Although efforts have been reinforced on an industrial scale to isolate lignin from the cooking liquors accruing in the pulping industry, mass applications of Kraft lignin not utilizing its caloric value are still sought. One possibility in this respect might be the use of lignin as a filler in commodity thermoplastics creating partially bio-based and inexpensive commodity polymer blends. In the present paper suchlike blends from softwood Kraft lignin and high density polyethylene (PE) with lignin loads up to 70 wt% will be presented. Both kneader and twin-screw extruder techniques have been employed under various processing regimes to produce the blends and testing the mechanical properties after injection molding. It turned out that (i) good interface adhesion generated by the use of a coupling agent (maleic anhydrite grafted PE), (ii) spherical lignin phase morphology and (iii) fine lignin spheres below 1 micrometer in diameter, are all beneficial for the blend mechanical properties, the latter two points implemented by appropriate compounding conditions. Under these an increase in tensile strength and modulus is noticed with increasing lignin content from 25 MPa and 1.2 GPa of pure PE to 35 MPa and 2.6 GPa for the 70 % lignin blend, respectively. The most striking result is the improvement (compared to pure PE) of the impact properties for 50 % lignin blends. Values as high as 8 kJ/m2 (compared to 6.4 kJ/m2 for PE) were found for the notched Charpy impact strength and no break in the un-notched test. Obviously, lignin is more than a simple filler if appropriate compounding conditions and coupling mechanisms are observed. Envisaged applications of this inexpensive partially bio-based polymer blend could be in the building and construction sector or other outdoor uses in agri- or horticulture.

Crucial role of processing regimes and compatibilization for toughening highly lignin filled polyethylene blends

253rd National Meeting (2017)

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