Bamboo flour modifying by grafted improves mechanical property of bamboo-plastic composites

Abstract: In order to improve the interfacial bonding strength of bamboo flour and polyethylene terephthalate glycol (PETG) matrix and broaden the application fields of bamboo flour filled PETG composites, in this study, we applied the method of AGET (activators generated by electron transfer) ATRP (atom transfer radical polymerization), and straightforwardly grafted methyl methacrylate (MMA) from the bamboo flour surface using the 2-bromoisobutyryl bromide (BIBB) functionalized bamboo flour as a macro-initiator, FeCl3·6H2O as the catalyst, triphenylphosphine (PPh3) as the ligand, and ascorbic acid as the reducing agent. And then Fourier transform infrared spectroscopy (FTIR) was used to examine the changes of surface groups before and after modification. Simultaneously, the bamboo flour filled PETG composites were prepared by a melt blending and compression molding process. The flexural properties of bamboo flour/PETG composites were investigated, and the impact fractured surfaces of unmodified and modified bamboo flour filled PETG composites were observed by an environmental scanning electronic microscopy micrograph (ESEM) in succession. In addition, the effect of the grafted bamboo flour on the dynamic thermal mechanical properties (storage modulus E', glass transition temperature Tg, and loss tangent tanδ) of bamboo flour/PETG composites was also investigated. The results showed that the obvious variety of FTIR of the bamboo flour after grafting modification (the intensities of the bands at 1732 cm-1 strengthened and the peak at 3000 and 2954 cm?1 appeared in the spectra of grafted substrates) confirmed that the grafting reaction had taken place; and PMMA was successfully grafted onto the bamboo flour surfaces. The flexural tests showed that the flexural properties of the grafted bamboo flour filled PETG composites were better than those of unmodified ones. When the grafted bamboo flour content was 30%, the flexural strength of the composite increased 16%, compared to bamboo flour/PETG composites of an equal amount of unmodified bamboo flour. This fact shows that the grafting modification of bamboo flour by coating a layer of PMMA is an effective method to improve internal bond strength between bamboo flour and PETG matrix. Furthermore, a dynamic mechanical analysis (DMA) and morphology observations well substantiated the above-mentioned mechanical results. The results of a dynamic mechanical analysis (DMA) showed that the peak value of tanδ decreased and the glass transition temperature (the position of the maximum in tanδ) decreased after grafting modification. Comparing with the corresponding tanδ curves of the composites, it was also found that the curves of the grafted bamboo flour filled PETG composites appeared to exhibit only one peak during the heating process. This result suggests that PMMA could act as a compatibilizer to enhance the interfacial compatibility between bamboo flour and a PETG matrix. From the impact fracture morphologies of ESEM, it can be concluded that the bamboo flour exhibits good dispersion in a PETG matrix after grafting modification, i.e., the grafted bamboo flour had better interfacial compatibility with a PETG matrix than unmodified ones, and interface bonding between grafted bamboo flour and a PETG matrix was good. The research results in this paper have great practical significance on improving the properties of bamboo flour/PETG bamboo-plastic composites by a bamboo flour surface treatment.