Salvatore D'Antone

Biodegradation of poly(vinyl alcohol) based materials

Poly(vinyl alcohol) (PVA) is recognized as one of the very few vinyl polymers soluble in water also susceptible of ultimate biodegradation in the presence of suitably acclimated microorganisms. Accordingly, increasing attention is devoted to the preparation of environmentally compatible PVA-based materials for a wide range of applications. The present article is aimed at providing a survey of the available information on the environmental fate of PVA and PVA-based materials. Literature data and recent advances on the biochemistry and microbial physiology of PVA biodegradation and on the influence of environmental conditions are discussed along with the biodegradation processes of other water-soluble materials. The biodegradation behaviors of several PVA-based materials including blends, composites and copolymers are also reviewed and discussed.

Degradation behaviour of block copolymers containing poly(lactic-glycolic acid) and poly(ethylene glycol) segments

The degradation behaviour of a new class of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) segments was studied under conditions mimicking those found in biological fluids. The dissolution times of the new PLGA-PEG multi-block copolymers mainly depend on the length of the PEG segments present in their structure, i.e., on their PEG content on a weight/weight basis. At higher PEG contents, partially degraded PLGA segments are brought in solution by attached PEG segments. In all cases, the dissolution rates decrease by increasing the total surface area of the specimens tested.

Biodegradation of nonionic surfactants. I. Biotransformation of 4-(1-nonyl)phenol by a Candida maltosa isolate

Results are reported concerning biodegradation of 4-(1-nonyl)phenol by cultures of a Candida maltosa strain isolated from aerobic sludge samples collected at a depuration plant treating wastewaters from a textile industry. The yeast was able to utilize 4-(1-nonyl)phenol as a sole carbon and energy source. Preliminary attempts to draw the actual metabolic pathway evidenced microbial attack on the alkyl chain with the production of 4-acetylphenol. To the best of our knowledge this is the first report describing a microorganism capable of attacking nonylphenol in axenic culture and at the same time allowing for the identification of its degradation products.

Biodegradation of poly(vinyl alcohol) in soil environment: Influence of natural organic fillers and structural parameters

The biodegradation of PVA blends with natural polymers, such as gelatin, lignocellulosic by-products (sugar cane bagasse), as well as poly(vinyl acetate), was investigated in respirometric tests aimed at reproducing soil burial conditions. The observed behavior is discussed in terms of the influence of each blend component on the overall extent of mineralization, by assuming a simple additive behavior. The collected data evidenced that the biodegradation of PVA and PVA-based materials is rather limited under soil burial conditions. Additionally, PVA depresses the biodegradation of some of the investigated blends, particularly when mixed with gelatin. On the contrary, the hydrophobic character of the natural polymer component as well as the residual content of acetyl groups of the used PVA samples seem to have a positive effect on the biodegradation propensity of the blend.

Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ε-caprolactone) or poly(ethylene glycol)

Abstract The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly( d , l -lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d , l -lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures.

Controlled Release of Herbicides Supported on Polysaccharide Based Hydrogels

Polymeric hydrogels based on polysaccharides, hydroxyethylcellu lose and dextran, were attained by cross-linking with epichlorohydrin. The cross-linked polymer beads were loaded with 2,4-dichlorophenoxyacetic acid by direct esterification in the presence of carbonyldiimidazole. Loads ranging be tween 0.5 and 2.2 mol of 2,4-dichlorophenoxyacetyloyl groups per glucose unit were obtained. The release of 2,4-D herbicide was investigated in buffered aqueous solution at different pH values (4, 7 and 9) and evaluated with respect to different structural parameters, such as nature of the polymer matrices, cross-linking extent and herbicide loading. A fairly slow release, ranging from 10 to 25% after four months, was recorded under neutral and acid conditions, whereas at pH 9 an initial burst in the release profile, reaching almost 90% release of 2,4-D loading, was observed. In the majority of the cases, the release kinetics are reproduced by the combination of two exponential decay processes, that differ by about three orders of magnitude in their absolute rates.

Multiblock copolymers based on segments of poly (D, L-lactic-glycolic acid) and poly(ethylene glycol) or poly(∈-caprolactone): A comparison of their thermal properties and degradation behavior

A comparison of the thermal properties of two classes of poly(D,L-lactic-glycolic acid) multiblock copolymers is reported. In particular, the results of differential scanning calorimetry, and thermogravimetric analysis of copolymers containing poly(ethylene glycol) (PEG) or diol-terminated poly(∈-caprolactone) (PCDT) segments are described. The influence of the chemical structure and the length of PEG and PCDT on thermal stability, degree of crystallinity and glass transition temperature (T g ) is discussed. Finally, an evaluation of the hydrolytic behavior in conditions mimicking the physiological environment is reported.

New Polyfunctional Derivatives of β-Cyclodextrin Suited for the Formulation of Drug Release Systems:

New functional derivatives of β-cyclodextrin were obtained by grafting β-cyclodextrin with epoxides of protected polyols, such as glycidyliso propylideneglycerol, glycidyldiisopropylidenexylitol and glycidyldiisopropyl idenearabitol. The glycidyl ether of 2-pyrrolidone was also used. The reaction products have a degree of substitution per glucose residue included between 0.5 and 1. Selective removal of protecting groups from cyclodextrin substituents, carried out under conditions not affecting the integrity of the cyclodextrin ring, gave rise to hydrosoluble cyclodextrin derivatives whose hydrophilic/hydropho bic balance was modulated by controlling the extent of deprotection. The un usual solubility in water, greater than 350%, for both protected and depro tected derivatives, represents a breakthrough for a wide variety of applications requiring polymeric materials with remarkable water solubility.

Thermal degradation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(e-caprolactone) or poly(ethylene glycol)

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(e-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.

Degradation of Poly(Ethylene Glycol)-Based Nonionic Surfactants by Different Bacterial Isolates from River Water

Different bacterial strains able to attack polyoxyethylene-type nonionic surfactants were isolated by enrichment procedure from the surface waters of the Arno River. Alkylphenol polyethoxylates and alkyl polyethoxylates, as well as polyethylene glycols, were degraded and assimilated by bacterial strains in axenic cultures. Degradative routes of polyethyleneoxide chains were investigated by matching each bacterial isolate with several types of nonionic surfactants and polyethers and by the identification of their degradation products isolated during aerobic digestion experiments. In accordance with previous reports, the first attack led to the shortening of the poly(oxyethylene) chains of the nonionic surfactants. It was found that the strains able to degrade PEG segments of nonionic surfactants possess enzymatic systems unable to degrade free PEGs, whereas those degrading the latter substrates cannot degrade PEG segments coupled to hydrophobic moieties.