Plasticizing effect of water on poly(lactide-co-glycolide)
University of Milan, Milano, Lombardy, Italy Journal of Controlled Release
(Impact Factor: 7.71).
12/2005; 108(1):1-9. DOI: 10.1016/j.jconrel.2005.07.009
The purpose of this research was to evaluate the effect and nature of hydration on the glass transition temperature (Tg) of poly(D,L-lactide-co-glycolide) and investigate the physical state of water within the polymer during hygrothermal aging. The polymer was incubated in water at 23, 30, 37 and 55 degrees C, while the vapor sorption studies were carried out at 37 degrees C using saturated salt solutions. The water content and the thermal behavior of PLGA-water system were assessed by Karl Fischer titration and modulated differential scanning calorimetry, respectively, the hygrothermal aging was monitored by gel permeation chromatography. Water depressed reversibly the Tg by about 15 degrees C regardless of the incubation conditions. The Tg then remained constant at approximately 30 degrees C for five days, except when degradation occurred. A broad ice melting peak was detected around 0 degrees C. In the sorption studies, a linear correlation (r2 0.9837) between the Tg and the moisture content was observed in the range of 0.3-2.6% w/w, but there was no discernible endothermic event associated with the melting of ice. Data were found to fit reasonably well to the Gordon-Taylor/Kelley-Bueche equation. There were no differences between bulk and vapor water aging. It is proposed that the water responsible for plasticizing the polymer was non-freezable (bound) water and the small fraction of such water which was absorbed at high relative humidity caused polymer degradation in the same manner as bulk water.
Available from: Zsombor Kristof Nagy
- "Therefore, in general the higher the Tg of the ASD the better the physical stability of the molecularly dispersed API. Tg is lowered by water (Blasi et al., 2005), that is why contact with water and high humidity should be avoided during production, downstream processing and storage. Hydrogen bonding has been shown to increase solid solubility of API in polymer and physical stability (Bhugra and Pikal, 2008; Vasanthavada et al., 2005). "
[Show abstract] [Hide abstract]
ABSTRACT: In this research the long-term stability (one year) of amorphous solid dispersions (ASDs) prepared by high speed electrospinning was investigated at 25°C/60% relative humidity (RH) (closed conditions) and 40°C/75% RH (open conditions). Single needle electrospinning and film casting were applied as reference technologies. Itraconazole (ITR) was used as the model API in 40% concentration and the ASDs consisted of either one of the following polymers as a comparison: polyvinylpyrrolidone-vinyl acetate 6:4 copolymer (no hydrogen bonds between API and polymer) and hydroxypropyl methylcellulose (possible hydrogen bonds between oxo or tertiary nitrogen function of API and hydroxyl moiety of polymer). DSC, XRPD and dissolution characteristics of samples at 0, 3 and 12 months were investigated. In addition, Raman maps of certain electrospun ASDs were assessed to investigate crystallinity. A new chemometric method, based on Multivariate Curve Resolution-Alternating Least Squares algorithm, was developed to calculate the spectrum of amorphous ITR in the matrices and to determine the crystalline/amorphous ratio of aged samples. As it was expected ITR in single needle electrospun SDs was totally amorphous at the beginning, in addition hydroxypropyl methylcellulose could keep ITR in this form at 40°C/75% RH up to one year due to the hydrogen bonds and high glass transition temperature of the SD. In polyvinylpyrrolidone-vinyl acetate matrix ITR remained amorphous at 25°C/60% RH throughout one year. Materials prepared by scaled-up, high throughput version of electrospinning, which is compatible with pharmaceutical industry, also gained the same quality. Therefore these ASDs are industrially applicable and with an appropriate downstream process it would be possible to bring them to the market.
Available from: Guijun Xian
- "As reported, moisture ingress into FRPs may degrade the mechanical properties and thermal properties (e.g., glass transition temperatures) due to plasticization . Water uptake may also lead to swelling of the composite structures , resulting in micro-cracking inside the composites, and in evolution of localized stress and strain fields in the fibrous composites  . Stress caused by swelling of matrix due to water ingress deteriorate the interface between the fiber and the resin   . "
[Show abstract] [Hide abstract]
ABSTRACT: In the present article, a pultruded basalt fiber-reinforced polymer (BFRP) plate was thermally aged at 135 °C and 300 °C for 4 h, and the aged BFRPs were sequentially immersed in distilled water and strong alkaline solution (pH = 13.5) at 20, 40 and 60 °C for six months. The moisture uptake behaviors due to thermal aging were investigated. As found, thermal aging at 300 °C brought in many voids, and obvious degradation of the cross-linking density (ρ) of the epoxy matrix due to thermal decomposition. Further immersion in alkaline solution leads to additional cracks and more serious hydrolysis of the matrix. Aging at 135 °C causes post-curing of the resin matrix, but deteriorates the bonding behavior between fiber and resin matrix, which is indicated by the enhanced coefficient of diffusion (D) along fiber directions. Two-stage water diffusion model can describe the water uptake process for aged and un-aged BFRPs efficiently. D along and perpendicular to the fibers are determined theoretically and experimentally. Due to the cracks, voids as well as fiber debonding occurred in the thermal aged BFRPs, much increased Ds, lowered activation energy for diffusion and even mass loss (in high temperature alkaline solution) were found.
Available from: Neda Samadi
- "Pore formation and pore closure are two important processes that control the release of the encapsulated macromolecular drugs in poly(D,L-lactide-co-glycolide)based drug delivery systems . It has previously been shown that the glass transition temperature of PLGA based systems in aqueous medium is around 10–15 °C and lower than in the dry state due the plasticizing effect of absorbed water  . Furthermore, it has been also observed that addition of plasticizing agents to PLGA microspheres exposed to relative high humidity led to pore closure . "
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.