Charles C. Lee

Poly(3‐hydroxybutyrate) (PHB) is a biodegradable polymer that represents a potential replacement for some traditional plastics. The properties of PHB are impacted by many variables including its molecular weight. There are many applications that can be fulfilled by low molecular weight PHB (LMWPHB). We have investigated the use of potassium phosphate (K ₂ HPO ₄ ) as a catalyst for degrading PHB. Potassium phosphate was demonstrated to degrade the polymer in a concentration‐dependent manner. Low concentrations (0.2%) of K ₂ HPO ₄ decreased the thermal stability of the polymer and rapidly reduced the molecular weight. Comparisons to related chemicals (potassium sulfate, potassium chloride, calcium phosphate, and sodium phosphate) demonstrated that the K ₂ HPO ₄ had the greatest effect on thermostability. Low amounts of K ₂ HPO ₄ , but not other salts, led to a decrease in the crystallization temperature and bimodal melting behavior, indicative of the formation of smaller crystallites. This is the first report of the use of K ₂ HPO ₄ to convert PHB into lower molecular weight species.

Our society relies heavily on plastic, but most plastic is petroleum-based and non-biodegradable resulting in major negative environmental impacts. Polyhydroxyalkanoates (PHAs) are a type of biopolymer that can be produced from microorganisms cultured on renewable feedstocks, such as glycerol. PHAs are biodegradable and have properties similar to petroleum-based plastics. Several Priestia megaterium isolates have been demonstrated in previous studies to produce PHA when cultured on glycerol, but there has been no comparison of strains available in public repositories. Such comparison would be useful to identify the most promising strains for further development. In this study, we screened a number of P. megaterium strains from readily accessible repositories for their ability to produce PHA from glycerol. The strains had a wide range of growth and PHA production characteristics on glycerol: cell dry weight (0.5–5.7 g/L), percent PHA (4–42%), PHA titer (0.1–1.9 g/L), and yield (26–303 mg/g). The time course of PHA production varied widely among the different strains. There was also a dramatic difference in molecular weights which ranged from 119 kD to 402 kD. This information will be valuable to groups in selecting a PHA strain to develop based on their specific requirements.

Single-use plastic foams are used extensively as interior packaging to insulate and protect items during shipment but have come under increasing scrutiny due to the volume sent to landfills and their negative impact on the environment. Insulative compression molded cellulose fiber foams could be a viable alternative, but they do not have the mechanical strength of plastic foams. To address this issue, a novel approach was used that combined the insulative properties of cellulose fiber foams, a binder (starch), and three different reinforcing paperboard elements (angular, cylindrical, and grid) to make low-density foam composites with excellent mechanical strength. Compression molded foams and composites had a consistent thickness and a smooth, flat finish. Respirometry tests showed the fiber foams mineralized in the range of 37 to 49% over a 46 d testing period. All of the samples had relatively low density (D_d) and thermal conductivity (TC). The D_d of samples ranged from 33.1 to 64.9 kg/m³, and TC ranged from 0.039 to 0.049 W/mk. The addition of starch to the fiber foam (FF+S) and composites not only increased D_d, drying time (T_d), and TC by an average of 18%, 55%, and 5.5%, respectively, but also dramatically increased the mechanical strength. The FF+S foam and paperboard composites had 240% and 350% higher average flexural strength (σ_fM) and modulus (E_f), respectively, than the FF-S composites. The FF-S grid composite and all the FF+S foam and composite samples had equal or higher σ_fM than EPS foam. Additionally, FF+S foam and paperboard composites had 187% and 354% higher average compression strength (CS) and modulus (E_c), respectively, than the FF-S foam and composites. All the paperboard composites for both FF+S and FF-S samples had comparable or higher CS, but only the FF+S cylinder and grid samples had greater toughness (Ω_c) than EPS foam. Fiber foams and foam composites are compatible with existing paper recycling streams and show promise as a biodegradable, insulative alternative to EPS foam internal packaging.

Many studies have been conducted to produce microbial polyhydroxyalkanoates (PHA), a biopolymer, from Pseudomonas sp. fed with various alkanoic acids. Because this previous data was collected using methodologies that varied in critical aspects, such as culture media and size range of alkanoic acids, it has been difficult to compare the results for a thorough understanding of the relationship between feedstock and PHA production. Therefore, this study utilized consistent culture media with a wide range of alkanoic acids (C7-C14) to produce medium chain length PHAs. Three strains of Pseudomonas putida (NRRL B-14875, KT2440, and GN112) were used, and growth, cell dry weight, PHA titer, monomer distribution, and molecular weights were all examined. It was determined that although all the strains produced similar PHA titers using C7-C9 alkanoic acids, significant differences were observed with the use of longer chain feedstocks. Specifically, KT2440 and its derivative GN112 produced higher PHA titers compared to B-14875 when fed longer chain alkanoates. We also compared several analytical techniques for determining amounts of PHA and found they produced different results. In addition, the use of an internal standard had a higher risk of calculating inaccurate concentrations compared to an external standard. These observations highlight the importance of considering this aspect of analysis when evaluating different studies.

The accumulation of anthropogenic heavy metals in soil is a major form of pollution. Such potentially toxic elements are nonbiodegradable and persist for many years as threats to human and environmental health. Traditional forms of remediation are costly and potentially damaging to the land. An alternative strategy is phytoremediation, where plants are used to capture metals from the environment. Industrial hemp (Cannabis sativa) is a promising candidate for phytoremediation. Hemp has deep roots and is tolerant to the accumulation of different metals. In addition, the crop biomass has many potential commercial uses after harvesting is completed. Furthermore, the recent availability of an annotated genome sequence provides a powerful tool for the bioengineering of C. sativa for better phytoremediation.

Poly‐3‐hydroxybutyrate (PHB) is a widely distributed carbon storage molecule in prokaryotes and can serve as a biodegradable plastic replacement. However, the handling and material properties of virgin PHB are not as robust as some traditional petroleum‐based plastics. Additives can be added to PHB to improve its qualities, but these additives are themselves often not biobased. A strategy was developed to utilize lower molecular weight PHB fragments derived from the recycling process as biobased additives. To simulate recycling, PHB was thermolyzed at elevated temperatures, and this degraded PHB (dPHB) was reactively processed with virgin PHB. Incorporation of dPHB nucleated and plasticized the virgin PHB as evidenced by increased crystallization temperature and crystallinity as well as decreased melt viscosity, stiffness, and melting temperature. Additionally, samples containing dPHB had increased toughness. Processing with dPHB decreased M_n, had little effect on M_w, and increased the Z‐average molecular weight, indicating branching. These results demonstrate a route for nucleating, plasticizing, and toughening virgin PHB by using recycled PHB. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47432.