Amounts Of Non-freezing Water Research Articles

The Influence of Viscosity and Non-freezing Water Contents Bounded to Different Hydroxypropyl Celluloses (HPC) and Hydroxypropyl Methylcelluloses (HPMC) on Stability of Acetylsalicylic Acid

The aim of the study was to examine the influence of non-freezing water (NFW) contents bound to hydroxypropyl methylcellulose (HPMC) or hydroxypropyl cellulose (HPC) binary mixtures using acetylsalicylic acid (ASA) as a model moisture-sensitive ingredient. Polysaccharides with significantly different physicochemical properties were mixed with acetylsalicylic acid at a ratio 1:1 (w/w). The measurements of NFW contents of hydrated samples were carried out using differential scanning calorimetry (DSC). In the method used, the dry mass normalized dependency of melting enthalpy (ΔH) and respective contents of water was found to be linear. NFW values were calculated after extrapolation ΔH to 0. For stability studies, HPC/ASA and HPMC/ASA mixtures were stored at 40°C and 75% RH for 5 weeks in the climatic chamber. The ASA hydrolysis was investigated using UV-Vis spectrophotometry. The amounts of NFW calculated for raw HPMC 3 cP and 100,000 cP were 0.49 and 0.42 g g−1, while for polymer and ASA mixtures, prepared from HPC type LF (126 cP) and MF (6300 cP) as well as from HPMC 3 cP and 100,000 cP were 0.23, 0.28 g g−1, 0.21 g g−1, and 0.33 g g−1 respectively. The measured NFW values were connected with appropriate concentrations of unhydrolyzed ASA.

Water structure in poly(2‐hydroxyethyl methacrylate): Effect of molecular weight of poly(2‐hydroxyethyl methacrylate) on its property related to water

AbstractLow molecular weight poly(2‐hydroxyethyl methacrylate) (polyHEMA) with a number average molecular weight (Mn) <22,600, were prepared by atom transfer radical polymerization. The molecular weight and end groups of the polyHEMA were varied, and the water content equilibrium moisture sorption and water structure were analyzed using differential scanning calorimetry (DSC) and X‐ray diffractometry (XRD). Higher water content was observed for polyHEMA with Mn < 10,000. DSC revealed that the amounts of nonfreezing water are affected neither by the molecular weight nor by the end groups of the polyHEMA. On the other hand, the amount of freezing water was affected by both the molecular weight and end groups of polyHEMA, especially for polyHEMA with Mn < 20,000. The XRD‐DSC measurements showed that water in polyHEMA form hexagonal ice and that the direction of crystal growth is dependent on the molecular weight. These findings indicate that the molecular weight of polyHEMA plays a significant role in the water structure in polyHEMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and Physical Properties of Reactive Amphiphilic Hydrogels Based on Poly(p-chloromethylstyrene) and Poly(ethylene glycol): Effects of Composition and Molecular Architecture

This paper describes the design, synthesis, and characterization of amphiphilic conetworks using linear or starlike poly(ethylene glycol), PEG, and linear or hyperbranched poly(p-chloromethylstyrene), PPCMSt. The initial synthetic strategy is based on the reaction between the hydroxyl end groups placed in the PEG and the primary and/or secondary alkyl chloride groups dispersed in the linear or hyperbranched component, respectively. It was found that the hybrid conetworks form in 55%−99% yields depending on the stoichiometric ratio of the two building blocks (19−0.5 g PEG per 1 g PPCMSt) and the type of polymer architecture. The dynamic swelling studies showed that the hydrogels absorb water quickly and reach equilibrium in 1−3 h. The architecture of starting polymer, PEG compositions, and temperature were the main factors affecting the equilibrium hydration of the cross-linked materials (700%−4200%). The observed high degree of swelling of these hydrogels in both water and organic solvents was attributed to the high network porosity, which was revealed by scanning electron microscopy (SEM) on freeze-dried specimens. The different states of water in the hydrated cross-linked matrices were measured by differential scanning calorimetry (DSC). The amounts of nonfreezing water, freezing bound water, and free water in the amphiphilic conetworks were dependent on their physicochemical structure.

Relationships between the textural changes and the contents of calcium, magnesium ions, and non-freezing water in the alcohol-insoluble solids of snap bean pods during cooking processes

The alcohol-insoluble solids (AIS) of snap bean ( Phaseolus vulgaris L.) pods after different cooking treatments were used as testing materials. The contents of calcium, magnesium ions and non-freezing water, which were analysed by differential scanning calorimetry, in the AIS were determined and compared with the firmness of the bean pod tissues after different cooking treatments. It was observed that the contents of calcium and magnesium ions in the AIS of the bean pods after direct cooking were lower than those of fresh and precooked bean pods, and were also lower than those of the bean pods after precooking followed by cooking. The contents of these metal ions were significantly and positively correlated to the tissue firmness ( P < 0.01). The degree of esterification (DE) of pectin in the tissue after precooking was 39.3%. The DE of of pectin in the tissue after precooking followed by cooking was 39.9%. These DE values were significantly lower ( P < 0.05) than that in the fresh tissue (46.0%) or that in the tissue after direct cooking (46.0%). Moreover, the amounts of non-freezing water in the AIS of fresh and precooked bean pods were larger than those of the bean pods after precooking followed by cooking and direct cooking. This also showed a significant and positive correlation to the tissue firmness ( P < 0.05). It was apparent that the linkages between the pectin molecules in the tissues of snap bean pods after precooking were changed. This change was caused by the action of pectinesterase in de-esterification of pectin molecules and subsequent formation of calcium or magnesium bridges between the free carboxyl groups of adjacent pectin molecules, which resulted in increases in the amounts of nonfreezing water in the AIS and in the tissue firmness. These results can be taken as further supporting evidence for the theory of the firming effect of precooking treatment of vegetables.

たばこ刻みの微細構造と吸着水の存在形態

The pore-size distribution and the state of water adsorbed on tobacco cut-fillers were examined by a nitrogen adsorption method and differential scanning calorimetry. The pore-size was distributed in the region of 1 to 5 nm in radius, and the population was the maximum at approximately 2 nm in radius. The results of differential scanning calorimetry showed that the amounts of nonfreezing water in Bright and Burley tobacco were 0.24 and 0.20 [kg of adsorbed water/kg of dry tobacco], respectively. These values well agreed with the amounts of water at adsorption equilibria at p/p°=0.8. The calculated thickness of the adsorbed water layer was 0.55 nm corresponding to that of 2 molecular layers, and most of the micro-pores in tobacco cut-fillers were considered to be filled with water at p/p°=0.8. Freezing water is surmised to be that of multi-layer adsorption.

Water binding and irreversible dehydration processes in cellulose acetate membranes

AbstractThe relative amounts of freezing and nonfreezing water in various water‐wet cellulose acetate (CA) membranes were determined by NMR techniques, from the initial heights of the water component in the free induction decay (MNR intensity). The results suggest that (1) a significant fraction of the water in various wet CA membranes does not freeze, probably because of strong interaction with the polymer; (2) the relaxation times T2 of the nonfreezing water are of the order of milliseconds indicating that they are still highly mobile compared with ice; (3) all the water contained in dense CA films or in membranes equilibrated at relative humidity of 0.93 does not freeze upon cooling the membranes from room temperature to −60°C; (4) the amounts of nonfreezing bound water in membranes is higher than the total amount of water absorbed from liquid water by a dense film of the same polymer. However, the amounts of nonfreezing water in various CA membranes as calculated from the “relative NMR intensities” is substantially lower than those calculated from DSC melting endotherms by assuming the heat of fusion of water in membranes to be identical to that of pure water. Various possible reasons for this discrepancy are discussed. Measurements on the first desorption‐adsorption cycle of wet CA membranes have also been performed. They suggest that during the first dehydration process, irreversible changes are induced in the structure of the membrane which result in a significantly lower accessibility of the polymer to interact with water. The extent of these irreversible changes in membrane structure is dependent on the details of the dehydration process being more pronounced at higher temperatures.

Freezing and nonfreezing water in cellulose acetate membranes

AbstractThe relative amounts of freezing and nonfreezing water in various cellulose acetate (CA) membranes were determined by differential scanning calorimetry. It was found that: (1) A significant fraction (17–40%) of the water (1.0–3.1 g H2O per gram dry CA) in any membrane does not freeze at temperatures as low as −60°C. (2) The amount of nonfreezing bound water (0.4–0.7 g nonfreezing water per gram dry CA) depends upon the nature of the membrane and is significantly higher than the total amount of water (all of which is nonfreezing) absorbed from liquid water by a dense film of the same polymer (∼0.18 g water per gram dry CA). The structures of the membranes were studied by scanning electron microscopy. The results suggest that the amounts of nonfreezing water in cellulose acetate membranes decrease with the increase in the packing density (compactness) of the polymer within the membrane. In dense films, the extent of polymer–polymer interactions within the polymeric matrix is high, and therefore the macromolecular chains are less accessible to bind water.