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Kelly, Peter V.

Publications and source records attributed to Kelly, Peter V..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

High-strength 3D printed poly(lactic acid) composites reinforced by shear-aligned polymer-grafted cellulose nanofibrils

This work demonstrates the application of pilot-scale surface functionalization of cellulose nanofibrils (CNFs) by aqueous grafting-through polymerization and subsequent spray drying in 3D printed poly(lactic acid) (PLA) composites. Grafted-CNF composites attain an ultimate tensile strength of 88 ± 3 MPa and a tensile modulus of elasticity of 7.8 ± 1.3 GPa in the printing direction at 20 wt% reinforcement loading. These increases, 42% and 139% over neat PLA, respectively, represent the strongest reported 3D printed CNF/PLA composite to date in the literature. The mechanisms behind these improvements are investigated by comparisons to neat PLA and unmodified spray-dried CNF/PLA controls using melt rheology, dynamic mechanical analysis, and assessment of the reinforcement dispersion. These experiments reveal that improved network formation and shear-induced alignment of the grafted CNFs facilitate the remarkable tensile properties of the printed composites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Polymer-Grafted Cellulose Nanofibrils with Enhanced Interfacial Compatibility for Stronger Poly(lactic acid) Composites

Cellulose nanofibrils (CNFs) are a promising reinforcement for biodegradable composite matrices such as poly(lactic acid) (PLA), but they require commercially scalable drying methods that preserve their fibrillar morphology along with improved interfacial interactions with polymer matrices. In this work, a water-based grafting-through polymerization scheme to modify CNFs improved spray drying behavior and reinforcement capacity in PLA composites. All polymer modifications yielded CNFs with a more fibrillar morphology after spray drying, increasing specific surface area by up to 490% compared to unmodified CNFs, values similar to conventional freeze drying. Polymer-grafted CNFs in PLA composites improved the tensile strength by 16% at 20 wt % loading and stiffness by 22% at a 10 wt % loading with two different graft-polymer chemistries compared to unmodified CNF composites. Surface energy heterogeneity measurements of the reinforcements and PLA matrix were employed to understand the improvements in composite properties. Polymer modifications lowered the total surface energy of the CNFs, and calculated ratios of work of adhesion to work of cohesion suggested improved interfacial compatibility for four of the modified CNFs with PLA. Rheological oscillatory shear studies of the composites correlated solid-like melt behavior, as demonstrated by storage moduli dominance, with higher tensile strength. Thermal analysis of the composites revealed that excessive plasticization by the poly(oligoethylene glycol methyl ether methacrylate)-grafted sample potentially offset mechanical property improvements imparted by the more fibrillar morphology. This work provides an opportunity for large-scale manufacturing of CNF/PLA composites via an entirely aqueous modification scheme and industrially relevant spray drying process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multifunctional polymer composite coatings and adhesives by incorporating cellulose nanomaterials

Regardless of their applications, polymers are still considered mechanically weak and functionally insufficient for certain demanding coating and adhesive uses. To address those issues, nanomaterials have been extensively studied as reinforcing fillers, which have been proven to effectively promote the performance of polymer coatings/adhesives. However, conventional nanofillers are expensive and non-biodegradable. Meanwhile, cellulose nanomaterials (CNMs), a class of nanomaterials produced from biomass feedstocks, can circumvent the drawbacks of conventional nanofillers. Here, this review paper first focuses on the multi-functionalities CNMs bring to polymer coatings, including mechanical reinforcement (wear resistance and hardness enhancement), gas barrier, flame resistance, corrosion resistance, self-healing (controlled-release), optical regulation, self-cleaning/antifouling, and antimicrobial characteristics. Then we discuss the benefits of CNM addition to polymer adhesives, such as mechanical enhancement, curing promotion, volatile organic compound (VOC) suppression, and electrical conductivity. Finally, we provide insights into future research efforts with CNMs. The goal of this paper is to promote the pilot-scale study and commercial use of CNMs as multifunctional additives in green and sustainable polymer composite coating and adhesive formulations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Aqueous-Based Polyimine Functionalization of Cellulose Nanofibrils for Effective Drying and Polymer Composite Reinforcement

Here a simple strategy was developed to synthesize polyimine-coated cellulose nanofibrils (CNF) for effective CNF drying and composite reinforcement. The polyimine was synthesized in an aqueous medium using a selective hydrophilic and hydrophobic component that forces the polyimine to precipitate, which prevents the reverse imine reaction. The polyimine coating allowed the CNF to be easily oven-dried while maintaining a fibrillar morphology to provide mechanical reinforcement in poly(ethylene terephthalate glycol) (PETG) composites. In comparison, poor mechanical performance and a heterogeneous fracture surface were observed when the coated CNF were incorporated into poly(l-lactide) (PLA) composites. It is hypothesized that intermolecular aromatic–aromatic interactions are formed at the interface between fibers and the polymer matrix in the PETG system, while no such phenomena occur in the PLA system. Overall, this facile strategy to produce modified, easily dried CNF can be adapted to produce polyimine-coated CNF with unique functionalities that are useful in a range of applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Aqueous Polymer Modification of Cellulose Nanofibrils by Grafting‐Through a Reactive Methacrylate Group

Abstract Modifying the surface of cellulose nanofibrils (CNFs) produced by mechanical refinement with a variety of polymer functional groups in an entirely water‐based system is challenging because only surface hydroxyl groups are accessible. To address this limitation, an entirely water‐based, polymer modification scheme is developed. CNFs are functionalized with a reactive methacrylate functional group followed by subsequent grafting‐through polymerization. This modification worked with a variety of water‐soluble and water‐insoluble (meth)acrylates and (meth)acrylamides, grafting up to 45 wt% polymer on to the CNFs. The reaction conditions introducing the methacrylate functional group are adjusted to vary the degree of functionality. Soxhlet extraction of modified samples demonstrates that the reactive methacrylate group is necessary to facilitate polymer grafting. The degree of functionalization of the polymers is studied via quantitative transmission IR spectroscopy and the morphology of the resulting cellulose nanofibrils is studied via a combination of optical, scanning electron, and atomic force microscopy. High levels of polymer modification do not significantly affect the micrometer‐scale fibril morphology.

Kelly, Peter V.↗