Bruce A. Ramsay

High performance LDPE/thermoplastic starch blends: a sustainable alternative to pure polyethylene

Abstract Thermoplastic starch (TPS), as opposed to dry starch, is capable of flow and hence when mixed with other synthetic polymers can behave in a manner similar to conventional polymer–polymer blends. This paper presents an approach to preparing polyethylene/thermoplastic starch blends with unique properties. A one-step combined twin-screw/single screw extrusion setup is used to carry out the melt–melt mixing of the components. Glycerol is used as the starch plasticizer and its content in the TPS is varied from 29 to 40%. Under the particular one-step processing conditions used it is possible to develop continuous TPS (highly interconnected) and co-continuous polymer/TPS blend extruded ribbon which possess a high elongation at break, modulus and strength in the machine direction. The PE/TPS (55:45) blend prepared with TPS containing 36% glycerol maintains 94% of the elongation at break and 76% of the modulus of polyethylene. At a composition level of 71:29 PE/TPS for the same glycerol content, the blend retains 96% of the elongation at break and 100% of the modulus of polyethylene. These excellent properties are achieved in the absence of any interfacial modifier and despite the high levels of immiscibility in the polar–nonpolar TPS–PE system. The 55:45 blend possesses a 100% continuous or fully interconnected TPS morphology, as measured by hydrolytic extraction. This highly continuous TPS configuration within the blend should enhance its potential for environmental biodegradation. The elongation at break in the cross direction of these materials, although lower than the machine direction properties, also demonstrates ductility at high TPS concentrations. At a glycerol content of 36% in the TPS, the blends demonstrate only very low levels of sensitivity to moisture. A high degree of transparency is maintained over the entire concentration range due to the similar refractive indices of PE and TPS and the virtual absence of interfacial microvoiding. Effective control of the glycerol content, TPS concentration and processing conditions can result in a wide variety of morphological structures including spherical, fiber-like, highly continuous and co-continuous morphologies. These various blend morphologies are shown to be the determining parameters with respect to the observed mechanical properties. This material has the added benefit of containing large quantities of a renewable resource and hence represents a more sustainable alternative to pure synthetic polymers.

PHB recovery by hypochlorite digestion of non-PHB biomass

Hypochlorite digestion of bacterial biomass from intracellular poly-β-hydroxybutyrate (PHB) has not been used on a large scale since it has been reported to severely degrade PHB. In this study, to minimize degradation, the initial biomass concentration, digestion time and pH of the hypochlorite solution were optimized. Consequently, PHB of 95% purity with a weight average molecular weight (MW) of 600,000 and a polydispersity index (PI) of 4.5 was recovered from biomass initially containing PHB with a MW of 1,200,000 and a PI of 3.

Polymer blends containing poly(3-hydroxyalkanoate)s

Abstract The remarkable properties of poly(3-hydroxyalkanoate)s (PHAs) have resulted in a growing interest in these polymers. They offer a wide variety of useful mechanical properties and show excellent biodegradability. However, they are still expensive and poly(3-hydroxybutyrate) (PHB) in particular is quite brittle. Polymer blending offers interesting possibilities to prepare less expensive biodegradable materials with useful mechanical properties. In this review the literature concerning PHA-containing blends has been summarized. Blends incorporating either PHB or copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (P(HB-HV)) were discussed. The thermal and crystallization behaviour of the blends, their mechanical properties, morphology and biodegradability have been reviewed. Among the conclusions drawn from the literature, it is evident that PHAs can form miscible blends with polymers containing the appropriate functional groups via hydrogen bonding and/or donor-acceptor interactions. The crystallization behaviour of the PHAs is influenced by both the miscible and immiscible components. Immiscible PHA-containing blends show improved apparent biodegradability when compared to miscible blends. Their apparent biodegradability (weight loss) is mostly controlled by the blend morphology. Blends of PHA with other biodegradable polymers also usually show improved biodegradability when compared with pure PHAs.

Processing and characterization of thermoplastic starch/polyethylene blends

Abstract The behaviour of gelatinized starch plasticized with glycerol (also known as thermoplastic starch (TS)) is studied as the dispersed component in a polyethylene (LDPE or LLDPE) matrix. A processing technique was developed to compound the blends in one continuous process in a co-rotating twin-screw extruder fed by a single-screw extruder. The use of the single-screw as a side feeder allowed for gelatinization of the starch before feeding it into the twin-screw at controlled temperature and pressure. The screw configuration of the twin-screw extruder maintained high pressure (⩾0.9 MPa) during blending to prevent early evaporation of water. These materials displayed morphological characteristics typical of immiscible polymer-polymer blends. The number-average diameter of the dispersed phase increased from 4 μm with 8 wt% TS to 18 μm with 36 wt% TS in LDPE blends. It ranged from 3 to 8 μm in LLDPE blends containing 7 to 39 wt% TS. These results therefore indicate the possibility of achieving a level of morphological control with respect to the size and shape of the dispersed phase in these systems. Dry granular starch, on the other hand, typically is dispersed as a spherical like particle with a fixed morphology of approximately 10 μm. The blends in this study, at high TS loadings, demonstrate high elongational properties at break even without addition of an interfacial modifier. The LDPE blend containing 22% TS had 240% elongation at break and its modulus was 109 MPa. The LLDPE blend containing 39% TS had more than 540% elongation at break, while the modulus was 136 MPa.

Extraction of poly-3-hydroxybutyrate using chlorinated solvents

Recovery of poly-3-hydroxybutyrate (PHB) in three chlorinated solvents with or without acetone pretreatment and degradation of extracted PHB (99% pure) in hot chloroform were studied. When lyophilized Alcaligenes eutrophus biomass was used, the best results were obtained with acetone pretreatment and solvent reflux for 15 min in methylene chloride or chloroform. Recovered PHB had a 95% purity and molecular weights (Mw) of 1,050,000 and 930,000 g/mol respectively. Further heating resulted in a serious Mw, loss at reflux temperatures. Degradation of extracted PHB at 110°C in chloroform was due to random and chain-end scission, the former being predominant.

Recovery of poly-3-hydroxyalkanoic acid granules by a surfactant-hypochlorite treatment

When Alcaligenes eutrophus biomass was treated with a surfactant and then washed with hypochlorite, the recovered poly-3-hydroxyalkanoic acid (PHA) granules were 97 to 98% pure with a molecular weight (MW) between 730,000 and 790,000, depending on the surfactant used. When treated with only surfactant, the MW was slightly higher than that obtained with the surfactant-hypochlorite treatment but the purity was 10% lower. PHA of higher purity but lower MW was obtained with just a hypochlorite treatment.

Identification of the key factors affecting composting of a weathered hydrocarbon-contaminated soil

The effects of the C/N ratio, CaCO3 and PO4 addition, and temperature profile on reactor-based composting of weathered hydrocarbon-contaminated soil were evaluated in a series of 30-day tests in temperature-controlled mini-composters. Soil containing 17,000 mg (kg dry soil)−1 mineral oil and grease (MOG) was composted with maple leaves and alfalfa. Although the leaves and alfalfa also contained MOG, degradation of contaminated soil derived MOG (total MOG degradation minus MOG degradation in a control with no soil) increased from 0 to 45% as the quantity of co-substrate increased from 0 to 63%. Simulation of biopile conditions (i.e., aeration and addition of mineral salts but no co-substrate) resulted in only 6% MOG degradation. Addition of CaCO3 before composting increased total MOG degradation from 23% to 43%. Total MOG degradation increased with decreasing C/N ratio. At a molar C/N ratio of 17, 43% of the total MOG was degraded in 30 days, while at a C/N ratio of 40 there was no total MOG degradation. When temperatures ranging from 23 to 60 °C were investigated, 50 °C maintained for 29 days resulted in the maximum degradation which was 68% of total initial MOG.

Active compost biofiltration of toluene

Composting of leaves and alfalfa (i.e. active compost) was used for thebiofiltration of toluene-contaminated air in a 6-L biofilter (initial bedheight: 180 mm). During the thermophilic phase (45 to 55 °C), toluenebiodegradation rates reached 110 gtoluene.m-3.h-1 at an inlet concentration ofabout 5 g.m-3.h-1 and a gas residence time of 90 seconds. Thehighest rates were obtained late in the thermophilic phase suggesting amicrobial adaptation was occurring. Biodegradation rates decreased rapidly(50% in 48h) in the cooling stage. Under mesophilic conditions, themaximum biodegradation rates that could be obtained by increasing the inlettoluene concentration were near 89 gtoluene.m-3.h-1 which issimilar to that reported in the literature for mature compost biofilters. Novolatile by-product was detected by gas chromatography. Mineralization of14C-toluene and benzene showed that they were completelydegraded into CO2 and H2O under boththermophilic and mesophilic conditions. Bacteria isolated from latemesophilic stage had the capacity to degrade all BTEX compounds but were notable to transform chlorinated compounds. No organisms were isolated whichcould use toluene as their sole source of carbon and energy at 50 °C.Active compost biofiltration should be an excellent process for thetreatment of gaseous BTEX by biofiltration. This is the first report ofthermophilic biofiltration of toluene.

A method for the isolation of microorganisms producing extracellular long-side-chain poly (β-hydroxyalkanoate) depolymerase

A simple method was developed for the preparation of an autoclavable, long-side-chain poly (β-hydroxyalkanoate) (LSC-PHA) colloidal suspension, which was used as a substrate for enzymatic degradation and to prepare agar overlay plates for the isolation of microorganisms producing extracellular LSC-PHA depolymerase. Six cultures producing extracellular LSC-PHA depolymerase were isolated from a composted hydrocarbon-contaminated soil. All were pseudomonads or related bacteria. All (with the possible exception ofXanthomonas maltophilia) could produce LSC PHA. Except forX. maltophilia none could hydrolyze poly (β-hydroxybutyrate). Screening of sevenPseudomonas strains known to accumulate LSC PHA showed that all were negative for extracellular LSC-PHA depolymerase production. It was concluded that extracellular LSC-PHA depolymerase producers are found mostly in the genusPseudomonas but that they are relatively uncommon.

Biological conversion of hemicellulose to propionic acid

Abstract A mixture of endo- and exoxylanases were used to produce a hemicellulose hydrolysate containing 29.6 g L −1 of xylose equivalents based on reducing sugars analysis. Propionibacterium acidipropionici was grown in a 2-l batch reactor in mineral salts medium containing 60% (v/v) hemicellulose hydrolysate, 5 g l −1 proteose peptone, and 2.5 g l −1 yeast extract. Propionic acid production was growth associated. The maximum specific growth rate and maximum specific propionic acid production rate were 0.1 and 0.23 g g −1 h −1 , respectively. Growth and acid production were inhibited at propionic acid concentrations greater than 2 g l −1 . The final concentration of propionic acid attained was 18 g l −1 . This study demonstrates the feasibility of propionic acid production by P. acidipropionici on an enzymatically hydrolyzed, hemicellulosic fraction of steam-exploded Populus tremuloides .