Thermoplastic polymer nanocomposites integrating cellulose nanocrystals (CNCs) have previously been demonstrated to possess mechanically adaptive properties, responding to changes in external environments by a dramatic change in stiffness/modulus. Traditionally, these nanocomposites are generated via solution casting approaches. Thermal processing via melt extrusion can form specific product shapes and/or impart preferential alignment, orientation for targeted mechanical performance.<br/><br/>The focus of this work is to establish the structure-process-property relationships surrounding thermal processing impact on the mechanical response of a thermoplastic urethane polymer containing 10 weight percent CNCs. We investigate monofilament extrusion followed by extrusion based 3-D printing into a desired format. Our work reveals the impact of thermal history of both processes on the mechanical response of CNC composites from a dry state (e.g. &lt;5% relative humidity, RH) to wet state (100% RH), and the corresponding hysteresis following cycling between wet and dry states. Additionally, we reveal the impact of extrusion on CNC orientation and mechanical response.<br/><br/>Preliminary results indicate drastic response with up to 5x reduction in storage modulus between wet and dry states, with comparable relative change over a temperature range of 25-40°C. Following melt extrusion into monofilament form, overall small changes in uniaxial (flow direction) storage modulus (&lt;10%) are observed in the dry state over a broad frequency range. We will present the corresponding impact on wet-state response and hysteresis when cycling between wet and dry states. Additionally, we will deconvolute the separate, competing contributions of CNC orientation and thermal decomposition; the former is expected to substantially increase modulus, while the latter is expected to reduce CNC coupling and decrease both modulus and expected response to environmental humidity.

Processing effects on mechanically adaptive response of cellulose nanocrystal composites

253rd National Meeting (2017)

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