Plasticizing Effect Of Water Research Articles

Service life assessment and moisture influence on bio-based thermosetting resins

In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, Tg. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and Tg data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3–10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. Tg measurements show that moisture inside the specimen decreases Tg; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites.

Water-induced shape memory effect of graphene oxide reinforced polyvinyl alcohol nanocomposites

A novel water-induced shape memory polymer based on polyvinyl alcohol (PVA) was prepared by introducing graphene oxide (GO). Due to the strong hydrogen bonding interaction between PVA and GO, some additional physically cross-linked points could be formed in PVA, which largely improved shape memory properties of PVA. Solvent-induced shape memory behavior was observed by immersing PVA/GO nanocomposites in water. The water-induced shape recovery was due to the decrease of glass transition temperature and storage modulus. This could be explained by the swelling plasticizing effect of water on PVA, as indicated by the obvious expansion in volume of PVA. On the other hand, the weakened hydrogen bonding between PVA and GO was also observed after immersing the PVA/GO nanocomposites in water. Thus both the plasticizing effect and the competitive hydrogen bonding were the two main reasons for the shape recovery of PVA/GO nanocomposites. This study provides a framework for developing new shape memory polymers (SMPs) and for better understanding the shape recovery mechanism in solvent-induced SMPs.

Ageing and moisture uptake in polymethyl methacrylate (PMMA) bone cements

Bone cements are extensively employed in orthopaedics for joint arthroplasty, however implant failure in the form of aseptic loosening is known to occur after long-term use. The exact mechanism causing this is not well understood, however it is thought to arise from a combination of fatigue and chemical degradation resulting from the hostile in vivo environment. In this study, two commercial bone cements were aged in an isotonic fluid at physiological temperatures and changes in moisture uptake, microstructure and mechanical and fatigue properties were studied. Initial penetration of water into the cement followed Fickian diffusion and was thought to be caused by vacancies created by leaching monomer. An increase in weight of approximately 2% was experienced after 30 days ageing and was accompanied by hydrolysis of poly(methyl methacrylate) (PMMA) in the outermost layers of the cement. This molecular change and the plasticising effect of water resulted in reduced mechanical and fatigue properties over time. Cement ageing is therefore thought to be a key contributor in the long-term failure of cemented joint replacements. The results from this study have highlighted the need to develop cements capable of withstanding long-term degradation and for more accurate test methods, which fully account for physiological ageing.

Moisture induced plasticity of amorphous cellulose films from ionic liquid

Amorphous cellulose films were created by regeneration from 1-Ethyl-3-methylimidazolium acetate (EmimAc) solutions. Their mechanical properties were analyzed as a function of water content. Cellulose with different molecular weights, i.e. microcrystalline cellulose (Avicel), Spruce cellulose and bacterial nanocellulose (BNC), were used for film preparation. All the regenerated films were free from EmimAc residues as shown by Fourier transform infrared spectroscopy (FTIR), amorphous as shown by wide angle X-ray spectroscopy (WAXS) and optical transparent. The equilibrium water content (w/w) was measured at different relative humidities. The plasticizing effect of water on the films was evidenced by both tensile tests and dynamical mechanical analysis (DMA) with humidity scans. The mechanical properties were clearly related to the proportional water uptake of the films. The sample with the longest cellulose chains, i.e. BNC, showed significantly larger elongation to brake at high moisture content which was owed to chain entanglements.

A Molecular Dynamics Approach for Predicting the Glass Transition Temperature and Plasticization Effect in Amorphous Pharmaceuticals

The objectives of this study were as follows: (i) To develop an in silico technique, based on molecular dynamics (MD) simulations, to predict glass transition temperatures (Tg) of amorphous pharmaceuticals. (ii) To computationally study the effect of plasticizer on Tg. (iii) To investigate the intermolecular interactions using radial distribution function (RDF). Amorphous sucrose and water were selected as the model compound and plasticizer, respectively. MD simulations were performed using COMPASS force field and isothermal-isobaric ensembles. The specific volumes of amorphous cells were computed in the temperature range of 440-265 K. The characteristic "kink" observed in volume-temperature curves, in conjunction with regression analysis, defined the Tg. The MD computed Tg values were 367 K, 352 K and 343 K for amorphous sucrose containing 0%, 3% and 5% w/w water, respectively. The MD technique thus effectively simulated the plasticization effect of water; and the corresponding Tg values were in reasonable agreement with theoretical models and literature reports. The RDF measurements revealed strong hydrogen bond interactions between sucrose hydroxyl oxygens and water oxygen. Steric effects led to weak interactions between sucrose acetal oxygens and water oxygen. MD is thus a powerful predictive tool for probing temperature and water effects on the stability of amorphous systems during drug development.

State diagram, sorption isotherm and color of blueberries as a function of water content

A state diagram of blueberries was developed using freezing and glass transition curves, and maximal-freeze-concentration condition in order to predict the behavior and physical changes of fresh and lyophilized blueberries. Freezing points (Clausius–Clapeyron equation) and glass transition temperature (Gordon–Taylor equation) were measured by differential scanning calorimetry (DSC). Color samples were measured by computer vision system. Isotherms data was fitted using GAB, Peleg and Iglesias–Chirife equations.Glass transition decreased as decreasing solids content due to water plasticizing effect. Lyophilized and fresh samples varied their color; however thermal properties were similar, principally affected by their constituents although the blueberry's matrix state changed. Maximum-freeze-concentration conditions was found as X′s=0.69 kg solid (kg blueberry)−1, T′g=−54.86 °C and T′m=−45.45 °C. In conclusion, a state diagram was developed using lyophilized fruit but it can be extrapolated to whole blueberry fruit.

Hydrothermal ageing of alfa fiber reinforced polyvinylchloride composites

This paper describes the influence of hydrothermal ageing behavior on the properties of alfa fiber reinforced polyvinylchloride composites (PVC/alfa). Hydrothermal ageing was carried out by immersing specimens in distilled water at 100°C over a 120h period. Composites without coupling agent showed higher water uptake than those with coupling agent. Tensile strength, Young’s modulus and thermal stability were found to decrease after hydrothermal ageing due to fiber damage and reduced fiber matrix interfacial bonding, while elongation at break was found to increase due to the plasticizing effect of water.

The Contribution of the Inherent Restricted Mobility of Glassy Sugar Matrices to the Overall Stability of Freeze-Dried Bacteria Determined by Low-Resolution Solid-State 1H-NMR

The aim of this work was to evaluate whether, in case of freeze-dried bacteria, the protective effect of a surrounding glassy matrix can be ascribed to its inherent restricted molecular mobility. Lactobacillus paracasei ssp. paracasei together with three different protectants (lactose, trehalose and dextran) was freeze-dried and stored at different temperatures and water activities (a w). The spin–spin relaxation time T 2 was determined by means of low resolution 1H-NMR spectroscopy and described in relation to the storage conditions and the glass transition temperature T g. Compared to the disaccharides, dextran generally showed lower absolute T 2 values and a weaker dependence on storage a w and temperature. For lactose and trehalose, the plasticising effect of water and temperature was significantly stronger. Their relaxation time T 2 was shown to be only dependent on ∆T, the temperature distance to T g. Furthermore, both disaccharides showed an increase in T 2 already 20–40 °C below T g. Thus, T g in reference to T 2 does not act as an absolute threshold. This fact could explain the finding of several publications that an absolute stability for freeze-dried bacteria can only be achieved 30–50 °C below T g. Further comparison between T 2 and the corresponding inactivation rates revealed that the relevance of mobility for the stability of lyophilisates is strongly temperature and system dependent. At low storage temperatures, a potential rate-limiting effect due to the lack of detrimental chemical and physical reactions is invisible. However, with increasing storage temperature, the restricted mobility is shown to become a rate limiting bottleneck. Thus, the harsher the environmental condition, the more relevant is the protective effect of a surrounding glassy matrix.

Effect of relative humidity on carvacrol release and permeation properties of chitosan based films and coatings

The influence of water vapour conditions on mass transport and barrier properties of chitosan based films and coatings were studied in relation to surface and structural properties. Water contact angles, material swelling, polymer degradation temperature, barrier properties (PO2, PCO2, WVP) and aroma diffusion coefficients were determined. The solvent nature and the presence of carvacrol influenced the surface and structural properties and then the barrier performance of activated chitosan films. Increasing RH from 0% to 100% led to a significant increase in material swelling. The plasticization effect of water was more pronounced at high humid environment, while at low RH the matrix plasticization was induced by carvacrol. The deposit of a thin chitosan layer on polyethylene decreased PO2 and PCO2 both in dry and humid conditions. The carvacrol release from the chitosan matrix was strongly influenced by RH. A temperature increase from 4 to 37°C also had an impact on carvacrol diffusivity but to a lesser extent than RH.

Different behavior of water in confined solutions of high and low solute concentrations

Water-glycerol solutions confined in 21 Å pores of the silica matrix MCM-41 C10 have been studied using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The results suggest a micro-phase separation caused by the confinement. Likely the water molecules coordinate to the hydroxyl surface groups of the pores, leaving most of the glycerol molecules in the centre of the pores. This makes the dynamics of glycerol almost concentration independent up to water concentrations of about 85 wt%. However, at higher water concentrations no substantial clustering of glycerol molecules should occur and the glass transition related dynamics exhibit an anomalous behaviour. Instead of a common plasticization effect of water, as for the corresponding bulk solutions (when no ice is formed), it is evident that water acts as an anti-plasticizer in the confinement at high water concentrations. We propose that the increased water concentration slows down the glass transition related dynamics in the deeply supercooled regime due to that a rigid hydrogen bonded network structure of water molecules is formed at low temperatures and low glycerol concentrations. This is in contrast to the situation in a homogenously mixed bulk solution of a high solute concentration where the water molecules will be less hydrogen bonded, and therefore are typically more mobile than the surrounding solute molecules. An almost complete hydrogen bonded network of water molecules may, even in confinements, be sufficiently rigid to slow down the relaxation of embedded solute molecules. It can also be expressed the other way around, i.e. small amounts of glycerol act as a plasticizer for water, due to its breaking up of the nearly tetrahedral network structure. From the here observed concentration dependent behaviour of the deeply supercooled bulk and confined solutions it seems, furthermore, evident that the Tg value of bulk water cannot be estimated from extrapolations of aqueous solutions.

Moisture desorption isotherms and glass transition temperatures of osmo-dehydrated apple and pear

The aim of this work was to evaluate osmo-dehydrated pear and apple stability on the basis of combined data of moisture desorption isotherms and glass transition temperatures (Tg) investigated in the temperature range of 30–60°C. Parallelipedic pieces of pears and apples were osmo-dehydrated at 30°C in sucrose syrups at 70% during 65min. To study their hygroscopic properties behavior, the osmo-dehydrated fruits were stored in static desiccators at 30, 45 and 60°C, and relative humidities ranging from 6 to 80%. The GAB model satisfactory described the relationship between the water activity (aw) and water content (X) of osmo-dehydrated fruits (r2≥0.994). Differential scanning calorimetry was used to measure Tg of osmo-dehydrated fruits conditioned at various water activities. A strong plasticizing effect of water on Tg was found with a large reduction of Tg when the water content increased. The dependence of Tg on water activity data was satisfactory correlated by the Roos model (0.993≤r2≤0.999). Whereas the Tg∼Xw was adequately described by Gordon and Taylor model (0.898≤r≤0.990). The changes of Tg∼aw and Tg∼Xw were established and the critical values of water contents were determined for the investigated range of temperature.

Membranes of poly(dl-lactic acid)/Bioglass® with asymmetric bioactivity for biomedical applications

In guided tissue/bone regeneration, membranes are used as barriers to prevent the faster growing soft tissue cells from entering the defect space and to regenerate periodontal ligament, cementum, and bone. The two sides of the membranes are in contact with distinct biological environments in which one faces a region in which osteointegration should be ideally promoted. Biocompatible and biodegradable composite membranes were produced by combining poly(d,l-lactic acid) and Bioglass® particles featuring an asymmetric bioactivity and a good integration between the polymeric and inorganic fractions. The asymmetric distribution of the osteoconductive particles was produced during the processing of the membrane using a solvent casting methodology. Only the inorganic-rich face promoted the deposition of bone-like apatite after immersing the composite membrane in simulated body fluid for 2 days. The mechanical properties of the membranes were evaluated using dynamic mechanical analysis by analyzing the viscoelastic properties and the glass transition of the samples in both dry and wet states. A clear plasticization effect of water was detected, but the composite membranes were found to be stiffer, at 37ºC, compared with the pure polymer. SaOs-2 cells attached on both the surfaces and proliferated after 7 days in culture.

A phenomenological and thermodynamic study of the water permeation process in corn starch/MMT films

Water transport in edible films of starch based products is a complex phenomenon due to the strong interaction of sorbed water molecules with the polymeric structure of starch. Moisture sorption isotherms of starch and starch/MMT films were obtained. The results indicated that nanoclay incorporation produces a decrease of water uptake at all temperatures analysed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the starch matrix. Effect of driving force and water activity (aw) values at each side of the film on permeability and diffusivity coefficients were analysed. The effect of the tortuous pathway generated by MMT incorporation was significant only in the middle and lower range of aw. At high aw range the plasticizing effect of water dominated and MMT incorporation had little effect on the water barrier properties of these films.

Effect of modified starch or maltodextrin incorporation on the barrier and mechanical properties, moisture sensitivity and appearance of soy protein isolate-based edible films

Abstract This work aimed to study the effect of starch (acetylated di-starch phosphate and starch acetate) and maltodextrin (DE 10.2 and DE 15.6) on the properties of soy protein isolate (SPI) films. Films were cast from heated (70 °C for 20 min) alkaline (pH 10) aqueous solutions of soy protein isolate (8%) containing glycerol (50% of SPI) as a plasticizer and starch or maltodextrin (20% of SPI). For all types of films, water vapor sorption kinetics during 24 h at 25 °C and 75% relative humidity (RH), diffusion coefficient of water vapor, water vapor permeability at 25 °C for two relative humidity differentials (40–75 and 40–100%), tensile strength and elongation at break, color and microstructure were determined after conditioning film specimens at 25 °C and 53% RH for 7 days. Addition of starch and maltodextrin had a significant effect on water vapor adsorption of soy films and increase of diffusion coefficient from 1.73 to 2.60 m2 s− 1. Water vapor permeability increased as relative humidity differentials increased and observed results can be correlated with the plasticizing effect of water. All films demonstrated low values of tensile strength (~ 1.14–1.96 MPa) and elongation at break (~ 25.6–34.7%). All films obtained were opaque and homogenous. Industrial relevance Edible films based on proteins are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. There is a real need to find methods for production of soy films with properties accepted by the industry. One of the solutions is preparation of composite films based on protein and polysaccharide components. This work deals with the physico-chemical behavior of two types of carbohydrate polymers (modified starch and maltodextrins) on the physical–chemical properties of edible films based on soy protein isolate. Moisture sorption and kinetics, mechanical and barrier properties have been studied and related to structure. This paper suggests that physico-chemical properties of soy protein isolate films can be modified by the incorporation of modified starch and maltodextrins.

Colorful and transparent poly(vinyl alcohol) composite films filled with layered zinc hydroxide salts, intercalated with anionic orange azo dyes (methyl orange and orange II)

Layered zinc hydroxide salts (zinc LHS) were intercalated with anionic orange azo dyes, namely methyl orange (MO) and orange II (OII), and co-intercalated with hydrated chloride anions. After characterization by X-ray diffraction (XRD), thermal analysis (TGA/DTA), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), the materials were used as fillers for poly(vinyl alcohol) (PVA). Colorful transparent films were obtained by wet casting, revealing good dispersion of the material into the polymer. In the case of zinc LHS/OII, PVA was intercalated between the zinc LHS layers. Evaluation of the mechanical properties of the PVA composite films revealed that the layered colorful materials were able to increase the mechanical properties of the PVA films only when the films were stored under lower relative humidity. As expected, films with higher water content displayed reduced tensile strength and modulus because of the plasticizing effect of water. As for the films stored at 43% relative humidity, more pronounced improvement of modulus was observed for 1 and 4% zinc LHS/OII, and enhanced tensile strength was achieved for 0.5 and 1% zinc LHS/OII. This effect can be attributed to better dispersion of the layered filler and its better adhesion to the PVA matrix.

Revisiting the thermal relaxations of poly(vinyl alcohol)

AbstractThe molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well‐established plasticizing effect of water on the glass‐transition temperature (Tg) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed Tg for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low‐ (from 20 to 80°C) and high‐ (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius‐type relaxations. However, once the moisture was properly eliminated, a single non‐Arrhenius α relaxation was clearly observed. X‐ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary βc relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Unified phase diagram of gelatin films plasticized by hydrogen bonded liquids

Plasticizing effects of water and glycerol are widely used in pharmaceutical applications of gelatin films. We investigated gelatin films containing water or water and glycerol equilibrated under a range of relative humidity. Films were characterized by differential scanning calorimetry running in classical and modulated modes. Glass and melting transition temperatures, relaxation and melting enthalpies and heat capacity changes were determined versus film composition and maturation time. This investigation quantifies the amount of collagen type structure through the melting enthalpy of triple helices. A unified phase diagram for glass and melting transition temperatures is presented as a universal curve for any proportion of water and glycerol in films versus a single parameter, which is the ratio of hydroxyl groups belonging to water or glycerol per amino-acid group and highlights the role played by the hydrogen bonding. The molecular mechanisms involved in the plasticizing effects are discussed.

Influence of sugar composition on water sorption isotherms and on glass transition in apricots

Desorption isotherms of fresh and osmotically treated (70%, 30°C) apricots have been measured at 30, 45 and 60°C by the static gravimetric method. A differential scanning calorimeter was used to determine the Tg of samples equilibrated with several water activities. The osmotic pretreatment affected the shape of the desorption isotherms because of biopolymer binding at low activities values and dissolution of sucrose at high activities values. At 45°C, isotherms of fresh and sucrose impregnated apricots are identical. At 60°C, sucrose impregnation depressed water activity, while at 30°C the opposite effect is observed. Evolution of moisture content at the first saturation layer expresses these effects of sucrose impregnation and temperature. Peleg model fitted the best experimental desorption isotherms of the fresh and osmotically treated apricots (0.990⩽r2⩽0.999, 0.005⩽S⩽0.045). A strong plasticizing effect of water on the Tg was found, with a great reduction in this value with increase in water activity.

Synthesis of styrene–acrylamide copolymer by surfactant‐free sonicated dynamic interfacial polymerization

This paper summarizes a study on emulsifier‐free ultrasonically assisted in situ dynamic interfacial emulsion copolymerization process of acrylamide and styrene. The resulting emulsions are stable and uniform for several months. Thermogravimetric analysis (TGA) curves and reaction conversion measurements have provided an important knowledge regarding the emulsifier‐free polymerization method. Solvent extractions (water, methanol, and xylene) have shown that the polymerization product is essentially a styrene–acrylamide copolymer. The copolymer produced is a block copolymer, PS‐b‐PAM, where each block contains small amounts of the other comonomer. The produced emulsions are film forming at room temperature in spite of the very high block Tgs, owing to a unique water plasticization effect of the polyacrylamide blocks. Some films prepared from the PS‐b‐PAM have resulted in clear and transparent films. The presented interfacial dynamic polymerization process is fast, reaching 81% conversion within 2 hr of sonication at 4°C (low temperature owing to molecular weight and kinetic considerations), and produces very stable PS‐b‐PAM emulsions. TGA was extensively used as an analytical tool for determination of the reaction parameters and composition of the acrylamide–styrene copolymers. Copyright © 2011 John Wiley & Sons, Ltd.

The Effect of Water Plasticization on the Molecular Mobility and Crystallization Tendency of Amorphous Disaccharides

To study how water plasticization affects the molecular mobility and crystallization tendency of freeze-dried trehalose, sucrose, melibiose and cellobiose. Freeze-dried disaccharides were subjected to different relative humidity atmospheres and their physical stabilities were evaluated. Lyophilizate water sorption tendencies and glass transition temperatures were modeled using Brunauer-Emmett-Teller (BET) and Gordon-Taylor (GT) equations, respectively. Sucrose and cellobiose crystallization tendencies were compared by using the concept of reduced crystallization temperature (RCT), and the molecular mobilities of trehalose and melibiose were compared by measuring their T(1)H relaxation time constants. Based on the BET and GT models, water sorption tendency and the resulting plasticizing effect were different in sucrose when compared to the other disaccharides. Trehalose and melibiose exhibited generally slower crystallization rates when compared to sucrose and cellobiose. Amorphous melibiose was shown to be particularly stable within the studied water content range, which may have partly been caused by its relatively slow molecular mobility. Slow amorphous-to-crystalline transition rate is known to be important for lyoprotecting excipients when formulating a robust drug product. The physical stabilities of amorphous trehalose and melibiose even with relatively high water contents might make their use advantageous in this respect compared to sucrose and cellobiose.