Journal
POLYMER DEGRADATION AND STABILITY
Volume 106, Issue -, Pages 54-62Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.polymdegradstab.2014.01.007
Keywords
Cellulose; Polylactide; Polyhedral oligomeric silsesquioxane; Crystallinity; Melt rheology; Tensile strength
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Funding
- NIST-EL Extramural Fire Research Grants Program [60NANB11D174]
- U. S. Air Force Office of Scientific Research [JWG:MIPR F1ATA03239G001 A1]
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Poly(lactic acid), PLA, was extruded with intumescing flame retardant formulations based on ammonium polyphosphate, APP. Nanofibrillated cellulose fibers (NFC), POSS-modified NFC (PNFC), and pentaerythritol (PER) were used as the additional carbon source. The effects of each additive and their intumescing combinations on polymer degradation, flammability, crystallization, melt rheology, and tensile properties were systematically examined. APP and PER catalyzed the degradation of PLA during extrusion, which increased the crystallinity of PLA, lowered the viscosity of the melt, reduced the moduli, and decreased the tensile strength of the composite. APP had the largest effect on physical properties, acting as a nucleating agent, decreasing tensile strength, and increasing elongation to break. The POSS moieties on PNFC acted as a slight plasticizer in melt rheology studies, but did not affect the glass transition temperature. PNFC formed a cross-linked network with APP when melt-blended with PLA, which reduced polymer degradation, decreased PLA crystallinity, reduced the melt viscosity, and improved composite stiffness relative to the neat extruded PLA. The PLA composites containing APP and PNFC had the best tensile properties of all the intumescing composites studied. The cross-linked network formed between cellulose, POSS, and PLA helps produce composites with superior flame retardant, rheological, and mechanical properties relative to other intumescing formulations. (C) 2014 Elsevier Ltd. All rights reserved.
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