Elongational flow studies on the molecular properties of collagen and its thermal denaturation

An elongational flow method established in polymer physics was applied to study dynamic structure and properties of biopolymers in solution. Type I collagen solutions in the dilute to semidilute region are studied in elongational flow fields, generated in a Taylor four-roll mill, for temperatures from 20°C through the melting temperature to 60°C. A nonlocalized birefringent signal, characteristic of stiff molecules, is observed at all temperatures. The conformational changes as a function of temperature can be divided into two separate temperature dependent stages. In stage I, at lower temperatures, the collagen molecule behaves as a rigid rod and the birefringent signal Δn rises as a function of increasing strain rate ε. Throughout this stage the type of molecular interaction in semidilute solution does not change but the rate of interaction is increased by thermal excitation. In stage II, a characteristic criticality in the Δn vs. ? plot is observed. For strain rates up to a characteristic value, ?₀, the birefringence remains zero and for ?>?₀ whole field bright birefringence is observed. The plateau values of birefringence, Δn_p, at high strain rates in the Δn vs. ? curve decreased with rising temperature in stage II. This criticality in behavior and the decreasing tendency in Δn_p with temperature are explained by the collagen molecule changing to a hinged-rod conformation. Thus the untwining of collagen as a function of temperature initiates at several places simultaneously, probably at specific amino acid sequences, within the collagen rodlike molecule.     

Role of hydrophobic bonding in the contraction of nylon 66 in phenolic solutions

Rate constants for intermolecular bond breaking (k₁) and bond re-formation (k₂) were calculated from contraction measurements. Variation of ΔH? and ΔS? for k₁ with phenol substituents and concentration suggests the existence of hydrophobic bonding between the solution and the polymer activated complex. This behavior has been substantiated by correlating ΔH? and ΔS? for k₁ with a parameter related to hydrophobicity.     

The polycondensation of lithium 11–bromoundecanoate in aqueous media

To obtain a biodegradable plastic, polycondensation, the substitution of bromine by carboxylate was carried out on lithium 11–bromoundecanoate. Using water as a solvent, the formation of a double bond was detected between 70 and 100°C, yielding a good quantity of polymer. Water is recommended as the best solvent for the reaction. Thermodynamic investigations were carried out by using ethylene glycol and water. The reaction is believed to proceed according to the S_N2 mechanism. The ΔH and ΔG values for condensation in ethylene glycol were slightly higher than for those in water, but the reaction rate in water at 70°C was 7 times greater than that in ethylene glycol. The enhancement of dissociation accounts for the advantageous condensation in aqueous media. Furthermore, ΔS shows negative values and ΔG shows positive values, meaning that the reaction should proceed exothermically and not spontaneously. Experiments to condense 11–bromoundecanoate in aqueous media were carried out for ten days in a water bath, kept at 70°C, using 25 mL of 0.05M 11–bromoundecanoate. The degree of polymerization for the resulting polymer was found to be 23 by the end group assay for both bromine and carboxylate. Neither a melting point nor glass transition point for the product were observed. The polymer formed decomposes at 300°C and instantly disperses. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 130–134, 2003     

Effect of thermal hysteresis on melting of syndiotacticity-rich poly(vinyl alcohol) hydrogel

The melting temperatures (T_M) of hydrogels prepared by chilling aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) at 0°C were measured rising temperature of gels from the initiative temperature (T_I) of 0–70°C (every 10°C). The apparent enthalpies of fusion of a junction ΔH's were estimated from the relation between the logarithm of polymer concentration (log C) and 1/T_M. ΔH depended on T_I, showing that the melting point of gels depended on a thermal hysteresis. The highest polymer concentration C_H in those of the gels which have no melting point above an initiative temperature was determined and ΔH was estimated from the relation between log C_H and the reciprocal melting point of the gels with C_H, 1/T_IM. The ΔH was 15.1 kJ/mol in the range of higher polymer concentrations and 43.9 kJ/mol in the range of lower concentrations.     

Study the effects of nanofiber on the polymer chain orientation using molecular dynamic in the circular duct flow

In this article, the effects of nanofiber on the polymer chain orientation are studied using molecular dynamic techniques in the circular duct flow. The conformational tensor models, which have root in the molecular dynamic, applied to simulate the polymer chain orientation in suspension of nanofibers. The effects of nanofiber aspect ratio are also investigated on the polymer chain orientation. The results show that the polymer chains are less oriented along the flow direction for more nanofiber concentration and consequently, the extensibility of the polymer chains decrease. In fact, the nanofibers prevent to stretch of polymer chains along the flow direction. Moreover, the results indicate that as increasing the aspect ratio of nanofibers, the c_zz components decrease but c_rr, c_θθ, and c_zr components increase. It reveals that the polymer chains are less oriented along the flow direction for higher aspect ratio of nanofibers, and consequently, the length of polymer chains is reduced. POLYM. ENG. SCI., 59:15–21, 2019. © 2018 Society of Plastics Engineers     

Some relationships for the orientational drawing of polymers

The orientational drawing of films from different thermoplastics has been studied. The value of the activation energy of drawing in the regions of forced elasticity (necking), high elasticity, and viscous flow (ΔE₁, ΔE₂, ΔE₃) has been found to vary directly with the activation energy for viscous flow of the melt (ΔE_η). Here ΔE₁ < ΔE₂ < ΔE₃ = ΔE_η. Thus Δ E_η characterizes the potential of thermoplastics for orientational drawing under different deformation conditions, since it reflects simultaneously both the intermolecular interaction level and chain flexibility. For maximum chain orientation, the calculated values for the change in the entropy are close to that of the entropy change during crystallization (melting) of the same polymer. The deformation of polymer may be described as a deformation of an entanglement network from the standpoint of classic elasticity theory. Some parameters for an entanglement network were calculated from the results of the drawing experiments. The density of the entanglement network (DEN) depend on the polymer composition: For flexible-chain polymers the DEN is less, for rigid-chain polymers (with coiled chains) it is higher. The DEN affects the maximum (prebreak) drawing ratio: The greater the DEN, the smaller the ratio to which a film can be drawn. At high orientation, the tensile strength of different polymer films tend to be similar, if drawing is not accompanied by crazing.     

Some thermodynamic properties of tetrafluoroethene-hexafluoropropene copolymers

Copolymers of tetrafluoroethene (TFE) with hexafluoropropene (HFP) have been prepared in the 0-14mol% HFP composition range. Their melting temperatures (T_m), enthalpies (ΔH_f) and entropies (ΔS_f) of first and second fusion, and crystallinities (X) according to x-ray diffraction(x.r.d.) and differential scanning calorimetry (d.s.c.) have been determined. The results indicate that ΔH_f/X_x.r.d of the polymer crystals decreases with higher HFP content.     

Cold forming of plastics part I. Draw forming of thermoplastic sheets

An experimental procedure is outlined to examine the potential of thermoplastic sheets in draw forming. Experiments carried out on a variety of materials indicate that the following requirements must be fulfilled for a thermoplastic sheet to be cold formable: (1) The glass transition of polymer should be above ambient temperature and above the temperature of forming, (2) tensile elongation at break should equal or exceed 30%, (3) ratio of tensile to compressive yield stress should equal or exceed 1.6 and (4) sheet must not yield locally (neck) when strained in tension. An experimental method has been developed to determine the compressive, friction and bending forces which oppose the drawing force exerted by the punch. It is shown that the compressive force is, in most cases, largest. A stress analysis is carried out leading to an expression correlating the maximum depth of draw as a function of basic properties of sheets such as tensile strength (S_t*) and compressive yield stress (S_c). The effect of rolling on drawability is examined and interpreted in terms of the ratio S_t*/S_c. The cold formed items have a lower heat distortion temperature than their thermoformed counterparts.     

Latent Heat Enhancement of Paraffin Wax in Poly(divinylbenzene-co-methyl methacrylate) Microcapsule

The preparation of divinylbenzene (DVB)-methyl methacrylate (MMA) copolymer microcapsule encapsulated Rubitherm27 (RT27) P(DVB-co-MMA)/RT27 used as heat storage material by the microsuspension polymerization was studied to improve the latent heats of the encapsulated RT27 with sufficient polymer shell strength. Percent loading of RT27 and DVB:MMA ratio were optimized. The optimal condition was 30% loading of RT27 and 30:70 (% w/w) of DVB:MMA ratio. The nonspherical microcapsules with a dent having core-shell morphology were obtained. The thermal properties of the encapsulated RT27 in the P(DVB-co-MMA)/RT27 capsules were measured by thermogravimetric analyzer and differential scanning calorimeter. The heats of melting (ΔH_m; 153 J/g-RT27) and crystallization (ΔH_c; 164 J/g-RT27) of the encapsulated RT27 in the prepared copolymer capsules were higher than those in PDVB and closed to those of bulk RT27 (162 and 168 J/g-RT27 for ΔH_m and ΔH_c, respectively).     

Influence of polymerization conditions on the viscosity of polyacrylamide via experimental design

Polyacrylamide was synthesized by a free‐radical inverse emulsion technique and optimized via statistical experimental design, with the objective of developing a polymer with a high viscosity within this synthesis technique. The factors considered to affect the response variable, the viscosity of the polymer, were initiator (K₂S₂O₈) concentration (c), reaction temperature (T), stirring rate (r), and initiator addition method (s, batch or dropwise). An experimental design of the four factors at two levels (2⁴) was carried out to study the effect of these process variables on the viscosity of the polymer. The results show that the main factor having an effect on the viscosity was T, with smaller contributions from r and cs. The optimum combination of values for the factors yielding maximum viscosity was T = 65°C, c = 1 mM, r = 230 rpm, and s = dropwise addition. A close fit was obtained between the experimental and predicted values of the viscosity of the polymer solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5719–5724, 2006     

Thermal stability of polyacrylonitrile in the melt formed by hydration

Differential scanning calorimetry (DSC) and intrinsic viscosity measurement have been used to investigate the thermal stability of PAN-based copolymer in the melt formed by hydration. Samples containing various water contents were annealed at temperatures between 160 and 180°C for periods up to 60 min. The melting point (T_m) and crystallization temperature (T_c) increased with annealing time, irrespective of annealing temperature and water content. The increase in T_m with annealing time was interpreted in terms of thermodynamic parameters. The decrease in the heat of fusion (ΔH_f) with the increase of annealing time implies that the number of nitrile groups is reduced during annealing in the melt. The decrease in the entropy of fusion (ΔS_f) calculated from T_m and ΔH_f suggests that the polymer chain becomes more rigid as the annealing time (or temperature) increases; however, the intrinsic viscosity does not increase during annealing. From both thermodynamic analysis and intrinsic viscosity, it is concluded that the increase in T_m is caused by chain rigidity mainly due to the intramolecular cyclization of nitrile groups. © 1992 John Wiley & Sons, Inc.     

Alpha relaxation study in poly(vinyl chloride)/poly(ethyl methacrylate) blends using thermally stimulated currents

Thermoelectrets of poly(vinyl chloride) (PVC) and poly(ethyl methacrylate) (PEMA) blends were prepared using the conventional thermal poling method. α‐Relaxation in this polyblend was investigated using thermally stimulated depolarization currents (TSDC). The global spectra of the polyblends revealed that the two polymers are not completely compatible. An Eyring relationship was verified through the linear relation between the activation enthalpy ΔH and the activation entropy ΔS. In addition, the thermal sampling (TS) data were used to determine the compensation parameters such as compensation temperature T_c and compensation time (τ_c). These parameters were used to calculate the density of disorder (DOD) for all samples, which was found to be close to 32%. © 2000 Society of Chemical Industry     

Solubility of alkanes in a polystyrene matrix

The solubilities of seven alkanes in a matrix of uncrosslinked polystyrene were measured at several different temperatures. A gravimetric method reported earlier was used to monitor the sorption of the solvents. The experimental measurements showed unambiguously that the solubility of the alkanes diffusing into a polystyrene matrix reached a constant and reproducible value typical for each system and temperature. These values could be interpreted very well with the Flory–Huggins solubility parameter (χ = a(entropic contribution to x) + b(enthalpic contribution to x)/T[absolute temperature in Kelvin (K)]) or with the van't Hoff equation (ln K_S = ΔS/R(gas constant) ? ΔH/RT, where K_S is the equilibrium constant, ΔS is the entropy change, and ΔH is the enthalpy change). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

IGC Characterization of PMMA Grafted onto CTMP Fiber

Inverse Gas Chromatography (IGC) was used to characterize chemithermomechanical pulp (CTMP) wood fiber surfaces modified by polymer grafting. From the retention times at infinite dilution over a range of temperatures, the differential heat of adsorption, ΔH^oA, the standard free energy, ΔG^oA, and the standard entropy of adsorption, ΔS^oA, have been determined for the n-alkanes vapors C₈-C₁₁ on CTMP wood fibers grafted with poly(methylmethacrylate) (PMMA) at various polymer loadings (PL). The dispersive component of the surface free energy γ^LS (London) has also been calculated by using a method based on the increment of ΔG^oA per CH₂ group. Comparison of results for the original material, CTMP and PMMA, with those of the grafted fibers has allowed the evaluation of surface modification. Grafted samples at high PL show values of ΔH^oA, ΔG^oA, and γ^LS approaching those of the pure PMMA indicating a high density of polymer chains grafts on the CTMP wood fiber.     

Reaction kinetics of graft copolymerization and thermochemical studies of the degradation of poly(vinyl alcohol) graft copolymer

Poly(vinyl alcohol) (PVA) is a water‐soluble and biomedical polymer. 2‐Acrylamido‐2‐methyl‐1‐propanesulfonic acid was grafted onto PVA using ammonium persulfate as radical initiator. The influences of synthesis conditions such as temperature, concentrations of initiator, PVA and monomer were investigated. Both the initial rate of grafting and the final percentage of grafting were increased by an increase in reaction temperature. The reaction kinetics were studied to determine the rate constants of the first‐order reactions. An activation energy of 16.3 kJ mol^?1 was found for the grafting reaction. The graft copolymers were characterized by IR and intrinsic viscosity measurements. A proposed mechanism of the grafting reaction is discussed. Kinetics of the thermal degradation were studied using a thermogravimetric method and the order of thermal stabilities are given. The apparent activation thermodynamic parameters, E_a, ΔH*, ΔS* and ΔG* were determined and correlated to the thermal stabilities of the homo‐ and grafted polymers. © 2001 Society of Chemical Industry     

Gels of syndiotacticity-rich poly(vinyl alcohol)–water/dimethyl sulfoxide or – water/ethylene glycol solutions

Gels of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) in mixed solvents of water/dimethyl sulfoxide (DMSO) or water/ethylene glycol (EG) were made by chilling at the temperatures of 0–70°C from those solutions with the polymer concentrations below 10g/dL. The melting points of the gels were measured warming the gel from the gelling temperature (T_gel) at a constant heating rate. The apparent enthalpy of fusion of a junction of gel, ΔH was estimated from the relation between the apparent melting temperature and the polymer concentration. The s-PVA gels made from the mixtures of the water/lower contents of DMSO or EG had a minimum at lower T_gel and a maximum ΔH at a higher T_gel. On the other hand, the s-PVA gels made from the mixtures of the water/higher contents of them had nearly a maximum ΔH at a higher T_gel. From those results, it was considered that the former gels received a high thermal history while the latter gels received only slight thermal history.     

Studies on whitening phenomena induced by some non-solvents on highly oriented glassy polymers

Whitening phenomena, characterized by optically opaque regions when a highly oriented glassy polymer is immersed in some liquids, were investigated as a function of temperature, extent of molecular orientation, different solvent and molecular weight, using oriented polymethyl methacrylate (PMMA) obtained by hot-stretching and cold drawn polycarbonate (PC). Whitened PMMA is highly porous resembling foamed plastics and shows the same T_g as in unwhitened PMMA, while whitened PC is denser with much smaller pores and exhibits melting behavior characteristic of solvent-induced crystallinity. Whitening progresses with a sharp boundary between whitened and unwhitened layers, which advanced at a constant velocity. This feature is similar to Case II transport. However, whitening differs from Case II sorption in that it only occurs in highly oriented polymers in contact with liquids of negligible sorption. Activation enthalpy of 44.1 and 39.7 kcal/mol has been found in a certain temperature range for PMMA/N-methyl formamide (N-MF) and PC/di-isopropyl amine (DIPA) respectively. At a given temperature, a higher extent of orientation leads to faster whitening process. Entropy correlation theory, in which the decrease in the configurational entropy (ΔS_c) due to orientation is assumed to approximate an inerease in the activation entropy, was employed to correlate the dependency of the whitening rate on orientation. For hotstretched PMMA, where ΔS_c is proportionl to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document} since affine deformation applies, a good correlation is observed. For cold drawn PC, correlation was poor, probably because ΔS_c cannot be expressed to be proportational to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document}. In PMMA, when the molecular weight is in the same order as the average molecular weight between entanglements, the orientation and the whitening rate are both lower than higher molecular weight speciments. This may be due to a smaller number of chain entanglements and consequent chain slippage. In PMMA, whitening induced liquids seem to have a solubility parameter somewhat greater (2.5 ～ 5.0) than that of PMMA. For PC, no consistent tendency is found.     

Equation of state for polymer solution

The flow pattern through a cloud of polymer segments is obviously different from the flow pattern around a solid object. It can be shown theoretically, however, that the partial viscosity due to the cloud can take the same value as for a solid sphere with the radius of gyration of the cloud as its radius. The specific viscosity of polymer solution has been derived as 2.5(c/c_I), with c_I being the internal concentration associated with a polymer molecule. The internal concentration is the ratio of mass over the volume of gyration of segments in a polymer chain. A radius of gyration exists for any type of polymers, flexible or rigid, exhibiting different kinds of dependence on the molecular weight. From the expression of the specific viscosity, the intrinsic viscosity is shown to be equal to 2.5/c^∗, c^∗ being the (minimum) internal concentration for the state of maximum conformational entropy. The equation for the specific viscosity, thus obtained, is expanded into a polynomial in c[η]. This formula is shown to agree with data for several kinds of polymers, with flexible, semi-rigid and rigid.The quantity 1/c_I can be interpreted as an expression for the chain stiffness. In polyelectrolytes, coulombic repulsive potentials affect the chain stiffness. The dependence of c_I on the effective population of polyions in the polyelectrolyte molecule is discussed.An equation of state for the polymer solution is formulated that included the internal concentration. The virial coefficients emerge as a result of c_I not always being equal to c^∗, and they are molecular weight dependent.     

Improving the compatibility of disperse dye mixtures using levelling agent — assessment through colour coordinates

The addition of a nonionic levelling agent to a dyebath containing a mixture of three disperse dyes in equal proportions and having similar hues (all in the red—yellow sector of colour space) significantly improved their compatibility, especially at higher applied depths of 3.0% and 4.5%. The dyed samples were measured for the differences in their colour coordinates with respect to the undyed substrate on a spectrophotometer attached to an IBM personal computer. The plots of ΔL* vs ΔC*_ab, ΔL* vs K/S, Δb* vs Δa*, Δa* vs K/S and Δ6* vs K/S clearly indicated the improvement in compatibility of the dye mixture.     

Concentration and temperature dependence of plasticizer diffusion into plasticized PVC

The diffusion of a plasticizer S₁ from a source made of PVC containing 25 wt% of S₁ into a medium made of PVC film containing another plasticizer S₂ in 15, 20, 25 and 30 wt%, was studied at temperatures ranging from 70 to 108°C. S₁ was generally diphenyl-iso-octyl phosphate (DPIP) and S₂ was dioctyl phthalate (DOP) but the reciprocal system was also studied in some cases. Starting from a reference point corresponding to a temperature of 70°C and a DOP concentration of 25 wt%, it was found experimentally that an increase Δv of the DOP volume fraction (v) or an increase ΔT of the temperature, led to the same variation of the diffusion coefficient of DPIP if ΔT/Δv ～ 139K. A reasonably close value can be obtained from a simple free-volume approach, using the literature data on the plasticizer action of DOP on PVC.