Thermoplastic Cellulose-Based Compound for Additive Manufacturing

The increasing environmental awareness is driving towards novel sustainable high-performance materials applicable for future manufacturing technologies like additive manufacturing (AM). Cellulose is abundantly available renewable and sustainable raw material. This work focused on studying the properties of thermoplastic cellulose-based composites and their properties using injection molding and 3D printing of granules.

The aim was to maximize the cellulose content in composites. Different compounds were prepared using cellulose acetate propionate (CAP) and commercial cellulose acetate propionate with plasticizer (CP) as polymer matrices, microcellulose (mc) and novel cellulose-ester additives; cellulose octanoate (C8) and cellulose palmitate (C16). The performance of compounds was compared to a commercial poly(lactic acid)-based cellulose fiber containing composite. As a result, CP-based compounds had tensile and Charpy impact strength properties comparable to commercial reference, but lower modulus.

CP-compounds showed glass transition temperature (Tg) over 58% and heat distortion temperature (HDT) 12% higher compared to reference. CAP with C16 had HDT 82.1 °C. All the compounds were 3D printable using granular printing, but CAP compounds had challenges with printed layer adhesion. This study shows the potential to tailor thermoplastic cellulose-based composite materials, although more research is needed before obtaining all-cellulose 3D printable composite material with high-performance.

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Article information: Immonen, K.; Willberg-Keyriläinen, P.; Ropponen, J.; Nurmela, A.; Metsä-Kortelainen, S.; Kaukoniemi, O.-V.; Kangas, H. Thermoplastic Cellulose-Based Compound for Additive Manufacturing. Molecules 2021, 26, 1701. https://doi.org/10.3390/molecules26061701

Materials in Production of Thermoplastic Cellulose Additive:
The cellulose for production of thermoplastic cellulose additives was commercial softwood dissolving grade pulp (Domsjö Fabriker AB, Sweden) with average Mw 520 kDa. The pulp was ozone pretreated according to a method described by Willberg-Keyriläinen et al. [35] to reduce the molar mass to 84 kDa. All other reagents were analytical grade and purchased from Sigma-Aldrich (Merck KGaA, Dramstadt, Germany).

Materials in Manufacturing of Cellulose-Based Compound:
Polymer matrices used for preparation of cellulose based compounds were cellulose acetate propionate without plasticizer (CAP) from Sigma-Aldrich (Merck KGaA, Darmstadt, Germany) with average Mn ~75,000, acetyl content 2.5 w-% and propionyl content 46 wt-%, and cellulose acetate propionate CELLIDOR CP300-13 (CP) (Albis Plastics GmbH, Hamburg, Germany) with phthalate free plasticizer content of 13% and melt flow rate 7.5 cm3/10 min (210 C, 2.16 kg) [39,40]. Cellulose fiber used in compounds in amount of 20 wt-% was microcrystalline cellulose VIVAPUR 105 (JRS Pharma GmbH, Weissenborn, Germany) with average particle size by Laser diffraction 15 m. In coupling of fiber and polymer was used reactive epoxidized linseed oil Lankroflex™ L (Valtris Specialty Chemicals, Independence, Ohio, USA). As additional plasticizer in compound in amounts of 4 wt-% and wt-17%, a thermoplastic cellulose-esters prepared at VTT according to method explained in chapter 3.2.1, were used. As commercial 3D printable reference material was used PLA-based compound containing 20% cellulose fiber (Cref).