Glass Transition Temperature Measurements Research Articles

Tuning salicylate‐based polymers to overcome lag time and extend release via copolymers and polymer blends

ABSTRACTThis work describes how physicochemical properties of salicylate‐based poly(anhydride‐esters) (PAEs) can be tuned for drug delivery and optimized by comparing copolymerization with polymer blending. These alterations reduced the lag time of drug release, while still maintaining a long‐term drug release profile. The chemical composition of the copolymers and polymer blends was determined by proton nuclear magnetic resonance and additional properties such as molecular weight, glass transition temperature and contact angle measurements were obtained. In vitro salicylic acid release from the copolymers and blends is studied in an environment mimicking physiological conditions. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 685–689

Investigation and correlation of drug polymer miscibility and molecular interactions by various approaches for the preparation of amorphous solid dispersions

Curcumin (CUR) was used as a poorly soluble drug whereas polyvinyl pyrrolidone K90 (PVP), Eudragit EPO (EPO), hydroxypropyl methylcellulose E5 (HPMC) and polyethylene glycol 8000 (PEG) were used as hydrophilic polymers. CUR polymer miscibility was evaluated by solubility parameter, melting point depression and glass transition temperature (Tg) measurements. Molecular interactions between CUR and polymers were determined by Fourier-transform infrared spectroscopy (FTIR) and Raman. Amorphous solid dispersions were prepared with CUR–polymer ratio of 70:30 (w/w) by solvent evaporation technique and were evaluated for dissolution enhancement using USP II method. Physical states of solid dispersions were characterized by X-ray diffraction (XRD) whereas thermal behaviors were investigated using modulated differential scanning calorimetry (MDSC). CUR–EPO system showed good miscibility through all the approaches, whereas immiscibility was found in other CUR–polymer systems. CUR–EPO and CUR–HPMC systems showed significant molecular interactions whereas CUR–PVP and CUR–PEG showed no molecular interactions. All solid dispersions showed significant dissolution enhancement with CUR–EPO showing highest dissolution rate during first 1h whereas CUR–HPMC was effective in maintaining high CUR concentrations for 6h. The study highlights the importance of investigating and correlating drug polymer miscibility and molecular interactions by various approaches for successful formulation of amorphous solid dispersions.

Sorbitol Crystallization-Induced Aggregation in Frozen mAb Formulations

Sorbitol crystallization-induced aggregation of mAbs in the frozen state was evaluated. The effect of protein aggregation resulting from sorbitol crystallization was measured as a function of formulation variables such as protein concentration and pH. Long-term studies were performed on both IgG1 and IgG2 mAbs over the protein concentration range of 0.1-120 mg/mL. Protein aggregation was measured by size-exclusion HPLC (SE-HPLC) and further characterized by capillary-electrophoresis SDS. Sorbitol crystallization was monitored and characterized by subambient differential scanning calorimetry and X-ray diffraction. Aggregation due to sorbitol crystallization is inversely proportional to both protein concentration and formulation pH. At high protein concentrations, sorbitol crystallization was suppressed, and minimal aggregation by SE-HPLC resulted, presumably because of self-stabilization of the mAbs. The glass transition temperature (Tg ') and fragility index measurements were made to assess the influence of molecular mobility on the crystallization of sorbitol. Tg ' increased with increasing protein concentration for both mAbs. The fragility index decreased with increasing protein concentration, suggesting that it is increasingly difficult for sorbitol to crystallize at high protein concentrations.

Density relaxation and particle motion characteristics in a non-ionic deep eutectic solvent (acetamide + urea): Time-resolved fluorescence measurements and all-atom molecular dynamics simulations

Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH3CONH2) and urea (NH2CONH2) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH3CONH2 + (1 - f)NH2CONH2] have been studied in a temperature range of 328-353 K which is ∼120-145 K above the measured glass transition temperatures (∼207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (∼70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (α2) and new non-Gaussian (γ) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.

Chemically cross-linkable polyimide membranes for improved transport plasticization resistance for natural gas separation

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide with enhanced transport plasticization resistance were synthesized to separate CO2 from CH4. Glycidol was used as a cross-linking agent to modify 6FDA-DAM:DABA (3:2) efficiently and form a transesterification reaction-based cross-linking. The conversion was calculated by solution 1H NMR. These materials were also characterized via density, glass transition temperature, permeation, and sorption measurements. Pure (CO2, CH4) and mixed gas (CO2/CH4) permeation was studied on dense films of these materials up to 700 psia (1000 psia) for pure CO2 (50%:50% CO2:CH4 mixed gas) feed. Compared to the 6FDA-DAM:DABA (3:2) membrane, CO2-induced plasticization resistance for cross-linked membranes was enhanced in aggressive feed streams. Under CO2 feed conditions at 35 °C, plasticization for the 41% glycidol-modified cross-linked membrane was not observed up to approximately 450 psia. Glycidol-induced cross-linking offers an excellent balance of selectivity, permeability, and plasticization resistance. The glycidol-modified 6FDA-DAM:DABA (3:2) is competitive with the earlier reported 1,3-propanediol modified materials. Possible issues such as resistance to contaminants may be final determinants in choice of approach; however, this topic was beyond the scope of the current study.

Synthesis and high-throughput characterization of structural analogues of molecular glassformers: 1,3,5-trisarylbenzenes.

We report the synthesis and characterization of an analogous series of small organic molecules derived from a well-known glass former, 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (α,α,β-TNB). Synthesized molecules include α,α,β-TNB, 3,5-di(naphthalen-1-yl)-1-phenylbenzene (α,α-P), 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene (α,α-A), 9,9'-(5-(naphthalen-2-yl)-1,3-phenylene)dianthracene (β-AA) and 3,3',5,5'-tetra(naphthalen-1-yl)-1,1'-biphenyl (α,α,α,α-TNBP). The design of molecules was based on increasing molecular weight with varied π-π interactions in one or more substituents. The synthesis is based on Suzuki cross-coupling of 1-bromo-3-chloro-5-iodobenzene with arylboronic acids, which allows attachment of various substituents to tailor the chemical structure. The bulk compounds were characterized using NMR spectroscopy and differential scanning calorimetry (DSC). Thin films of these compounds were produced using physical vapor deposition and were subsequently annealed above the glass transition temperatures (Tg). For each molecular glass, cooling rate-dependent glass transition temperature measurements (CR-Tg) were performed using ellipsometry as a high-throughput method to characterize thin film properties. CR-Tg allows rapid characterization of glassy properties, such as Tg, apparent thermal expansion coefficients, apparent activation energy at Tg and fragility. DSC measurements confirmed the general trend that increasing molecular weight leads to increasing melting point (Tm) and Tg. Furthermore, CR-Tg provided evidence that the introduction of stronger π-interacting substituents in the chosen set of structural analogues increases fragility and decreases the ability to form glasses, such that β-AA has the largest fragility and highest tendency to crystallize among all the compounds. These strong interactions also significantly elevate Tg and promote more harmonic intermolecular potentials, as observed by decreasing value of the apparent thermal expansion coefficient.

An essential work of fracture study of the toughness of thermoset polyester coatings

Abstract The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, Tg, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, we, at Tg was found to decrease with increasing cross-link density from around 20 kJ/m2 at a cross-link density of 0.4 × 10−3 mol/cm3 to around 5 kJ/m2 for cross-link densities of approximately 1 × 10−3 mol/cm3 or higher. A maximum in the essential work of fracture was observed at around Tg when we was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.

The Properties of Sepiolite Nanofibers Reinforced Polycarbonate/Poly(acrylonitrile-butadiene-styrene) Composites Using a PS-co-MAH Compatibilizer

We prepare polycarbonate/poly(acrylonitrile-butadiene-styrene) composites which are reinforced with sepiolite nanofibers and use a polystyrene-maleic anhydride copolymer for improving polycarbonate/poly(acrylonitrile-butadiene-styrene) compatibility. By measuring glass transition temperatures and morphologies, we conclude that the copolymer effectively improves the compatibility. Further, polycarbonate/poly(acrylonitrile-butadiene-styrene) composites containing various amounts of sepiolite are prepared. It is found that the surface-modified sepiolite nanofibers are well-dispersed in the polymer matrix, and the mechanical properties and heat resistance are increased with the sepiolite contents increasing. The influences of sepiolite nanofibers on the melt flowability are also investigated. With these results, the composite with the optimum properties is provided.

Synthesis and characterization of ternary glasses in the system Na2Se-Ga2Se3-GeSe2

Chalcogenide glasses in the system Na2Se-Ga2Se3-GeSe2 (NGGS) have been synthesized and characterized using Raman spectroscopy as well as density and glass transition temperature measurements. Results are compared to those from the analogous system BaSe-Ga2Se3-GeSe2 (BGGS) in an attempt to shed light on the comparative roles of Na and Ba as modifying elements in chalcogenide networks. In general, both NGGS and BGGS glasses exhibit the corner-sharing network of (Ga/Ge)Se4 tetrahedra that is characteristic of glasses containing Ga–Ge–Se. Some amount of tetrahedral edge-sharing and Ge–Ge bonding exists, but the concentration of Ge–Ge bonds in the network is heavily dependent on both the ratio R=Na2Se(BaSe)/Ga2Se3 and the type of the modifying element. The addition of Na2Se to an NGGS glass with R<1 efficiently removes Ge–Ge bonding such that their concentration essentially goes to zero by the chemical threshold R=1. In contrast, the addition of BaSe to a BGGS glass with R<1 removes the Ge–Ge bonds less efficiently, such that a non-zero concentration still exists at R=1. On the other hand, compared to BGGS glasses, increasing R results in a rapid drop in the glass transition temperature of NGGS glasses with R>1 indicating that Na2Se is a much more efficient modifier that lowers the connectivity of the Ga–Ge–Se tetrahedral network via the formation of non-bridging Se atoms.

Measurement and Comparison of Glass Transition and Sticky Point Temperatures of Distillers Dried Grains with Solubles (DDGS) with Varying Condensed Distillers Solubles (CDS) and Drying Temperature Levels

ABSTRACTDistillers dried grains with solubles (DDGS) is the main coproduct of the U.S. fuel ethanol industry and has significantly impacted the livestock feed markets in recent years. Particle agglomeration and subsequent flowability problems during storage and transport are often a hindrance, a nuisance, and expensive. This paper aims at characterizing the glass transition (Tg) and sticky point (Ts) temperatures of DDGS samples prepared with varying condensed distillers solubles (CDS) levels (10, 15, and 20%, wb), drying temperatures (100, 200, and 300°C), and moisture contents (0, 10, and 20%, db), and it discusses implications on DDGS flowability behavior. Distillers wet grains were combined with specified levels of CDS and dried in a convection‐style laboratory oven to produce DDGS. Subsequently, predetermined amounts of water were added to the DDGS to achieve desired moisture content levels. To determine Tg (°C), a differential scanning calorimeter was used, whereas Ts (°C) was determined through a novel technique with a rheometer. Results indicated high correlations between observed Ts and observed Tg (R2 = 0.87) data for DDGS samples. Also, the empirical model for predicted Tg = f (drying temperature, CDS level, and moisture content) based on the Gordon–Taylor model showed favorable R2 (0.74). Stickiness of DDGS increased with an increase in moisture content, indicating flow problems resulting from moisture. It was found that drying temperatures and CDS levels each had significant effects on Tg and Ts as well.

Plasticizer compatibility testing: Dynamic mechanical analysis and glass transition temperatures

Plasticizer compatibility with the polymer, which implies that plasticizer and polymer will remain closely associated as the finished polymer product is used, is critically important in determining whether a flexible poly(vinyl chloride) (PVC) product will have an acceptably long service life. However, with traditional test methods, it is often difficult to distinguish degrees of compatibility among relatively compatible ingredients (ingredients that do not dissociate themselves from the polymer in a very short time or under very mild storage conditions). Dynamic mechanical analysis is a commonly used technique for measuring glass transition temperatures, which can be a useful property in comparing additives' compatibilities. Unlike many polymers, flexible PVC shows two glass transition temperatures, one for the polymer segments that show syndiotactic (but noncrystalline) stereochemistry, and one for the polymer segments that show atactic stereochemistry. The glass transition temperature for the atactic segments of flexible PVC provides some information about the plasticizer's compatibility. When the dynamic mechanical analysis temperature sweep for a plasticized PVC compound detects a particularly low glass transition for the atactic polymer segments, this can be an indication that the plasticizer is relatively incompatible with the PVC. J. VINYL ADDIT. TECHNOL., 21:7–11, 2015. © 2014 Society of Plastics Engineers

Mechanical performance degradation of glass fiber insulation material after neutron irradiation

Epoxy based glass fiber reinforced plastic composites G-10 CR grade are suitable material for electrical insulation breaks of the superconducting fusion device. At IPR, under the national fusion program, characterization of G-10 CR material with the neutron irradiation dose is studied. This study will help us towards the indigenous development project of electrical insulation breaks for future superconducting fusion magnets under the radiation environment. The insulation material has been irradiated by 14 MeV neutrons D-T generator in the Fusion Neutronics Laboratory, I.P.R. The mechanical and electrical performance was investigated after irradiation (with a fluence of 8.63×1014 n/m2) at room and cryogenic temperature condition. The results show that the mechanical degradations (by ∼ 9 to 30%) after neutron irradiation in tensile strength and impact strength at 300 K and 77 K. In this paper, we present the experimental details of the neutron irradiation and the data have been compared using MCNP code for flux calculation on glass fiber insulation composite along with Stycast 2850 GT epoxy. Investigation of mechanical, electrical, SEM analysis for internal surface morphology, glass transition temperature measurement of insulation material and its test results at 300 K and 77 K before and after neutron irradiation will be presented.

135 Measured glass transition temperatures within cells following slow cooling: Implications for cryopreservation and freeze drying

Following slow rates of cooling, at which cellular dehydration occurs, it is assumed that the intracellular environment vitrifies. However, the glass transition (Tg) temperature has not previously been determined for any cell type during cooling. Using differential scanning calorimetry (DSC), we have measured intracellularTg, in a range of cell types (bacteria, algae, yeasts) when cooled slowly in the presence of extracellular ice, where no cryoprotectants were added. Under the experimental conditions used, any intracellular freezing would have been detected by the release of latent heat associated with the change in entropy that accompanies the phase transition from liquid water to ice in the cell during cooling, or the reverse during warming; none was seen. Vitrification was detected by the variation in heat flow associated with the change in heat capacity, together with the absence of any release of latent heat. No vitrification signal was seen in control runs (medium without cells). The signal detected in the sample runs was the glass transition temperature of the maximally freeze-concentrated intracellular compartment (conventionally designated Tg’). The observed values of Tg’ ranged from just below −10 °C in thermophilic bacteria and the ice-nucleating bacterium Pseudomonas syringae, to around −25 °C in three species, including the snow alga Chlamydomonas nivalis. These temperatures are well above typical environmental temperatures for high latitudes in winter, indicating that intracellular vitrification must be a process of widespread ecological relevance for free-living single cells. These findings have a number of implications for cryopreservation: (a) During slow cooling, vitrification will occur at a high sub zero temperature and the cell will be osmotically unresponsive during subsequent cooling. On warming the vitrified cells will be exposed to an extracellular hypertonic stress before the cell interior become liquid. This set of physical events are not described in any current model of freezing injury, it is assumed that the cell is osmotically reactive at all temperatures down to the Tg of the extracellular solution. (b) Vitrification would be expected to stop any damaging intracellular events, but damage to the plasmalemma may still occur at the outer surface by direct exposure to hypertonic solutions. (c) Freeze drying of cells will always occur at a temperature below the intracellular vitrification temperature Source of funding: INRA, CEPIA Department, UMR 782 GMPA, F 78850 Thiverval Grignon, France. Conflict of interest: None declared. fonseca@grignon.inra.fr

Extrusion-cooking of starch protective loose-fill foams

One of the most interesting alternatives to EPS is extrusion of starch-based materials. TPS-based biocomposites can be processed, in a one-step process, via an extrusion-cooking. Wide program of the experimental works with application of extrusion-cooking for production of starchy loose-fill foams has been started in the Department of Food Process Eng., Lublin University of Life Sciences in 2012. The object of the study is to achieve commercially acceptable biodegradable products based on locally produced potato, corn and wheat starch, which can replace popular EPS. Results of the first phase of the study are presented in the paper. The measurements of glass transition temperature of TPS samples showed that with glycerol content growth in the blend, the Tg of the obtained material decreases almost linearly. In the case of potato TPS, the highest observed Tg was 187.7̊C for 7.0% glycerol and the lowest was at 18.1̊C for 30% glycerol. Properties of the loose-fill foams highly depend on raw materials and process parameters used in production. In addition of plasticiser or other additives, different temperature of processing is causing changes in product's properties. All starch-based foams had high open-cell content and the expansion was attributable to the escape of water as steam during processing, resulting more than 80% open cells. The foam density of starch-based products ranged between 18.7 and 30.5kg/m3. The products were at least 2.5 times more dense than EPS-based foams. The best products achieved by us up till now are the corn TPS-based foams containing 3% plasticizer and 1% poly-vinyl alcohol. The energy consumption during extrusion-cooking depended on the material composition of the blends, temperature and the screw rotation speed used during processing. Average value of SME was about 2.52×105J/kg, which is equivalent to 0.07kWh/kg.

Salt-Concentration Dependence of the Glass Transition Temperature in PEO–NaI and PEO–LiTFSI Polymer Electrolytes

We measured glass transition temperatures Tg as a function of the salt concentration in polymer electrolyte systems consisting of poly(ethylene oxide) (PEO) complexed either with sodium iodide (NaI) or lithium bis(trifluorosulfonylimide) (LiTFSI). At homologous compositions, Tg of PEO–NaI is found to be generally larger than that of LiTFSI. The present Tg values are markedly higher than previously reported reference data. Also the observed nonlinear concentration dependence differs from earlier studies. These findings are tentatively attributed to the more stringent preparation and measuring conditions maintained in the present work, thereby keeping organic solvent residues and water contamination at low levels. Also the high molecular weight of the polymer may have some influence. The measurements were performed by differential scanning calorimetry after quenching from the melt. We find that ex situ immersion quenching in liquid nitrogen leads to lower degrees of crystallinity than in situ quenching in t...

Synthesis and characterization of differently substituted phenyl hepta isobutyl‐polyhedral oligomeric silsesquioxane/polystyrene nanocomposites

Variously substituted polyhedral oligomeric silsesquioxanes (POSSs)/polystyrene (PS) nanocomposites of general formula R7R′(SiO1.5)8/PS (where R = isobutyl and R′ = 4‐methoxyphenyl, 4‐methylphenyl, 3,5‐dimethylphenyl, 4‐fluorophenyl, 2,4‐difluorophenyl, 4‐chlorophenyl) were prepared by in situ polymerization of styrene in the presence of 5% w/w of POSS. The actual filler concentration in the obtained nanocomposites was checked by 1H NMR spectroscopy. Scanning electron microscopy and FTIR spectroscopy evidenced the presence of filler‐polymer interactions. Inherent viscosity (ηinh) determinations indicated that the average molar mass of polymer in halogenated derivatives was lower than neat PS, and were in agreement with calorimetric glass transition temperature (Tg) measurements. Finally, a comparative study concerning the thermal stability of synthesized nanocomposites was carried out in both inert (flowing nitrogen) and oxidative (static air) atmospheres into a thermobalance, in the scanning mode, at 10°C min−1, and the temperatures at 5% mass loss (T5%), of various compounds were determined. The results were discussed and interpreted. POLYM. COMPOS., 35:151–157, 2014. © 2013 Society of Plastics Engineers

Ameliorating property gradients in photocured polymer lattices via thermal curing

An experimental study has been performed to assess the efficacy of thermal curing in ameliorating the property gradients that ensue from photo-curing of thiol-ene lattices. Through measurements of glass transition temperatures and complex moduli of the constituent thiol-ene as well as strain distributions during compression testing of the lattices, we show that the lattice can be homogenized with a 24h curing treatment at 160°C. In addition to homogenization, the treatment yields an elevated glass transition temperature (to 50°C) relative to that of the pristine material or that after a lower temperature (130°C) cure. The resulting elastic response of the lattice at ambient temperature is essentially rate-independent over a strain rate range spanning four orders of magnitude. Finally, comparisons of the measured strengths with model predictions indicate that, through modest changes in either the slenderness ratio or the material properties, the mode of failure (yielding- vs. buckling-dominated) and hence the strain rate sensitivity of the lattice strength could be readily tailored.

Variously substituted phenyl hepta cyclopentyl-polyhedral oligomeric silsesquioxane (ph,hcp-POSS)/polystyrene (PS) nanocomposites

A comparative study concerning the thermal stability of polystyrene (PS) and six POSS/PS nanocomposites of general formula R7R′(SiO1.5)8/PS (where R = cyclopentyl and R′ = phenyl, 4-methoxyphenyl, 4-tolyl, 3,5-xilyl, 4-fluorophenyl, and 2,4-difluorophenyl) was carried out in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5 % w/w of POSS, but the actual filler concentration in the obtained nanocomposites, determined by 1H NMR spectroscopy, was in all cases slightly higher than that in the reactant mixtures. FTIR spectra of nanocomposites evidenced the presence of filler-polymer interactions. Inherent viscosity (ηinh) determinations indicated that the average molar mass of polymer in methylated and fluorinated derivatives was lower than neat PS, and were in agreement with calorimetric glass transition temperature (Tg) measurements. Degradations were performed into a thermobalance, in the scanning mode, at 10 °C min−1, and the temperatures at 5 % mass loss (T5 %), of various nanocomposites were determined. The effects of various substituents of the POSS phenyl group on the thermal stability of nanocomposites were evaluated. The results were discussed and interpreted.

Amphiphilic polymers bearing gluconolactone moieties: Synthesis and long side-chain crystalline behavior

The synthesis and characterization of amphiphilic polymers bearing gluconolactone moieties has been described. In a first step, an unprotected glycomonomer 2-[({[4-(d-gluconamid-N-yl)butyl]amino}carbonyl)oxy]ethyl acrylate, HEAG, has been synthesized. Posterior, this glycomonomer has been copolymerized with methyl methacrylate at different compositions and the kinetic behavior has been also studied calculating the monomer reactivity ratios by Kelen–Tüdös extended equation. In addition, the long side-chain crystalline behavior of these carbohydrate-based copolymers with high composition of glycomonomer has been examined by using conventional and modulated differential scanning calorimetry and X-ray diffraction measurements. At the same time, the phase separation behavior of carbohydrate-based copolymers with lower HEAG content has been determined by their glass transition temperature measurements. Finally, the thermal stability of all these amphiphilic copolymers has been evaluated by thermogravimetric analysis.

Designing green plasticizers: Influence of alkyl chain length on biodegradation and plasticization properties of succinate based plasticizers

Phthalate diesters such as di (2-ethylhexyl) phthalate (DEHP) are considered ubiquitous contaminants and are poorly biodegraded in the environment. Moreover, both the parent compound and stable metabolites such as mono (2-ethylhexyl) phthalate (MEHP) are linked to several negative impacts on the environment and human health. Earlier work established that saturated diester compounds, such as succinates, showed better biodegradation characteristics and comparable plasticizer properties compared to DEHP. In this work we examine the effect of alkyl chain length of succinate molecules on plasticizer and biodegradation properties. This included both the side chains (n-ethyl to n-octyl) as well as substituents on the middle part of the succinate molecule. We showed that the common soil bacterium Rhodococcus rhodocrous could rapidly break down all unsubstituted succinates, without the appearance of stable metabolites. Furthermore, the organisms used the plasticizer metabolites as carbon source. The introduction of a large cyclohexyl substituent on the succinate resulted in a poorer degradation rate. Glass Transition Temperature (Tg) measurements were performed to evaluate plasticizer properties and showed that longer side chains reduced the Tg more efficiently, while large cyclohexyl substituents on the succinate decreased this effect. However, all compounds performed better or equal to DEHP at reducing the Tg.