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1. Compostable, fully biobased foams using PLA and micro cellulose for zero energy buildings

   https://doi.org/10.1038/s41598-020-74478-y  

   Oluwabunmi, Kayode ; D’Souza, Nandika Anne ; Zhao, Weihuan ; Choi, Tae-Youl ; Theyson, Thomas ( October 2020 , Scientific Reports)

   Ecological, health and environmental concerns are driving the need for bio-resourced foams for the building industry. In this paper, we examine foams made from polylactic acid (PLA) and micro cellulose fibrils (MCF). To ensure no volatile organic compounds in the foam, supercritical CO₂(sc-CO₂) physical foaming of melt mixed systems was conducted. Mechanical and thermal conductivity properties were determined and applied to a net zero energy model house. The results showed that MCF had a concentration dependent impact on the foams. First structurally, the presence of MCF led to an initial increase followed by a decrease of open porosity, higher bulk density, lower expansion ratios and cell size. Differential Scanning Calorimetry and Scanning Electron Microscopy revealed that MCF decreased the glass transition of PLA allowing for a decrease in cell wall thickness when MCF was added. The mechanical performance initially increased with MCF and then decreased. This trend was mimicked by thermal insulation which initially improved. Biodegradation tests showed that the presence of cellulose in PLA improved the compostability of the foams. A maximum comparative mineralization of 95% was obtained for the PLA foam with 3 wt.% MCF when expressed as a fractional percentage of the pure cellulose reference. Energymore »simulations run on a model house showed that relative to an insulation of polyurethane, the bio-resourced foams led to no more than a 12% increase in heating and cooling. The energy efficiency of the foams was best at low MCF fractions.

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2. Multi-Fold Enhancement in Compressive Properties of Polystyrene Foam Using Pre-delaminated Stearate Functionalized Layer Double Hydroxides

   https://doi.org/10.3390/polym12010008  

   Ogunsona, E. ; Dagonon, K. ; D'Souza, N. A ( December 2019 , Polymers)

   Developing an environmentally benign styrene foam is a critical environmental need. Supercritical CO2 use in foams has proven to be a valuable path. Adding fillers to increase bubble nucleation has been pursued concurrently. A prominent filler used is high surface area fillers, such as smectic clays. However, all studies to date show a limit of 152% in compressive moduli and 260% in the compressive stress. The values, even with such gains, limit structural application. A seminal work in 1987 by Suh and Cotton proved that carbonyl linkages in calcium carbonates and CO2 interact and impact nucleation efficiency and performance in supercritical CO2 foams. In this paper, a high surface area clay (layer double hydroxides) which begins in an exfoliated state, then functionalized with a long chain alkyl carboxylate (stearic acid) is synthesized. The result is a remarkable multi-fold improvement to the compressive properties in comparison to polystyrene (PS); a 268% and 512% increase in compressive modulus and strength, respectively. Using a pre-delaminated approach, the higher surface area was achieved in the clays. The presence of the stearate improved the interactions between the clay galleries and PS through hydrophobic-hydrophobic interactions. The glass transition temperature of the nanocomposites was observed to shiftmore »to higher values after foaming. The results point to a new path to increase performance using a pre-delaminated clay with functional groups for environmentally benign foams« less
3. Polyelectrolyte Complex Stabilized CO2 Foam Systems for Hydraulic Fracturing Application

   https://doi.org/10.2118/187489-MS  

   Anandan, Rudhra ; Johnson, Stephen ; Barati, Reza ( September 2017 , SPE Liquids-Rich Basins Conference- North America)

   Hydraulic fracturing of oil and gas wells is a water intensive process. Limited availability, cost and increasing government regulations restraining the use and disposal of fresh water have led to the need for alternative fracturing fluids. Using CO2 foam as a fracturing fluid can drastically reduce the need for water in hydraulic fracturing. We address the addition of polyelectrolyte complex nanoparticles (PECNP) to surfactant solutions to improve foam stability, durability and rheological properties at high foam qualities. Polyelectrolyte pH and polyanion/polycation ratios were varied to minimize particle size and maximize absolute zeta potential of the resulting nanoparticles. Rheological tests were conducted on foam systems of varying surfactant/PECNP ratios and different foam quality to understand the effect of shear on viscosity under simulated reservoir conditions of 40°C and 1300 psi. The same foam systems were tested for stability and durability in a view cell at reservoir conditions. Supercritical CO2 foam generated by surfactant alone resulted in short lived, low viscosity foam because of surfactant drainage from foam lamellae. However, addition of PECNP strengthens the foam film by swelling the film due to increased osmotic pressure and electrostatic forces. Electrostatic interactions reduce dynamic movement of surfactant micelles, thereby stabilizing the foammore »lamellae, which imparts high durability and viscosity to supercritical CO2 foams. From the rheology test results, it was concluded that increasing foam quality and the presence of PECNP resulted in improved viscosity. Also, foam systems with PECNP showed promising results compared with foam generated using surfactant alone in the view cell durability test. The addition of optimized polyelectrolyte nanoparticles to the surfactant can improve viscosity and durability of supercritical CO2 foam during hydraulic fracturing, which can lead to large reductions in water requirements.

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4. Bioinspired cellular sheath-core electrospun non-woven mesh

   https://doi.org/10.1007/s42247-019-00043-7  

   Rizvi, H.R. ; D’Souza, N. ; Ayre, B. ; Ramesh, D. ( January 2019 , Emergent materials)

   Fibers are valuable to biomedical applications. Used as sutures or meshes, there is an increased dual need to provide functionality such as drug delivery. Porosity represents a high surface area to volume architecture. Coaxial fibers with porous and non-porous layers offer a new design framework for fiber design that can resolve dual needs of mechanical robustness with transport phenomena. Using preferential solubility of a polymer in supercritical CO2, we develop a new architecture using biocompatible polymers based on porous core-sheath fiber fabrication technique. Polycaprolactone was selected as the CO2 miscible phase and Poly(butyrate adipate terephthalate)(PBAT) as the immiscible phase. The mechanical performance of the fibers was investigated using quasi static and dynamic loading. SEM images indicate no physical detachment of the two polymer surface after CO2 exposure indicating a successful amalgamation of polymers at the boundary of core and sheath. PCL as a sheath and as a core showed an increase of 650% and 468% in tensile strength compared to pristine PCL and PBAT. Introduction of porosity on the surface of coaxial fiber fPCL(cPBAT) further enhanced the yield strength increases by 40%. Dynamic mechanical analysis was used to analyze the viscoelastic properties of the fibers. The storage and loss modulusmore »for coaxial fibers shows superior modulus throughout the glassy, glass transition and rubbery region as compared to the pristine PCL and PBAT, showing enhancement in both the elastic and viscous response of the material. The results indicate a new approach that is free of volatile organic solvents to manipulate the architecture of the cross-section of the electrospun fiber and tailor mechanical properties to the required application.« less
5. Partially-Perforated Self-Reinforced Polyurea Foams

   https://doi.org/10.3390/app10175869  

   Do, Sophia ; Huynh, Nha Uyen ; Reed, Nathan ; Mohammad Shaik, Atif ; Nacy, Somer ; Youssef, George ( September 2020 , Applied Sciences)

   This paper reports the unique microstructure of polyurea foams that combines the advantages of open and closed cell polymeric foams, which were synthesized through a self-foaming process. The latter was the result of aggressive mechanical mixing of diamine curative, isocyanate, and deionized water at ambient conditions, which can be adjusted on-demand to produce variable density polyurea foam. The spherical, semi-closed microcellular structure has large perforations on the cell surface resulting from the concurrent expansion of neighboring cells and small holes at the bottom surface of the cells. This resulted in a partially perforated microcellular structure of polyurea foam. As a byproduct of the manufacturing process, polyurea microspheres nucleate and deposit on the inner cell walls of the foam, acting as a reinforcement. Since cell walls and the microspheres are made of polyurea, the resulting reinforcement effect overcomes the fundamental interfacial issue of different adjacent materials. The partially perforated, self-reinforced polyurea foam is compared to the performance of traditional counterparts in biomechanical impact scenarios. An analytical model was developed to explicate the stiffening effect associated with the reinforcing microspheres. The model results indicate that the reinforced microcell exhibited, on average, ~30% higher stiffness than its barren counterpart.