The effect of heat treatment on water sorption in polylactide and polylactide composites via changes in glass‐transition temperature and crystallization kinetics

Water sorption into polylactide (PLA) and polylactide‐montmorillonite (PLLA‐MONT) composites containing 5 wt % of montmorillonite (MONT) under different heat treatment conditions was studied using the quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) technique. Results showed that water sorption in neat polymer films and composite films increased with heat treatment temperature up to 120 °C. Differential scanning calorimetry was used to measure the glass‐transition temperature and isothermal crystallization kinetics of all samples. The mobility of the amorphous domain in all samples increased with heat treatment temperature, indicated by the decrease in glass‐transition temperature. PLA composites crystallized at a much faster rate than neat PLA did because MONT acted as a nucleating agent. Under the same heat treatment condition, water sorption in PLLA‐MONT composites was always higher than that in neat PLA due to the presence of the hydrophilic hydroxyl groups on the surface of MONT particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Differences in water sorption and proton conductivity between Nafion and SPEEK

Water sorption, volumetric expansion, and proton conductivity of 1100 EW Nafion and 555 EW sulfonated polyetheretherketone (SPEEK) were compared as functions of water activity at 60 and 80 °C. Water sorption in Nafion occurs with a small positive volume of mixing, ～0.005 cm³/cm³. In contrast, water sorption in SPEEK has a large negative volume of mixing ～?0.05 cm³/cm³. The percolation thresholds for proton conduction occur at hydrophilic volume fractions of 0.10 in Nafion and 0.30 in SPEEK. Proton conductivity increases quadratically with hydrophilic volume fraction above the percolation threshold. The different percolation thresholds suggest the hydrophilic domains in Nafion grow from lamella, whereas the hydrophilic domains in SPEEK grow from spheres. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1437–1445, 2011     

新型热塑性淀粉的制备和性能

以二甲基亚砜(DMSO)为增塑剂, 通过熔融共混法制备了一种新型热塑性淀粉(TPS), 研究不同增塑剂含量对材料结构和性能的影响, 并与甘油及甘油/水复合增塑淀粉体系进行了比较. FTIR结果显示, DMSO能够与淀粉产生强烈而稳定的氢键相互作用. WAXD和SEM的研究结果表明, DMSO的加入破坏了淀粉的有序结构, 实现了淀粉的塑化, 形成均一的非晶连续相. 同甘油及甘油/水增塑体系相比, DMSO与淀粉的羟基形成更为稳定的氢键, 能够有效抑制淀粉的重结晶. 动态力学和拉伸力学性能测试结果表明, 经过DMSO的增塑, 有效降低了淀粉的玻璃化转变温度, 改善了材料的韧性, 增塑效率要好于甘油及甘油/水复合增塑体系.     

Bionanocomposites of Cassava Starch and Synthetic Clay

Starch-based biofilms containing synthetic Laponite clay and glycerol were prepared using a solvent casting technique. Electron microscopy images showed predominance of the exfoliated type of nanocomposite. Dynamic mechanical analysis revealed a larger influence of glycerol content on the polymer β relaxation and T _g than the clay content. Gas barrier properties were influenced by clay particles and plasticizer content. An increase of clay content led to lower gas permeability values. Although both glycerol and Laponite are hydrophilic, no significant changes were observed on the water sorption by starch films at different relative humidity values. Mechanical properties are kept similar after the inorganic filler incorporation.     

Combining renewable gum rosin and lignin: Towards hydrophobic polymer composites by controlled polymerization

Rosin polymer–grafted lignin composites were prepared via “grafting from” atom transfer radical polymerization (ATRP) with the aid of 2‐bromoisobutyryl ester‐modified lignin as macroinitiators. Three different monomers derived from dehydroabietic acid (DA) were used for execution of grafting from ATRP, while DA was separately attached onto lignin by a simple esterification reaction. Kinetic studies indicated controlled and “living” characteristics of all monomer polymerizations. Thermal studies indicated that rosin polymer–grafted lignin composites exhibited glass transition temperatures in a broad temperature range from ～20 to 100°C. The grafting of both DA and rosin polymers significantly enhanced hydrophobicity of lignin. Static contact angle measurement of water droplets showed ～90° for all these rosin modified lignin composites. X‐ray photoelectron spectroscopy demonstrated that the surface of rosin–lignin composites was dominated with chemical compositions originating from the hydrocarbon rich rosin moiety. The impartation of hydrophobicity of rosin into lignin provided excellent water resistance of this class of renewable polymers, as all rosin‐modified lignin composites showed water uptake below 1.0 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Real-time neutron reflectivity study of the early stages of diffusion into and dissolution of glassy polymers

The early stages of the penetrant behavior of a series of phthalate plasticizers into thin films of glassy, high-molecular-weight deuterated poly(methyl methacrylate) (dPMMA) have been studied with in situ real-time neutron reflectivity. After an initial induction phase, both dioctyl phthalate and diisononyl phthalate penetrate the dPMMA films, as indicated by an increase in the thickness. In both cases, a fast linear rate of swelling of the polymer is followed by another behavior that is much slower. The slowdown in the velocity of the plasticizers at or near the transition point is assumed to occur because of a balancing of the misfit-induced pressure and the osmotic pressure, which is responsible for the initial plasticizer ingress. In contrast, and unexpectedly, lower molecular weight dibutyl phthalate does not swell dPMMA, but after an initial induction period, the polymer film begins to dissolve. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3267–3281, 2004     

Nonmigratory internal plasticization of poly(vinyl chloride) via pendant triazoles bearing alkyl or polyether esters

Branched and linear nonmigratory internal plasticizers attached to PVC by a pendant triazole linkage were synthesized and investigated. Copper-free azide-alkyne thermal cycloaddition was employed to covalently bind triazole-based phthalate mimics to PVC. To systematically investigate the effect of plasticizer structure on glass transition temperature, several architectural motifs were explored. Free volume theory was considered when designing many of these internal plasticizers: hexyl-tethers were utilized to generate additional space between the triazole-phthalate mimic and the polymer backbone. Miscibility of these triazole-plasticizers in PVC is important: variation of the ester moieties on the triazole possessing alkyl and/or poly(ethylene oxide) chains produced a wide range of glass transition temperatures (T_g): from anti-plasticizing 96 °C, to highly efficient plasticized materials exhibiting T_g values as low as −42 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2397–2411     

Barrier and mechanical properties of modified starches

The study addressed starch-based coatings on paper and fabrics. Coated materials and free starch films containing different amounts of a well-established plasticizer (glycerol) or potential plasticizer (mainly polyols) were tested with respect to water vapour permeance (WVPe), water vapour permeability (WVP), glass transition temperature (T_g), and mechanical strength (tensile tests). Both normal and high- amylose potato starch were used. These starches were modified by (a) oxidation, (b) oxidation and hydroxypropylation or (c) oxidation and hydrophobically modified by reaction with octenyl- or alkenyl-substituted succinic acid anhydride. Free films of hydroxypropylated high-amylose potato starch showed a lower WVP than did the corresponding starches based on regular potato starch. The WVP of the hydrophobically modified regular potato starches was substantially higher than that of films of the corresponding hydroxypropylated starches. The expected hydrophobic effect of the succinic acid anhydrides in terms of a reduced WVP could not be observed. When glycerol was used as a plasticizer, about 30 parts (by wt.) per hundred parts of starch were needed in order to reduce the T_g and to cause observable changes in the mechanical properties of the free films.     

Physicochemical properties of plasticized corn zein films: NMR and adsorptivity studies

Water sorption isotherms of corn zein-based films are typical sigmodial curves. The presence of plasticizers greatly increase film water sorption at intermediate and high water activities. The presence of a plasticizer increases water vapor permeabilities of zein films. The extent of such effect depends on the plasticizer type and concentration used for film formation.     

Water sorption and transport in blends of polyethyloxazoline and polyethersulfone

Water sorption and transport properties for a series of homogeneous blends of hydrophobic polyethersulfone and hydrophilic polyethyloxazoline are reported. Only blends that remained homogeneous after exposure to liquid water were studied in detail. Equilibrium solubility of water in the blend films increases with increasing hydrophilic polymer content. For all materials, equilibrium sorption isotherms show dual-mode behavior at low water vapor activities and swelling behavior at high activities. The sorption/desorption kinetics for PES are generally Fickian, but two-stage behavior is evident in blends containing 10 and 20% polyethyloxazoline. Diffusion coefficients decrease with increasing polyethyloxazoline content, owing to a decrease in the fractional free volume. For all materials, the diffusion coefficient shows a positive dependence on water vapor activity or concentration due to plasticization of the material by high levels of sorbed water, but it becomes a greater function of activity as the composition of hydrophilic polymer in the blend is increased. Since the decrease in the diffusion coefficient is greater than the increase in the solubility coefficient, the permeability coefficient decreases with increasing hydrophilic polymer content. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 993–1007, 1997     

Antiplasticization and local elastic constants in trehalose and glycerol mixtures

We have performed molecular dynamics simulations of glassy trehalose with various amounts of glycerol in order to explore the tendency for glycerol to antiplasticize the glass. We find that below a temperature of 300 K, the average density of the system containing 5%(wt) glycerol is larger than that of the pure trehalose system; the glass transition temperature is decreased, and the elastic constants are essentially unchanged. Taken together, these phenomena are indicative of mild antiplasticization, a type of behavior generally observed in polymeric systems. We have calculated the local elastic constants in our glassy materials and, consistent with previous simulations on a coarse-grained polymer, we find evidence of domains having negative elastic moduli. We have explored the ability of various measures of the Debye-Waller factor u(2) to predict the stiffness of our systems in terms of their elastic constants. We find that u(2) is indeed correlated with the behavior of the bulk elastic constants. On a local level, a correlation exists between the local moduli and u(2); however, that correlation is not strong enough to arrive at conclusive statements about the local elastic properties.     

Water sorption and diffusion studies in an epoxy resin system

The kinetics of water absorption in epoxide materials was studied by the aid of a diglycidyl ether of bisphenol‐A–triethylenetetramine (DGEBA–TETA) epoxy–resin system containing various amounts of the plasticizer THIOCOL (0–40 phr). The presence of plasticizer permits the formation of products with different crosslinking densities and hydrophilic characters. Dynamic water absorption experiments were carried out at 15, 40, and 70°C. For the fitting of the experimental results, a new model was used, based on a model proposed earlier by Jacobs and Jones. This model considers epoxide product as a two‐phase system consisting of a master phase (where the major part of the water is absorbed), which is homogeneous and nonpolar (phase 1), and of a second phase with different density and/or hydrophilic character (phase 2). By making the assumption that water diffusion can take place independently in the different phases of the material in accordance with Fick's second law, we can calculate the diffusion coefficient D and the water content at saturation M_∞ for each phase separately. Equilibrium water sorption measurements were performed at 40°C, and the data were analyzed and discussed based on the Guggenheim–Anderson–de Boer (GAB) equation, the results being in support of the two‐phase model used in the analysis of absorption kinetics. The linear expansion coefficient and the glass transition temperature of the materials, employed in the discussion of the results, were measured by thermomechanical analysis. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1165–1182, 1999     

Effect of hydrophilicity on the properties of a degradable polylactide

A series of polylactide networks has been prepared by the copolymerization of a biodegradable oligolactide macromer with hydrophobic methyl methacrylate monomer and hydrophilic hydroxyethyl acrylate monomer, with different amounts of the hydrophilic monomer. The incorporation of the hydrophilic units into the network has been characterized with thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical spectrometry. A homogeneous material results, showing a single glass‐transition temperature and a characteristic relaxation behavior that is not the sum of those of the pure components separately. Additional hydrophilic units in the network chains lower the rubbery modulus, keeping a high modulus value at room temperature, and manifestly increase the degradation rate of the polymer. This can be attributed both to the higher water swellability of the network when hydrophilic units are present and to the higher water diffusion coefficient in a network, which has a lower crosslinking density. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 656–664, 2006     

Compatibility of cross-linked polymers with plasticizers by glass transition temperature measurement and swelling tests

To elucidate the compatibility of polymer and plasticizer components of binders a study of polymer–plasticizer interactions by differential scanning calorimetry (DSC) and swelling tests was conducted. The glass transition temperatures (T_g's) of mixtures of polymers and plasticizers, both cured and uncured, were determined with a DSC technique. Results with the PEG polymer systems were complicated by the partial crystallization of the polymer from the polymer/plasticizer mixtures. The PGA polymer system did not exhibit this behavior. However, the T_g's of cured PGA with various plasticizer mixtures made complicated departures from linearity (plots of T_g versus weight fraction of plasticizer) that indicated polymer–plasticizer interaction. By using least-squares analysis of data plotted by the equation Values of the interaction parameter K were determined for cured PGA in various plasticizer systems. These K values are in good agreement with the molecular flexibility of the plasticizers based on their molecular structure. The results of swelling tests are discussed to elucidate further the nature of the interaction of these polymers with plasticizers. Calculated polymer-plasticizer interaction values (χ) from the swelling tests correlated with the solubility parameter (δ) for a given class of polymer (polyether, polyester) and plasticizer (nitrate ester, ether-type). The efficiency of a plasticizer in reducing the T_g of a polymer (below the linearly interpolated value) was found not to be related to the swelling behavior of the polymer in the plasticizer.     

Ultrasonic characterization of the kinetics of water sorption in hydrogels

A complex mechanism characterizes the water uptake kinetics in hydrogels, as a consequence of the strong structural changes occurring in the material during the sorption process. Water acts as a plasticizer, reducing the glass transition temperature of the polymer below the sorption temperature and determining a glass transition in the polymer. In this study the changes in the ultrasonic attenuation and velocity in semicrystalline Poly-vinyl-alcohol (PVA) hydrogel films during water sorption are measured by a pulse-echo system. The ultrasonic wave propagation is applied to monitor the position of the swollen/unswollen fronts and to the measurement of velocity and attenuation. The structural changes in PVA hydrogels, monitored by Wide Angle X-ray Diffractometry (WAXD), performed during the sorption process, are correlated with the ultrasonic data.     

An overview on the recent developments in reactive plasticizers in polymers

This review is about the reactive plasticizer. Plasticizers are small molecules with low molecular weight. These compounds typically have an esteric structure. The plasticizers reduce the glass transition temperature, and the viscosity of the polymer also enhances the flexibility and processability of polymer materials. The main problem of these additives is that, over time, they migrate from the polymeric matrix and exude to the surface of polymeric matrix. As a result, the physical and mechanical properties of the polymer are affected. Various strategies, such as increasing molecular weight of plasticizer, selection of oligomeric structure for plasticizer, and adding nanoparticles of minerals, have been investigated to reduce and eliminate migration. An approach that has recently been of great interest to researchers is the use of reactive plasticizers. In this approach, plasticizers covalently bond to the polymeric chains and prevent migration.     

Poly(methyl acrylate)/poly(hydroxyethyl acrylate) sequential interpenetrating polymer networks. Miscibility and water sorption behavior

Sequential poly(methyl acrylate)/poly(hydroxyethyl acrylate) interpenetrating polymer networks with different poly(hydroxyethyl acrylate) contents were prepared by free radical polymerization of hydroxyethyl acrylate inside the previously polymerized poly(methyl acrylate) network. Differential scanning calorimetry on dry samples shows that the interpenetrating polymer networks exhibit phase separation, and no differences are found between the glass transition temperatures of the two phases present in the interpenetrating polymer network and those of the pure components. Thermally stimulated depolarization current experiments were used to study the influence of water sorption on the mobility of the different molecular groups in the poly(hydroxyethyl acrylate) phase of the interpenetrating polymer network. Isothermal water sorption of the interpenetrating polymer networks and pure poly(methyl acrylate) and poly(hydroxyethyl acrylate) networks is analyzed with different theories to compare the behavior of the poly(hydroxyethyl acrylate) phase in the interpenetrating polymer networks with that of the pure poly(hydroxyethyl acrylate) network. Diffusion coefficients of water in the interpenetrating polymer networks are obtained by means of dynamic sorption experiments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1587–1599, 1999     

Viscoelastic characteristics of plasticized cellulose nanocomposites

The plasticization effects of cellulose diacetate composite systems including nanoparticles (montmorillonite, MMT) and plasticizers(diethyl phthalate, DEP) were investigated by the time–temperature superposition technique and viscoelastic modeling. Exhibiting the highest modulus value in the glass state, the viscoelastic modulus of the MMT nanocomposite rapidly decreased above the glass‐transition temperature (T_g). The Arrhenius‐type activation energy of pristine cellulose acetate showed the lowest value of activation energy and both DEP‐plasticized and MMT‐reinforced systems exhibited increased values of activation energy. Although the free volume fraction at the T_g decreased with the plasticizer content, it increased with the incorporation of MMT, seemingly preventing the polymer chains from being arranged in an ordered structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 59–65, 2005     

Development and characterization of plasticized polyamides by fluid and solid plasticizers

Polyamides are semicrystalline polymers that are useful in a wide range of applications in the plastics industry. Some applications require higher flexibility and improved workability of polyamides; thus, a plasticization approach that eases compounding and processing procedures and produces better desired product properties can be utilized. Common plasticizers are high‐boiling liquid esters, but solid plasticizers also have been considered. The present research has focused on plasticization of nylon 66/6 (80/20) copolymer by using selected low molecular weight organic materials. Plasticization of the copolyamide was studied with glycerin mono stearate, benzene sulfonamide, and methyl 4‐hydroxybenzoate as the solid plasticizers and diethylhexyl phthalate as the liquid plasticizer. The materials were prepared and characterized by thermal, mechanical, dynamic, rheological, and morphological properties. The experimental results were supported by simulated polymer and plasticizer interactions using molecular dynamic simulations. Plasticization and antiplasticization phenomena were observed and discussed. The plasticizers were classified by their efficiency in reducing T_g and by modification of the other polyamide properties. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of benzenesulfonamide plasticizers on the glass‐transition temperature of semicrystalline polydodecamide

The effect of various benzenesulfonamide (BSA) plasticizers on the amorphous phase of semicrystalline polydodecamide (PA‐12) has been investigated. MonoBSAs appear as efficient glass‐transition temperature (T_g) depressors because of their miscibility with the host polyamide (PA), low glass transition, and small molecule size. PA‐12's T_g shifts from 50 to about 0 °C at 20 mol % of the most efficient molecules. Comparatively, the more bulky bisBSAs appear to induce less important absolute T_g decreases (30 K at 20 mol %), although these appear as more important when considering the polymer T_g to plasticizer T_g difference. This unexpected observation could be ascribed to both the amide‐sulfonamide interactions and the sterically generated disorder within the polyamide because of the plasticizer molecule's size. Phase‐separation behavior of BSA plasticizers within the host PA has also been investigated. Crystalline phenyl‐SO₂NH₂, for instance, dephased beyond 20 mol % in PA‐12, forming distinct 1–2 micrometer wide crystalline domains as a result of its high propensity to crystallize upon cooling from the melt. By contrast, slow crystallizing N,N‐dimethylBSA, which lacks any specific interaction for PA‐12, remained nevertheless dispersed at a molecular level (metastable state, no phase separation) when vitrification of the host PA‐12 amorphous phase occurred on cooling. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2208–2218, 2002