Online Pre-Treatment of Thermomechanical Pulp with Emulsified Maleated Polypropylene for Processing of Extruded Thermoplastic Composites

Abstract

The effectiveness of maleated polypropylene (MAPP) in emulsified form for the pre-treatment of thermo-mechanical pulp (TMP) before extrusion with polypropylene fibres was evaluated. MAPP in pellet form, which was applied during the compounding step, served as a benchmark. In addition, commercial softwood flour was included as a reference. The influence of the temperature during the defibration process and the presence or absence of the coupling agent on composite performance were evaluated. Composites were processed with a high wood content of 70 wt.%, which is common for extruded profiles. It was found that TMP based on Robinia (Robinia pseudoacacia L.) conferred higher strength properties to the composites compared to TMP based on Scots pine (Pinus sylvestris L.), which was attributed to the higher length/diameter ratio of fibres in Robinia. However, under the conditions of this study, strength properties were superior and water uptake and swelling were reduced when wood flour was used instead of TMP. On the other hand, in many formulations, larger improvements in flexural and tensile strength due to MAPP were found for the TMP-based composites compared to the wood flour-based composites. This could be due to the larger surface/volume ratio for TMP compared to wood flour and more efficient stress transfer from fibres to the matrix. Results from X-ray photoelectron spectroscopy (XPS) showed that TMP surfaces were more hydrophobic than wood flour due to coverage with lignin, which reduced the effectiveness of MAPP. Esterification between the emulsified MAPP and fibre surfaces was determined using Fourier-Transform Infrared (FTIR) spectroscopy, but some non-activated maleic anhydride remained. Under the conditions of this study, MAPP added during compounding provided better performance compared to MAPP which included a non-ionic emulsifier and which was added during the refining process. Lower temperature (150 °C) during defibration was shown to be beneficial for the strength properties of composites compared to high temperature (180 °C) when MAPP was included in the formulations.

Characterisation of Polypropylene Composite Reinforced with Chemi-Thermomechanical Pulp from Oil Palm Trunk via Injection Moulding Process

“…However, it could be observed that the pulp loading percentage has a significant influence on the physical and mechanical properties of the WPCs. WPCs highly filled with wood fibre and pulp have obvious advantages in terms of their environmental friendliness, application scenarios, and market competitiveness, and they are continuously being developed [ 40 , 41 ]. Most published papers have reported 60% as the maximum loading percentage of filler to produce WPCs with good properties [ 7 ].…”

Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene

“…MAPP is usually added to the matrix, but can also be added to the fibers; 25 it increases the compatibility between fiber and matrix through hydrogen bonding or esterification between the maleic anhydride and the hydroxyl groups on the fibers 26,27 . Compared to nonlignin containing fibers, 25,27–29 MAPP is less effective as a compatibilizer between TMP and PP. This is due to the presence of lignin on the TMP surface.…”

“…Maleic anhydride grafted polypropylene (MAPP) is a common compatibilizer used for wood-thermoplastic composites. MAPP is usually added to the matrix, but can also be added to the fibers; 25 it increases the compatibility between fiber and matrix through hydrogen bonding or esterification between the maleic anhydride and the hydroxyl groups on the fibers. 26,27 Compared to nonlignin containing fibers, 25,[27][28][29] MAPP is less effective as a compatibilizer between TMP and PP.…”