Rubbery Materials Research Articles

Singlet probes based on coumarin derivatives substituted in position 3; spectral properties in solution and in polymer matrices

Spectral properties of coumarin derivatives (2H-1-benzopyran-2-one), substituted with a bulky group in position 3, were investigated in solvents and in polymer matrices. The bulky electron donating groups in position 3 were phenyl-, phenyltio-, 2-methylphenyltio-, 2,6-dimethylphenyltio-, benzyl-, phenoxy-, dimethylamino- and benzoylamino-. The absorption spectra of all the derivatives are dominated by a broad band with a maximum at 340 nm (log ε∼4.0), which were not influenced by the polarity or viscosity of the environment. The fluorescence of these derivatives is strongly influenced by the polarity of the solvent and viscosity of the surroundings. In high viscosity solvents and in polymer matrices, the quantum yields of around 0.1 and a lifetime of around 2 ns was observed. In low viscosity non-polar solvents such as cyclohexane, the quantum yields lower than 0.01 were observed. The fluorescence of coumarin probes was quenched by polar methanol with a bimolecular rate constant, k q, larger than diffusion controlled limit indicating static quenching. The increased polarity of the mixed solvent introduces processes such as intramolecular charge transfer or twisted intramolecular charge transfer which effectively compete with fluorescence. The dependence of quantum yield of fluorescence on temperature was determined in viscose solvents and polymer matrices. The activation energy of radiation-less process ( E a) increased in going from phenyl to more the bulky 2,6-dimethylphenyltio group in non-polar high viscosity polybutene oil and polar glycerol supporting the idea that the radiation-less process is related to rotation of the group in position 3. The E a value is lower in rubbery matrices such as polyoctenamer or atactic polypropylene than in glassy polymers such as polystyrene, poly(methyl methacrylate) or polyvinyl chloride. 3-Phenylcoumarin, due to its spectral properties, seems to be the most suitable probe for monitoring microviscosity in polymers.

Mechanical Properties and Deformation Behavior of the Double Gyroid Phase in Unoriented Thermoplastic Elastomers

The mechanical properties of the double gyroid (DG) cubic phase in glassy−rubbery block copolymer systems are examined. The stress−strain properties of an isoprene-rich polystyrene/polyisoprene/polystyrene (SIS) triblock and a polystyrene/polyisoprene (SI) starblock DG, both comprised of two separate interpenetrating glassy networks embedded in rubbery matrices, are compared to those of the sphere, cylinder, and lamellar morphologies. This 3-dimensionally interpenetrating periodic nanocomposite is found to have superior properties over those of its classical counterparts, attributable to the morphology rather than to the volume fraction of the glassy component, the architecture of the molecule, or the molecular weight. The DG is the only polygranular/isotropic thermoplastic elastomer morphology which exhibits necking and drawing and which requires considerably higher stresses for deformation up to 200% strain than any of the three classical microdomain morphologies. The deformation behavior of the DG is f...

The Considère condition and rapid stretching of linear and branched polymer melts

We analyze the onset of “necking” and subsequent filament failure during the transient uniaxial elongation of viscoelastic fluid samples in extensional rheometers. In the limit of rapid elongation (such that no molecular relaxation occurs), the external work applied is all stored elastically and the Considère criterion originally developed in solid mechanics can be used to quantitatively predict the critical Hencky strain to failure. By comparing the predictions of the Doi–Edwards model for linear homopolymer melts with those of the “Pom-Pom” model recently proposed by McLeish and Larson [J. Rheol. 42, 81–110 (1998)] for prototypical branched melts we show that the critical strain to failure in rapid elongation of a rubbery material is intimately linked to the molecular topology of the chain, especially the degree of chain branching. The onset of necking instability is monotonically shifted to larger Hencky strains as the number of branches is increased. Numerical computations at finite Deborah numbers also show that there is an optimal range of deformation rates over which homogeneous extensions can be maintained to large strain. We also consider other rapid homogeneous stretching deformations, such as biaxial and planar stretching, and show that the degree of stabilization afforded by inclusion of material with long-chain branching is a sensitive function of the imposed mode of deformation.

Viability and thermal stability of a strain of Saccharomyces cerevisiae freeze-dried in different sugar and polymer matrices.

The viability and thermal stability of a freeze-dried yeast strain were studied in relation to some physical properties of the matrices in which the cells were freeze-dried. Samples of inoculum with solutions of the matrix components [polyvinylpyrrolidone (PVP), maltose, trehalose, maltodextrins, or mixtures of maltodextrin and trehalose] and controls without matrices were freeze-dried and then equilibrated at several relative humidities. Viability was determined before and after freeze-drying and after heat treatment (100 min at 70 degrees C). Freeze-drying with trehalose, PVP, maltose or 1.8-kDa maltodextrin, and mixtures of maltodextrin/trehalose increased viability in comparison with controls. The 3.6-kDa maltodextrin was ineffective at protecting the cells during freeze-drying. The glass transition temperature (Tg), which depends on moisture content, was indicated as a possible factor to determine the stability of labile materials. Protective effects of the excipients during thermal treatment were analysed in relation to the physical changes (collapse or structural shrinkage) which were dependent on the Tg of the systems. The presence of a certain amount of amorphous disaccharides during freeze-drying and heating was found to be a critical factor for ensuring cell viability, which was protected even in rubbery (above Tg) matrices.

Reevaluation of general partitioning model for sorption of hydrophobic organic contaminants by soil and sediment organic matter

AbstractThis evaluation of the polymer‐based Flory–Huggins sorption theory has shown that the model predicts relatively concentration‐independent χ values for rubbery matrices, concentration‐dependent χ values for more glassy matrices, and highly concentration‐dependent, largely negative interaction parameters for sorption of phenanthrene onto Green River kerogen, Ohio Shale II kerogen, Illinois No. 6 and Wyoming coals, and poly(phenyl methacrylate). These greatly negative enthalpic contributions to the interaction parameter are only to be expected where specific sorbate‐sorbent interactions exist, such as in polar sorbate–polar sorbent systems. The failure of the nonlinear partitioning model is explained in terms of its inability to predict these increased interactions of sorbing solutes within microvoids present within glassy matrices. Calculations of sorbent solubility parameters through use of this model do, however, provide good agreement with literature solubility parameter values for specific sorbents; it may thus prove useful for partial characterization of sorbents for which solubility parameters are unknown.

The “food polymer science” approach to flour functionality and ingredient technology in biscuit baking

An overview is made on the food polymer science approach developed by the authors. The quality and performance of flours for the production of cookies and crackers have been shown to depend upon the major functional polymeric components of flour: gluten protein, damaged starch, and pentosans. Of these, damaged starch and soluble pentosans in soft-wheat flours are detrimental to the commercial production of low-moisture cookies and crackers. The detrimental effects of soluble pentosans in flours can be eliminated through the use of pentosanase enzyme in cookie and cracker doughs. Three commercialized applications of this industrial enzyme technology have been patented by Nabisco. The food polymer science approach to baking technology has also been used to study finished-product attributes such as texture, in the context of the thermomechanical properties (e.g. modulus) of glassy solid and rubbery liquid matrices. Results of various studies have clearly demonstrated that products in a glassy solid physical state (at T < T g ) are hard and crisp in texture, but upon increasing plasticization by water (such that T g is depressed below the observation T), are transformed to a rubbery or viscous liquid state, wherein textural hardness (and mechanical modulus) and crispness are dramatically reduced.

Mechanical behavior and structure of rubber modified vinyl ester resins

Vinyl esters are used widely as thermoset matrix materials for reinforced composites; however, they suffer from low-impact resistance. Substantial enhancement of the toughness of brittle polymers may be achieved by dispersing elastomeric inclusions or rubber particles in the polymer matrix, inducing multiple crazing and shear yielding of the matrix. The main objectives of this work are morphological characterization of vinyl ester/reactive rubber systems and investigation of the mechanical and fracture behavior of these systems. Additional studies focused on rubber endcapped vinyl ester in the absence and presence of added reactive rubber. The initial compatibility of the liquid rubber with the liquid resin was studied. This is a key factor, along with cure conditions, in determination of the possible morphologies, namely, the degree of phase separation and particle size. The initial rubber/resin compatibility was found poor and all attempts to improve it by means of surfactants or ultrasonic treatment have not been successful. The flexure mechanical and fracture behavior of the cured resin/rubber systems was investigated. Three basic types of crack propagation behavior, stable, unstable, and stick-slip, were observed. Fracture toughness of various resin/rubber systems was evaluated and was found to increase with increased content of rubbery second-phase material. However, there is some payoff in stiffness and flexural strength of the cured resins. The addition of rubber does not affect the resin toughness at impact conditions. Analysis and interpretation of fractures morphology show that both multiple crazing and external cavitation play an important role in the fracture mechanism of the rubber modified specimens. No shear yielding is evident. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 647–657, 1999

Calculation of J2-integral for 2-D cracks in rubbery materials

A numerical scheme, incorporated with the finite element method, is developed for calculation of the J 2-integral for 2-D cracks appearing in rubbery fields under large deformation. The scheme is formulated based on the concept of the generalized version of the domain integral method. Due to the nature of J 2, the method is shown to be “patch-independent” in a modified sense, and so the near-tip region is always included in the calculation. The proposed technique is therefore particularly addressed to appropriate modeling of the near-tip singular mechanical behavior in order to circumvent the unavoidable imprecision associated with the finite element approximations in the vicinity of the crack tip. The numerical results show that no a priori information on the asymptotic singular behavior is required in order to achieve an acceptable value of J 2. The computation procedure is generally feasible for different rubbery material models.

Ultrasonic characterization of water sorption in poly(2-hydroxyethyl methacrylate) 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. The water sorption involves the transformation of a glassy, moderately crosslinked polymer in a rubbery material. In this study, the changes in the ultrasonic attenuation and velocity in crosslinked poly(2-hydroxyethyl methacrylate) [poly(HEMA)] hydrogel films during water sorption are measured by scanning laser acoustic microscopy (SLAM) and a pulse-echo system. In particular, the pulse-echo technique provides additional valuable information, thanks to its capability for monitoring the position of the swollen/unswollen fronts during water sorption. The evolution of the attenuation observed by SLAM is analyzed in terms of reflections on macroscopic discontinuities and absorption mechanisms. Finally, the propagation of ultrasonic waves acts as a dynamic mechanical test of the material; and, therefore, the measured longitudinal velocity and ultrasonic attenuation are applied to the calculation of the storage bulk longitudinal modulus of the poly(HEMA) hydrogels during water sorption.

FE calculation of elastodynamic energy release rate for rubbery materials

The elastodynamic energy release rate for rubbery material problems with a stationary crack under dynamic loads in the context of large deformation is calculated by the modified domain integral method with finite element solutions. General 2-D problems, including plane stress, plane strain, and axisymmetric cases, are considered in the formulation. The modified DIM is verified to be patch-independent. Although this property does not eliminate the need to include the singular near-tip area in. the calculation, it is observed in the numerical results that acceptable solutions of ERR are calculated even though an accurate near-tip model is not ensured.

Numerical evaluation of J 2 -integral for rubbery materials under dynamic loads with finite element method

The J2-integral for rubbery material problems with a stationary crack under dynamic large deformation is calculated with finite element solutions. General 2-D problems, including plane stress, plane strain, and axisymmetric cases, are considered in the formulation. The numerical procedure is verified to be path-independent in a generalized sense, and the near-tip region is hence always included in the calculation. A numerical treatment for simulation of the integration around the near-tip area is therefore proposed. It is demonstrated numerically that, with this treatment, the calculation is very insensitive to the crack tip finite element grid. In fact, no detailed information on the complicated asymptotic dynamic singular behavior for rubbery materials is required in the calculation.

Some physical characteristics of double-networked natural rubber

ABSTRACT: A double-networked natural rubber (DNNR) was prepared by a ‘‘two-stepcrosslinking’’ method, in which the crosslinking was achieved while the natural rubberwas in a stretched condition. The swelling behavior, tensile properties, creep, recovery,and permanent set were investigated. Generally, the observed mechanical propertiesof DNNR, such as the Young’s modulus, tensile strength, toughness, creep, recovery,and permanent set, were considerably improved as the residual extension was in-creased. They were, however, rather inferior to those of a single-networked naturalrubber and showed a minimum at a lower residual extension of about 1.55. The degreeof crosslinking and elongation at break were not greatly affected by the residual exten-sion. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 917–924, 1997 Key words: natural rubber; double networks; swelling; tensile property; creep andrecovery INTRODUCTION having different strain conditions. Based on thetheory, the degree of permanent set can be de-When a rubbery material is crosslinked in a state scribed quantitatively by using only two factors:of macroscopically zero strain, i.e., in the typical (1) the relative ratio of the number of the twomanner of the rubber industries,

Synthesis of poly(propylene-glycol-diacrylates) and properties of the photocured networks

A series of poly(propylene-glycol-diacrylates) (PPGDA) having molecular weights (MW) in the range 300–3,000 and an acrylic functionality near to two were synthesized by acrylation of the corresponding hydroxy-terminated oligomers with acrylic acid in the presence of p-toluensulphonic acid as a catalyst. The M¯n of the acrylated products was found slightly lower than that of the starting oligomers, indicating the occurrence of an acidic degradation reaction which does not influence the acrylic functionality. The acrylated oligomers were ultraviolet (UV) cured until a complete double bond disappearance was obtained: only in the presence of tripropylene-glycol-diacrylate (TPGDA) were small amounts of residual unsaturations revealed. Rubbery materials were usually obtained, with the exception of TPGDA. The properties of the cured PPGDA were investigated by means of differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical thermal analysis. The Tg values were found to decrease by increasing the MW of the used oligomers, that is, by increasing the length of the chain between the two acrylic double bonds. A good agreement with the Nielsen equation was found. Moreover, the equilibrium swelling values in water were measured; the obtained values were interpreted in terms of the solubility parameters of the oligomers and of the crosslinking density of the networks. Finally, some mixtures of PPGDA oligomers with a typical epoxy-acrylate resin were UV cured; their properties confirm the high flexibilizing effect of the PPGDA oligomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:491–497, 1997

Dispersion of normal modes in cis 1,4 polybutadiene

AbstractAmong the synthetic polymers of commercial potential, poly‐butadiene is an important rubbery material and it encompasses the bulk elastomers in use. To the best of our knowledge, a complete normal coordinate analysis with full phonon dispersion curves for cis 1,4 polybutadiene (CPBD) have not been reported so far. In the present communication, we report a complete normal coordinate analysis with full dispersion curves, density‐of‐states and calculation of heat capacity. The normal coordinate analysis has been carried out using the Urey‐Bradley force field and the Wilson's GF matrix method as modified by Higgs. A comparison has been made with trans 1,4 polybutadiene (TPBD). The prominent features of the dispersion curves like crossing over and regions of zero‐slope away from the zone centre are discussed. To check the validity of the force field used and the assignments, normal mode calculations are also performed for unsaturated C‐deuterated and fully deuterated CPBD.

Influence of glycerol and water content on the structure and properties of extruded starch plastic sheets during aging

The properties of starch plastic sheets were investigated by stress—strain measurements in relation with starch crystallinity. Granular potato starch was plasticized with different amounts of glycerol and water by extrusion. The materials were amorphous directly after processing. During aging above the glass transition temperature at various humidities single helical (V and E-type) and double helical (B-type) crystallinity was formed. The rate of crystallization is a function of water and glycerol content. The amorphous rubbery materials were soft and weak with high elongations. During aging the materials became less flexible with higher elastic modulus and tensile stress. The changes are related to changes in water content and glass transition temperature and to changes in B-type crystallinity. The changes in stress—strain properties are explained by the formation of helical structures and crystals, which results in a reinforcement of the starch network by physical crosslinking. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1411–1422, 1997

On the Ogden Strain-Energy Function

Abstract The Ogden strain-energy function for rubber appears to be gaining popularity among users of finite element analysis. This paper discusses some of the special features of this material model. It explains why nonlinear regression analysis of stress-strain data obtained from just one mode of deformation may yield an Ogden strain-energy function that is unsatisfactory for predicting behavior in other deformation modes. It suggests the regression analysis be constrained such that some of the coefficients are chosen based upon the known behavior of rubbery materials.

Allergic fungal sinusitis

Allergic fungal sinusitis is a challenging problem. It probably results from entrapment of fungal forms in the sinuses of patients with associated atopy. The characteristic clinical picture is pansinusitis (unilateral more than bilateral) and polyposis, recurrent despite previous surgeries. Radiographic studies present a characteristic pattern. At surgery, in addition to polyps and pansinusitis, the most distinctive finding is allergic mucin. This tenaceous, dark, rubbery material contains numerous eosinophils and Charcot-Leyden crystals, and fungal stains show the presence of noninvasive hyphae. Fungal cultures may or may not be positive. The differential diagnosis of allergic fungal sinusitis includes allergic mucin sinusitis, mycetoma, or saprophytic fungal growth within a diseased sinus. Treatment involves adequate surgical exenteration, the use of corticosteroids (topical and systemic), and postoperative cleaning. Despite warnings to the contrary, immunotherapy with fungal antigens may be of significant benefit.

Single-monolayer in situ modulus measurements using a SAW device Photocrosslinking of a diacetylenic thiol-based monolayer

We report direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer. We measured a change in elastic modulus of 5×1010 dyn cm-2 as a result of UV-induced photocrosslinking of a single surface-confined monolayer of the conjugated diacetylenic thiol HS(CH2)10Câ–·CCâ–·C(CH2)10CO2H (DAT). The modulus measurement was made on a monolayer of DAT chemisorbed upon a gold film on the surface of a 97-MHz ST-quartz surface acoustic wave (SAW) delay line. The ratio of the changes recorded in SAW velocity and attenuation, ca. 4:1, suggests that the measured effect is mainly a change in the elastic (real) component of the complex shear modulus, viscous changes playing a lesser role. In relation to typical polymer modulus values, the change of 5×1010 dyn cm-2 is consistent with a change from a rubbery material (G′≈107–108 dyn cm-2) to a fairly rigid, glassy material (G′≈1010 dyn cm-2), reasonable for comparison of the monolayer in its as-adsorbed and crosslinked forms. This report of the direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer is consistent with previous insitu measurements of this process using thickness-shear mode resonators

Chemical and morphological analysis of explanted polyurethane vascular prostheses: the challenge of removing fixed adhering tissue

During in vivo experiments to evaluate the biocompatibility and biostability of alternative biomaterials, the ideal protocol for the handling and preservation of the explanted material is often compromised in order to meet the needs of both the pathologist and the materials scientist. Expiants surrounded by tissue are often fixed in formalin or glutaraldehyde to facilitate later pathological and histological analysis, but the subsequent removal of such fixed tissue from thermally sensitive and less chemically stable polymers, such as polyurethanes, poses major problems for the materials scientist, who does not wish to modify the chemical, physical or morphological characteristics of the underlying biomaterial. The present study has attempted to find a solution to this problem by exposing virgin specimens of the microporous polyurethane Vascugraft ® vascular prosthesis to six different cleaning conditions, all known to be effective in removing fixed tissue. These conditions included the use of 20% aqueous potassium hydroxide solution for 48 h at room temperature, 5% sodium bicarbonate solution for 5 min at the boil, and 9, 10, 11 and 12 n hydrochloric acid for 48 h at room temperature. The appearance and chemical properties of the virgin and treated specimens were compared using electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, gel permeation chromatography for molecular weight and differential scanning calorimetry techniques. The use of temperatures close to the boil resulted in the formation of a translucent, rubbery material with gross changes in the microporous and microfibrous structure. The strongly acidic and alkaline conditions caused a loss in the surface carbonate group content. In addition, 12 n hydrochloric acid reduced the molecular weight and urethane content. Consequently, 9 n hydrochloric acid is recommended as the cleaning agent of choice for removing fixed tissue from this type of microporous polyurethane. Control experiments on virgin material should also be included in any cleaning protocol.

Mechanical properties of thermoplastic waxy maize starch

The properties of thermoplastic amylopectin materials were investigated by stress-strain and relaxation measurements as a function of water content and crystallinity. Granular waxy maize starch was plasticized by extrusion with water and glycerol. The materials are amorphous after processing. The sharp fall in modulus at a water content of 10% is characteristic of a glass to rubber transition of an amorphous polymer. The materials are brittle below their glass transition temperature with a modulus of approximately 1000 MPa and an elongation of less than 20%. The amorphous rubbery materials are soft and weak with moduli of 0–10 MPa and tensile strengths of 0–2 MPa. The materials are viscoelastic, show plastic flow, and form a highly entangled polymer matrix, resulting in high values of elongation (500%), due to the high amylopectin molecular mass. Above glass transition temperature the amylopectin forms inter- and intramolecular double helices, crystallizing in a B-type crystal. The initial increase in modulus, tensile strength, and relaxation time is the result of the lower mobility of the amylopectin molecules and the reinforcement of the network by physical crosslinking. The drastic reduction of the elongation and the formation of cracks is the result of intramolecular crystallization. At crystalline junction zones the internal stress is increased and the interaction between molecules is reduced. © 1996 John Wiley & Sons, Inc.