Overall Rate Of Degradation Research Articles

Composites retard hydrolytic crack growth

Degradable polymers are under intense development for sustainability and healthcare. Evidence has accumulated that the chemical reaction that decomposes a polymer an also grow a crack. Even under a small load, the crack speed can be orders of magnitude higher than the overall rate of degradation, leading to premature failure. Here, we demonstrate that a crack slows down markedly in a composite of two degradable materials. In a homogeneous degradable material, the stress concentrates at the crack tip, so that a relatively small applied stretch induces a high stress and a high rate of reaction. The fracture behavior of a composite that consists of two degradable materials, a stiff material for the fibers and a compliant material for the matrix, with strong adhesion between both, is different: The soft matrix blunts the crack and distributes the stresses at the crack tip over a long length of the fibers. The same rate of reaction requires a larger applied stretch. This stress de-concentration retards crack growth in the composite. We demonstrate this concept using a composite made of stiff polydimethylsiloxane (PDMS) fibers in a soft PDMS matrix. In the presence of water molecules in the environment, siloxane bonds in the PDMS hydrolyze, causing hydrolytic crack growth. We show that a hydrolytic crack grows much more slowly in a PDMS composite than in homogeneous PDMS, and may even arrest in the composite. It is hoped that this concept will contribute to the development of degradable materials that resist premature failure.

Assessing Performance of Cattle Dung and Waste Cooked Foods in Producing Biogas as Single Substrate and Mixed Substrates in Kampala Uganda

Biogas is anaerobic degradation product formed from aqueous slurry of organic waste in a digester. It can be produced from cattle dung, (cd)chicken droppings, decaying leaves, kitchen waste foods, (kwf), sewage sludge, slaughter house, goat, pig or sheep manure, Aqueous slurry of 200 g/L of mixed or single substrate of cattle dung or/and kitchen waste evolved up to 400mL of biogas at ambient temperatures. The rate of gas evolution reached 5 mL/day on the 15th day using 25 % cd mixed slurry. The overall rates of degradation attained in the mixtures were 1.42 + 0.26 mL/g for cd; 1.58+0.33 mL/g for kwf; 1.78+ 0.38 mL/g for 75 % cd mixed substrate; 1.78+ 0.29 mL/g for 50 % cd mixed substrate; 1.92+ 0.21 mL/g for 25 % cd mixed substrate slurries in the 200 g/L load. The comparative rate of biogas formation ranged from1.25 to 1.35 which was in agreement with the range published in literature of 0.8 to 5.5. Biogas can be synthesized efficiently at ambient temperature in Kampala as was done at mesophilic temperatures elsewhere. However, it may be necessary to attempt producing biogas at different pH and temperatures as well as using other substrates and inoculums.

Mechanism and kinetics of the hydrolytic degradation of amorphous poly(3-hydroxybutyrate)

Amorphous poly(3-hydroxybutyrate) films prepared by compression molding and solvent casting were degraded in aqueous media at different pH values. The time dependence of degradation was monitored by the measurement of weight loss, the extraction of the degradation products from the degrading sample, as well as by UV-Vis spectrophotometry and HPLC analysis of the aqueous solution. The results proved that degradation takes place mainly in the bulk of the samples and not on their surface. The overall rate of degradation depends strongly on pH; it increases with increasing pH values. Metabolite extraction and chromatography proved that degradation does not occur randomly, but with larger frequency at the end of the chains. By assuming that the hydrolysis of PHB is a SN2 type nucleofil substitution reaction, a kinetic model was proposed which describes the formation of various degradation products. The diffusion of metabolites was also accommodated into the model thus the concentration in the aqueous solution could also be predicted well. The correlation between prediction and experimental results is excellent. The model can be extended also for the description of the hydrolytic degradation of other aliphatic polyesters.

Enzymatic action as switch of bulk to surface degradation of clicked gelatin‐based networks

Polymer degradation occurs under physiological conditions in vitro and in vivo, especially when bonds susceptible to hydrolysis are present in the polymer. Understanding of the degradation mechanism, changes of material properties over time, and overall rate of degradation is a necessary prerequisite for the knowledge‐based design of polymers with applications in biomedicine. Here, hydrolytic degradation studies of gelatin‐based networks synthesized by copper‐catalyzed azide‐alkyne cycloaddition reaction are reported, which were performed with or without addition of an enzyme. In all cases, networks with a stilbene as crosslinker proofed to be more resistant to degradation than when an octyl diazide was used. Without addition of an enzyme, the rate of degradation was ruled by the crosslinking density of the network and proceeded via a bulk degradation mechanism. Addition of Clostridium histolyticum collagenase resulted in a much enhanced rate of degradation, which furthermore occurred via surface erosion. The mesh size of the hydrogels (>7 nm) was in all cases larger than the hydrodynamic radius of the enzyme (4.5 nm) so that even in very hydrophilic networks with large mesh size enzymes may be used to induce a fast surface degradation mechanism. This observation is of general interest when designing hydrogels to be applied in the presence of enzymes, as the degradation mechanism and material performance are closely interlinked. Copyright © 2016 John Wiley & Sons, Ltd.

Fabrication of anti-poisoning core-shell TiO2 photocatalytic system through a 4-methoxycalix[7]arene film

TiO2 nanoparticles with unique crystalline-core/disordered-shell structures were synthesized in a one step process by employing 4-methoxycalix[7]arene nanoreactors. The nanoparticles were anchored on the surface of quartz beads as a monolayer and showed high visible-light driven photocatalytic activity, excellent long term durability and anti-poisoning property. Photocatalytic performance of the TiO2 nanoparticles was tested in a packed bed and complete decolorization of methyl orange was achieved under ultraviolet light or visible light. The decolorization process followed first-order kinetics and showed different behaviors for ultraviolet and visible radiation, while the overall rates of degradation were the same.

Photodegradation of Trace Trichloronitromethane in Water under UV Irradiation

This study’s objective was to study the photodegradation of TCNM (trichloronitromethane) in water under UV light. The effects of light intensity, nitrate ions, chloride ions, humic acid, and pH on the photochemical degradation of TCNM were investigated under the irradiation of low pressure mercury lamp (λ= 254 nm, 12 W). The photodegradation rate of TCNM was found to increase with increasing the concentration of nitrate ions, chloride ions, humic acid, pH, and light intensity. The photodegradation of TCNM was examined at pH 6.0 with initial concentrations (C0) of TCNM at 10.0–200.0 µg/L. The overall rate of degradation of TCNM was modeled using a pseudofirst-order rate law. Finally, the proposed mechanism involved in the photodegradation of TCNM was also discussed by analysis. Results of this study can contribute to the development of new source control strategies for minimization of TCNM risk at drinking water and wastewater utilities.

Monochloramination of Resorcinol: Mechanism and Kinetic Modeling

The kinetics of monochloramination of resorcinol, 4-chlororesorcinol, and 4,6-dichlororesorcinol have been investigated over the pH range of 5-12, at 23 +/- 2 degrees C. Monochloramine solutions were prepared with ammonia-to-chlorine ratios (N/Cl) ranging from 1.08 to 31 mol/mol. Under conditions that minimize free chlorine reactions (N/Cl > 2 mol/mol), the apparent second-order rate constants of monochloramination of resorcinol compounds show a maximum at pH values between 8.6 and 10.2. The intrinsic second-order rate constants for the reaction of monochloramine with the acid-base forms of the dihydroxybenzenes (Ar(OH)(2), Ar(OH)O(-), and Ar(O(-))(2)) were calculated from the apparent second-order rate constants. The stoichiometric coefficients for the formation of 4-chlororesorcinol by monochloramination of resorcinol and 4,6-dichlororesorcinol by monochloramination of 4-chlororesorcinol were found to be equal to 0.66 +/- 0.05 and 0.25 +/- 0.02 mol/mol, respectively at pH 8.6. A kinetic model that incorporates reactions of free chlorine and monochloramine with the different acid-base forms of resorcinol compounds simulated well the initial rates of degradation of resorcinol compounds and was useful to evaluate the contribution of free chlorine reactions to the overall rates of degradation of resorcinol at low N/Cl ratios.

Degradation of commercially important polyhydroxyalkanoates in tropical mangrove ecosystem

This paper presents the degradation trends of selected polyhydroxyalkanoate (PHA) films in a tropical mangrove environment. The biodegradability of homopolymer poly(3-hydroxybutyrate) [P(3HB)] and its co-polymers, poly(3-hydroxybutyrate- co-5 mol% 3-hydroxyvalerate) [P(3HB- co-5 mol% 3HV)] and poly(3-hydroxybutyrate- co-5 mol% 3-hydroxyhexanoate) [P(3HB- co-5 mol% 3HHx)], was investigated along with P(3HB) films containing 38 wt% titanium dioxide (TiO 2) [P(3HB)–38 wt% TiO 2]. The degradation of these formulations was monitored for 8 weeks at three different zones in an intermediate mangrove compartment along Sungai Pinang, adjacent to a famous fishing village on south of Penang Island. The degradation rate was observed both on the surface and in the sediment and was expressed in percentage of weight loss. The microbial enumeration done using sediment from the different zones indicated similar colony-forming unit (CFU) counts even though differences were noticed in the degradation profile of the various films in the respective zones. The results obtained revealed that co-polymers disintegrated at similar or higher rate than the homopolymer, P(3HB). However, the incorporation of TiO 2 into PHB films caused the degradation rate of P(3HB)–38 wt% TiO 2 composite film to be far slower than all the other PHA films. The overall rate of degradation of all PHA films placed on the sediment surface was slower than those buried in the sediment. Microscopic analyses showed that the surface morphology of P(3HB- co-5 mol% 3HHx) was more porous compared to P(3HB) and P(3HB- co-5 mol% 3HV) films, which may be an important factor for its rapid degradation.

Factors affecting the degradation and drug‐release mechanism of poly(lactic acid) and poly[(lactic acid)‐co‐(glycolic acid)

AbstractThis paper reviews the most important factors affecting the degradation and drug‐release rate of bio‐erodible polymers for better control in biomedical applications. There are several factors that influence the overall rate of degradation, in addition to pH and copolymer composition. In general, polymer degradation is accelerated by greater hydrophilicity in the backbone or end groups, lesser crystallinity, lower average molecular weight, and smaller size of the finished device. At the moment, literature reflects contradictions about the role played by chemically reactive additives, crystallinity and degradation path. Factors affecting degradation and drug‐release rate are discussed in their decreasing order of importance, including intrinsic properties of polymers and processing parameters. Copyright © 2004 Society of Chemical Industry

Biodegradable cellulose diacetate-graft-poly(L-lactide)s: enzymatic hydrolysis behavior and surface morphological characterization.

Enzymatic hydrolysis of selected copolymers of cellulose diacetate-graft-poly(L-lactide)s (CDA-g-PLLAs) were conducted with proteinase K for film specimens, which were solely quenched from the molten state or, further, annealed at temperatures below or above their glass transition temperatures. The hydrolysis rates depended seriously on the thermal history, as well as on the graft modification. Especially, the heat treatment, followed by physical aging or crystallization of the originally amorphous materials, was a key factor to control subtly their enzymatic degradation behavior. Atomic force microscopy revealed that the enzymatic hydrolysis transformed the surface of the respective films into a more undulated one with a number of fine protuberances, for example, of several hundred nanometers in height and a few micrometers in width. Attenuated total reflection FTIR spectroscopy ensured selective release of lactyl units from the surface region. In visual appearance, some degraded films exhibited even an iridescent color due to an effect of interference of visible light reflected on the surface. These observations suggest a conception of "spatiotemporally controlled degradation", leading to a new method not only for regulation of the overall rate of degradation but also for fine surface abrasion of polymer materials.

Detection of giant myofibrillar proteins connectin and nebulin in fish meat by electrophoresis in 3-5 gradient sodium dodecyl sulfate polyacrylamide slab gels.

An improved method was investigated for sodium dodecyl sulfate polyacrylamide slab gel electrophoresis (SDS-PAGE) to facilitate the analysis of the giant myofibrillar proteins, connectin and nebulin, in fish meat by using jack mackerel (Trachurus japonicus) as the sample fish. It was established that separation of the alpha-connectin band from the beta-connectin band by SDS-PAGE could be achieved by using 3-5% gradient gels with glycerol to facilitate the formation of a gradient with polymerization at 35 degrees C. SDS-PAGE samples of white dorsal muscle from the jack mackerel were homogenized with a 2% SDS solution containing an inhibitor mixture (1 microg/mL of phenylmethanesulfonyl fluoride, 1 microg/mL of leupeptin, and 1 microg/mL of E-64) and heated at 50 degrees C for 20 min. Heating these samples at 100 degrees C for 2 min resulted in the disintegration of connectin but did not affect nebulin. A purified myofibril sample and a whole muscle sample showed similar changes in the overall rate of degradation of whole connectin and nebulin during the postmortem storage period, but it was clear that beta-connectin was cleaved from alpha-connectin during the preparation of myofibrils at the early stage postmortem. Storage of the SDS-PAGE samples at -85 degrees C was preferable to storage at -18 degrees C for a long period.

Oxidative Degradation of Monoethanolamine

Oxidative degradation of monoethanolamine (MEA) was studied at 55 °C, typical of absorbers for CO2 removal from flue gas. The rate of evolution of NH3, which was indicative of the overall rate of degradation, was measured continuously in a batch system sparged with air. Dissolved iron from 0.0001 to 1 mM yielded oxidation rates from 0.37 to 2 mM/h in MEA solutions loaded with 0.4 mol CO2/mol MEA. Ethylenediaminetetraacetic acid (EDTA) and N,N-bis(2-hydroxyethyl)glycine effectively decreased the rate of oxidation in the presence of iron by 40−50%. Ferrous caused oxidation in unloaded MEA with stoichiometry from 0.1 to 0.33 mol NH3/mol Fe2+. Fe2+ from 0.0001 to 3.2 mM yielded rates from 0.12 to 1.1 mM/h. Ferric did not appear to catalyze oxidation in unloaded MEA.

Thermal degradation of polystyrene

Thermal degradation of plastic wastes offers the possibility of recovering energy and useful chemicals. Polyethylene and polypropylene pyrolysis have been discussed already in previous works (E. Ranzi, M. Dente, T. Faravelli, G. Bozzano, S. Fabini, R. Nava, V. Cozzani, L. Tognotti, J. Anal. Appl. Pyrol., 40–41 (1997) 305–319 and T. Faravelli, G. Bozzano, C. Scassa, M. Perego, S. Fabini, E. Ranzi, M. Dente, J. Anal. Appl. Pyrol., 52 (1999) 87–103). This paper aims to develop a detailed kinetic model of polystyrene thermal degradation. The predictions of overall rates of degradation and volatile product distribution are compared with experimental results obtained by different authors at different pressure and temperature conditions. In order to reduce the computing times required by the numerical integration of the kinetic model, a flexible lumping procedure has also been introduced.

Hydrolytic degradation of tyrosine-derived polycarbonates, a class of new biomaterials. Part II: 3-yr study of polymeric devices

The kinetics and mechanisms of in vitro degradation of tyrosine-derived polycarbonates, a new class of polymeric biomaterials, were studied extensively at 37°C. These polymers carry an alkyl ester pendent chain that allows the fine-tuning of the polymer's material properties, its biological interactions with cells and tissue, and its degradation behavior. The polymer carrying an ethyl ester pendent chain, poly(DTE carbonate), has been established as a promising orthopedic implant material, exhibiting bone apposition when in contact with hard tissue. Tyrosine-derived polycarbonates are relatively stable and degrade only very slowly in vitro. Therefore, accelerated studies were conducted at 50 and 65°C to observe the behavior of polymers during the later stages of degradation. Varying the pendent chain length affected the rate of water uptake, initial degradation rate, and physical stability of the polymeric devices. During the 3-yr study, the polymer degraded by random chain cleavage of the carbonate bonds, accompanied by a relatively small amount of pendent chain de-esterification. No mass loss was observed during this period at 37°C, but mass loss was readily evident during the accelerated studies at 50 and 65°C. Thus, it is reasonable to assume that mass loss will occur also at 37°C, albeit only after extensive backbone carbonate cleavage and pendent chain ester hydrolysis. The dimension and surface area of the devices influenced the initial degradation rate, but did not significantly affect the overall rate of degradation. No evidence of “acid dumping” or the release of acidic residues found during the degradation of poly( d, l-lactic acid) were observed for this family of tyrosine-derived polycarbonates.

Degradation of 4-fluorobiphenyl in soil investigated by 19F NMR spectroscopy and 10C radiolabelling analysis

The incubation of the model pollutant [U- 14C]′-4-fluorobiphenyl (4FBP) in soil, in the presence and absence of biphenyl (a co-substrate), was carried out in order to study the qualitative disposition and fate of the compound using 14C-HPLC and 19F NMR spectroscopy. Components accounted for using the radiolabel were volatilisation, CO 2 evolution, organic solvent extractable and bound residue. Quantitative analysis of these data gave a complete mass balance. After sample preparation, 14C-HPLC was used to establish the number of 4FBP related components present in the organic solvent extract. 19F NMR was also used to quantify the organic extracts and to identify the components of the extract. Both approaches showed that the composition of the solvent extractable fractions comprised only parent compound with no metabolites present. As the 14C radiolabel was found to be incorporated into the soil organic matter this indicates that metabolites were being generated, but were highly transitory as incorporation into the SOM was rapid. The inclusion of the co-substrate biphenyl was to increase the overall rate of degradation of 4FBP in soil. The kinetics of disappearance of parent from the soil using the data obtained were investigated from both techniques. This is the first report describing the degradation of a fluorinated biphenyl in soil.

A new approach for measuring the rate of pyrolysis of cross-linked polymers: evaluation of degradation rate constants for cross-linked PMMA

Low molecular weight samples of PMMA have previously been observed to degrade at 400 °C via scission-initiated chain unzip in which the majority of the molecules depropagate to the end and are effectively terminated in this way. It was considered by the authors that if a cross-link were present within the PMMA molecule the unzip may be halted and the overall rate of degradation of the PMMA sample thereby reduced. In the present work, samples of cross-linked low molecular weight PMMA have been prepared by free radical polymerisation using azo-bis-isobutyronitrile as an initiator, carbon tetrachloride as a transfer agent and ethylene glycol dimethacrylate as a cross-linking agent. The rate of evolution of MMA monomer from these polymers has been measured and compared with equivalent samples prepared without a cross-linking agent. The samples have all been prepared in situ on the filament subsequently used for pyrolysis. This novel approach has not yet been previously reported, and is the ideal approach for studying the kinetics of intractable cross-linked material. It has been found that cross-linking low molecular weight PMMA does inhibit the rate of evolution of MMA monomer at 400 °C. An explanation of this may be attributed to cross-link units in the chain impeding the unzipping reaction.

Thermal degradation of polyisobutylene: effect of end initiation from terminal double bonds

The effect of terminal double bonds on the thermal degradation of polyisobutylene was examined by using a structurally well-defined sample ( M n0 = 7.09 × 10 3) prepared by hydrogenation. The end initiation reactions from a terminal trisubstituted double bond (TTD) and a terminal vinylidene double bond (TVD) lead to the formation of a primary terminal macroradical (R p·) and a tertiary terminal macroradical (R t·), respectively. It is expected from kinetic analysis that the extent of occurrence of R p· is 2–3 times higher than that of R t· depending on the functionalities f TTD and f TVD and M n of the reacting polymer, in addition to the random initiation from the scission of skeletal CC(C) 2, and that the stationary ratio [R p·] [R t·] becomes slightly lower by hydrogenation. The effect of hydrogenation was found to be a decrease in the overall rate of degradation, owing to a marked decrease in the end initiation rate. However, the integrated concentration ratio [R p·] [R t] , which is estimated from the composition ratio of the interesting components, does not decrease, but increases. This result shows that this concentration ratio scarcely depends on the initiation reactions. A similar relationship between the ratio [R p·] [R t] and M n of the molten polymer matrix was found for the degradation of samples with and without TVD and TTD. This result supports the view that [R p·] decreases markedly with decreasing M n during the degradation, owing to a marked depression of the regeneration rate of R p· resulting from an increase in the rate of diffusion-controlled termination.

Effects of insulin concentration and self-association on the partitioning of its A-21 cyclic anhydride intermediate to desamido insulin and covalent dimer.

In the pH range 2-5, human insulin degrades via deamidation at the A-21 asn and covalent dimerization. Both products form via a common cyclic anhydride intermediate, a product of intramolecular neucleophilic attack by the A-21 carboxyl terminus. This study examines the influence of [insulin] and self-association on the partitioning of the intermediate to products. Insulin self-association was characterized (pH 2-4) by concentration difference spectroscopy. Deamination rates (pH 2-4) and concurrent rates of covalent dimer formation (pH 4) were determined versus [insulin] at 35 degrees C by initial rates. A mathematical model was developed to account for the overall rate and product composition profile versus pH and [insulin]. Between pH 2-4, insulin self-associates to form non-covalent dimers with a pH independent association constant of 1.8 x 10(4) M-1. The overall rate of degradation is governed by intermediate formation, while product distribution is determined by competition between water and the phe B-1 amino group of insulin for the anhydride. In dilute solutions, deamidation is first-order in [insulin] while covalent dimerization is second-order. Thus, deamidation predominates in dilute solutions but the fraction of covalent dimer formed increases with [insulin]. At high [insulin], self-association inhibits covalent dimer formation, preventing exclusive degradation via this pathway. The model accurately predicts a maximum in covalent dimer formation near pH 4. A mechanism is described which accounts for the complex dependence of insulin's degradation rate and product distribution profile on pH (between 2-5) and [insulin]. If these results can be generalized, they suggest that covalent aggregation in proteins may be inhibited by self-association.

Reductive transformations of halogenated aromatic hydrocarbons in anaerobic water‐sediment systems: Kinetics, mechanisms and products

AbstractThe degradation of several classes of halogenated aromatic hydrocarbons in methanogenic sediment‐water systems was examined in laboratory studies. Several transformation processes were shown to occur, leading to formation of a variety of products. In the study a clear distinction could be made between transformation processes taking place immediately upon incubation of the compounds and processes taking place after a characteristic period of varying length. γ‐Irradiation was used to quench biological reactions and thus assess the impact of those processes on the overall rates of degradation of the studied compounds. The kinetics of both the initial and the final processes were pseudo‐first‐order, with half‐lives ranging from <0.46 d to no detectable degradation for a number of multiply halogenated benzenes. Compounds were selected with the aim of obtaining a maximum variation in chemical reactivity and physical properties. The sediments were selected with the aim of assessing several environmental factors influencing the kinetics of reduction.

REDUCTIVE TRANSFORMATIONS OF HALOGENATED AROMATIC HYDROCARBONS IN ANAEROBIC WATER-SEDIMENT SYSTEMS: KINETICS, MECHANISMS AND PRODUCTS

The degradation of several classes of halogenated aromatic hydrocarbons in methanogenic sediment-water systems was examined in laboratory studies. Several transformation processes were shown to occur, leading to formation of a variety of products. In the study a clear distinction could be made between transformation processes taking place immediately upon incubation of the compounds and processes taking place after a characteristic period of varying length. γ-Irradiation was used to quench biological reactions and thus assess the impact of those processes on the overall rates of degradation of the studied compounds. The kinetics of both the initial and the final processes were pseudo-first-order, with half-lives ranging from <0.46 d to no detectable degradation for a number of multiply halogenated benzenes. Compounds were selected with the aim of obtaining a maximum variation in chemical reactivity and physical properties. The sediments were selected with the aim of assessing several environmental factors influencing the kinetics of reduction.