Dynamic Mechanical Analysis Analysis Research Articles

Processing and Thermal Behaviors of Poly (Butylene Succinate) Blends with Highly-Filled Starch and Glycerol

Fully-biodegradable and highly-filled thermoplastic starch plasticized with glycerol (GTPS)/poly (butylene succinate) (PBS) blends were prepared by Haake Mixer. Processing properties, thermal behaviors including melting and crystallization behavior, crystal structure, and compatibility of the blends were investigated using differential scanning calorimeter (DSC), wide angle X-ray diffractometer (WAXD), scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). The maximum and equilibrium torques decreased with the rising of glycerol contents and the dropping of PBS contents. GTPS30/PBS blends exhibited double melting endothermic peaks in the DSC thermograms, which related to the crystallization behavior and compatibility of the blends, but no double peaks for GTPS40/PBS. The addition of starch and glycerol could lead to higher crystallinity and lower crystallization rate of PBS, but would not change the crystal types and crystallite sizes of PBS according to DSC and WAXD analysis. SEM and DMA results gave the evidence to confirm the better compatibility of GTPS40/PBS. Besides, higher storage modulus in glassy state of GTPS/PBS blends than PBS could be seen from DMA analysis, which was the contrary in rubbery state.

Nanoindentation and dynamic mechanical properties of PP/clay nanocomposites

Polypropylene/clay nanocomposites were prepared by melt blending technique. A PP homopolymer was melt blended with commercial nanoclay masterbatch at different concentration (5, 10 and 15 wt% of nanoclay) using Laboratory Mixing Extruder (LME). The morphology of the nanocomposites was characterized using Scanning Electron Microscope (SEM). The viscoelastic and thermo-mechanical properties were analyzed via Dynamic Mechanical Analysis (DMA). The morphological analysis showed that the nanoclay was well distributed in the PP matrix. The DMA analysis showed an increase in storage modulus of nanocomposites which indicates an enhancement of stiffness and thermal stability of the prepared nanocomposite samples. In addition, a nanoindentation test was performed to determine the dynamic nanomechanical properties of two nanocomposites samples (NS-5 and NS-15). Load sweep test results showed that NS-15 has a slightly higher storage and loss modulus than that of NS-5. Both the samples also showed a decreasing modulus as a function of depth, indicating the presence of a stiffer surface layer in the samples. Frequency sweep tests were also performed on each sample, and display a moderate viscoelasticity with modulus values that increased slightly as a function of frequency. Load-controlled ramping force scratch test was also carried out and the results showed that NS-15 had a greater elastic recovery than sample NS-5 as well as a greater overall scratch resistance.

Polycarbonate/molybdenum disulfide/carbon black composites: Physicomechanical, thermal, wear, and morphological properties

AbstractTo investigate the influence of molybdenum disulfide (MoS2) as solid lubricant and filler on the polycarbonate (PC) and carbon black (CB) composites, PC containing one weight percentage of CB powder was compounded and extruded with 0.5, 1.0, 2.0, and 3.0 weight percentage of MoS2 powder in a co‐rotating twin screw extruder. Thus, the fabricated PC/CB/MoS2 composites were characterized for physicomechanical properties such as density, void content, surface hardness, tensile behaviors, and impact strength. The thermal characteristics of the composites have been studied by differential scanning calorimetry and dynamic mechanical analysis (DMA). The effect of MoS2 content, loads and sliding distances on wear characteristics of the composites were evaluated using pin‐on‐disc equipment. It was found that wear, friction, and laser etching resistance of PC/CB/MoS2 composites increased with increase in MoS2 content along with improvement in tensile and impact strengths. DMA analysis indicates the storage modulus of PC/CB/MoS2 composites increased with increase in MoS2 content below the glass transition temperature (Tg) of PC. Worn surfaces and laser etched surfaces were examined with scanning electron microscopy and optical microcopy respectively to have better insight of the wear and laser etching mechanism. It was observed that the MoS2 as solid lubricant played major role in improving resistance to wear, friction, and laser etching. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Dynamic mechanical properties of dental nanofilled light-cured resin composites: Effect of food-simulating liquids

This work is aimed at the study by dynamic mechanical analysis (DMA) of viscoelastic properties that is, the elastic modulus (E′), the loss modulus (E″), the loss tangent (tanδ) and the glass transition temperature (Tg), of two current commercial light-cured resin composites, Filtek Supreme Body and Filtek Supreme Translucent, characterized as nanofilled. These composites show differences in the filler content and type. For DMA analysis the bar-shaped specimens were divided into groups of three samples each. The first group consisted of dry samples measured 1 h after light-curing (at room temperature) during which they were placed in a desiccator at 37 °C. The other groups consisted of samples which had been stored in air, distilled water, artificial saliva SAGF or ethanol/water solution (75 v/v), at 37±1 °C for 1, 7, 30 or 90 days. DMA tests were performed on a Diamond Dynamic Mechanical Analyzer (Perkin–Elmer) in bending mode. A frequency of 1 Hz was applied and a temperature range of 25–185 °C, while a heating rate of 2 °C/min were selected to cover mouth temperature and the materials’ likely Tg. The studied dry composites showed comparable values for their properties in spite of their differences in the filler content and type. Storage of composites in air 37 °C for 1 day caused a significant post curing which was not continued during storage up to 90 days. Water and artificial saliva showed the same effect on composites. They caused both post curing and plasticization. Ethanol/water solution 75% v/v had a more strong effect than water and artificial saliva due to its organophilic nature. It caused post curing, plasticization and most probably degradation of the bond filler–silane coupling agent.

The compatible and mechanical properties of biodegradable poly(Lactic Acid)/ethylene glycidyl methacrylate copolymer blends

The Fourier transform infrared results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the epoxy groups of molecules of Ethylene Glycidyl Methacrylate Copolymer (EGMC) during the reactive extrusion processes of PLAxEGMCy specimens. The tensile and tear strength values of PLAxEGMCy blown-film specimens in machine and transverse directions improve significantly, and reach their maximal values as their EGMC contents approach an optimum value of 6 wt.%. The melt shear viscosity values of PLAxEGMCy resins, measured at varying shear rates, are significantly higher than those of the PLA resin, and increase consistently with their EGMC contents. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) of PLA and PLAxEGMCy specimens reveal that the percentage crystallinity, peak melting temperature, and onset re-crystallization temperature values of PLAxEGMCy specimens reduce gradually as their EGMC contents increase. In contrast, the glass transition temperatures of PLAxEGMCy specimens increase gradually in conjunction with their EGMC contents. Demarcated porous morphology with several connected fungi-decomposed cavities was found on the surfaces of the PLAxEGMCy specimens after being buried for specific amounts of time, in which the sizes of the fungi-decomposed cavities found on the surfaces of buried PLAxEGMCy specimens reduce significantly as their EGMC contents increase. Further DMA and morphological analysis of PLAxEGMCy specimens reveal that the EGMC molecules are compatible with PLA molecules at EGMC contents equal to or less than 2 wt.% because no phase-separated EGMC droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLAxEGMCy specimens, respectively. The possible reasons for these remarkable properties of the PLA/EGMC specimens are proposed in this study.

Thermo plasticization and characterization of kenaf fiber by benzylation

Kenaf fibers were heterogeneously benzylated in aqueous alkaline solution. The benzylated kenaf fibers were characterized by Fourier Transform Infrared (FTIR), dynamic mechanical analysis (DMA), scanning electron microscope (SEM), universal tensile machine (UTM), and the contact angle test. The results showed that the degree of benzylation depended on the reaction time, as assessed by the weight gain. The DMA analysis showed that the glass transition temperature of kenaf fiber decreased from 140 to 118°C after benzylation, while the weight gain increased from 5 to 120%. The benzylated kenaf fibers exhibited good melt processability and were readily hot pressed into sheets. The sheet containing with fibers, which were benzylated for 3h, exhibited 17.5MPa in tensile strength, and the hydrophilic property of the sheet was greatly decreased as a function of benzylation time.

Thermo-mechanical properties and structural features of diglycidyl ether of BIS phenol a cationically cured by electron beam radiation

The thermo-mechanical properties and structural features of diglycidyl ether of bisphenol A cationically cured by electron beam radiation have been studied by FT-NIR spectroscopy, dynamic mechanical analysis (DMA), MTDSC and AFM. The influence of formulation (onium salt nature and content, presence of additives) and of EB-treatment parameters (doses, thermal treatment) on the glass transition temperature (Tg) have been investigated. The conditions for achieving a high level of conversion together with the control of the final Tg values were determined. The presence of several relaxation peaks observed by DSC and DMA analysis suggests the presence of heterogeneities in the formed network. AFM analyses reveal the presence of nanoclusters interpreted as local variations of cross-link densities in the formed network.

Thermal properties of low-density polyethylene/ALPHA- alumina nanocomposites

Low-density polyethylene (LDPE) nanocomposites with alumina as filler were prepared by melt intercalation process by using Haake Rheomix at 125°C for 12 min followed by compression moulding. Prior to blending of the alumina with LDPE, alumina particles were dispersed by using ultrasonication process. Surfactant was used to modify the alumina surface in order to enhance the interaction between alumina and LDPE. The melting temperature and crystallinity of nanocomposites were investigated by differential scanning calorimetry (DSC). Studies on dynamic mechanical analysis (DMA) were made to follow the changes in dynamic mechanical properties upon addition of nanoalumina to LDPE. Thermal stability of the nanocomposites was studied by using thermal gravimetric analysis (TGA). It was found that the crystallinity and melting temperature of LDPE/alumina decreased with the increase in alumina content. The results on TGA and DMA analysis revealed that the thermal stability of LDPE improved with the addition of alumina particle.

Fabrication and Properties of Shape Memory Polyurethane Surface Modified Vapor Grown Carbon Nanofiber Composites

Shape memory polyurethane (SMPU)/Vapor grown carbon nanofibers (VGCNF) composites with different surface functionalized method were prepared via sol-gel process. The structure and properties of the composites were investigated by scanning electron microscopy (SEM), universal testing machine, and dynamic mechanical analysis (DMA). The results show that the dispersion of VGCNF with surface modification in matrix is better than that of pristine. The mechanical properties of the composites with VGCNF modified by concentrated nitric acid deteriorated substantially. However, both the tensile strength and elongation at break of the composites combined surface modification of silane coupling agent and sol-gel method increased obviously. The substantially improved mechanical properties are mainly attributed to the cross-link between coupling agent and the network structure of SiO2 produced during the sol-gel process. The DMA analysis suggests that the surface treatment of the VGCNF exhibit obviously effect on the dynamic mechanical properties of the composites.

Determination of CTEs of cured epoxy and polyester (PET) stitching threads

Coefficients of thermal expansion (CTEs) of constituents in fiber-reinforced composites are among the key thermal parameters that need to be defined for material selection, modeling and structural design. This article presents an experimental approach for determining the CTEs of two constituents in a non-crimp fabrics (NCFs) reinforced composite system by means of dynamic mechanical analysis (DMA), mechanical tests at various temperatures and the principle of composite micromechanics. The constituents include the matrix (a cured epoxy resin) and the polyester (PET) stitching threads that are used to assemble multi-layered reinforcements comprising NCFs. CTEs of the cured epoxy resin were measured by both DMA and thermal mechanical analysis, and CTEs of PET threads were successfully estimated from those of the epoxy resin and a PET/epoxy composite in both transverse and longitudinal directions by means of composite micromechanics. DMA was found, in this study, to be an effective technique that can be used to determine the CTEs of polymers and polymer threads in a wide range of temperatures on the basis of proper calibration.

Preparation and characterization of poly (vinyl butyral)‐leather fiber composites

AbstractThis study reports the preparation and characterization of composites with recycled poly (vinyl butyral) (PVB) and wet blue leather fiber with leather contents of 30, 50, and 70 wt%, using an extruder equipped with a Maillefer single screw operated with a flat extrusion die. The components of the composites were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy (FTIR). After extrusion, the PVB/leather composite plates were compression‐molded to obtain specimens for testing the tensile properties, hardness, abrasion resistance, and tear strength. The morphologies of the composites were analyzed by scanning electron microscopy (SEM). The DMA and FTIR analyses showed that the recycled PVB contained plasticizer remained in the polymer matrix after extrusion. The SEM analysis revealed good interfacial adhesion between the PVB matrix and the leather fibers. Increasing the leather content in the composites led to a significant increase in the tensile modulus and a reduction in the tensile strain at breaks. The Shore hardness of the composites increased with the wt% of leather, whereas the abrasion resistance decreased. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers.

DMA analysis to predict the performance of waterborne coatings

In previous studies some waterborne coatings, specifically formulated for the scope of the research, were studied during an artificial weathering process by means of dynamic mechanical analysis (DMA) technique. In those studies the chemical and physical parameters which mainly affect the performance of coatings and their evolution during weathering were measured. The aim was to predict the performance of coatings for exterior wood during their service life by means of accelerated artificial tests and instrumental measures. In this study four commercial products were artificially weathered following the European standard EN 927-6. The changes in the mechanical properties were measured by means of the DMA as reported in the previous studies. With this research the authors have verified the capability of this method to predict the performance in use of coatings.

Compatible and tearing properties of poly(lactic acid)/poly(ethylene glutaric‐co‐terephthalate) copolyester blends

AbstractFourier transform infrared and nuclear magnetic resonance results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the hydroxyl groups of FePol (FP) molecules during the melt‐blending of PLAxFPy specimens. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) experiments of PLA and PLA/FP specimens suggest that only small amounts of poor PLA and/or FP crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature, and onset re‐crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to a minimum value as the FP contents of PLAxFPy specimens reach 6 wt %. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt %, as no distinguished phase‐separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA were successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tearing properties of PLA/FP specimens are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 913–920, 2010

DMA analysis and wood bonding of PVAc latex reinforced with cellulose nanofibrils

Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied. The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites, increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state, but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition (tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1.

Compatible and crystallization properties of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

AbstractDifferential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and dynamic mechanical analysis (DMA) properties of poly(lactic acid)/ poly(butylene adipate‐co‐terephthalate) (PLA/PBAT) specimens suggest that only small amounts of poor PLA and/or PBAT crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature and onset re‐crystallization temperature values of PLA/PBAT specimens reduce gradually as their PBAT contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA analysis reduce to the minimum value as the PBAT contents of PLAxPBATy specimens reach 2.5 wt %. Further morphological and DMA analysis of PLA/PBAT specimens reveal that PBAT molecules are miscible with PLA molecules at PBAT contents equal to or less than 2.5 wt %, since no distinguished phase‐separated PBAT droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/PBAT specimens, respectively. In contrast to PLA, the PBAT specimen exhibits highly deformable properties. After blending proper amounts of PBAT in PLA, the inherent brittle deformation behavior of PLA was successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tensile properties of PLA/PBAT specimens are proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Recycled poly(ethylene terephthalate)/linear low‐density polyethylene blends through physical processing

AbstractPoly(styrene‐ethylene/butylene‐styrene) (SEBS) was used as a compatibilizer to improve the thermal and mechanical properties of recycled poly(ethylene terephthalate)/linear low‐density polyethylene (R‐PET/LLDPE) blends. The blends compatibilized with 0–20 wt % SEBS were prepared by low‐temperature solid‐state extrusion. The effect of SEBS content was investigated using scanning electron microscope, differential scanning calorimeter, dynamic mechanical analysis (DMA), and mechanical property testing. Morphology observation showed that the addition of 10 wt % SEBS led to the deformation of dispersed phase from spherical to fibrous structure, and microfibrils were formed at the interface between two phases in the compatibilized blends. Both differential scanning calorimeter and DMA results revealed that the blend with 20 wt % SEBS showed better compatibility between PET and LLDPE than other blends studied. The addition of 20 wt % of SEBS obviously improved the crystallizibility of PET as well as the modulus of the blends. DMA analysis also showed that the interaction between SEBS and two other components enhanced at high temperature above 130°C. The impact strength of the blend with 20 wt % SEBS increased of 93.2% with respect to the blend without SEBS, accompanied by only a 28.7% tensile strength decrease. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Microsphere pressure sensitive adhesives—acrylic polymer/montmorillonite clay nanocomposite materials

In this study, the synthesis and characterization of acrylic polymer/montmorillonite (MMT) clay nanocomposite pressure sensitive adhesives (PSA) are presented. Different types and amounts of modified and unmodified montmorillonite clays were dispersed in ethyl acrylate (EA)/2-ethylhexyl acrylate (2-EHA) monomer mixture, which was then polymerized using a suspension polymerization technique. Polymerization was monitored in-line using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The adhesion properties of the synthesized nanocomposite materials were determined using standard measurements of tack, peel and shear strength. Viscoelastic properties of dried adhesive films were analyzed using dynamic mechanical analysis (DMA). The results showed that the kinetics of suspension polymerization was independent of the addition of MMT clays. On the other hand, adhesive properties were strongly influenced by the type and the amount of MMT clay added. While peel strength and tack gradually decreased with higher amount of modified MMT clay, a substantial increase in shear strength was determined with a maximal value at 1wt% of added MMT clay. Moderate influence on tack, peel and shear strength was observed when the unmodified type of MMT clay was used. DMA analysis showed an increase in storage modulus (G′) for adhesives synthesized with MMT clay addition, but no significant differences were determined between particular types of MMT clays. A decrease in tanδ value for adhesives with 1wt% of added MMT clay was observed, which also concurs with higher shear strength and implies to the improved cohesion of adhesive.

Mechanical behaviors of polypropylene/carbon nanotube nanocomposites: The effects of loading rate and temperature

Polypropylene (PP) nanocomposites reinforced with 0.1, 0.3, 0.5 and 1.0 wt% multi-walled carbon nanotubes (MWNTs) were prepared via melt-compounding in a twin-screw extruder followed by injection molding. The effects of MWNT additions on the structure, mechanical and yielding behavior of PP were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests. XRD traces showed that PP crystallized exclusively in α-form within the nanocomposite, indicating that the presence of MWNT did not influence the crystal structure of PP/MWNT nanocomposites via injection processing. DSC results confirmed that the corporation of MWNT enhanced the nucleation process on PP crystallization. It was also found that the glass transition temperature ( T g) and the activation energy (Δ E) increased with the increase of the amount of MWNT, demonstrating that the mobility of the polymer chain is reduced in the presence of MWNT. DMA analysis showed that the storage modulus and heat deflection temperature of PP/MWNT nanocomposite are improved considerably by adding only 0.3–0.5 wt% MWNT. The PP/MWNT nanocomposites were found to be strain rate and temperature dependence. Their yield stress was described successfully by Erying's equation. An index “ n” was proposed to characterize the reinforcing effect of MWNTs in PP at a given temperature. The results showed that the n values for the PP/MWNT nanocomposites tend to increase with increasing test temperatures, indicating that the reinforcing effect of MWNTs in PP matrix is more pronounced at higher temperatures.

Effects of acrylonitrile content on the coordination crosslinking reaction between acrylonitrile–butadiene rubber and copper sulfate

The effects of acrylonitrile content in acrylonitrile–butadiene rubber (NBR) on coordination crosslinking reaction were investigated in the system of NBR filled with copper sulfate (CuSO 4) particles by means of dynamic mechanical analysis (DMA), equilibrium swelling method, differential scanning calorimetry (DSC) and tensile test. DMA analysis showed that higher the acrylonitrile content in NBR, higher the storage modulus of the CuSO 4/NBR composite. The results of equilibrium swelling method and DSC displayed the crosslink density and glass transition temperature of CuSO 4/NBR composites increased with increment of the acrylonitrile content, respectively. And the tensile strength of CuSO 4/NBR composites became strong with the acrylonitrile content rising. All the results showed that increase acrylonitrile content of NBR could accelerate the coordination crosslinking reaction between NBR and CuSO 4. The tensile strength of CuSO 4/NBR composites increased with increment of acrylonitrile content, which was attributed to increased interfacial contact area and enhanced interfacial adhesion between CuSO 4 and NBR.

Analysis of HNBR-Montmorillonite Nanocomposites

Morphologies and dynamic mechanical properties of hydrogenated acrylonitrile butadiene rubber (HNBR) filled with organophilic layered silicates (OLS) were investigated. The results from transmission electron microscopy (TEM), small angle X-ray scattering (SAXS, especially X-ray diffraction on larger structures) and dynamic mechanical analysis (DMA) favor the notion of local filler-filler network-like clusters consisting of exfoliated silicate layers. Especially, processing under high shear forces leads to an anisotropic structure of the network. Due to the orientation of the clusters the aspect ratio (at small deformations) increases. This is in accord with the large reinforcing effect observed for these materials. For example, the stress at 50% elongation from tensile test can be increased at 33% with 5 phr OLS compared to the unfilled reference. We estimate the activation energy of the immobilized polymer layer around the filler structures and show that the values depend on the spatial direction (the values are between 3.4 kJ/mol and 4 kJ/mol). As a result, the DMA–analysis could be used as a supporting method to evaluate orientation effects of the filler structures.