The Studies Of The Functionalization Of Polypropylene

Polypropylene (PP), one of the conventional thermoplastics, is widely used due to its desirable and beneficial properties, such as high mechanical strength, inertness to various chemical reagents, nontoxicity, low price and ease in the molding, and so forth. However, as a conventional PP it exhibits some limitations, such as the poor polarity leading to its incompatibility with some polar polymers and inorganic fillers, lower melt strength and poor toughness, which imply that it can not be applied in some domain. To extend its applicable domain, the conventional PP was modified by various methods:improving its polarity by grafting the polar monomers, glycidyl methacrylate (GMA), on PP chains (PP-GMA), introducing some long chain branches (LCB) onto the PP macromolecules using the prepared PP-GMA by a novel method and mixing the cellulose microfibrils (CMF) grafted with some soft PBA chains into PP matrix to improve the mechanical properties of PP. It would be more extensively utilized if the limitations are improved. Therefore, the studies for the modifications of conventional PP in some unsatisfying properties are very important.To improve the polarity and introduce some functional groups on PP chains for the preparation of LCB PP, melt grafting reaction of GMA grafted onto PP was studied using a Thermal Haake. The results showed that the grafting efficiency of GMA was increased because of the using of powder PP which can absorb liquid monomers and disperse various compositions into the PP matrix. By adding styrene as the comonomer, the grafting efficiency was increased also, and the degradation of PP was restrained well. The optimum conditions under which the graft efficiency was increased to 94.0%and the melt flow rate was decreased to the lowest value were obtained by studying the amount of St and initiator and the reaction temperature. It was found that the grafting efficiency of GMA is the highest when 12g St,12g GMA and 1.4g DCP are added into 100g powder PP on the base of 100g powder at 170℃.To improve the melt strength of conventional PP and study the rheological properties of long chain branching (LCB) polypropylene (PP), long chain branches (LCB) were grafted onto the linear PP by melt grafting reaction in the presence of a novel chain extender, poly (hexamethylendiamine-guanidine hydrohloride) (PHGH). The branching reactions between the functionalized PP and PHGH were confirmed by transient torque curves and FTIR, and using FTIR the amount of LCB grafted on PP was determined. The increase of melt strength of the modified PP was confirmed by the melt flow properties and melt strength, implying the approach is feasible. By differential scanning calorimetry (DSC) and polarized microscope measurements, it was found that for LCB PP the crystallization temperature decrease significantly and the crystal size is smaller in comparison with that of linear PP, which will benefit the mechanical properties and the processing in some practical applications. Also, the viscoelastic properties of the LCB PP and linear PP under shear flow were investigated for distinguishing LCB PP from linear PP. It was found that the elastic response of LCB PP at low frequencies was significantly enhanced in comparison with that of the linear PP, implying a presence of a long relaxation time mode that was not revealed in linear PP. Moreover, the branching levels of LCB PP were quantified using a detailed method, which was in correspondence with the molar amount of PHGH grafted on PP. In step-shear measurement, the fast and slow relaxation processes characterizing the linear viscoelastic properties were observed also for nonlinear relaxation moduli. The dependence of the damping for the slow process of the modified PP on shear strain was much weaker than that of the fast process. For modified PPs, strain hardening under elongatioanal flow was pronounced at all strain rates applied. Moreover, the critical strain for rupture of the strand was further improved with the increasing degree of branching, indicating it could find application in foaming.Immobilizing poly (butyl acrylate) (PBA) on cellulose microfibril (CMF), in the form of powder, generate new possibilities of accomplishing biocomposites with a hard core and a soft shell for reinforcing polymer matrices. The biocomposites, CMF-PBA, were obtained by the reaction of the hydroxyl groups on CMF surface with a-bromoisobutyryl bromide (BIBB), followed by polymerization in situ with butyl acrylate (BA) using atom transfer radical polymerization (ATRP) conditions. To predetermine the molecular weight of poly (butyl acrlate) (PBA) on CMF, the result of 0.0008mol of bromine in 1g of CMF-Br (macroinitiator) was quantified by gravimetric measurement. The two synthesized CMF-PBA samples with the designed polymerization degrees of 10 and 15 respectively were characterized by FTIR, TGA, Water Contact Angle, and SEM. The grafted polymer chains were obtained by the hydrolysis of the CMF backbone and analyzed by GPC. The results obtained from these analytical techniques confirm that the graft polymerization occurred from CMF backbone and the hydrophobicity of the obtained biocomposites was evidently enhanced, moreover, the cut-off chains had well-controlled molecular weight and polydispersity. Through SEM measurement of the polypropylene (PP) biocomposites blended with CMF-PBA, it was found that the compatibility of CMF in PP matrix was increased distinctly compared with the PP composites mixed with PP-GMA compatilizer and original CMF.Surface-initiated atom transfer radical polymerization (SI-ATRP) of butyl acrylate (BA) on cellulose microfibrils (CMF) was conducted in an attempt to create controllable hydrophobic chains on CFM. The macroinitiator CMF-Br was prepared according to the previous details and followed by the ATRP of BA using two catalyst systems, CuIBr/2,2’-bipyridine (BPY) and CuIBr/pentamethyl-diethylenetriamine (PMDETA). The molecular weight (MW) and polydispersity of the grafted PBA cleaved from CMF via hydrolysis was determined using GPC. The results indicated that the PMDETA system exhibited relatively poor control over the ATRP; whereas the BPY system produced the PBA with tailored chain lengths and narrow polydispersities but experienced a rather slow polymerization process. To optimize the polymerization with the CuBr/PMDETA system, several influencing factors were investigated, including the type of solvents, reaction temperature and the use of co-catalyst CuIIBr2. A model was also adopted and fitted with the current experimental data in an attempt to elucidate the mechanisms of SI-ATRP.