Influence of vinyl ester/styrene network structure on thermal and mechanical behavior

A series of polyurethane networks were prepared from MDI (4,41-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a Tg (glass transition temperature) of −60 °C, and the aromatic hard segments display a Tg of about 128 °C. Two Tgs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.

Effects of corn oil on glass transition temperatures of cassava starch

ABSTRACTThermal behavior of a coextruded microlayer composite with 388 alternating layers of polycarbonate and polymethyl methacrylate (PMMA) was investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Two distinct glass transition temperatures were observed with DSC for the coextruded composite, however both were shifted very slightly towards each other, compared to the glass transition temperatures of the pure components, indicating limited miscibility. Adhesion between the alternating microlayers appeared to be very good; delamination did not occur after the microlayer composite was subjected to a high speed impact test. Adhesion is attributed to limited miscibility since little mixing resulted from the laminar flow which was required in the coextrusion process. DMA results revealed an additional damping peak, which was not observed with DSC, at a temperature between the glass transitions of the two components. This intermediate transition peak is more sensitive to change in frequency compared to the response for the individual pure components.

It is generally believed that only intermolecular, elastically-effective crosslinks influence elastomer properties. The role of the intramolecular modifications of the polymer chains is marginalized. The aim of our study was the characterization of the structural parameters of cured elastomers, and determination of their influence on the behavior of the polymer network. For this purpose, styrene-butadiene rubbers (SBR), cured with various curatives, such as DCP, TMTD, TBzTD, Vulcuren®, DPG/S8, CBS/S8, MBTS/S8 and ZDT/S8, were investigated. In every series of samples a broad range of crosslink density was obtained, in addition to diverse crosslink structures, as determined by equilibrium swelling and thiol-amine analysis. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the glass transition process, and positron annihilation lifetime spectroscopy (PALS) to investigate the size of the free volumes. For all samples, the values of the glass transition temperature (Tg) increased with a rise in crosslink density. At the same time, the free volume size proportionally decreased. The changes in Tg and free volume size show significant differences between the series crosslinked with various curatives. These variations are explained on the basis of the curatives’ structure effect. Furthermore, basic structure-property relationships are provided. They enable the prediction of the effect of curatives on the structural parameters of the network, and some of the resulting properties. It is proved that the applied techniques—DSC, DMA, and PALS—can serve to provide information about the modifications to the polymer chains. Moreover, on the basis of the obtained results and considering the diversified curatives available nowadays, the usability of “part per hundred rubber” (phr) unit is questioned.

The effects of primary amine catalyzed thio-acrylate Michael reaction on the kinetics, mechanical and physical properties of thio-acrylate networks

Investigation of the curing behaviour of carbon fibre epoxy prepreg by Dynamic Mechanical Analysis DMA

In this study, Dynamic Mechanical Analyzer (DMA) was used to study the effect of nanoparticles, which is nanosilica, on glass transition temperature (Tg) of epoxy polymer. A series of epoxy based nanosilica composite with 5-25 wt% nanosilica content was prepared using mechanical stirring method. The weight fractions of nanosilica in epoxy were 5 wt%, 13 wt% and 25 wt%. 30mm x 10mm x 3mm size specimens were tested using DMA machine from room temperature up to 180oC at 2°C/min heating rate. From the analysis of the results, dynamic modulus and glass transition temperature of pure polymer and nanosilica filled polymer were obtained. The glass transition of a polymer composite is a temperature-induced change in the matrix material from the glassy to the rubbery state during heating or cooling. Glass transition temperature Tg was determined using several method: storage modulus onset, loss modulus peak, and tan δ peak. The results showed that the presence of nanosilica reduced Tg of epoxy polymer.

Acid surface modified carbon nanotube (MCNT)‐, carbon nanotube (CNT)‐filled fluoroelastomer (FE), and unfilled‐FE were prepared (MCNT/FE, CNT/FE, and FE). Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed that the glass transition temperature (Tg) of MCNT/FE is less than that of CNT/FE and FE. The storage modulus of CNT/FE is higher than that of MCNT/FE over the whole temperature range. Storage modulus in rubbery state is higher in the case of MCNT/FE when compared to FE, however, in glassy state, it is slightly higher. For MCNT/FE at glassy and rubbery state, loss modulus is less than that of CNT/FE. Loss modulus in rubbery states is higher in the case of MCNT/FE compared to FE and in glassy states for both are the same. The DSC, DMA, and X‐ray diffraction (XRD) results confirmed that the FE and filler/FE is partially crystalline mostly in γ‐form. MCNT and CNT together with shear and high temperature, induced γ‐crystallinity in the FE, γ‐phase melting of MCNT/FE is higher than that of CNT/FE and FE. Most probably MCNT/FE obeys behaviors of thin films with high surface energy substrate interactions, while in CNT/FE the substrate surface energy is lower. XRD and DSC showed that MCNT causes more γ‐crystallinity in FE compared to others. Tetrafluoroethylene segments crystals have the degree of crystallinity in the order of CNT/FE > MCNT/FE > FE. The γ–phase crystal size is in the order of FE > CNT/FE > MCNT/FE. XRD, DSC, and DMA results for FE and filler/FE confirmed each other. POLYM. COMPOS., 37:3341–3353, 2016. © 2015 Society of Plastics Engineers

Secondary relaxations in poly(allyl-alcohol), PAA, and poly(vinyl alcohol), PVAPart I. Mechanical relaxations compared with mechanical behavior of cellulose and dextran in the presence of polar solvent

The slow molecular mobility in the amorphous solid and supercooled liquid phases of brucine, an anti-cancer drug. A study by differential scanning calorimetry (DSC), thermostimulated currents (TSC) and dielectric relaxation spectroscopy (DRS)

Poly(methyl methacrylate) (PMMA), with a glass transition temperature (Tg) over 100 °C, shows good mechanical and optical properties and has broad applications after being machined with single-point diamond turning (SPDT) at room temperature. Because of the high Tg, current efforts mostly focus on optimizing machining parameters to improve workpiece precision without considering the modification of material properties. Cryogenic cooling has been proven to be an effective method in assisting ultra-precision machining for certain types of metals, alloys, and polymers, but has never been used for PMMA before. In this work, cryogenic cooling was attempted during the SPDT of PMMA workpieces to improve surface quality. The machinability and surface properties of cryogenically cooled PMMA were investigated based on the mechanical properties at corresponding temperatures. Nanoindentation tests show that, when temperature is changed from 25 °C to 0 °C, the hardness and Young's modulus are increased by 37% and 22%, respectively. At these two temperature points, optimal parameters including spindle speed, feed rate and cut depth were obtained using Taguchi methods to obtain workpieces with high surface quality. The surface quality was evaluated based on the total height of the profile (Pt) and the arithmetic mean deviation (Ra). The measurement results show that the values of Pt and Ra of the workpiece machined at 0 °C are 124 nm and 6 nm, respectively, while the corresponding values of that machined at 25 °C are 291 nm and 11 nm. The test data show that cryogenic machining is useful for improving the form accuracy and reducing the surface roughness of PMMA. Moreover, the relationship between temperature, material properties and machinability weas established with dynamic mechanical analysis (DMA) data and a theoretical model. This can explain the origin of the better surface quality of the cryogenic material. The basis of this is that temperature affects the viscoelasticity of the polymer and the corresponding mechanical properties due to relaxation. Then, the material property changes will affect surface profile formation during machining. The experimental results and theoretical analysis show that cryogenically cooled PMMA has good machinability and improved surface quality when using SPDT compared to that at ambient temperature.

There has been a lot of interest in characterizing polymer chain dynamics of rubber compounds because it is thought to underpin the exceptional mechanical properties of composites. We studied the effect of precipitated silica on segmental mobility of cis‐polybutadiene rubber by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the calorimetric glass and melting transitions of silica‐filled master batch materials were essentially identical to those of the gum rubber, showing no dependence of silica loading and silane treatment. And, we observed in calorimetric measurement a change in the melting transition step for the vulcanizates. The results were correlated to the change of chemical crosslinks caused by various factors filler agglomeration and adsorption effect that tended to decrease chemical crosslink density and silane modification increased it. The DMA results demonstrated that the second peak in loss modulus versus temperature curve for the quenched vulcanizates was assigned to melting peak, and this peak disappeared at a slow cooling rate, which coincided well with DSC results. Moreover, crystalline parts constrained amorphous regions such that the glass transition temperature was raised for the cooled vulcanizates with high chemical crosslinks.

The increasing demand for high-performance composites has driven the need for sustainable alternatives to conventional petroleum-based resins. This research introduces a novel glycerol-derived bio-epoxy resin and investigates the effect of catalyst concentration on its curing behaviour, network structure, and thermomechanical performance. Four catalyst concentrations were evaluated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA) combined with tensile, flexural, and compression testing. DSC results revealed that increasing the catalyst concentration significantly lowered the curing activation energy, shifting the exothermic peak temperature from 194.8 °C to 145.2 °C. DMA revealed that the glass transition temperature (Tg), crosslinking density, and stiffness consistently increased up to an optimal catalyst concentration, reaching a maximum Tg of 109.0 °C. Further increases in catalyst content led to slight reductions in Tg and crosslink density due to the formation of a heterogeneous network. The optimal concentration enhanced tensile and compressive strength by 32.8% and 9.3%, respectively. At excessive catalyst concentration, strength properties deteriorated despite increased material rigidity. These findings confirm the critical role of catalyst in governing polymerisation kinetics and network structure, demonstrating that an optimal catalyst percentage is essential for maximising strength and durability, making the bio-epoxy a viable, high-performance alternative for advanced composite manufacturing.

A material combination that may be applied as transparent armour is glass-clad polyurethane. These are comprised of a relatively thin glass strike face and a relatively thick (transparent) polyurethane backing layer. Three transparent polyurethane samples were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC results identified the glass transitions and in some cases the melting and crystallisation processes. The DMA experiments were only performed on heating around the glass transition region to further investigate this transition. The experiments were performed at three different frequencies (1, 10 and 100 Hz); the shift of the glass transition with the frequency was clearly observed. The method of time-temperature superposition was used to extrapolate the results to higher frequencies as the magnitude of the strain-rate occurring within ballistic applications is in the order of 1000 s-1 or higher. Polyurethane with a rubbery behaviour at normal (low) strain rates can be stiff and brittle when used as an armour component (temperature below its dynamic T g value). © 2011 Akademiai Kiado, Budapest, Hungary.

Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol and different polyols with a M n of 2000 by a one‐shot, hand‐cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV‐visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695–701, 2007. © 2007 Society of Plastics Engineers.