Dynamic Mechanical Investigations Research Articles

Characterization of industrial low-density polyethylene: a thermal, dynamic mechanical, and rheological investigation

Thestudy of commercial low-density polyethylenes (LDPEs) has always focused on the effects of the molecular architecture of the polymer on its shear and extensional rheological properties due to their direct influence on manufacturability. However, the complex morphology of industrial-grade LDPEs also affects the crystallization kinetics and dynamic mechanical properties of the polymers, which are key to the processibility and applications. Therefore, a comprehensive investigation was conducted into the areas of crystallization kinetics, crystallinity, dynamic mechanical, and linear and non-linear shear rheological properties of two industrial-grade LDPEs to build a cohesive insight into the influence of morphology on these material properties. We further analyzed the steady-state and transient shear viscosity data obtained from the two LDPEs in comparison with constitutive model predictions using the hierarchical multi-mode molecular stress function (HMMSF) and found excellent agreement within experimental accuracy between predictions by the HMMSF model and shear stress as well as normal stress data of the LDPEs investigated.

Manufacturing technology and dynamic mechanical investigation of moisture‐resistant Luffa cylindrica‐reinforced epoxy composites

AbstractNatural fiber (NF)‐reinforced thermosetting composites exhibit excellent properties but, due to the usually hygroscopic nature of the fibers, these composites may suffer from the effects of moisture absorption. Luffa cylindrica is a NF, potentially useful in the manufacture of composite materials, but it is highly hygroscopic. A technology is developed for the fabrication of moisture‐resistant L. cylindrica‐reinforced epoxy composites and the various parameters that affect the process are investigated using long‐term moisture absorption experiments and dynamic mechanical analysis of dry and moist specimens. The technology concludes to a L. cylindrica‐reinforced bilayer matrix made of a first linseed oil‐modified precured epoxy and a final unmodified epoxy layer. This composite offers a reduced water absorbance by 33% and an almost identical Tg compared to the non‐modified epoxy reinforced with L. cylindrica. The same technology is used to manufacture water‐resistant L. cylindrica‐reinforced composites from both, environmentally friendly, matrix and reinforcement.

On the possibility of replacement of calcium carbonate by a high-performance, economically viable filler in polyethylene composites

Calcium carbonate (CaCO3) is frequently added to polyethylene (PE) as a filler to reduce costs. An alternative to CaCO3, calcium fluoride (CaF2) was proposed in this research. PE/CaCO3 and PE/CaF2 composites in a wide composition range (0–60 wt.%) were prepared through a parallel twin screw extruder. Results indicated better interaction of CaF2 with PE matrix which improved samples yield stress. Statistical analysis showed the filler type was more influential factor on the yield stress while filler loading was not a statistically significant one. In contrast, crystallinity was strongly depended on the filler loading. The dynamic mechanical and rheological investigations revealed that PE/CaF2 composites had higher stiffness at ambient temperature and possessed lower viscosity below 40 wt.% of filler loading compared to PE/CaCO3 which could reduce the processing cost. Therefore, regarding its low price and good functional properties, CaF2 can be a promising alternative to CaCO3.

Dynamic Mechanical Analysis Investigations of PLA-Based Renewable Materials: How Are They Useful?

Interest in renewable polymers increased exponentially in the last decade and in this context poly(lactic acid) (PLA) became the leader mainly for practical reasons. Nevertheless, it is outstanding also from a scientific point of view, because its thermal and morphological properties are offering challenging new insights. With regard to dynamic mechanical analysis (DMA), PLA does not have the classical behavior of a thermoplastic polymer. Often, overlapping events (enthalpic relaxation, glass transition and crystallization) that occur as the temperature increases make the DMA result of a PLA look inexplicable even for polymer scientists. This review offers a perspective of the main phenomena that can be revealed in a DMA experiment and systematizes the information that can be obtained for every region (glassy, glass transition, rubbery, cold-crystallization and melting). Also, some unusual patterns registered in some cases will be commented upon. The review intends to offer indices that one should pay attention to in the interpretation of a DMA experiment, even if the investigator has only basic skills with DMA investigations.

Advanced hybrid materials from epoxy, oxidized UHMWPE fibers and silane surface modified silicon nitride nanoparticles

Aiming the development of highly performant polymer-based hybrid materials, the typical bisphenol-A based epoxy resin was reinforced with oxidized UHMWPE fibers and various amounts of silane surface modified silicon nitride (Si3N4) nanoparticles. The reinforcing phases underwent optimized surface modifications to create a fully connected network for an improved stress transfer between the constituents. The efficiency of the grafting methodology was confirmed by vibrational and morphological analyses. Meanwhile, the effects of the adopted modifications techniques on the mechanical properties were thoroughly discussed. Furthermore, static and dynamic mechanical investigations along with impact tests were conducted to study the effects of various amounts of Si3N4 nanoparticles on the overall performances of the epoxy/UHMWPE composite. The obtained results confirmed the great benefits from creating a fully connected hybrid network. The as such developed hybrids can be seen as promising materials for the intended use.

Investigation of the energy absorption properties of cross-linked polyethylene foams

We performed the dynamic mechanical investigation of cross-linked polyethylene (XL-PE) foams, which are the most commonly used polymer foams for damping purposes. Our experiments were primarily focused on analyzing the energy-absorbing capability of foams with different densities and studying the relationship between cell structure and shock absorption. The cell structure and energy absorption properties of the foams were determined by mechanical tests and microscopic examination. The samples were subjected to falling dart and falling weight impact tests using different weight geometries and impact energy. Our experiments showed that the impact damping properties of foams are significantly influenced by the deformation mechanisms in the cellular structure during dynamic loading since excessive deformation of the cell walls leads to the compaction of the foam, and therefore a significant reduction in impact damping capability.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

Jute/Kevlar Fibre Reinforced Epoxy Composites: A Dynamic Mechanical Study

This paper depicts the impact of Kevlar (artificial fiber) and jute (regular fiber) on thermal property utilizing dynamic mechanical investigation. The examination is performed by manufacture of different Kevlar fiber content levels for the layers of the jute overlays. Overlays for dynamic mechanical investigation tests were carried out by hand lay up method and tried at a temperature scope of 30 to 150°C. Recurrence of the movements were fixed at 1 Hz and the strain ampleness displayed at 0.1%, which was well inside the direct viscoelastic locale. The warming rate was 3°C/min for all temperature examine trials. Storage modulus (E’), Loss modulus (E”) and loss factor (tan δ) were assembled in the midst of the test and plotted to frame against temperature. An extension away in storage and loss modulus and augmentation in the loss factor were looked for all composite overlays demonstrating progressively adaptable direct of the composites as differentiated to the unadulterated jute composites overlays. Results exhibited that glass change (transition) temperature augmentations to elevated temperatures in composite overlays

Multifunctional piezoelectric elastomer composites for smart biomedical or wearable electronics

The development of nanogenerators that is capable of converting mechanical energy into electricity could enable extraordinary advances in biomedical devices and wearable consumer electronics. Piezoelectric composites have no intricate assemblies, providing a compact and reliable alternative to energy interconversion in biomedical electronics. This work deals with the development of a new class of piezoelectric elastomer composite which is integrated multiple potential functionalities. To fully understand and exploit the unique properties of the composited material, characterisations in terms of general mechanical, dynamic mechanical, and dynamic piezoelectric experimental investigations have been conducted. Three prototypes with individual application have been successfully built up utilising the piezoelectric elastomer composite. The versatility of the composite developed in this work presents its outstanding potential in building self-powered systems or biomedical implanted sensors.

Reversible Actuation Ability upon Light Stimulation of the Smart Systems with Controllably Grafted Graphene Oxide with Poly (Glycidyl Methacrylate) and PDMS Elastomer: Effect of Compatibility and Graphene Oxide Reduction on the Photo-Actuation Performance.

This study is focused on the controllable reduction of the graphene oxide (GO) during the surface-initiated atom transfer radical polymerization technique of glycidyl methacrylate (GMA). The successful modification was confirmed using TGA-FTIR analysis and TEM microscopy observation of the polymer shell. The simultaneous reduction of the GO particles was confirmed indirectly via TGA and directly via Raman spectroscopy and electrical conductivity investigations. Enhanced compatibility of the GO-PGMA particles with a polydimethylsiloxane (PDMS) elastomeric matrix was proven using contact angle measurements. Prepared composites were further investigated through the dielectric spectroscopy to provide information about the polymer chain mobility through the activation energy. Dynamic mechanical properties investigation showed an excellent mechanical response on the dynamic stimulation at a broad temperature range. Thermal conductivity evaluation also confirmed the further photo-actuation capability properties at light stimulation of various intensities and proved that composite material consisting of GO-PGMA particles provide systems with a significantly enhanced capability in comparison with neat GO as well as neat PDMS matrix.

Features of Curing of a Diane Epoxy Oligomer Modified with Epoxyphosphazene

The results of rheokinetic, dynamic mechanical, and calorimetric investigations of the process of curing of an epoxy oligomer ED-20 blend with epoxyphosphazene by a low-molecular-weight polyamide L-20 are analyzed. It is shown that the phenomenological curing kinetics of all studied systems is characterized by the presence of two stages of the process: a second-order reaction followed by a self-retarded second-order reaction upon reaching the isothermal glass transition of the system.

Effect of acrylonitrile butadiene styrene on the shape memory, mechanical, and thermal properties of thermoplastic polyurethane

A polymer blend based on thermoplastic polyurethane (TPU) and acrylonitrile butadiene styrene (ABS) was prepared using a melt‐blending technique, and its mechanical, thermal, and shape memory properties were investigated. According to the scanning electron microscopy morphology results, when the content of ABS was less than 20 wt%, the TPU appeared as a continuous phase, and ABS appeared as a dispersed phase. The presence of distinguishable boundaries at the polymer interfaces indicated that the TPU/ABS blend was an immiscible system. Furthermore, the 80/20 blend sample exhibited the best dispersion of ABS in TPU. Tensile testing indicated that addition of ABS to the TPU matrix led to improvement of the Young's modulus as well as reduction of the elongation at break and tensile strength. The impact resistance of the blends depended on the amount of ABS, and the maximal growth was observed for the 80/20 blend. Dynamic mechanical investigations support the morphological and mechanical results. The differential scanning calorimetry results also indicated that the two polymers were immiscible. The shape memory test results indicated that as the amount of ABS increased to 20 wt% in the TPU polymer and the shape recovery of the blend first slightly decreased and then suddenly decreased to 66.5% with the addition of 30 wt% of ABS. J. VINYL ADDIT. TECHNOL., 24:E96–E104, 2018. © 2017 Society of Plastics Engineers

AC-Impedance, Dynamic mechanical analysis and DSC investigations on poly(methyl methacrylate)–LiTf polymer electrolyte systems

Gel polymer electrolytes synthesized from Poly(methylmethacrylate) (PMMA) as the host, ethylene carbonate (EC)/propylene carbonate (PC) as plasticizer and LiCF3SO3 (LiTf) as a salt has been prepared using solution casting technique. X-ray characterization confirms the complete dissociation of the LiTf salt in the gel polymer. The effect of LiTf salt on ionic conductivity, ionic transference number (tion) and mechanical characteristics were investigated. The ac impedance has been studied to evaluate the ionic conductivity. It was observed that the ionic conductivity of the prepared gel reached the highest value of 6.60 x 10-5 S/cm at 10.2 wt.% (1M) of LiTf salt. The temperature dependence studies showed that the samples were ionic conductors and seemed to obey the Vogel–Tamman–Fulcher (VTF) rule. Dynamic mechanical analysis (DMA) indicates that the LiTf salt induces a remarkable increase in the storage modulus of the matrix at temperatures above the glass transition (rubbery plateau region).

Melt rheological behavior of PMMA nanocomposites reinforced with modified nanoclay

Poly(methyl methacrylate) (PMMA) nanocomposites containing nanoclay with and without compatibilizer (PMMA-g-MA) were prepared by melt blending followed by compression molding in order to investigate the rheological and flammability properties of developed nanocomposites. The rheological measurements at various temperatures and frequencies were performed using rheometer with parallel-plate geometry. The frequency sweep result revealed that storage modulus improved with the addition of nanoclay at lower frequency and gradually changed from liquid-like behavior to solid-like behavior due to the formation of percolating network structure. For all the samples, complex viscosity decreased as the temperature increased. Similarly, dynamic mechanical investigations exhibited a significant enhancement in storage modulus at lower temperature due to reinforcing effect of nanoclay. The flammability test also demonstrated that rate of burning was reduced by 37% with the addition of nanoclay.

Influence of molecular structure of blend components on the performance of thermoplastic vulcanisates prepared by electron induced reactive processing

Polypropylene (PP)/ethylene propylene diene rubber (EPDM) thermoplastic vulcanisates (TPVs) were prepared by electron induced reactive processing without use of any chemical vulcanizing agent, co-agent or other type of additive. Thus, the composition of PP/EPDM blend is not changed by this novel process and relationships between raw material, process, morphology and properties of TPVs can be studied in a simple way. Consequently, the molecular mass of PP as well as the amount and nature of diene (ethylidene norbornene or vinyl norbornene) were varied. Based on detailed mechanical, dynamic mechanical, morphological, thermal and rheological investigations as well as equilibrium solvent swelling measurements and sol–gel analyses it was found that molecular mass, amount and nature of diene influence the cross-linking efficiency. In addition, the use of low molecular mass blend components leads to PP-EPDM phase graft-links as well as increased values of elongation and tensile strength at break.

Miscibility analysis, viscoelastic properties and morphology of cyclic olefin copolymer/polyolefin elastomer (COC/POE) blends

Miscibility of cyclic olefin copolymer/polyolefin elastomer (COC/POE) blends over full composition range was investigated through determination of viscoelastic characteristics both at melt and solid state as well as by direct morphological analysis using experimental and theoretical approaches. The melt viscosity, storage modulus and Han diagrams were used for analyzing the rheological behavior. It was found that the storage modulus of neat COC was higher than that of neat POE, while the modulus of the blends were in between the modulus of the neat components. Palierne and Gramspacher–Meinssner models were used in order to predict the storage and loss moduli of COC and POE. Better correspondence of Palierne model with the experimental results was observed as compared to the other model. Contrary to the Veenstra model, the calculated modulus via Coran model was reasonably in good agreement with the experimental results for blends with co-continuous morphology. Dynamic mechanical investigations have revealed that COC/POE blends were immiscible which firmly supported the morphological and rheological findings.

Toughening of glass fiber reinforced Nylon 66 with EPDMMAH: Dynamic mechanical, rheological, and morphological investigations

AbstractIn this research the variation of mechanical and rheological properties of the composite as a function of different processing parameters and ethylene propylene diene monomer (EPDM) rubber content was studied. The optimum amount of dicumyl peroxide (DCP) to achieve the highest percentage of grafting of maleic anhydride to EPDM was obtained by Fourier transform infrared (FTIR) spectroscopy. In general, immiscibility between nylon 66 and EPDM, and their high interfacial tension makes their blending difficult. Maleic anhydride was grafted to EPDM to reduce interfacial tension between two phases. Also the blends were prepared at highest possible speed of mixing (screw speed in extrusion) and lowest temperature to reach a well mixed sample which can be seen in scanning electron microscopy (SEM) images and impact strength results. Dynamic mechanical thermal analysis (DMTA) tests were conducted to evaluate the miscibility of the components and to measure the glass transition temperature of the blends. Rheological measurement showed that the viscosities of the components of the blend getting closer to each other when EPDM content, time of mixing and shear rate increase.

Segmental Dynamics in net -poly(methyl methacrylate)- co -poly(n-butyl acrylate) Copolymer Networks

Dynamic mechanical spectroscopy and differential scanning calorimetry investigations of segmental dynamics are reported for net-poly(methyl methacrylate)-co-poly(n-butyl acrylate) copolymer networks. Three characteristic temperatures, namely, Vogel (T∞), glass transition (T g ), and crossover (T c ), were used to define cooperativity range and a new reduced temperature parameter (Solidness, S). The results showed that broadness of the α -dispersion (glass transition) and cooperativity length scale at the glass transition temperature decreased with increasing butyl acrylate content and T g -scaled temperature dependence of the relaxation time (fragility). However, the cooperativity range (T c –T∞), decreased with increasing fragility index. Furthermore, the solidness at T g (S(T g )) was nearly independent of chemical structure of the samples. Finally, a correlation was found between two measures of cooperativity length scale in the glass transition region, namely, average volume of cooperatively rearranging regions, V CRR , and the number of basic units in an act of rearrangement in the glass transition region, Z(T g ), determined from two completely independent experimental techniques.

Morphology of poly[(t-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-b-(t-butyl acrylate)] pentablock terpolymers and their thermal conversion to the acrylic acid form

The morphology of a synthesized poly[(tert-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-(tert-butyl acrylate)] pentablock terpolymer was determined using transmission electron microscopy, atomic force microscopy and small angle X-ray scattering methods. The outer blocks of this material were converted to the acrylic acid form by a thermal process that caused a beta-scission reaction in a simple thermal process, as verified by FTIR and NMR spectroscopies as well as thermogravimetric analysis. An initial heat-vacuum treatment induced a morphology that was more disordered relative to the precursor material, but when these samples were recast in THF solvent and annealed again, a considerably more refined and ordered morphology consisting of hexagonally packed cylinders resulted. This simple heat treatment allows for the tert-butyl groups to be converted to acrylic acid groups without dissolving the polymer or further sample cleaning. A dynamic mechanical investigation of the PtBuA form revealed three or two relaxation features depending interpretations based on the presence of three-phase morphology or a two-phase morphology in which there are mixed hard block domains.

Blends of silicone rubber and liquid crystalline polymer

Blends of silicone rubber(VMQ) and liquid crystalline polymer(LCP) were prepared by the melt mixing technique. Mechanical, XRD, thermal and dynamic mechanical investigations are reported for the pure silicone rubber and blends. The mechanical properties, viz. the tensile strength, tear strength and elongation at break, of the silicone rubber decreased with the addition of LCP. The SEM study on the tensile fractured surface of the blends revealed that they had a two phase structure, and that the failure was mainly due to fiber pull out, which suggests that the VMQ and LCP are incompatible in all of the proportions examined in this study. However, the FTIR study shows that there was a partial interaction between the VMQ and LCP, but which may not be sufficient to grip the fibrils under the applied load. In the XRD analysis, it was observed that the crystalline structure of the silicone rubber deteriorated in the presence of LCP. The DMA study suggested that the storage modulus of the silicone rubber was improved with the addition of LCP, due to the high modulus of the LCP phase. The thermal stability of the silicone rubber was greatly reduced by the addition of LCP, due to the latter having a thermal stability lower than that of silicone rubber.