose using potassium persulfate and ammonium persulfate as reaction initiator was studied. The molecular structure, appearance, crystallinity, thermal stability and mechanical properties of graft cellulose were characterized using infrared spectrometer, scanning electron microscope, X-ray diffractometer, thermo gravimetric analyzer and electronic universal testing machine. The effects of various reaction parameters on grafting ratio, such as mass of monomer, concentration of initiator, reaction time and reaction temperature were evaluated. The main conclusions are as follows:(1) NaOH, urea, thiourea and water were mixed in a ratio of 4:4:4:38.5(w/w), as the available solvent of cellulose. And the optimum temperature to swell cellulose was-10℃. Such solvent changed the crystalline form of cellulose fromⅠtoⅡ, thereby lengthening interplanar crystal spacing and making the molecule of cellulose more accessible to solvent.(2) The optimum conditions for the cellulose grafting were as follows:the mass ratio of monomer to cellulose 1:1, initiator concentration 0.2mol/L, reaction temperature 30℃, reaction time 75min. The grafting ratio reached 57% under these optimum conditions. The grafting occurred mainly on the surface and within the amorphous region of the cellulose, the crystallinity was not destroyed.(3) The tensile strength of grafted cellulose was enhanced with increasing graft ratio, and failure strain of grafted cellulose was decreased with increasing graft ratio. The tensile strength of grafted cellulose increased to 0.84MPa and failure strain of grafted cellulose reduced to 5.5% when the grafting ratio reached 57%. The crack of grafted cellulose was found to be ductile fracture, before which grafted cellulose absorbed energy significantly.