Antiplasticization Effect Research Articles

Plasticizer concentration and the performance of a diffusion-controlled polymeric drug delivery system

A study of the competing effects of two plasticizers on the drug release from a diffusion-controlled, polymeric drug delivery system (PDDS) is presented. The formulation was prepared by hot melt extrusion and consisted of soluble starch as the polymer, theophylline as the drug and sorbitol as plasticizer. Through measurement of physical properties, it was demonstrated that both water and sorbitol antiplasticize soluble starch. At low water concentrations, the mechanical strength of the compacts made from soluble starch increased with increasing water concentration. With even higher water concentrations, the strength of the starch compacts began to decrease. A similar trend for mechanical properties was obtained for hot melt extrudates as a function of sorbitol concentration. The drug release profiles obtained exhibit two valleys, which can be explained as the simultaneous plasticizing effect of water from the dissolution medium and the antiplasticizing effect of sorbitol from the formulation. An important consequence is that significant unexplained variability in drug release from sustained release PDDS is possible as a result of small fluctuations in plasticizer concentration in the formulation if antiplasticizing effects are not considered as part of formulation development.

Stabilization of Low Glass Transition Temperature Indomethacin Formulations: Impact of Polymer-Type and Its Concentration

The objectives of this study were to formulate and stabilize amorphous formulation of low T(g) drug (Indomethacin, INM) with selected polymers and compare these formulations based on solubility and dissolution rate studies. Eudragit EPO (EPO), Polyvinylpyrrolidone-vinyl acetate copolymer (PVP-VA), and Polyvinylpyrrolidone K30 (PVPK30) were selected as hydrophilic polymers. The melt extrudates were characterized using differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), intrinsic dissolution rate and solubility studies. The formation of single-phase amorphous form was confirmed by DSC and PXRD. The melt extrudates showed a higher intrinsic dissolution rate (IDR), and solubility compared to the pure drug. The amorphous drug in solid solutions with EPO, PVP-VA, and PVPK30 showed tendency to revert back to crystalline form. However, the rate of reversion was dependent on the nature and concentration of the polymer. The solid solution with high ratio of EPO provided superior stabilization of the amorphous INM from crystallization. The stability of the amorphous form of INM could not be related to the glass transition temperature of the formulation as the mechanism of stabilization with EPO appears to be molecular interaction rather than immobilization. The presence of specific molecular interactions between INM and EPO was also shown by the antiplasticization effect.

Drug–polymer interaction and its significance on the physical stability of nifedipine amorphous dispersion in microparticles of an ammonio methacrylate copolymer and ethylcellulose binary blend

Using spectroscopic and thermal analysis, this study investigated drug-polymer interaction and its significance on the physical stability of drug amorphous dispersion in microparticles of an ammonio polymethacrylate copolymer (Eudragit RL) (RL) and ethylcellulose (EC) binary blend (RL/EC = 2:1 w/w) prepared for use in controlled release of poorly water-soluble drugs. Solid dispersion of the model drug, nifedipine in the microparticles could be described as an ideal amorphous mixture for drug loadings up to 11% w/w. The antiplasticizing effect of the polymer blend was indicated by a significant increase in the glass transition point from approximately 50 degrees C for the amorphous nifedipine to approximately 115 degrees C for its solid solution. Moreover, shifts in infrared vibration wavenumber of nifedipine carbonyl and amine groups suggested that the hydrogen bonds (H-bonds) originally formed among nifedipine molecules were broken and replaced by those formed between nifedipine and polymers in the microparticles. Further infrared analysis on nifedipine amorphous dispersions with a single polymer, namely RL or EC, confirmed the proposed hydrogen-bonding interactions; and their stability study results suggested that both antiplasticizing effects and hydrogen bonding of EC and RL with nifedipine might be responsible for the physical stability of the microparticles of nifedipine amorphous dispersion with a RL/EC binary blend.

Kinetics of re‐embrittlement of (anti)plasticized glassy polymers after mechanical rejuvenation

AbstractMechanical rejuvenation is known to dramatically alter the deformation behavior of amorphous polymers. Polystyrene (PS)—for example, typically known as a brittle polymer—can be rendered ductile by this treatment, while a ductile polymer like polycarbonate (PC) shows no necking anymore and deforms homogeneously in tensile deformation. The effects are only of temporary nature, as because of physical aging the increasing yield stress, accompanied by intrinsic strain softening, renders PS brittle after a few hours, while for PC necking in tensile testing returns in a few months after the mechanical rejuvenation treatment. In this study, it is found that physical aging upon rejuvenation in both PS and PC can be delayed in two different ways: (1) by reducing the molecular mobility through antiplasticization and (2) by applying toughening agents (rubbery core–shell particles). For the first route, even though progressive aging is found to decrease with increasing amounts of antiplasticizer added, dilution of the entanglement network results in enhanced brittleness. Besides antiplasticization effects, also some typical plasticization effects are observed, like a reduction in matrix Tg. For the second route, traditional rubber toughening using acrylate core–shell modifiers also results in a reduced yield stress recovery, and ductile tensile deformation behavior is observed even 42 months after mechanical rejuvenation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 134–147, 2008

Efeitos plastificante e antiplastificante do glicerol e do sorbitol em filmes biodegradáveis de amido de mandioca

In this work were studied the plasticizing – antiplasticizing effects of glycerol and sorbitol on moisture sorption and mechanical properties of cassava starch films. Films were produced by casting with cassava starch (3g starch/100 g filmogenic solution) and different concentrations of glycerol or sorbitol (0, 5, 10, 15, 30 and 40 g/100 g starch). Glycerol and sorbitol acted as antiplasticizers when used at a low concentration (≤ 15 g/100 g starch) and low values of water activity (≤ 0,58). The antiplasticizing effect could be demonstrated by the decrease in hydrophilicity and in flexibility of the films at these conditions. At higher concentrations and higher water activity values, the employed plasticizers exerted its plasticizing effect

The solid state structure of polycarbonate blends with lead phthalocyanine

The physical properties of polycarbonate blends containing the nonlinear optical dye lead tetracumylphenoxy phthalocyanine were characterized. Blends with up to 20 wt% dye were prepared and characterized in terms of density, refractive index, glass transition temperature, loss modulus, subambient relaxation behavior, and free volume hole size from positron annihilation lifetime spectroscopy. The dye strongly affected the physical properties of the blend. The initial 0.1 wt% dye produced a dramatic increase in the density. A similar trend in the refractive index was accounted for by the change in density using a relationship between density and refractive index derived from the Lorentz–Lorenz equation. Increasing the dye content to 8 wt% led to a large reduction in the glass transition temperature. An increase in E′ and a decrease in the subambient γ-relaxation intensity accompanied the large decrease in T g. This behavior fit the conventional concept of antiplasticization, which has been described for other low molecular weight diluents in PC. Recognizing that the dye was present as a mixture of monomer, dimer and higher aggregates, it was shown that the monomer form was responsible for the antiplasticization. In the glass, dimer and higher aggregates were viewed as nanoparticle fillers. It was confirmed that the antiplasticization effect was due to a reduction in excess hole free volume of the polymer.

Effects of antiplasticization on the thermal, volumetric, and transport properties of polyethersulfone

AbstractThe aim of this work was to study the effects of the addition of low molar mass additives such as N‐phenyl‐2‐naphthylamine (PNA) and hexafluoro‐bisphenol‐A (HFBPA) on the volumetric, thermal and transport properties of polyethersulfone (PES). The additive incorporation resulted in changes in molecular mobility and properties of the glassy PES matrix associated with antiplasticization. The changes in molecular mobility were accompanied by reductions in water vapor permeability of the PES of up to 93% for 30 wt % incorporation of PNA and of up to 70% for the addition of 20 wt % of HFBPA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2627–2633, 2007

Dielectric study of the antiplasticization of trehalose by glycerol

Recent measurements have suggested that the antiplasticizing effect of glycerol on trehalose can significantly increase the preservation times of proteins stored in this type of preservative formulation. In order to better understand the physical origin of this phenomenon, we examine the nature of antiplasticization in trehalose-glycerol mixtures by dielectric spectroscopy. These measurements cover a broad frequency range between 40 Hz to 18 GHz (covering the secondary relaxation range of the fragile glass-former trehalose and the primary relaxation range of the strong glass-former glycerol) and a temperature (T) range bracketing room temperature (220 K to 350 K). The Havriliak-Negami function precisely fits our relaxation data and allows us to determine the temperature and composition dependence of the relaxation time tau describing a relative fast dielectric relaxation process appropriate to the characterization of antiplasticization. We observe that increasing the glycerol concentration at fixed T increases tau (i.e., the extent of antiplasticization) until a temperature dependent critical "plasticization concentration" xwp is reached. At a fixed concentration, we find a temperature at which antiplasticization first occurs upon cooling and we designate this as the "antiplasticization temperature," Tant. The ratio of the tau values for the mixture and pure trehalose is found to provide a useful measure of the extent of antiplasticization, and we explore other potential measures of antiplasticization relating to the dielectric strength.

Plasticizing Effects of Beeswax and Carnauba Wax on Tensile and Water Vapor Permeability Properties of Whey Protein Films

ABSTRACT: The possible plasticizing effect of beeswax (viscoelastic wax) and carnauba wax (elastic wax) on tensile and water vapor permeability properties of whey protein isolate (WPI) films was studied. For the experiments, 3 groups of films with different WPI:glycerol ratios (1:1; 1.5:1; 2:1, 2.5:1, and 3:1) were prepared. The 1st group was made without the addition of wax, and the latter 2 groups were made with the addition of beeswax and carnauba wax, respectively, mixing 1 part of wax to 1 part of WPI. Lipid particle size, water vapor permeability, tensile properties, and thickness of films were analyzed and measured. The results show that the incorporation of beeswax produced a plasticizing effect in WPI:glycerol films, whereas carnauba wax produced an anti-plasticizing effect. The moisture barrier properties of WPI:glycerol films benefit from the addition of beeswax, by both increase of the hydrophobic character and decrease of the amount of hydrophilic plasticizer required in the film.

The effect of plasticizers on thermoplastic starch compositions obtained by melt processing

The effect of the type and amount of plasticizer on the mechanical, thermal and water-absorption properties of melt-processed thermoplastic starch was investigated. In general, monohydroxyl alcohols and high molecular weight glycols failed to plasticize starch, whereas shorter glycols and sorbitol were effective. The quantity and type of plasticizer did not affect appreciably the crystallinity of the processed samples, but influenced the mechanical properties of these TPS in two opposite ways, viz. a softening effect due to the plasticizing of the amorphous phase and stiffening one due to an antiplasticization effect.

Characterization of Physico-Mechanical Properties of Indomethacin and Polymers to Assess their Suitability for Hot-Melt Extrusion Processs as a Means to Manufacture Solid Dispersion/Solution

The objective of the study was to characterize the physical and viscoelastic properties of binary mixtures of drug and selected polymers to assess their suitability for use in the hot-melt extrusion (HME) process as a means to improve solubility by manufacturing either solid dispersion or solid solution. Indomethacin (INM) was selected as a model drug. Based on comparable solubility parameters, the selected polymers were Eudragit EPO (EPO), polyvinylpyrrolidone/vinyl acetate copolymer (PVP-VA), polyvinylpyrrolidone K30 (PVPK30), and poloxamer 188 (P188). The various drug and polymer systems were characterized for thermal and rheological properties as a function of drug concentration to provide an insight into miscibility and processibility of these systems. From the thermal analysis studies, a single T(g) was observed for the binary mixtures of INM/EPO, INM/PVP-VA, and INM/PVPK30, indicating miscibility of drug and polymer in the given ratios. In the case of mixtures of INM/P188, two melting endotherms were observed with decreasing drug melting point as a function of polymer concentration indicating partial miscibility of drug in polymer. As part of the rheological evaluation, zero rate viscosity (eta(o)) and activation energy (E(a)) was determined for the various systems using torque rheometer at varying shear rates and temperatures. The eta(o) for binary mixtures of drug and EPO, PVP-VA and PVPK30 were found to be significantly lower as compared to pure polymer, indicating disruption of the polymer structure due to miscibility of the drug. On the other hand, INM/P188 mixtures showed a higher eta(o) compared to pure polymer indicating partial miscibility of drug and polymer. With respect to E(a), the mixtures of INM/EPO showed an increase in E(a) with increasing drug concentration, suggesting antiplasticization effect of the drug. These findings corroborate the thermal analysis results showing increase T(g) for the various binary mixtures. The mixtures of INM/PVP-VA showed a decrease in the E(a) with the increasing drug concentration suggesting a plasticization effect of the drug. The understanding of thermal and rheological properties of the various drug/polymer mixtures help established the processing conditions for hotmelt extrusion (such as extrusion temperatures and motor load) as well as provided insight into the properties of the final extrudates. Using the actual hot-melt processing, a model was developed correlating the zero rate viscosity to the motor load determined by rheological evaluation.

Antiplasticization of cereal-based products by water. Part II: Breakfast cereals

Corn and wheat bran flakes were equilibrated to different water activities and subjected to compression in bulk. Relationship between both force and work of compression and water activity was analyzed using Peleg's and Fermi's equations. Scanning electron microphotographs were used to analyze microscopic structure of flakes.In both analyzed flakes an antiplasticizing effect of water was observed. Beyond water activity 0.6–0.7 plasticizing effect of water was noticed. In the antiplasticizing range of water activities response of flakes to compressing force was related to microstructure of the material. Relationship between both the force and work of compression and water activity in corn flakes was curvilinear and could not be approximated by the Fermi's equation. Corn flakes showed rather homogenous porous structure with continuous air cell wall matrix. Influence of water activity on both the force and work of compression in wheat bran flakes was well described by the Fermi's equation. The flakes showed microstructure with many discontinuities and resembling agglomerate. The antiplasticizing effect of water was less evident than that in corn flakes and the compression either force or work changed little with water activity until a critical value was reached.

Mechanical gradient interphase by interdiffusion and antiplasticisation effect—study of an epoxy/thermoplastic system

A stoichiometric amine–epoxy formulation was cured in the presence of a thermoplastic, namely poly(vinylpyrrolidone) (PVP). The epoxy system consisted of the resin diglycidyl ether of bisphenol A (DGEBA) and the aromatic curing agent 4,4′-diaminodiphenylsulfone (DDS). As shown for this system in a former study by Oyama et al. [Oyama HT, Lesko JJ, Wightman JP. J Polym Sci B 1997;35:331–46. [36]], preferential absorption of amine molecules by PVP can occur. In the present study, the focus is on the variations of local elastic properties within the epoxy interphase adjacent to the PVP layer. The curing was performed close to the glass transition temperature, Tα, of the PVP film, namely at 170°C. Variations of the local amine concentration were tracked using energy-dispersive analysis of X-rays (EDX), by taking benefit of the sulfur contained in DDS. Using temperature-dependent dynamic mechanical analysis (DMA), a series of epoxy reference samples of different amine–epoxy concentration ratios, r, was investigated in order to work out the relationship between r and the epoxy storage modulus at room temperature. In the excess-epoxy regime, r<1, the modulus is observed to increase with departure from the stoichiometric ratio, r=1. Considering the respective suppression of the β-transition, the observed characteristic can be explained by an antiplasticisation effect. Depth-sensing indentation (DSI) experiments across the epoxy/PVP interphase provided evidence for strong modulus variations. In consistency with the EDX and the DMA data, in the vicinity of the PVP layer the local epoxy modulus is increased. The total change of the epoxy Young's modulus is ∼1.1GPa. However, the total width of the modulus decay of ∼175μm is ∼2.5 times larger than the one of the DDS concentration gradient. This finding is discussed in terms of additional spatial variations of the DGEBA concentration as well as long-range diffusion currents of DDS induced by the interdiffusion processes and their effect on the final network of crosslinks.

Interactive plasticizing–antiplasticizing effects of water and glycerol on the tensile properties of tapioca starch films

The effects of water and glycerol as diluents on physical properties of glassy tapioca starch films were studied. Water and glycerol depressed the calorimetric glass transition temperature ( T g) of the tapioca starch films. In glycerated and non-glycerated starch films, the tensile modulus ( E) was plasticized by moisture. Glycerol acted as an antiplasticizer on film modulus when present at a low concentration (2.5%) in drier films ( a w≤0.22). Both strain-at-break and toughness of starch films increased to a maximum as a w was increased to a critical level (0.22–0.32) before decreasing with further humidification. In contrast, minima in those two properties were observed in films containing 10–15% glycerol at a w=0.11 and 0.22. The presence of small amounts of glycerol was able to exert classic antiplasticizing effects on possibly all tensile properties studied, but only in relatively drier systems. On the other hand, antiplasticization by water manifested itself only in mechanical properties determined at high deformation (i.e. tensile strength and toughness).

Matrix relaxation and change of water state during hydration of peat

In this study, hydration of a peat sample was investigated with differential scanning calorimetry (DSC) in terms of glass transition behavior and the formation of freezable and unfreezable water. Special attention was drawn to the development of these characteristics in the course of hydration and to plasticizing and antiplasticizing effects of water. Freezable water was formed above a water content threshold of Θ crit = (23 ± 7)% and revealed structured melting peaks indicating freezable bulk-like water and freezable bound water. The freezable bound water revealed a broad, kinetically controlled melting endotherm, and the melting barrier increased with increasing hydration time. Glass transitions were found in between 43 °C and 68 °C with a change in heat capacity of Δ C = (0.13 ± 0.08) J g −1 K −1. Glass transition behavior does not fully match the theoretical expectations and is linked with water binding. Water reveals a short-term plasticizing function in the range of days as well as a slow antiplasticizing function in the range of weeks or even months. The findings are consistent with the hydrogen bond based cross-linking model (HBCL) suggested in a previous study. Non-equilibrium and matrix relaxation are considered the rule rather than the exception in nature and underline the ecological relevance of hydration, the relevance for sorption and transport phenomena was well as possibly for soil development.

Effects of Hydrophilic Plasticizers on Mechanical, Thermal, and Surface Properties of Chitosan Films

Chitosan films were plasticized with four hydrophilic compounds, namely, glycerol (GLY), ethylene glycol (EG), poly(ethylene glycol) (PEG), and propylene glycol (PG). Our objective was to investigate the effect of plasticizers on mechanical and surface properties of chitosan films. The stability of plasticized films was observed by storage for 3 and 20 weeks in an environmental chamber at 50 +/- 5% RH and 23 +/- 2 degrees C. Plasticization improves the chitosan ductility, and typical stress-strain curves of plasticized films have the features of ductile materials, except the film made with 5% PG that exhibits as a brittle polymer and shows an antiplasticization effect. In most cases, the elongation of plasticized films decreases with the storage time, which might be due to the recrystallization of chitosan and the loss of moisture and plasticizer from the film matrix. Although at the beginning the mechanical properties of films made with PG, at high plasticizer concentration, are comparable to those of films made with EG, GLY, and PEG, their stability is poor and they tend to become brittle materials. The surface properties, analyzed by contact angle measurement, reveal that plasticization increases film hydrophilicity. It is found that GLY and PEG are more suitable as chitosan plasticizers than EG and PG by taking into account their plasticization efficiency and storage stability. Furthermore, a plasticizer concentration of 20% (w/w) with GLY or PEG seemingly is sufficient to obtain flexible chitosan film with a good stability for 5 months of storage.

Mass uptake study of the diffusion of water and SBF into poly(2-hydroxyethyl methacrylate-co-tetrahydrofurfuryl methacrylate) containing aspirin or vitamin B12

The ingress of water and Kokubo simulated body fluid (SBF) into poly(2-hydroxyethyl methacrylate) (PHEMA), and its co-polymers with tetrahydrofurduryl methacrylate (THFMA), loaded with either one of two model drugs, vitamin B12 or aspirin, was studied by mass uptake over the temperature range 298–318 K. The polymers were studied as cylinders and were loaded with either 5 wt% or 10 wt% of the drugs. From DSC studies it was observed that vitamin B12 behaved as a physical cross-linker restricting chain segmental mobility, and so had a small anti-plasticisation effect on PHEMA and the co-polymers rich in HEMA, but almost no effect on the T g of co-polymers rich in THFMA. On the other hand, aspirin exhibited a plasticising effect on PHEMA and the co-polymers. All of the polymers were found to absorb water and SBF according to a Fickian diffusion mechanism. The polymers were all found to swell to a greater extent in SBF than in water, which was attributed to the presence of Tris buffer in the SBF. The sorptions of the two penetrants were found to follow Fickian kinetics in all cases and the diffusion coefficients at 310 K for SBF were found to be smaller than those for water, except for the polymers containing aspirin where the diffusion coefficients were higher than for the other systems. For example, for sorption into PHEMA the diffusion coefficient for water was 1.41 × 10−11 m2/s and for SBF was 0.79 × 10−11 m2/s, but in the presence of 5 wt% aspirin the corresponding values were 1.27 × 10−11 m2/s and 1.25 × 10−11 m2/s, respectively. The corresponding values for PHEMA loaded with 5 wt% B12 were 1.25 × 10−11 m2/s and 0.74 × 10−11 m2/s, respectively.

Glass Transitions in Peat: Their Relevance and the Impact of Water

This contribution aims to expand the macromolecular view of fractionated natural organic matter (NOM)to organic matter in whole soils. It focuses on glass transition behavior of whole soil organic matter (SOM) and its interrelation with water through use of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Three processes of structural relaxation related to macromolecular mobility were distinguished. Process I occurs in thermally pretreated and very low water-content samples and corresponds to classic glass transition behavior. Process II occurs in water-containing samples, where water is believed to act as an antiplasticizing agent in the peat at water contents below 12%, causing decreased macromolecular mobility and increased glass transition temperature. We suggestthe formation of hydrogen bond-based cross-links being responsible for this antiplasticizing effect. Process III represents a slow swelling process induced by water uptake with a time constant of swelling in the order of days, with water acting as a plasticizing agent. Results from this work are of particular importance for environmental systems as changes in environmental conditions (e.g., water content, temperature) may induce slow structural relaxation processes in NOM over periods of time ranging from days to weeks. These influences on NOM macromolecular mobility lead to continuous changes in physicochemical properties that may greatly influence sorbate-sorbent interactions in surface and subsurface environments.

Effect of supercritical carbon dioxide on the crystallization and melting behavior of linear bisphenol A polycarbonate

AbstractThe crystallization and melting behavior of bisphenol A polycarbonate treated with supercritical carbon dioxide (CO2) has been investigated with differential scanning calorimetry. Supercritical CO2 depresses the crystallization temperature (Tc) of polycarbonate (PC). The lower melting point of PC crystals increase nonlinearly with increasing treatment temperature. This indicates that the depression of Tc is not a constant at the same pressure. Tc decreases faster at a higher treatment temperature than at a lower temperature. The leveling off of the depression in Tc at higher pressures is due to the antiplasticization effect of the hydrostatic pressure of CO2. The melting curves of PC show two melting endotherms. The lower melting peak moves to a higher temperature with increasing treatment temperature, pressure, and time. The higher temperature peak moves toward a higher temperature as the treatment temperature is increased, whereas this peak is independent of the treatment pressure, time, and heating rate. The double melting peaks observed for PC can be attributed to the melting of crystals with different stability mechanisms. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 280–285, 2004

Epoxy/alumina nanoparticle composites. I. Dynamic mechanical behavior

AbstractWe studied the influence that alumina nanoparticle addition has on the dynamic mechanical spectra of an amino‐cured epoxy resin. A suppression of the short‐scale cooperative motions related to the β relaxation and an increase in the activation energy for the β relaxation of the epoxy matrix was observed as the alumina content increased. This is explained in terms of an antiplasticization effect of the alumina nanoparticles on the epoxy resin. An estimation of the effective thickness of the nanoparticle–matrix interfacial region was done based on the reduced damping. The dependence of the composites' reduced modulus on the alumina nanoparticles content is very well fitted by the generalized Kerner equation. The best‐fit parameter values suggest the presence of small and strong agglomerates in the composites at room temperature. At temperatures above the Tg, these agglomerates start to behave as weak ones because of the polymer matrix softening and particle–particle and particle–matrix slippage and friction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3774–3785, 2003