Dynamic Mechanical Modulus Research Articles

Dynamic mechanical properties of agricultural residues‐filled polystyrene

AbstractAgricultural residues (cotton straw) were added as very small particles to polystyrene (PS) at different weight ratios by using a melt‐mixing technique. The dynamic mechanical tests were performed over a wide range of temperatures and frequencies by using an ARES rheometer (Rheometrics Scientific) operated in the dynamic mode. The dynamic mechanical properties in terms of the storage modulus (G′), loss modulus (G″), compliance moduli, loss tangent, and dynamic viscosity were studied and compared for PS and PS composite. The results showed that the dynamic mechanical moduli and viscosity were found to increase with the addition of cotton straw and rise further with its loading increasing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 37–40, 2004

Relationship between Dynamic Mechanical Properties and Water Absorption of Unsaturated Polyester and Vinyl Ester Glass Fiber Composites

The effect of hydrothermal degradation on polyester and vinyl ester mat glass fiber composites on viscoelastic properties is investigated by dynamic mechanical thermal analysis and flexural modulus. The adhesion between fiber and matrix is studied by short-beam shear test and by SEM microphotographs. Storage modulus in the glass state (Tg - 50 K) and rubber state (Tg + 50 K) is also analyzed for the matrix and composites samples, before and after water immersion. Loss tangent (δ) is analyzed taken into account the values obtained for the materials in moisture sorption experiments.

Thermotropic liquid‐crystalline copolyester (Rodrun LC3000)/thermoplastic elastomer (SEBS) in situ composites: II. Mechanical properties and morphology of monofilaments in comparison with extruded strands

AbstractMonofilaments of in situ composites were prepared from an immiscible blend of a thermotropic liquid‐crystalline polymer (TLCP), Rodrun LC3000, and a thermoplastic elastomer, styrene–(ethylene butylene)–styrene (SEBS), by a melt spinning process. Mechanical properties and the morphology of the composite monofilaments were investigated and compared with those of the extruded strands previously reported. The stresses at all tensile strains of the composite monofilaments were much higher than those of the extruded strands. The tensile strengths of both extruded strands and monofilaments were comparable, but the elongation at break of monofilaments dropped considerably. The tension sets of composite monofilaments were slightly higher than those of extruded strands. All composite monofilaments with TLCP content of ≤15 wt % exhibited good elastic recovery under the applied strain up to 200%. The dynamic mechanical storage modulus at 25°C of 10 wt % TLCP composite monofilament increased fourfold compared with that of the composite extruded strand and fivefold compared with that of the neat SEBS monofilament. The dramatic enhancement in the mechanical properties of in situ composite monofilaments is due to the formation of finer and longer TLCP fibrils (length‐to‐width ratio > 100) than those formed in the extruded strands. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 518–524, 2003

Synthesis and characterization of aromatic polyesters and copolyesters from 4,4′‐(1‐hydroxyphenylidene)diphenol and 4,4′‐(9‐fluorenylidene)diphenol

AbstractTwo isophthalic polyesters from 4,4′‐(1‐hydroxyphenylidene)diphenol (BAP/ISO) and 4,4′‐(9‐fluorenylidene)diphenol (BF/ISO), and three different copolyesters containing 75, 50, and 25 mol % of BAP/ISO were synthesized by interfacial polycondensation. This preparation method yielded polymers and copolymers that produced flexible and transparent films when they were cast from solution. Proton NMR spectrometry studies showed that the isophthalic copolyesters were obtained as random copolymers with differences in comonomer composition no larger than 2.5 mol % with respect to the expected compositions. Wide‐angle X‐ray diffraction measurements indicated that all the polyesters and copolyesters were amorphous. The copolyesters showed amorphous patterns with maxima that fell between those of the polyesters. It was also found that thermal properties such as glass‐transition temperature, onset of decomposition temperature, thermal stability, dynamic mechanical storage modulus, and maximum on the α‐transition of the damping factor tan δ of BF/ISO were higher than those of BAP/ISO. The values of these thermal properties in the copolyesters fell between those of the polyesters and were dependent on the amounts of BF/ISO and BAP/ISO present in the copolyester in a linear fashion. Therefore, the thermal properties of a given copolyester can be predicted directly from the comonomers' composition. Overall, it shows that the interfacial polycondensation method is suitable to obtain these copolyesters in a controlled manner and that their properties can be tailored to be between those of the homopolyesters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2515–2522, 2002

Theoretical Study of Molecular Association and Thermoreversible Gelation in Polymers

This paper reviews our recent theoretical studies of molecular association and thermoreversible gelation in polymer solutions and blends. We first classify fundamental types of association, and propose their static and dynamic characterization. We then develope general theory of associating polymers to study phase transitions induced by molecular association. These transitions include macro- and microphase separation, micellization, hydration, thermoreversible gelation and liquid-crystalization. As for the origin of associative forces, we focus on hydrogen bonding and hydrophobic aggregation. Detailed study on thermoreversible gelation with multiple cross-link junctions is presented. Paying special attention to the multiplicity and sequence length of the network junctions, we derive phase diagrams with coexisting gelation and phase separation, and compare them with experimental data. Local and global structures of the gel networks are studied from molecular point of view. The theory is applied to more complex thermoreversible gels such as binary networks (interpenetrating networks, alternating networks and randomely mixed networks), hydrated networks with high-temperature gelation, gelation strongly coupled to polymer conformational transitions such as coil-to-helix transition. To study dynamics of thermoreversible gels, a simple transient network model is introduced, and creation and annihilation of junctions in the networks are theoretically described. Stationary non-linear viscosity and the dynamic mechanical moduli are calculated as functions of the shear rate, frequency and the chain disengagement rate. From the peak of the loss modulus, the lifetime τ× of the junction is estimated, and from the high frequency plateau of the storage modulus, the number of elastically effective chains in the network is found. Transient phenomena such as stress relaxation and stress overshoot are also theoretically studied. Results are compared with the recent experimental reports on the rheological study of hydrophobically modified water-soluble polymers.

Effect of Carbon Black Morphology on Dynamic Mechanical Properties of Rubber.

Carbon black samples with almost all the same properties (i.e., nitrogen surface area, CTAB surface area, DBP absorption, compressed DBP absorption and tint strength) except aggregate size distribution were tested by disk centrifuge photosedimentometry. The effect of the aggregate size distribution on rubber vulcanizates was evaluated by the dynamic mechanical modulus as a probe. The values of c storage modulus (ΔE') decreased when the aggregate size distribution became broader. This occurred because the ΔE' levels were determined by the aggregate-aggregate interaction, rather than by the carbon black-polymer interaction, when the aggregate size distribution was broader, where ΔE' is the difference between the largest and smallest values of dynamic storage modulus E' observed under the dynamic strain amplitude dependence test.

Advanced Fluid Information. Flows in Polymer Networks.

A simple transient network model is introduced to describe creation and annihilation of junctions in the networks of associating polymers. Stationary non-linear viscosity is calculated by the theory and by Monte Carlo simulation to study shear thickening. The dynamic mechanical moduli are calculated as functions of the frequency and the chain disengagement rate. From the peak of the loss modulus, the lifetime T × of the junction is estimated, and from the high frequency plateau of the storage modulus, the number of elastically effective chains in the network is found. Transient phenomena such as stress relaxation and stress overshoot are also theoretically studied. Results are compared with the recent experimental reports on the rheological study of hydrophobically modified water-soluble polymers.

High temperature lifetime of polyimide/poly(silsesquioxane)-like hybrid films

Decomposition kinetics in thermogravimetric analysis (TGA) and dynamic mechanical relaxation in dynamic mechanical analysis (DMA) are used to study the high temperature lifetime of the new type of polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid films, which are designed to form three-dimensional structures with linear polyimide blocks and a crosslinked PSSQ-like structure. Both TGA and DMA analysis reveal that the PI/PSSQ-like hybrid films have a longer lifetime (are more reliable) with regard to their thermal and mechanical characteristics than that of pure PI. Even just 2 wt% of p-aminophenyltrimethoxysilane (APTS) in a PI/PSSQ-like hybrid film can significantly improve the service lifetime by as much as at least four times in a TGA decomposition kinetic study. The dynamical relaxation data are well fitted to the calculated WLF (Williams-Landel-Ferry) master curves. In a series of X-PIS (PI modified with APTS) hybrid films, decreasing the PI block chain length increases the decomposition activation energy, lifetime (in both TGA and DMA) and relaxation modulus. In a series of X-PIS-y-PTS [PI modified with APTS and phenyltrimethoxysilane (PTS)] films, the decomposition activation energy and lifetime (in TGA) increase with the PTS content. Interestingly, the dynamic mechanical relaxation modulus of 10000-PIS-100-PTS film is lower than that of the corresponding 10000-PIS film at frequency > 102 rad/sec, but higher at frequency < 102 rad/sec. The 10000-PIS-100-PTS has a lower relaxation time than the 10000-PIS at the modulus 5×108 Pa, but the relaxation time of the former becomes higher at 5×107 Pa.

Study ofβ relaxation in polypropylene fibres modified by several techniques

Polypropylene fibres prepared from polypropylene (PP) blended with 8 wt % of an ethylene aminoalkylacrylate copolymer were studied by means of 1 H nuclear magnetic resonance (NMR) and dynamic mechanical techniques. Measurements were carried out on the fibres spun at the spinning speeds 400 and 1200 m.min -1 and then drawn to the draw ratio λ = 3.5. Spin - lattice relaxation time T 1 and storage E' and loss E components of a dynamic mechanical modulus were measured in the temperature region of the glass transition. Broad line NMR spectra were detected at 313 K. The experimental results show that drawing of the fibres prepared at both spinning speeds results in a restriction of the molecular motion. Simultaneously with the restriction, a chain mobility enhancement was observed in noncrystalline regions of the fibres. Similar effects were induced also by rising the spinning speed. Reasons for this behavior are discussed in the paper.

Polymerization and viscoelastic behavior of networks from a dual-curing, liquid crystalline monomer

The network formation and viscoelastic behavior of a liquid crystalline monomer, whose structure includes both acrylate and acetylene reactive groups, have been studied. By combining both photo and thermal polymerization, the networks can be formed in two separate steps, with the initial photopolymerization dominated by acrylate crosslinking and subsequent thermal polymerization dominated by acetylene crosslinking. In addition, the monomer exhibits a liquid crystalline phase. Photopolymerization while in the liquid crystal phase locks in the molecular ordering. Dynamic mechanical analysis shows that networks formed from the liquid crystalline phase have lower crosslink densities and narrower distributions of molecular weights between crosslinks when compared to networks formed from the isotropic phase (and at higher polymerization temperatures). After thermal postcure at 250°C, the networks formed from the isotropic monomer have a 23% higher dynamic mechanical storage modulus (in the glassy state) than the networks formed from the liquid crystalline monomer. The thermally postcured networks have unusually high glass-transition temperatures, which exceed 300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1183–1190, 1999

Study of a plasticized-unoriented P(VF2/VF3) (73/27 mol%) copolymer. I. The effects of crystallization conditions on morphology, physical, and thermal properties

The results of a study on the effects of a plasticizer, tricresyl phosphate, on the mechanical and thermal properties of unoriented films of poly(vinylidene fluoride–trifluoroethylene) (VF2/VF3) copolymer (73/27 mol%) are presented. Films were prepared by both quenching and slow-cooling from the melt with plasticizer concentrations of 0, 5, and 10% by weight. For the slow-cooled films, a reduction in crystallinity by 25% was observed for the heavily plasticized films, together with a reduced dynamic mechanical modulus (≈ 58%) and an increased dielectric constant (≈ 200%). For the quenched films, a small increase in crystallinity was observed together with a reduced modulus and an increased dielectric constant. Measurements of the temperature dependence of the modulus and dielectric constant at 10 Hz. were also carried out from −100°C to 100°C. This data showed that for slow-cooled films the glass transition temperature decreased from −28°C to -52°C at the highest doping level. DSC thermal analysis shows a decrease in the Curie transition (≈ 4°C) and melting temperatures (≈ 9°C) for the quenched films, while the slow-cooled films only showed a decrease in melting temperature (≈ 10°C), while the Curie transition temperature was unaffected. In addition, evidence of a two-phase system or a nonferroelectric crystal phase is noted by the presence of two Curie transition temperature peaks. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 19–28, 1999

A comparison of the α-relaxation of amorphous poly(aryl-ether-ether-ketone) (PEEK) probed by dielectric and dynamic mechanical analysis

A re-examination of the α-relaxation of amorphous PEEK is performed based on dielectric (DEA) and dynamic mechanical (DMA) probes. The skewed arc shapes of the DEA and DMA data presented in Cole-Cole coordinates indicate the necessity to use the Havriliak-Negami (HN) equation to analyse the data. The analysis of isochronal scans measured in a wide frequency range is performed by fitting the HN equation to the complex inverse of the dielectric susceptibility simultaneously with the complex dynamic mechanical modulus. The satisfactory quality of the simultaneous DEA/DMA fit provides strong support to the general scaling character of the α-relaxation and the similarity of the nature of relaxing units examined by both probes.

Swelling and static-dynamic mechanical behavior of mica-reinforced linear and star-branched polybutadiene composites

Physical properties of mica-reinforced linear (LPB) and star-branched polybutadiene (SPB) composites have been studied with special reference to the effect of silane coupling agent, degree of crosslinking, and degree of mica loading, as well as the molecular architecture of polybutadienes. Tensile properties increase and swelling decreases with addition of mica for linear polybutadiene. Star-branched polybutadiene shows a reverse behavior, especially beyond 5% of mica. The improvements in mechanical properties are more pronounced in the case of silane-treated mica compositions of both type of polybutadienes. Dynamic mechanical spectra were obtained for linear and star-branched polybutadienes. Effects of mica loading and silane treatment on dynamic moduli are discussed. Dynamic mechanical moduli (E′, E′) of composites increase with increasing mica content for linear polybutadiene but decrease for star-branched polybutadiene beyond certain mica loadings. Effective damping regions were determined in terms of frequency and temperature. The glass transition temperature (Tg) increased slightly, and the damping peak (tan δ) broadened due to the rubber—filler interaction, especially after silane treatment for both polymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1943–1952, 1997

Thermorheological consequences of crystalline-phase crosslinking in polyamide fibers

Wet-spun fibers of a diacetylene-containing aliphatic polyamide (PADA 6,22) were exposed to controlled dosages of electron-beam radiation to selectively crosslink the crystalline regions via a topochemical diacetylene to polydiacetylene conversion. For aligned polymer chains in an oriented fiber, the polydiacetylene crosslinks are created perpendicular to the fiber direction; interference microscopy revealed that the refractive index increased in this direction. Dynamic mechanical spectroscopy and torsional modulus measurements showed that the noncrystalline phase remains essentially unaffected by electron-beam irradiation up to 60 Mrad. Thermal stress analysis demonstrated that higher shrinkage stresses are retained by the irradiated fibers at temperatures approaching the effective thermomechanical melting temperature of the nonirradiated fiber (200°C); thermal deformation analysis also revealed that much lower extensions are exhibited by the crystalline-phase crosslinked fibers at these temperatures. The results suggest that crystalline-phase crosslinking of functionally modified semicrystalline polymers constitutes a mechanism for enhancing structural integrity at elevated temperatures without reducing amorphous-phase flexibility. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2613–2622, 1997

The aggregation state of polyimide

The aggregation state of polyimide in solution and in the solid state were studied using the NMR and fluorescence techniques. The experiment results show that the decay of spin-spin relaxation of polyimides with concentration can be described as a single exponential, biexponential, triexponential, biexponential profile. Meanwhile, the intensities of fluorencence spectra increase rapidly with the concentration, and some peaks have a red-shift. Based upon these experiment results, it can be concluded that polyimide in solution is very flexible, and there are several critical concentrations at which polyimide has distinctly different aggregation states. The existence of intermolecular charge transfer interaction between polyimide chains has been proved, and the interaction has a profound effect on the glass transition temperature, T g , and the dynamic mechanical modulus of polyimide.

Internal Friction of Amorphous Zr65Al7.5Cu27.5-Films

Using a vibrating reed device with micro structurized Si reeds the dynamic mechanical properties Young's modulus and damping of thin films deposited on the reeds are measured simultaneously with the curvature of the specimen. The curvature yields the internal stress of the film. As an example, measurements on amorphous Zr 65 Al 7.5 Cu 27.5 -films are shown and compared with measurements on amorphous splat cooled specimen of the same composition. A pronounced damping peak in the thin films is observed slightly below room temperature which is attributed to hydrogen relaxation jumps.

Relaxation Patterns of Nearly Critical Gels

We measure the complex rheological behavior of nearly critical gels and analyze the data by searching for characteristic patterns and abstracting those patterns into a self-consistent model. The sample is a linear, flexible, nearly monodisperse polybutadiene which gets cross-linked on its vinyl side groups. The dynamic mechanical storage and loss moduli of cross-linking polymers change smoothly during the liquid−solid transition, while equilibrium rheological properties (e.g., zero-shear viscosity and equilibrium compliance) diverge. During gelation, the relaxation occurs in a distinct pattern which can be described in a quantitative way with a minimum number of parameters. The pattern can be understood as a combination of the BSW spectrum (representing the precursor relaxation behavior) and the self-similar Chambon−Winter gel spectrum (modeling the terminal relaxation due to growing clusters). The spectrum is cut off at the material's longest relaxation time, λmax. Our model parameters, λmax and Ge (equilibrium modulus), exhibit characteristic scaling behavior with respect to the distance from the gel point, |p − pc|. The relaxation exponent, n, in the terminal zone is a function of the extent of reaction. Hence, dynamic scaling (requires constant n values) is not valid for our system. The proposed model passes the self-consistency test by predicting the mechanical behavior (at different frequencies) as a function of the extent of reaction and other rheological observations during the sol−gel transition.

Mechanical and Thermal Properties of Biodegradable Polyurethanes Derived from Sericin.

In this study, from the viewpoint of biodegradable polymers and waste disposal, polyurethane (PU) foams and films containing sericin were prepared from sericin and diphenylmethane diisocyanate (MDI). Polyethylene glycol (PEG, diol type) and polypropylene glycol (PPG, triol type) were used as a part of the polyol. Mechanical and thermal properties of PU's containing sericin were measured by tensile test and thermal analysis. Sericin could be used as a polyol of PU's and the strength and the glass transition temperature of PU films containing sericin increased with increasing sericin content. The strength of PU foams depended strongly on their apparent density. From the dynamic mechanical analysis (DMA), loss modulus (E) and tan δ curves showed three peaks, α, β, γ in the region from high to low temperatures. The α and β peaks which are assigned to the main chain motion and local mode motion shifted to the higher temperature region with increasing sericin content. The γ peak was almost constant at -130°C.

Model with experimental evidences for the morphology of binary blends of a thermosetting polycyanate with thermoplastics

A proposed mechanical model based on our modification of the conventional Takayanagi model was successfully used to describe the dynamic mechanical modulus data of binary blends of a high-temperature thermosetting polycyanate (Bisphenol E dicyanate) with thermoplastics (polysulfone or poly(ether imide)). The model parameters were found to quantitatively agree well with the physical compositions of the phases in the blends. The modeling results suggested interesting shifts in the phase continuity of the blends as a function of the thermoplastic contents. At low thermoplastic contents (10% and below), the blends exhibited a simple continuous-dispersed phase morphology, with the continuous polycyanate phase surrounding the dispersed phase

Pultruded fibre-reinforced polyurethane composites. III. Static mechanical, thermal, and dynamic mechanical properties

A proprietary process has been developed for the manufacture of polyurethane (PU) pultruded composites. The blocked isocyanate (NCO)-terminated PU prepolymer synthesized in this study was prepared from ϵ-caprolactam blocked blends of toluene diisocyanate and branched polyester. The static mechanical and thermal properties of various fibres (glass, carbon and Kevlar-49 aramid fibre) reinforced blocked PU composites have been studied. Results show that the static mechanical properties (i.e. tensile strength, specific tensile strength, flexural strength, specific flexural strength, flexural modulus and impact strength) and thermal properties (heat deflection temperature (HDT) increase with fibre content. Kevlar-fibre/blocked-PU composites possess the highest impact strength, specific tensile strength and HDT, whereas carbon-fibre/blocked-PU composites show the highest tensile strength, flexural strength, specific flexural strength and flexural modulus. Experimental results for tensile strength of all composites except carbon-fibre/blocked-PU composites follow the rule of mixtures. The deviation from the mixtures' rule of the properties of the carbon-fibre/blocked-PU composite is due to fibre breakage during processing. The glass-transition temperature (T g) increased slightly and the damping peak (tan δ) was broadened as a consequence of fibre reinforcement. The dynamic mechanical moduli (G', G“) of pultruded blocked PU composites are apparently higher than those of the matrices. The moduli (G', G“) increase with increasing fibre and filler content, and the damping peak becomes broad. The effect of postcuring on the degree of crosslinking, T g and dynamic modulus will be discussed.