Wil V. Srubar

Evaporation-based method for preparing gelatin foams with aligned tubular pore structures.

Gelatin-based foams with aligned tubular pore structures were prepared via liquid-to-gas vaporization of tightly bound water in dehydrated gelatin hydrogels. This study elucidates the mechanism of the foaming process by investigating the secondary (i.e., helical) structure, molecular interactions, and water content of gelatin films before and after foaming using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. Experimental data from gelatin samples prepared at various gelatin-to-water concentrations (5-30 wt.%) substantiate that resulting foam structures are similar in pore diameter (approximately 350 μm), shape, and density (0.05-0.22 g/cm(3)) to those fabricated using conventional methods (e.g., freeze-drying). Helical structures were identified in the films but were not evident in the foamed samples after vaporization (~150 °C), suggesting that the primary foaming mechanism is governed by the vaporization of water that is tightly bound in secondary structures (i.e., helices, β-turns, β-sheets) that are present in dehydrated gelatin films. FTIR and TGA data show that the foaming process leads to more disorder and reduced hydrogen bonding to hydroxyl groups in gelatin and that no thermal degradation of gelatin occurs before or after foaming.

The Future of LCAs and EPDs: Incorporating Service-Life in the Environmental Impact Assessments of Green Building Materials

Recent efforts in the development of innovative, “green” building materials and components have primarily focused on reducing the initial embodied energy and carbon of conventional materials (e.g., concrete, plastics). While these efforts are often commended and advocated by sustainable material certification programs and green building rating schema, recent research has shown that reducing the cradle-togate impacts of building materials may actually compromise their long-term durability, effectively reducing their ultimate in-service lifetime. This paper highlights research progress on the implementation of a next-generation sustainable materials evaluation framework that reconciles initial reductions in environmental impact (e.g., embodied energy, embodied carbon) and the effects on service life through integrated service-life/lifecycle assessment models for innovative materials. Using “green” concrete as a case-study example, this paper demonstrates that the “sustainability” of a material is spatiotemporally dependent and that end-of-life (functional obsolescence) is an important metric that must be considered in evaluating sustainable material alternatives.

Embodied Carbon of Wood and Reinforced Concrete Structures Under Chronic and Acute Hazards

Quantifying the total life cycle embodied carbon of wood and reinforced concrete structures necessitates calculation of use-phase impacts, including expected in-service damage and replacement due to chronic and acute environmental hazards. Such prediction is difficult and often omitted in whole-building life cycle assessment (WBLCA).

On-Demand Microwave-Assisted Fabrication of Gelatin Foams

Ultraporous gelatin foams (porosity >94%, ρ ≈ 0.039–0.056 g/cm3) have been fabricated via microwave radiation. The resulting foam structures are unique with regard to pore morphology (i.e., closed-cell) and exhibit 100% macroporosity (pore size 332 to 1700 μm), presence of an external skin, and densities similar to aerogels. Results indicate that the primary foaming mechanism is governed by the vaporization of water that is tightly bound in secondary structures (i.e., helices, β-turns, β-sheets) that are present in dehydrated gelatin films but not present in the foams after microwave radiation (700 Watts).

Nanoscale hygromechanical behavior of lignin

The nanoscale hygromechanical behavior of lignin is presented in this work. Three atomic force microscopy experimental methods were used to correlate moisture sorption of lignin to its mechanical behavior. First, sorption isotherms were established using cantilever mass sensing and subsequently predicted using the Guggenheim–Anderson–de Boer model. The sorption isotherms of lignin particles followed a repeatable and cyclic trend reaching a maximum moisture content of ≈ 17% at ≈ 79% relative humidity (RH). Second, 3D nanomechanical contrast images were obtained using contact resonance force microscopy (CR-FM) to observe the hygromechanical response of lignin over three RH cycles. Finally, force volume mapping and the Hertz model were used to compute the elastic modulus of lignin as a function of moisture content. As RH increased, CR-FM measurements revealed initial topographical heterogeneity, as well as notable surface softening, especially in initially smooth domains. The average elastic modulus of the smooth domain decreased from 9.0 to 4.3 to 2.4 GPa as the moisture content increased from 0.024 to 9.1 to 17.3%, respectively. Cyclic measurements confirm that the elastic modulus of lignin rebounds upon moisture desorption.

Biobased FRPs for Retrofit and Rehabilitation of Civil Infrastructure

Applications of glass- and carbon-fiber reinforced polymers (FRPs) in construction have increased in recent years due to the deterioration of civil infrastructure and the numerous advantages of FRPs. Many advantages of conventional polymers and FRPs, however, are also disadvantages, especially when considering their environmental impact. The low cost of many polymers is an artifact of their inexpensive petrochemical feedstock, and their strength and chemical recalcitrance make them very difficult to degrade after their service life. This work concerns the development and characterization of sustainable, low-carbon alternatives to traditional FRP materials. Epoxy-like resins derived from animal proteins are combined with natural fibers to produce fully biobased FRP composites. Preliminary results demonstrate that these biobased FRPs exhibit similar mechanical properties to traditional FRPs. In this paper, the advantages and disadvantages of using natural FRPs in structural applications are discussed, along with the development of predictive models to facilitate novel materials design.

Engineered Biobased Composites for Construction: Material Development, Multiscale Modeling, and Long-Term Durability

Fully biodegradable composite materials fabricated using natural fiber reinforcements and biopolymeric matrices derived from poly(β-hydroxybutyrate) (PHB) and PHBco-poly(β-hydroxyvalerate) (PHBV), are being investigated as potential alternatives to traditional residential construction materials. The materials are envisioned to be rapidly renewable by using biogas from their anaerobic biodegradation as the feedstock for microbial production of the biopolymer and using plant-based materials for composite reinforcement and fillers. These biobased composites are being engineered to satisfy acceptable stiffness, strength, ductility, and in-service durability performance criteria while maintaining the propensity for rapid out-of-service anaerobic biodegradation. In this paper a brief overview of research on material development, mechanical properties, and multiscale modeling, as well as moisture absorption and long-term durability of PHBV-wood fiber filled composites with and without fiber treatments is given. This research is an interdisciplinary collaboration between structural, environmental, and chemical engineers.

NONLINEAR MICROMECHANICAL MODELING OF HYGROTHERMAL EFFECTS ON STRUCTURAL BIOBASED COMPOSITE MATERIALS

Biobased composite materials fabricated from bacterial poly(β-hydroxybutyrate)-co-poly(β-hydroxyvalerate) (PHBV) resins reinforced with natural oak wood flour are being investigated as viable replacements to traditional, ecologically insensitive construction materials. The material properties achievable by these composites, which biodegrade anaerobically under specific conditions, are comparable to that of dimensional lumber; however, natural fiber composites remain particularly susceptible to hygrothermal degradation of the fiber–matrix interface because of the incongruent hydrophobicity of the biopolymer and the hydrophilicity of the cellulosic fibers.