Degradation Of Polylactide Research Articles

Carbonated calcium phosphates are suitable pH-stabilising fillers for biodegradable polyesters

Carbonated amorphous calcium phosphates were prepared with different carbonate content. Their ability to neutralise acidity was probed by time-resolved titration experiments with lactic acid, the monomer that results from degradation of polylactide. The results show that although calcium phosphate as such can reduce acidity, their buffering range lies at a pH of about 4, i.e. outside the physiological range. This is not related to the rate of dissolution. Carbonated calcium phosphates as well as calcium carbonate (calcite) alone are able to keep the pH around 7.4. Consequently, carbonated calcium phosphates are suitable basic filler materials as they are able to compensate acidity, and to buffer within the physiological pH-range.

Degradation of Polylactide by Commercial Proteases

Fifty-six commercially available proteases were tested for polylactide-degrading activity. Little or no activity was found in acid and neutral proteases, while some alkaline proteases formed appreciable amounts of lactic acid from polylactide. These polylactide-degrading proteases were derived from Bacillus species and had catalytic activity even under neutral, as well as alkaline, conditions. Savinase (Novo Nordisk) degraded polylactide the fastest among the enzymes tested and its specific activity corresponded to about one-half of proteinase K. Polylactide-degrading activity was not always present in the enzymes that affected keratin, while polylactide-degrading proteases commonly hydrolyzed keratin. A significant correlation was observed between degrading activities of polylactide and keratin in alkaline proteases.

Enzymatic degradation of polylactide stereocopolymers with predominant d-lactyl contents

Three stereocopolymers, namely PLA 40, PLA 25, and PLA 10, were synthesized by ring opening polymerization of 40/60, 25/75 and 10/90 l-lactide/ d-lactide feeds, respectively. Polylactide (PLA) films with dimensions of 10×10×0.4 mm were prepared by compression molding and machining. Enzymatic degradation of the films was investigated at 37°C in a pH=8.6 Tris–HCl buffer in the presence of proteinase K. It was confirmed that proteinase K preferentially degrades l-lactyl units as opposed to d-lactyl ones. With only 10% of l-lactyl units in its chains, PLA 10 showed a non negligible enzymatic degradation, while degradation of PLA 40 and PLA 25 was much more pronounced. The higher water uptake ratio in the case of PLA 40 and PLA 25 could also have facilitated the enzymatic attack. On the other hand, there appeared to be a relationship between enantiomeric composition, T g and hydrophilicity of PLA polymers. The more regular the polymer chains, the higher the T g and, the less hydrophilic the polymer. The presence of residual monomer can also lower the T g and enhance the hydroplilicity of PLA polymers.

Rapid (bio)degradation of polylactide by mixed culture of compost microorganisms—low molecular weight products and matrix changes

Poly(l-lactide) (PLLA) was rapidly (bio)degraded by a mixed culture of compost microorganisms. After 5weeks in biotic environment, the films had fragmented to fine powder, while the films in corresponding abiotic medium still looked intact. Analysis of the low molecular weight products by GC-MS showed that microorganisms rapidly assimilated lactic acid and lactoyl lactic acid from the films. At the same time, a new degradation product, ethyl ester of lactoyl lactic acid was formed in the biotic environment. This product cannot be formed by abiotic hydrolysis and it was not detected in the abiotic medium. The degradation of the PLLA matrix was monitored by differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and scanning electron microscopy (SEM). A rapid molecular weight decrease and increasing polydispersity was observed in the biotic environment. In the abiotic environment only a slight molecular weight decrease was seen and the polydispersity started decreasing towards 2.0. This indicates different degradation mechanisms, i.e. preferred degradation near the chain ends in the biotic environment and a random hydrolysis of the ester bonds in the abiotic environment. SEM micrographs showed the formation of patterns and cracks on the surface of the films aged in biotic medium, while the surface of the sterile films remained smooth. The SEM micrographs showed a large number of bacteria and mycelium of fungi growing on the surface of the biotically aged films.

Hydrogen isotope exchange as a means of labeling lactides

Lactic acid-containing polymers obtained by the ring opening polymerization of lactides are now commercially available as bioresorbable polymers, or as devices that can be assimilated by the human body, or by living species present in the outdoor environment. Studying the mechanisms of lactide polymerization or polylactide degradation and monitoring the fate of the degradation compounds produced from the polymers when they degrade in complex media is thus very important and basically feasible via the labeling of polymer chains. Therefore, the possibility of exchanging some of the protons borne by lactide monomer molecules by deuterium or tritium was investigated. The substitution reactions involving deuterium were conducted and optimized using the High Temperature Solid State Catalytic Isotopic Exchange (HSCIE) method and applied to solid DL-lactide in the presence of various catalysts. The most active and stable catalyst was palladium on calcium carbonate. The analyses of the resulting deuterated compounds by 1H NMR and mass spectrometry showed that substitution involved mainly the tertiary proton and that the reaction temperature and flask volume were critical factors. The experimental conditions that led to convenient hydrogen-deuterium exchange yields were then applied to hydrogen-tritium exchange. Highly radioactive DL-lactide having a specific activity of 150 GBq/mmol. (4.05 Ci/mmol.) was successfully synthesized. Copyright © 1998 John Wiley & Sons, Ltd.

Polylactide Degradation by an Amycolatopsis sp

By applying the plate count and clear-zone methods, it was confirmed that polylactide (PLA)-degrading microorganisms are sparsely distributed in soil environments. An Amycolatopsis isolate was successfully isolated. Microbial degradation of PLA film was demonstrated; i.e., about 60% of the 100-mg film initially added was degraded by the strain after 14 days of liquid culture.

New aspects of determination of polymer heterogeneity by 2‐Dimensional orthogonal liquid chromatography and maldi‐tof‐ MS

AbstractLiquid Adsorption Chromatography at Critical Conditions (LACCC) of polymers in combination with Matrix‐Assisted Laser Desorption / Ionization Time‐Of‐Flight Mass Spectrometry (MALDI‐TOF‐MS) and different types of detectors is a very convenient method for the characterization of polymer heterogeneities. A pathway for working out these methods is given. Additionally to the coupling of different chromatographic modes a device for post‐column reaction detection is described and applied. Examples of applications are given for aliphatic and aromatic polyesters. MALDI‐TOF‐MS, reaction detection and relations between “critical” solvent composition and structure of polyesters are discussed. Conclusions concerning the mechanism of thermal degradation of polylactides are shown.

In vitro degradation of polylactide and poly(lactide‐co‐glycolide) microspheres

AbstractPolyactide (PLA) and poly(lactide‐co‐glycolide) (PLGA) were prepared by bulk ring‐opening polymerization of lactide or lactide/glycolide using stannous octoate as initiator. PLA and PLGA microspheres with an average diameter of 65–100 μm were prepared by a solvent evaporation process. An in vitro degradation test of different molecular weight PLA and of different composition PLGA were carried out in pH 7.4 buffer solution at 37°C in the form of microspheres. Quantitatively, the degree of degradation was monitored by gel permeation chromatography (GPC), by measurement of mass loss and determination of lactic/glycolic acid in degradation medium, and qualitatively, by observing the morphological changes of microspheres with a scanning electron microscope (SEM). The decrease in weight average molecular weight (Mw) for PLA with higher molecular weight is faster at the first degradation stage; afterward, the tendency of Mw to decrease for PLA with different molecular weight is almost the same. PLGA degrades much faster than does PLA, and the degradation rate is significantly enhanced with the increase of glycolic acid (GA) content in copolymers.

Degradation studies of some polyesters and polycarbonates: Part 4—Poly(ethylene oxalate)

Techniques used in previous studies of the thermal degradation of polylactide (Parts 1 and 2) and polyglycollide (Part 3) have been applied to poly(ethylene oxalate). The monomer has been found to be stable under vacuum but to undergo some spontaneous polymerisation on storage in air at atmospheric pressure. Polymerisations have been carried out under nitrogen at 150–160°C, with and without catalyst. The polymer is less stable than polylactide and polyglycollide, showing a threshold temperature for decomposition under programmed heating (10°/min) at about 200°C and a rate maximum in the region of 320°C. The products of degradation are monomer, oligomer, carbon dioxide, carbon monoxide, ethylene, acetaldehyde and several other minor products. In isothermal degradation at 260°C under vacuum, the products included 49% by weight monomer and 30% oligomer; the major components making up the remaining 21% of the original sample weight comprised carbon dioxide, carbon monoxide and ethylene. There is negligible involatile residue of degradation. A mechanism is presented in which homolysis at the oxalate linkage is proposed as the initial process, all the observed products being explicable by subsequent scissions of the initially formed macroradical.

Degradation studies of some polyesters and polycarbonates—2. Polylactide: Degradation under isothermal conditions, thermal degradation mechanism and photolysis of the polymer

The thermal degradation of polylactide has been studied at several temperatures in the range 230–440°C and the variation of product distribution with temperature has been examined. From experiments at 240–270°C, an energy of activation of 28·5 kcal mol −1 (119 kJ mol −1) has been calculated. Mass spectra have been obtained for polylactide and for the cold ring fraction of degradation products in TV A experiments. Both lactide and polylactide have also been heated under closed system conditions and the products have been identified. A mechanism is presented for the thermal degradation, based upon a hydroxyl end-initiated ester interchange process giving cyclic oligomers, lactide, acetaldehyde and carbon monoxide, together with a series of reactions at somewhat higher temperatures dependent upon chain homolysis, giving the same products and also carbon dioxide and methylketene. The photolysis of polylactide at 30°C, using the medium pressure mercury lamp, has been briefly examined.