Plasticizing effect of water on poly(lactide-co-glycolide)

ArticleinJournal of Controlled Release 108(1):1-9 · December 2005with57 Reads
Impact Factor: 7.71 · DOI: 10.1016/j.jconrel.2005.07.009 · Source: PubMed
Abstract

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.

    • "...he 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 ..."
      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.
    Full-text · Article · Feb 2016 · International Journal of Pharmaceutics
    B. Démuth B. Démuth A. Farkas A. Farkas H. Pataki H. Pataki +11 more authors... A. Balogh A. Balogh
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    • "...res) due to plasticization [7]. Water uptake may also lead to swelling of the composite structures [8], resulting in micro-cracking inside the composites, and in evolution of localized stress and strain..."
      As reported, moisture ingress into FRPs may degrade the mechanical properties and thermal properties (e.g., glass transition temperatures) due to plasticization [7]. Water uptake may also lead to swelling of the composite structures [8], resulting in micro-cracking inside the composites, and in evolution of localized stress and strain fields in the fibrous composites [9,10]. Stress caused by swelling of matrix due to water ingress deteriorate the interface between the fiber and the resin [7,11,12].
    [Show abstract] [Hide abstract] ABSTRACT: In this article, a pultruded unidirectional basalt fiber-reinforced polymer (BFRP) plate was thermally aged at 135 °C and 300 °C for 4 h, and subsequently immersed in distilled water or strong alkaline solution (simulating concrete pore water, pH = 12.6–13) for 3 months. The variation of the tensile and interlaminar shear (ILSS) properties of the BFRP plates was studied. Thermal aging exhibited a slight effect on both the longitudinal tensile properties and the interlaminar shear strength, although thermal decomposition of the resin matrix started at 300 °C and brought in a high void content (4.8%). FTIR and DMTA results indicate that thermal aging lead to postcuring and oxidation of the resin matrix, leading to an increase of the glass transition temperatures. Thermal aging accelerated the degradation of the BFRP plates in distilled water or alkaline solution at 20, 40 and 60 °C. In the studied hash immersion conditions of 60 °C alkaline solution for 3 months, the unaged, 135 °C aged and 300 °C aged BFRP samples showed reduction in the tensile strength by 43.2%, 62.3% and 74.1%, respectively. The higher the thermal aging and immersion temperatures, the more deterioration of the mechanical properties occurred. Alkaline solution immersion showed more adverse effects compared to the distilled water. The detrimental effects of the thermal aging were attributed to the formation of voids and cracks through which water or alkaline solution tended to easily penetrate into the BFRPs. The degradation of the resin due to thermal aging and immersion was analyzed with dynamic mechanical thermal analysis and scanning electron microscopy analysis. The long term variation of the tensile strength of BFRPs was evaluated based on the Arrhenius equation.
    Full-text · Article · Aug 2015 · Composites Part B Engineering
    0Comments 3Citations
    • "...res) due to plasticization [7]. Water uptake may also lead to swelling of the composite structures [8], resulting in micro-cracking inside the composites, and in evolution of localized stress and strain..."
      As reported, moisture ingress into FRPs may degrade the mechanical properties and thermal properties (e.g., glass transition temperatures) due to plasticization [7]. Water uptake may also lead to swelling of the composite structures [8], resulting in micro-cracking inside the composites, and in evolution of localized stress and strain fields in the fibrous composites [9] [10]. Stress caused by swelling of matrix due to water ingress deteriorate the interface between the fiber and the resin [7] [11] [12].
    [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.
    Full-text · Article · Dec 2014 · Polymer Degradation and Stability
    0Comments 4Citations
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