The investigation on states of water in different hydrophilic polymers by DSC and FTIR

The interaction between polymers and water in four hydrophilic polymer aqueous solutions were investigated by DSC and FTIR. DSC result shows that the different hydrophilic polymer/water mixtures have various water calorimetric behaviors in the melting temperature range of freezable bound water as well as free water. The melting temperature of freezable water and the amount of non-freezable water in the mixtures vary with the change of chemical structure of polymers. The melting point of the freezable bound water doesn’t change with the water content, revealing that water bound weakly to polymer chains can form a stable crystalline structure at high water content. For the three hydrophilic polymer/water mixtures with C=O group, the weight ratio of non-freezable water to polymers is constant, but varies with polymer chemical structures. The FTIR spectra confirmed the formation of the hydrogen bonds and it was found that there exist different states of water based on various strengths of hydrogen bonds. The OH stretching bands indicated the fraction of strongly bound water decreases with increasing water content. It was concluded that at least in hydrophilic polymer aqueous solutions with polar sites in polymer chains, the formation of non-freezable water is ascribed to the hydrogen bonds between hydrophilic polymers and water molecules. Different strengths of hydrogen bonds can affect the thermal behaviors of water in the hydrophilic polymer/water mixtures.     

The state of water in the series of sulfonated poly (phthalazinone ether sulfone ketone) (SPPESK) proton exchange membranes

The different states of water in a series of SPPESK membranes, including sulfonated poly (phthalazinone ether sulfone ketone) (SPPESK) membrane, cross-linked (XL) SPPESK membrane and SPPESK/polyacrylic acid (PAA) semi-interpenetrating polymer network (sIPN) membrane were investigated by low temperature differential scanning calorimetry (DSC) measurements. Only one melting peak was observed for each DSC curve, therefore the free water cannot be distinguished from freezing bound water in the experimental condition. The melting temperature of the freezable water was found to decrease when the content of the freezable water reduced. The content of non-freezing bound water decreased with the increase in total water uptake in each type of the membranes. It indicates that the total water uptake cannot exactly reveal the ability of tight water retention of the membranes. As compared with SPPESK/PAA membrane, SPPESK and XL-SPPESK membranes presented a higher ability of water retention because of higher content of non-freezing bound water measured. A schematic structural model is given to explain the interrelation of distribution of ionic groups (hydrophilic groups) and structure of polymers to the content of non-freezing bound water.     

Properties of a semi-crystalline and an amorphous thermotropic liquid crystalline polymer

The physical properties, thermal stability, rheology and tensile properties of a commercial semi-crystalline and an amorphous thermotropic liquid crystalline polymer (TLCP) have been investigated. Analysis by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) confirm the presence of a small melting endotherm and a glass transition in the former material. The as-received amorphous TLCP exhibits no obvious melting endotherm and a strong glass transition is detected. The flow and tensile properties of the semicrystalline polymer are dominated by the presence of the crystalline to nematic transition temperature. The properties of the amorphous TLCP appear to be governed by increasing mobility afforded by increasing temperature. Based on flow behaviour and further DSC analysis it has been shown that under appropriate annealing conditions the as-received amorphous TLCP can develop solid crystalline order.     

NMR and calorimetric investigation of water in a superabsorbing crosslinked network based on cellulose derivatives

In this study we have investigated the state of water in a superabsorbing network based on hydroxyethylcellulose (HEC) and carboxymethylcellulose sodium salt (CMCNa) crosslinked with divinylsulfone (DVS).This type of network, at low degree of crosslinking, when exposed to distilled water is able to form a stable hydrogel containing an amount of water as high as 1000 times its own weight.De-hydrated/re-hydrated networks, containing different amounts of absorbed water, have been studied using differential scanning calorimetry (DSC) and NMR relaxometric methods. DSC analysis allowed the evaluation of freezable and non-freezable fractions of absorbed water showing also the presence of two types of freezable water. On the other hand, NMR relaxometry evidenced the presence of two hydration shells, characterized by a different mobility, which in both cases is lower than that of bulk water.An excellent quantitative agreement was found in the determination of the amount of freezable water using the two techniques.A comparison of the state of water in the crosslinked network and in the corresponding uncrosslinked mechanical mixture shows that in the last case micro-heterogeneity arises.     

Mechanism and kinetics of ultra‐high molecular weight polytetrafluoroethylene sintering

The effect of sintering time on the melt evolution of Ultra‐High Molecular Weight Polytetrafluoroethylene was studied in situ by high temperature Wide Angle X‐ray Scattering, and by cyclic thermal loading profiles within a Differential Scanning Calorimeter (DSC) and Thermo‐Mechanical Analyzer (TMA). Results obtained from these techniques support the concept of molecular ordering in the melt state as a function of sintering time well above the melting temperature. TMA, which is not a conventional technique for monitoring thermal transitions, is shown to be sensitive enough for such purposes. Both DSC and TMA exhibit nonequilibrium melt behavior even 30°C above its equilibrium melting temperature for long time periods. A correlation between the DSC and TMA results is established. The cyclic thermal profile leads to a dramatic growth in enthalpy of crystallization/melting. The mechanism for this growth is associated with two independent processes; isothermal annealing at the sintering temperature and lamellar thickening in the solid state. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40967.     

PVA水凝胶中水的状态研究

用环氧氯丙烷作交联剂,制备了聚乙烯醇（PVA）亲水水凝胶。并用示差扫描量热法（DSC）对不同含水量的此种亲水水凝胶进行了测试,获得了各种状态水进入水凝胶聚合物网络体系的先后顺序情况,并研究了PVA水凝胶中三种状态水的含量随水凝胶含水量的变化而变化的规律。     

Differential scanning calorimetry of aqueous polymer solutions and gels

The melting phenomena of aqueous polymer solutions and gels have been investigated by differential scanning calorimetry (DSC). The polymers used were synthetic polyacrylamide and poly(vinyl alcohol) samples as well as guar and xanthan gums. By using an empirical relation, the energy measured from the area under the melting peak yielded heats of mixing and sorption, when fitted by an association factor computed from the data. This factor (independent of the concentration) is a measure of the water fraction associated with the polymer and has a definite and characteristic value for a given polymer in water. When a crosslinking agent (potassium pyroantimoniate or chromic nitrate) was added to the water–polymer system, the association factor varied with the polymer concentration; the macromolecular chains thus become less accessible to penetrating water. If a branched gel was obtained owing to the formation of chemical crosslinks, a hump appeared on the melting peak.     

Phase behavior and molecular mobility in polyurethane/styrene–acrylonitrile blends

Differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and dynamic mechanical thermal analysis (DMTA), covering together a wide range of temperatures and frequencies, were employed to investigate molecular mobility and microphase separation in blends of crosslinked polyurethane (PUR) and styrene–acrylonitrile (SAN) copolymer, prepared by reactive blending with polymer polyols. The results by each technique indicate that the degree of microphase separation of PUR into hard‐segment (HS) microdomains and soft‐segment (SS) microphase increases on addition of SAN. The various techniques were critically compared to each other, with respect to their characteristic time and length scales, on the basis of activation diagrams (Arrhenius plots). The results show that for the dynamic glass transition of the PUR SS microphase the characteristic time scales at the same temperature are similar for DMTA, DSC, and TSDC and shorter for DRS. In terms of fragility, the PUR/SAN blends are classified as fragile systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1071–1084, 2001     

A water dispersed Titanium dioxide/poly(carbonate urethane) nanocomposite for protecting cultural heritage: Preparation and properties

A water dispersed Titanium dioxide/poly(carbonate urethane) nanocomposite was prepared by means of cold mixing of single components via sonication. The work was aimed at achieving a new material with properties suitable for eco-sustainable applications in cultural heritage as protective coating. The nanocomposite water dispersion prepared was subsequently deposited on Petri dish and, after water casting at room temperature, homogeneous, transparent, colourless film samples were obtained. TGA, DSC, DMTA, ATR-FTIR, FESEM and WAXS techniques were then applied in order to investigate the thermal and visco-elastic behaviours along with morphology and structure of the nanocomposite. Moreover, through methylorange decomposition, an azoic dye representative of environmental pollution, a photocatalytic test was set up on nanocomposite film samples assessing that the 1% (wt/wt) content of Titanium dioxide nanoparticles was able to confer self-cleaning ability. Interrelationships among structure, properties and uses in conservation of this kind of nanomaterial were appraised.     

水在聚乙烯醇/水体系中的状态及氢键作用

水在聚乙烯醇(PVA)中的状态直接影响PVA的热塑加工.采用DSC和Raman光谱研究了水含量对其在PVA中的状态及氢键作用的影响.结果表明:水在PVA中以3种状态存在,随水含量增加,非冻结合水比例减小,可冻结合水和自由水比例增加.通过高斯分峰可将Raman光谱水的羟基伸缩振动峰分为5种羟基振动峰叠加,分别代表多氢键结合水分子的羟基对称与反对称伸缩振动,双氢键结合水分子羟基伸缩振动,单氢键结合水分子羟基伸缩振动,无氢键或弱氢键相互作用水分子的羟基伸缩振动.水含量增加,单氢键结合与多氢键结合水分子含量增加,而双氢键结合与无氢键结合水分子含量减少.     

Effect of minor addition of xanthan on cross‐linking of rice starches by dry heating with phosphate salts

Effects of xanthan on the crosslinking of normal and waxy rice starches using a mixture of phosphate salts (sodium trimetaphosphate and sodium tripolyphosphate, 99 : 1, dry solid basis) were investigated. The starch (158.4 g, dry solids) was dispersed in an aqueous solution containing xanthan and phosphate salts (1.6 and 0.6 g in 280 mL water, respectively), and the slurry was dried overnight at 45°C until the moisture content was less than 10%. The dry cake was then ground into powders and heated for 2 h at 130°C in a convection oven. The pasting viscosity, paste clarity, melting and in vitro digestion behaviors of the starches with modifying agents (xanthan and phosphate salts) were investigated. The heat treated starches displayed enhanced shear stability and reduced breakdown, as evidences of crosslinking. Xanthan (1.0% based on starch solids) enhanced the crosslinking effects in the viscosity profile. Waxy rice starch evidenced more profound viscosity changes than did normal rice starch, indicating it was more susceptible to the heat treatment. The waxy rice starch heated with the mixture of phosphate salts and xanthan exhibited a continuous increase in pasting viscosity without any breakdown. Under a DSC analysis, melting enthalpy decreased but melting temperature increased somewhat as results of the heat treatment with xanthan. In an in vitro digestion analysis, the starches treated with xanthan exhibited decreases in the maximum digestion level, and increases in the resistant starch (RS) content. Dry heating, however, increased the digestion rate and glycemic index (GI) regardless of the presence of phosphate salts or xanthan indicating that the starches were thermally degraded. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Toughening of a trifunctional epoxy system. II. Thermal characterization of epoxy/amine cure

The cure of a trifunctional epoxy resin with an amine coreactant was studied using two thermal analysis techniques: differential scanning claorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). These techniques were used to monitor the development of both the thermal and mechanical properties with cure. Detailed kinetic analysis was performed using a variety of kinetic models: nth order, autocatalytic, and diffusion-controlled. The reaction was found to be autocatalytic in nature during the early stages of cure while becoming diffusion-controlled once vitrification had taken place. By combining the results obtained from DSC and DMTA, the degree of conversion, at which key events such as gelation and vitrification take place, were determined. A TTT diagram was constructed for this epoxy/amine system showing the final properties that can be achieved with the appropriate cure history. © 1996 John Wiley & Sons, Inc.     

Origin of the intermediate damping peak in microlayer composites

A comparison of glass transition temperatures measured by differential scaning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) was made using mi9crolayer composites with many alternating layers of two polymers. What appeared to be a third transition at a temperature intermediate between the glass transitions of the two components was observ ed in DMTA but not DSC. The mechanical orgin of this intermediate damping peak in the layered composites was established. The viscoelastic properties of each polymer were modelled by a spring and dashpot in series, and the composite as a parallel arrangement of two Maxwell elements. It was shown that an anomalous damping peak can appear between the glass transition temperatures when the modulus of the composite can not drop below the modulus of the glassy layers, although the viscosity of the composite continues to be defined by the viscosity of the rubbery layers in this temperature range. The intermediate damping peak may be a general feature in the dynamic mechanical behavior of co-continuous multiphase systems including polymer blends and continuous fiber composites.     

Viscoelastic,thermo-mechanical and environmental properties of composites based on polypropylene/poly(lactic acid) blend and copper modified nanoclay

Poly(lactic acid) (PLA)/polypropylene (PP) blends composites were prepared by incorporating 3 wt.% of copper modified montmorillonite (MMT-Cu²⁺), obtained using cation exchange in a CuSO₄ solution, and 10 wt.% of polypropylene-graft-maleic anhydride (PP-g-MA) as a compatibilizer then varying the PLA content until 50 wt.%. These materials were subjected to several investigations such as X-rays diffraction, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile and environmental tests. The DMTA analysis showed that the glassy PLA high stiffness and the PP crystalline phase compensate the decrease in the storage modulus occurring during the PP and PLA glass transitions, respectively. The variations of tan δ revealed no changes on the PP and PLA phases glass transitions temperatures which indicate the immiscibility of the two polymers, as supported by DSC analysis. Blends composites SEM micrographs stated the immiscibility of the system resulting in the poor adhesion of the PLA droplets to the PP matrix. Also, the blends composites exhibited intermediate tensile properties between those of PP and PLA. The incorporation of MMT-Cu²⁺ to the (50/50) PP/PLA blend accentuated its aptitude to water absorption and ensured an efficient antimicrobial activity over a satisfactorily long period of around six months.     

Thermal transitions of poly(vinyl alcohol) hydrogel sensed by a fluorescent probe

Fluorescence from the fluorescein molecule has been used to study of phase transition processes in five poly(vinyl alcohol) (PVA) hydrogels in the temperature range 75–350 K. These hydrogels were prepared with PVA with molecular weight = 124,000–186,000, 99+% hydrolyzed, by repeated freezing–thawing cycles in five compositions: 9.9, 11.1, 13.3, 16.5, and 20.9 PVA w/w %. Plots of total fluorescence intensity versus temperature, normalized with the fluorescence signal at 75 K, and of the emission wavelength maximum versus temperature indicated that the dynamic of the guest deactivation was dependent on the hydrogel thermal transitions. These thermal transition processes were compared to three model systems: uranine (fluorescein di‐sodium salt) in water, fluorescein in water/ethanol (85%/15% v/v), and fluorescein/PVA homopolymer. Small spectral shifts were obtained for these model systems over the entire temperature range attributed to the hot band effect. Nevertheless, larger spectral shifts were obtained for hydrogels, indicating that shifts of the chemical dissociation equilibrium was occurring in this last case. Slope changes of both intensity and wavelength maximum plots versus temperature occurred at the same temperature values, and we attributed the onset of the hydrogel thermal transition as the sol–gel transition occurring at T ≅ 370 K; at 320 K we observed the glass transition temperature of PVA plasticized by water molecules; at T ≅ 240 ± 5 K we attributed the melting point of water molecules bonded to the PVA chains (freezable bond molecules); at T ≅ 270 ± 5 K we observed the melting point of free water molecules (bulk water); and, at 135–145 K the water glass transition. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 815–824, 2000     

Stiffness xanthan hydrogels: synthesis,swelling characteristics and controlled release properties

Summary  New xanthan hydrogels were synthesized at 90 C in water acid media using adipic acid dihydrazide (ADH) as crosslinking agent, in the presence of 1-ethyl-3[3-dimethyl amino] propyl carbodiimide hydrochloride (EDCI) as reagent. In these conditions, xanthan chains are in a predominantly helical conformation and through rheological measurements the influence of the temperature over the helix-coil transition was assessed. Xanthan hydrogels with different concentration in polysaccharide and ADH were obtained and characterised by elemental analysis and swelling properties. High concentration of xanthan (i.e. 25gL^-1) is needed to obtain gel due to the low available carboxylic functions in the helical conformation. During the swelling analysis, it was noted that high temperature (i.e. 90 C) favoured the conformational transitions within the network. The drug loading and releasing properties were estimated using methylene blue as model molecule and different experimental pH and ionic strength conditions.     

Application of thermal methods in the characterisation of poly(urethane-urea)s formed by reaction injection moulding

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) have been used in conjunction with tensile testing and transmission electron microscopy (TEM) to characterise novel segmented poly(urethane-urea) (PUU) network materials formed by reaction injection moulding (RIM). Materials were based on a modified liquid 4,4′-diphenylmethane diisocyanate and a polyether triol in admixture with one of three hindered aromatic diamines: 3,5-diethyltoluene diamine (DETDA); methylene-bis-2,6-diisopropylaniline (MMIPA); methylene-bis-(2-methyl-6-isopropylaniline) (MMIPA). The materials ranged from tough translucent elastomers to opaque brittle plastics depending on the chemical nature and weight fraction of the hard segments (HS). DSC and DMTA studies showed the PUU materials to be phase-separated; this was confirmed by TEM and tensile testing. The soft-segment glass transition temperatures (DSC and DMTA) were independent of composition but varied with diamine structure. Hard-segment glass transition temperatures could only be evaluated by DMTA and no evidence of crystallinity was found by thermal methods or by wide angle x-ray diffraction. Heat capacity measurements and DMTA suggested that some degree of phase mixing had occurred, to a greater extent in the DETDA and MDIPA systems. Phase inversion was observed by DMTA and confirmed at ～55% hard-segment content for DETDA systems by tensile testing.     

Blends of low‐density polyethylene and liquid crystalline polymer

Blends of low‐density polyethylene (LDPE) and a glass‐filled thermotropic liquid crystalline polymer (LCP‐g) have been prepared by melt mixing techniques. The thermal transitions, dynamic behavior, morphology and crystalline properties of the blends have been measured by DSC, DMTA, SEM and XRD respectively. The crystallinity decreased with increase in LCP‐g content in the blends. At higher levels of LCP‐g, crystal growth is favored in the PE phase. From DSC, it is found that the thermal stability of the blends increased with the LCP‐g content. The variation of storage modulus, loss modulus and stiffness as a function of blend ratio suggested the phase inversion at the 40–50% level of LCP‐g in the blend. SEM studies revealed that with the increase in LCP‐g content, the flow of the matrix was restricted.     

A unique crystallization and double melting behavior of a polyimide derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 1,4-bis(3-aminopropyl)piperazine

A unique crystallization and melting behavior of a novel semicrystalline polyimide derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 1,4-bis(3-aminopropyl)piperazine were studied by differential scanning calorimetry (DSC) with and without temperature modulation and wide-angle X-ray diffraction (WAXD). Polymer samples isolated from a chloroform solution showed melting transitions in the DSC. However, WAXD traces showed crystallinity only after annealing above the glass transition, for about 2 h. For samples crystallized from the melt, crystallization could be achieved only in a narrow crystallization range of 200-220 °C, after 10 h. A maximum crystallinity of this polyimide was found to be 30%. Two distinct melting transitions were observed by DSC, which could be explained using a partial disordering—reorganization—final melting model.