Abstract
The surfaces of poplar wood fibers were modified using high-temperature hot air (HTHA) treatment and silane coupling agent. The single factor test was then used to investigate the performances (e.g., the change of functional groups, polarity, cellulose crystallinity, and thermal stability) of modified poplar wood fibers (mPWF) through Fourier transform infrared spectrometry, X-ray diffraction and thermo-gravimetric analysis for the subsequent preparation of wood-plastic composites (WPCs). The effect of HTHA treatment conditions—such as temperature, inlet air velocity, and feed rate—on the performances of WPCs was also investigated by scanning electron microscopy and dynamic mechanical analysis. The main findings indicated that HTHA treatment could promote the hydration of mPWF and improve the mechanical properties of WPCs. Treatment temperature strongly affected the mechanical properties and moisture adsorption characteristics of the prepared composites. With the increase of treated temperature and feed rate, the number of hydroxyl groups, holocellulose content, and the pH of mPWF decreased. The degree of crystallinity and thermal stability and the storage modulus of the prepared composites of mPWF increased. However, dimensional stability and water absorption of WPCs significantly reduced. The best mechanical properties enhancement was observed with treatment temperature at 220 °C. This study demonstrated the feasibility for the application of an HTHA treatment in the WPC production industry.
Highlights
Derived from wood or agricultural materials—such as kenaf, jute, hemp, flax, or other natural resources—natural fibers have been widely used as reinforced materials for plastics [1]
The results showed that the contents of holocellulose decreased from 76.14% to 72.14% with the increase of treatment temperature from 100 ◦ C to 180 ◦ C and the slightly increased of lignin contents, while the change of the mechanical properties of bamboo/high-density polyethylene (HDPE) composites is not obvious
The Fourier Transform Infrared Spectrometry (FTIR) spectra attribution results for the wood fibers modified through high-temperature hot air and silane coupling agent are shown in Table 2 and Figure 1
Summary
Derived from wood or agricultural materials—such as kenaf, jute, hemp, flax, or other natural resources—natural fibers have been widely used as reinforced materials for plastics [1]. Water evaporation in natural fibers leads to the emergence of pores during the compounding process, which can result in inferior performances of wood-plastic composites (WPCs). The natural fibers must be pretreated to control moisture content at 1% to 3% [2]. The natural fibers can still be prone to agglomeration, due to the formation of hydrogen bonds between cellulose molecules that contain many hydroxyl groups and cause uneven dispersion during mixing [3,4]. The majority of polar (hydrophilic) natural fibers are not compatible with non-polar (hydrophobic) substances, due to the existence of hydroxyl groups on the cellulose and hemicellulose of natural fibers.
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