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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Phase-Change Thermoplastic Elastomer Blends for Tunable Shape Memory by Physical Design

Shape-memory polymers (SMPs) change shape upon exposure to an environmental stimulus.1-3 They are of considerable importance in the ongoing development of stimuli-responsive biomedical4,5 and deployable6 devices, and their function depends on the presence of two components.7 The first provides mechanical rigidity to ensure retention of one or more temporary strain states and also serves as a switch capable of releasing a temporary strain state. The second, a network-forming component, is required to restore the polymer to a prior strain state upon stimulation. In thermally-activated SMPs, the switching element typically relies on a melting or glass transition temperature,1-3,7 and broad or multiple switches permit several temporary strain states.8-10 Chemical integration of network-forming and switching species endows SMPs with specific properties.8,10,11 Here, we demonstrate that phase-change materials incorporated into network-forming macromolecules yield shape-memory polymer blends (SMPBs) with physically tunable switching temperatures and recovery kinetics for use in multi-responsive laminates and shape-change electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Design of Graft Block Polymer Thermoplastics

Graft block polymers are defined by several architectural parameters, including backbone flexibility, graft density, backbone length, side-chain composition, and side-chain length. In this work we probe the impacts of each of these parameters on the phase behavior, rheological properties, and mechanical performance of these materials. Specifically, we examine two sets of materials prepared from backbones of different inherent flexibility. One set was prepared from poly[(n-butyl acrylate)-co-(2-hydroxyethyl acrylate)] (B$_x$E$_y$) copolymers; the other was prepared from hydroxypropyl methyl cellulose (HPMC) samples. Sequential ring-opening transesterification polymerization from these hydroxyl-functionalized macroinitiatiors yielded a diblock graft architecture containing a rubbery interior block and semicrystalline exterior blocks tethered to a flexible (B$_x$E$_y$) or rigid (HPMC) backbone. Good control over side-chain molar mass and composition and judicious choice of the graft block segments enabled the preparation of materials that were either ordered or disordered in the melt state. In the former case, crystallization destroys existing order in the material; in the latter case crystallization induces new microphase separation in the bulk. Many of the structure–mechanical property relationships observed for graft block copolymers with rigid backbones are maintained for graft block polymers with semiflexible backbones, including the tendency for samples to remain transparent when stretched. However, interestingly, we note the effects of graft density and backbone length are quite different depending on the rigidity of the backbone.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tough, Rapidly Swelling Thermoplastic Elastomer Hydrogels for Hemorrhage Control

We present a novel elastomer with an amphiphilic triblock/graft architecture, allowing it to rapidly swell in water and form a tough hydrogel. The design was motivated by uncontrolled hemorrhage, responsible for 80–90% of potentially survivable deaths of US soldiers over the past 15 years. The polymer is 5.7 times as absorbent and 3 times as tough as a state of the art gauze-based hemostatic dressing. It swells to equilibrium within seconds in phosphate buffered saline due to a microphase-separated morphology featuring a continuous mobile ionic phase supported by hydrophobic glassy domains and rubbery linkages, as observed by transmission electron microscopy and small-angle neutron scattering. Thickness-dependent swelling is as much as an order of magnitude faster than many tough hydrogels in the literature, yet toughness is comparable as a function of water content. Furthermore, the polymer is combined with gauze to form a rapidly swelling, fiber-reinforced hydrogel composite with promising mechanical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Coal-Filler-Based Thermoplastic Composites as Construction Materials: A New Sustainable End-Use Application

This paper investigates coal’s viability as an alternative filler to wood flour in Wood Plastic Composites (WPCs) – a class of materials used in building applications in lieu of pressure-treated wood. Coal Plastic Composites (CPCs) were fabricat-ed with 15 – 60 wt.% coal combined with high density polyethylene and their physical (mechanical, water absorption and metal leaching) and chemical (oxidative degradation and flammability) properties were compared with commercial WPCs. In addition, mass and energy balances (10 tonne/hr basis) and life cycle analyses (60 wt.% filler and 1 tonne ba-sis) were conducted on CPCs and WPCs to assess environmental impact during manufacturing. At 60 wt.%, CPCs had a higher flexural strength, slower oxidative degradation and burn rate, and lower water absorption in comparison to com-mercial WPCs, suggesting better performance and stability in building applications. Furthermore, CPC manufacturing showed 44% lower greenhouse gas emissions and 62% less energy usage in comparison with WPC. These results indi-cate that direct utilization of coal as a filler in construction composite applications may yield lower cost products with lower associated emissions and energy demand compared to existing WPC materials, potentially yielding a more sustain-able end-use for coal than current uses such as power production.

Coal Plastic Composites, Wood Plastic Composites, ↗