Thermomechanical pulp (TMP), among other natural fibers, features characteristics that make it a promising candidate for the utilization in polymer composites. This review is providing an overview on the current state of research on TMP reinforced polymer composites. More than 50 references were reviewed. The cited literature is catalogued according to pretreatments, batch or continuous procedures, processing at laboratory or industrial scale, fiber contents, polymer types, coupling agents as well as wood species. The reinforcing potential of TMP utilized in composites is demonstrated. Tensile strength was found to be peaking at a fiber content of around 40 wt %. Fiber morphology is presumed to be an important determinator for composite properties. Specific mechanical energy [kWh/kg] is presented as an indicator suitable to compare the influence of various processes on fiber morphology. Furthermore, the feed-in and dosing issue that generally accompanies the utilization of cellulosic fibers is described and possible solutions are discussed.

In most countries, fibreboards are not recovered after utilization but burned for energy production. This study aims at recovering fibres from industrial fibreboards and reusing them as reinforcement elements in wood polymer composites (WPC). Recovered fibre (RF) material was generated by the thermo-hydrolytic disintegration of medium and high density fibreboards bonded with urea-formaldehyde resin. Various formulations of RF and polypropylene were used with or without the addition of the coupling agent to manufacture WPC using a co-rotating extruder. Test specimens were produced via injection moulding whereby those containing 'virgin' fibres served as a reference with respect to mechanical and physical properties. WPC formulations containing RF and 'virgin' fibres exhibited similar results, but composites containing RF exhibited improved mechanical and water-related properties, especially without coupling agent. The study indicates that recovered fibres are suitable to produce WPC with very similar physico-mechanical properties as those from 'virgin' fibres.

The distinctive length and morphology characteristics of thermomechanical produced wood fibers make it a promising candidate for the utilization in polymer composites. However, due to the low bulk density of these fibers, the feeding into the compounding process (i.e., extruders) is quite challenging. In this study, a novel simultaneous defibration and compounding process are conducted in order to solve the feed‐in problem of thermomechanical fibers. A disc‐refiner was used to defibrate wood chips to fibers and compound the fibers with neat polymer granulates in one process step. After the process, the material showed typically thermomechanical fibers with chopped polymer particles which were inseparably attached to the fiber. The observed mechanical properties of the composites were slightly lower than some literature values. With field emission scanning electron microscopy and X‐ray microtomography analysis, voids and a polymer enriched surface were found influencing the composites performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45859.

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