Ahmad & Gramlich publication on refining energy use in CNF production
An article by ASCC researchers Dr. Ahmad A. L. Ahmad and Dr. William Gramlich was published in Celluloseon March 4, 2024. This paper shares methodology on pre-treatment to pulp in cellulose nanofibril (CNF) production. The goal of this research is to understand the correlation between the pre-treatment and reduced energy consumption in the CNF production process.
Abstract
Pretreatment of pulp is a critical step in the fibrillation process to improve the quality and efficiency for cellulose nanofibril (CNF) production. This work employed a straightforward and entirely aqueous methacrylation and subsequent grafting-through polymerization technique to modify bleached softwood kraft pulp (BSKP). Specifically, methacrylate groups, poly(acrylamide) (PAM), and poly(methyl methacrylate) (PMMA) were chemically affixed to the surface of BSKP fibers, which was confirmed using FTIR spectroscopy. Bench-scale experiments were scaled up to pilot scale to prepare the modified BSKP samples, these were subjected to fibrillation using a Supermasscolloider (SMC), and the net cumulative energy (NCE) expended was monitored during the fibrillation process. Notably, the modified BSKP samples exhibited a substantial reduction in NCE, with the methacrylate modified BSKP sample achieving a 68% reduction in NCE expenditure to attain 90% fines as compared to the fibrillation of unmodified BSKP and producing methacrylate modified cellulose nanofibrils (Met-CNFs). Furthermore, we delved into the impact of polymeric surface modifications, both pre-and post-fibrillation, on fiber and fibril behavior, including the water retention value (WRV), hard-to-remove water (HR-Water), and rheological behavior. The attached polymer’s hydrophilicity and hydrophobicity influenced the physical properties of the CNFs. Additionally, we executed a post-grafting polymerization process on the produced Met-CNFs. This additional step allowed us to modify nanofibril surfaces, yielding increased surface functionalization and producing modified CNFs that could be used for composite applications.
ASCC-TIDC research on weight distribution in bridges with FRP composite tub girders
A publication by ASCC Graduate Research Assistant Jon Pinkham, Dr. William G. Davids, and Dr. Andrew Schanck was published in the Journal of Bridge Engineering on March 13, 2024. This article shares assessment of live load distribution analysis for fiber-reinforced polymer (FRP) composite tub girders used in highway bridges. The goal of this research is to further understand how much weight each part of a bridge using FRP composite tub girders can support.
Abstract
In the design of conventional steel and concrete highway girder bridges, the amount of live load carried by a single girder is quantified through distribution factors (DFs). However, moment DFs for the recently developed fiber-reinforced polymer (FRP) composite tub (CT) girders are not defined in current design codes, leaving questions as to these bridges’ live load distribution. To address this, two diagnostic live load tests were performed on an in-service CT girder bridge under heavy truck loads. The measured strains from each test were analyzed and compared with predictions from a calibrated, high-fidelity finite-element (FE) model, which was shown to accurately predict the live load distribution. Then, a simplified FE model was developed that was also shown to accurately predict the live load distribution at a significant computational discount. The simplified model was subsequently used in a parametric study to assess current CT girder design practices, which were found to be consistently conservative. One conclusion was that unintended end restraint of the girder significantly impacted the maximum measured flexural strains, and the high-fidelity FE model required modification and calibration to capture this effect. However, simplified FE models that were not calibrated to the field data were shown to reasonably accurately predict the live load distribution to the most heavily loaded, interior girders. Ultimately, the results of this study show that live load moment DFs should be developed that are specific to the CT girder to ensure efficient future designs with this new technology.
This research investigates the durability of large-format 3D-printed thermoplastic composite material systems under environmental exposure conditions of moisture and freeze–thaw. Durability was evaluated for two bio-based composite material systems, namely wood-fiber-reinforced semi-crystalline polylactic acid (WF/PLA) and wood-fiber-reinforced amorphous polylactic acid (WF/aPLA), and one conventionally used synthetic material system, namely short-carbon-fiber-reinforced acrylonitrile butadiene styrene (CF/ABS). The moisture absorption, coefficient of moisture expansion, and reduction of relevant mechanical properties—flexural strength and flexural modulus—after accelerated exposure were experimentally characterized. The results showed that the large-format 3D-printed parts made from bio-based thermoplastic polymer composites, compared to conventional polymer composites, were more susceptible to moisture and freeze–thaw exposure, with higher moisture absorption and greater reductions in mechanical properties.
Advanced Structures & Composites Center