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

Arne Schirp,Claudia Schirp

doi:10.3390/fib9030017

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.

Highlights

There has been continued interest in the use of wood fibres as opposed to wood flour in the production of wood-plastic composites (WPC), especially for the development of new applications
Mechanical Properties of WPC Made with thermo-mechanical pulp (TMP) Fibres and Coupling Agent
It has been proposed that the application of maleated polypropylene (MAPP) to wood improves interfacial adhesion by modifying the fibre surface energy and improving the fibre dispersion in the plastic matrix [28,42]

Summary

Introduction

There has been continued interest in the use of wood fibres as opposed to wood flour in the production of wood-plastic composites (WPC), especially for the development of new applications. Wood fibres can be produced by thermomechanical pulping, which is the common process to manufacture fibres for medium-density fibreboard (MDF), or by chemical pulping methods such as Kraft pulping. The main difference in the pulping processes is the target to either preserve or dissolve certain wood components, predominantly lignin, which bonds the fibres together. Most of the lignin remains, whereas for papermaking, lignin is removed to obtain strong inter-fibre bonding. A commercial product in which cellulose fibres are used is “Fibromer” from the company Mondi. The aspect ratio of a bleached Kraft pulp fibre is about 100, which offers a high reinforcement and weight savings potential. While the density of glass-fibre reinforced PP is 2.5 g/cm , the density of

Methods

Results

Conclusion