Binary composites of high-crystalline fibrous cellulose with polypropylene (PP) or maleic anhydridegrafted polypropylene (MAPP) were prepared by melt-mixing with different contents of cellulose from 0 to 60 wt %. Ternary composites of cellulose with PP and MAPP were also prepared to investigate the effects of MAPP as a compatibilizer between cellulose and PP. Scanning electron microscopy revealed that the addition of MAPP generates strong interactions between a PP matrix and cellulose fibers: All cellulose fibers are encapsulated by layers of the matrix and connected tightly within the matrix. Thus, the tensile strength and Young's modulus of MAPP-containing composites increase with an increase in MAPP and cellulose content, in contrast to the decrease in tensile strength of a PP-based binary composite with an increase in cellulose.Cellulose fibers act as a nucleating agent for the crystallization of PP, which is promoted by the addition of MAPP through an increase of the crystallization temperature of PP in the composite. Accordingly, both cellulose and MAPP facilitate the thermooxidative stability of PP composites in the following order: MAPP/cellulose Ͼ PP/MAPP/cellulose Ͼ PP/cellulose Ͼ PP. Relative water absorption increases with an increase in cellulose content, decreasing with the addition of MAPP. MAPP-containing cellulose composites have high potential for applications as environmentally friendly materials.

ABSTRACT:The ball milling of cellulose and maleic anhydride grafted polypropylene (MAPP) induced the formation of ester bonds between OH groups of cellulose and maleic anhydride groups of MAPP, in marked contrast to the melt mixing of the original cellulose and MAPP, through which the esterification was hardly observed. This esterification was hardly dependent on the chemical structure of MAPP. In agreement with the enhanced interfacial adhesion due to the formation of ester bonds, a composite prepared via ball milling revealed an improvement in the tensile strength with respect to a melt-mixed composite.

Fibrous cellulose and maleated polyethylene (FC-MPE) composites were prepared under melt mixing by maleation of polyethylene (PE) to obtain maleic anhydride (MA) grafted PE (MPE) and successive compounding of the resultant MPE with fibrous cellulose (FC). When increasing the content of added MA to 2 wt %, the grafting efficiency of MA decreases gradually to 84% and the grafted MA chains become longer. Scanning electron microscopy (SEM) reveals strong adhesion of MPE to FC in the FC-MPE composite, which is probably due to the increased compatibility between MPE and FC, in contrast to no adhesion of unmaleated PE (UPE) to FC in the FC-UPE composite. This difference in interfacial structure between the FC-MPE and FC-UPE composites results in quite different mechanical properties for them. With an increase in the FC content to 60 wt %, the tensile strength of the FC-MPE composite increases significantly and reaches 125% that of pure PE. Furthermore, the larger Young's modulus, larger bending elastic modulus, and smaller elongation of the FC-MPE composite strongly indicate effective transfer of the high tensile strength and elasticity of FC to the MPE matrix through the strong adhesion between FC and MPE.

The microstructure of maleic anhydride (MA) grafted polyethylene (PE), MA-g-PE, has been successfully characterized by high-resolution NMR and FT-IR spectroscopy. The carbonyl asymmetric and symmetric stretchings of MA-g-PE exhibit lower shifts with an increase in the grafting degree of MA, suggesting stronger inductive interactions between different grafts in a solid state. The 1H and 13C NMR spectroscopy of [2,3-13C2]MA grafted PE with a low molecular weight (lmPE), [2,3-13C2]MA-g-lmPE, demonstrates that [2,3-13C2]MA-g-lmPE contains fewer succinic anhydride (SA) oligomeric grafts with a terminal unsaturated MA ring (oligo-MA) in addition to more SA oligomeric grafts terminated with a saturated SA ring (oligo-SA), the only structure that had been observed prior to this study. The formation of oligo-MA and oligo-SA can be explained by a mechanism based on two different termination processes:  disproportionation between a grafting radical and a macroradical on a secondary carbon in lmPE or another grafting radical as well as hydrogen abstraction of a grafting radical from a secondary carbon on lmPE.

Composites consisting of a polypropylene (PP) and highly crystalline cellulosic microfibers were prepared by melting mixing with the maleic anhydride grafted polypropylene (MAPP) as a compatibilizer. The results show that even with addition of a small amount of MAPP, the mechanical properties of the composites improved dramatically. The improvement is attributed to stronger interfacial adhesion caused by esterification between anhydride groups of MAPP and hydroxyl groups of cellulose, although the number of the ester bonds is too few to be detected by FT‐IR spectroscopy. It was also found that tensile strength and Young's modulus increased with the increasing MAPP contents in the composites, and the optimum MAPP content is about 10 wt% for the composite with cellulose content of 30 wt%. SEM indicated that the interfacial adhesion between cellulose fibers and PP improved in MAPP‐containing composites. The DSC results showed that MAPP has little effect on melting and crystallization temperatures of PP in the composites. POLYM. COMPOS., 26:448–453, 2005. © 2005 Society of Plastics Engineers