Mechanical Analysis Techniques Research Articles

Fracture mechanisms in biopolymer films using coupling of mechanical analysis and high speed visualization technique

The aim of this study was to provide a detailed description of the fracture mechanisms in three different biopolymer thin materials: gelatin, hydroxypropyl cellulose (HPC) and cassava starch films. That was achieved by using a combination of fracture mechanics methodology and in situ visualization with high speed imaging technique. By analyzing the unstable and stable crack propagation that occurs in these materials, the brittle to ductile transition induced by water plasticization was assessed and discussed. Each biopolymer material exhibited a distinctive brittle and ductile fracture mode, which were described in this work. In order to evaluate the occurrence of permanent deformation in the proximity of the crack propagation front, FTIR maps with polarized light microscopy were employed, which enabled the visualization of structural homogeneity and cohesivity. The differences in fracture behaviour were interpreted taking into account the structural organization within these materials during stretching. The coupling of mechanical data and advanced visualization techniques was a particularly effective method to describe and interpret the complex fracture mechanisms in biopolymer materials which is strongly affected by their interaction with water molecules.

Strain induced transient effects of filler reinforced elastomers with respect to the Payne‐Effect: experiments and constitutive modelling

AbstractFiller‐reinforced rubber shows many interesting nonlinear effects under cyclic deformations. As a result of the dynamic loading, a change in the materials' microstructure and hence in the dynamic behaviour of the elastomer is observed. In this context, the frequency‐, amplitude‐, temperature‐, and the preload‐dependence are well‐known effects. Additionally, pronounced thermomechanical couplings are observed, e.g., heat build‐up phenomena. Mechanical coupling effects can be demonstrated by studying the transient dynamic behaviour of the Payne‐effect (amplitude dependence). Using the technique of dynamical mechanical analysis (DMA) the mentioned effects can be investigated in a very comfortable way. To study the process dependence of the dynamic modulus, bimodal DMA tests and transient multistep tests have been carried out. The non‐trivial postprocessing of the bimodal measurements is shortly explained in the paper. The approach of finite nonlinear viscoelasticity with additional internal variables provides an excellent basis for constitutive material modelling. The thermodynamical consistency of the developed constitutive model is demonstrated. This offers the possibility to represent thermomechanical coupling effects like the dissipative heat build‐up. A series of numerical results of FEM simulations under more complicated transient loading histories, computed with the developed and implemented material model, are presented.

Investigation of the degree of homogeneity and hydrogen bonding in PEG/PVP blends prepared in supercritical CO 2: Comparison with ethanol-cast blends and physical mixtures

The degree of homogeneity and H-bond interaction in blends of low-molecular-mass poly(ethylene glycols) (PEG, M w = 400, 600, 1000) and poly(vinylpyrrolidone) (PVP, M w = 9 × 10 3) prepared in supercritical CO 2, ethanol and as physical mixtures were studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) techniques. Homogeneity of samples prepared in supercritical CO 2 were greater than physically mixed samples, but slightly less than ethanol-cast samples. PEG–PVP H-bond interaction was higher for ethanol-cast blends when compared to blends prepared in supercritical CO 2. This reduced interaction was attributed to a combination of: (1) shielding of PEG–PVP H-bond interactions when CO 2 is dissolved in the blend; (2) rapidly reduced PEG and PVP chain mobility upon CO 2 venting, delaying rearrangement for optimum PEG–PVP H-bond interaction.

Characterisation of the effects of a titanium micro particle filler on a polyether-block-amide host matrix

The body of work described in this research article outlines the use of titanium microparticles as fillers in the production of a polyether-block-amide (Pebax 5533) based composite for medical applications. Virgin polyether-block-amide was compared with titanium filled composites with loadings of 40 and 60% by weight prepared using twin screw extrusion and compression moulding. The materials were characterised using a range of mechanical, thermal, toxicological and surface analysis techniques. Fourier transform infrared spectroscopy indicated that no chemical interaction occurred between the filler particles and the host polymer matrix. Thermal analysis of the composites indicated that as the blend composition varied, so too did the melting behaviour. The inclusion of the titanium microparticles was observed to increase the flow viscosity, tensile strength, hardness and Young’s modulus of the composites whilst also resulting in a rougher surface with lower surface energy.

Free volume and microstructural investigation of poly(ethylene terephthalate)-g -acrylic acid (PET-g-AA) copolymer films

Acrylic acid (AA) was grafted onto PET films by preirradiation method using a 60Co γ-radiation source. Microstructural investigation of the PET-g-AA copolymers has been carried out by wide angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA) and positron annihilation lifetime spectroscopy (PALS) techniques. The WAXD results showed only marginal variation in the crystallinity of the graft copolymers. Dynamic mechanical analysis showed an increase in the temperature of the α-relaxation and the tan δ value of subroom temperature secondary relaxations. From the PALS results, a complex variation of the free volume parameters, i.e. the o-positronium lifetime ( τ 3), its intensity ( I 3), fractional free volume ( f v ) and the intermediate lifetime component was observed for the graft copolymers. Multiple phenomena of the effect of secondary relaxations, additive behavior of the individual polymer free volume parameters and effects from interfacial defects have been invoked to understand the fluctuational nature of the free volume properties in the graft copolymers.

Geomechanical modeling of an extensional fault-propagation fold: Big Brushy Canyon monocline, Sierra Del Carmen, Texas

Field structural data from the Big Brushy Canyon monocline developed in Cretaceous strata of west Texas are combined with nonlinear finite element modeling to help bridge the gap between geometric, kinematic, and mechanical analysis techniques for understanding the deformation history of reservoir-scale geologic structures. The massive Santa Elena Limestone is offset along a steep normal fault, and fault displacement is accommodated upward by the folding of the Buda Limestone and Boquillas Formation and the thinning in the intervening Del Rio Clay. Mesostructures within competent Buda Limestone beds are concentrated in the monocline limb instead of the hinge and include bed-perpendicular veins that accommodate bed-parallel extension and bedding-plane slip surfaces that offset the veins and accommodate flexural slip. Finite element models were constructed to reproduce the monocline geometry and deformation distribution as well as to assess the effect of material properties and boundary conditions on structural evolution. The initial model configuration replicated the assumed predeformational geometry, included frictional sliding surfaces to allow for bedding-parallel slip, and used a displacement boundary condition at the base of the Santa Elena footwall to simulate fault motion. Geometry and strain evolution were tracked so that (1) fold shape, (2) cumulative extension, and (3) layer-parallel shear strain could be compared to field observations. Iterative model runs successfully matched field data and revealed the importance of benchmarking the model results against monocline geometry, layer-parallel extensional strain, and bedding slip in the natural example. Our results illustrate the potential use of this modeling approach whereby calibration is performed using available data and is followed by strain measurement throughout the model domain to aid in prediction of subseismic faults and fractures. This geomechanical modeling approach provides a powerful tool for site-specific subsurface deformation prediction in hydrocarbon reservoirs that incorporates details of the local mechanical stratigraphy and structural setting.

Thermoplastic Starch-Glycerol-Lignosulfonate Blends: Mixtures of Thermally Molded Blends Studied in a Ternary Diagram

The aim of this research was to survey all possible combinations of cornstarch (S), lignosulfonate (LS), and glycerol (G) that may be used in preparing thermally molded thermoplastics. A ternary diagram was developed to define the best range of compositions for production of these thermoplastics in accordance with ASTM D 638-M. Dynamic mechanical analysis technique (DMA) revealed more than one glass relaxation, influenced by glycerol content. In stress—strain tests, incorporation of LS decreased the stress and increased strain considerably, in comparison with their respective S—G matrices. The total amount of water absorbed by the specimens increased proportionally to relative humidity (RH) and glycerol content. An increase in LS content requires longer time to reach steady state for the absorption process. Moreover, the diffusion coefficient of water in the thermoplastic rose significantly with the amount of glycerol. However, the diffusion coefficient results did not show a simple, monotonic relation with the values of RH or with absorbed water content.

Creep compression behaviour of a polyurethane foam from cryogenic temperatures: size effect and long-term prediction

The objective of this work was to predict the long term behavior of Polyurethane foam (PU) at very lowtemperature, by applying the timetemperature superposition principle (TTSP). The experimental background of the TTSP was based on a Dynamical Mechanical Analysis technique. Two issues arise from this experimental approach: the relevance of the temperature range to apply the TTSP, and the possible sizeeffect associated to the small DM A samples. Firstly, on the studied temperature range (�170°C; +180°C) many transitions hbeen observed, particularly from �20°C. Thus to apply the TTSP, it would be necessary to limit the temperature range (between temperature of molecular transitions, i.e. from �20°C up to 80°C). At very low temperatures, DMA spectra did not evidence any viscoelastic domain. However a deformation has been measured during creep tests in the same temperature range. So it would be necessary to determine which micromechanism is responsible for the observed deformation. Secondly, it was important to determine if the volume of DMA sample was representative. Several techniques have shown that a representative volume would be reached between 8 and 12mm 3 .

Thermal properties of novel clay containing nanocomposites based on low density polyethylene/ ethylene-octene copolymer blends

AbstractThermal behaviour of low-density polyethylene (LDPE)/ ethylene-octene copolymer (POE)/ organo-montmorillonite (org-MMT) nanocomposites, prepared via melt compounding were studied by means of differential scanning calorimetry (DSC), thermogravimetry analysis (TGA) and dynamic mechanical thermal analysis (DMTA) techniques. These nanocomposites showed different levels of intercalated structures depending on clay content, blend composition and compatibilization. Addition of polyethylene grafted maleic anhydride (PE-g-MA), as a compatibilizer, improved the intercalation process. The nanocomposites with 5% org-MMT and 5% PE-g-MA showed improved storage modulus and thermal stability in dynamic mechanical and thermal analysis, respectively. The degradation trends of nanocomposites were almost similar to the neat blends in nitrogen environment, but in air atmosphere thermal stability of the nanocomposites increased. The DSC results showed that the org-MMT layers dispersed in the nanocomposites could act as nucleation agents for the crystallization of the LDPE matrix. The results indicated that clay dispersion and interfacial adhesion, and consequently thermal properties of nanocomposites, are greatly affected by addition of PE-g-MA.

Characterization of mouthguard materials: Thermal properties of commercialized products

Objectives Several mechanisms have been purported to describe how mouthguards protect the orofacial complex against injury. As the properties needed for these mechanisms to be effective are temperature and frequency dependent, the specific aim of this study was to provide a comprehensive thermal characterization of commercial mouthguard materials. Methods Five commercially representative thermoplastic mouthguard materials (Essix™ Resin, Erkoflex™, Proform™-regular, Proform™-laminate, and Polyshok™) were tested. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were implemented to measure thermal transitions and mechanical properties. Measurements were conducted three times per sample. One-way ANOVA and one-sample t-tests were used to test for differences between commercial products on selected mean thermal property values. Results The DSC measurements indicated no differences between commercial materials for mean glass transition ( p = 0.053), onset melt ( p = 0.973), or peak melt ( p = 0.436) temperatures. Likewise, DMA measurements revealed no differences between commercial materials for the mean glass transition ( p = 0.093), storage modulus ( p = 0.257), or loss modulus ( p = 0.172) properties, respectively. The one-sample t-tests revealed that glass transition temperatures were different from intra-oral temperature ( p < 0.005) for all materials. Significance Commercialized mouthguard materials are sensitive to repetitive heating and cooling cycles, prolonged thermal treatment, and have glass transitions well below their end-use intra-oral temperature. As such, these materials are functioning as elastomers and not optimal mechanical damping materials. Dental clinicians, healthcare practitioners, or end-users should be aware that these materials are at best problematic with respect to this protective mechanism.

Long-term water immersion ageing characteristics of GFRP composites

This paper evaluates the water absorption characteristics of glass fibre reinforced polymers after long-term exposure to a hygrothermal environment. In particular, three types of laminates, fabricated using woven and non-crimp triaxial glass fabric with a polyester matrix, were immersed in deionised water baths for 2.5 years (30 months) at temperatures of 43, 65 and 93 °C. In order to assess the effects of through-thickness delaminations on the water absorption characteristics, a series of specimens were impacted prior water immersion with low-velocity impact using three energy levels of 2.5, 5 and 10 J. The changes in the thermo-mechanical properties of laminates after water immersion were examined using the dynamic mechanical thermal analysis (DMTA) technique. The results revealed that the long-term water uptake profiles had no similarities to the classical Fickian absorption behaviour and they were markedly different for each water immersion temperature. At higher temperatures a multi-stage diffusion was observed, which was attributed to the microporosity of the laminates as well as to the osmotically enhanced uptake through the interfaces, with the peak values showing dependency on the type of material system. The impact damage on laminates immersed in water did not cause any marked change in the maximum water absorption level or at the absorption rate compared to the undamaged specimens. DMTA have shown matrix plasticizing effects at 43 °C and some post-curing effects at 65 and 93 °C while the effect of the time of immersion at all temperatures tested resulted in a decrease of the value of storage modulus.

Physical aging of polycarbonate block copolymers: Ductility rejuvenation below the glass transition temperature

AbstractThermal aging of block copolymers of bisphenol A polycarbonate and polydimethylsiloxane (BPAPC and PDMS) have been studied. Changes in notched izod impact performance and yield stress are reported following aging at 120°C and 130°C for up to 20 days. Retention of impact at 120°C of the block copolymers was found to improve with increasing size of siloxane domains in the polycarbonate matrix. Quite contrary to our expectation, the retention of impact for a given sample at 130°C was found to be better than that of at120°C. These block copolymers showed (thermo) reversible ductility rejuvenation behavior at 130°C when the samples heat‐aged at 120°C were shifted from 120 to 130°C. Transmission electron microscopy, small‐angle X‐ray scattering, and dynamic mechanical analysis techniques were used to probe the observed phenomenon. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

XRD studies of UV-irradiated chitin based polyurethane elastomers

Chitin based polyurethane (PU) elastomers constituted on 4,4´-diphenylmethane diisocyanate (MDI), poly( ε-caprolactone) (PCL) and extended with blends of chitin/1,4-butane diol were synthesized via two step polymerization technique. The synthesized samples were irradiated for 50, 100 and 200 h in an UV exposure chamber as such the spectral distribution of the light is good match for terrestrial solar radiation. The crystalline behavior of the irradiated PU samples were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC) and dynamic mechanical thermal analysis (DMTA) techniques. The effect of irradiation time and chitin contents on crystallinity were studied and investigated. The maximum decrease in the crystalline behavior of samples after irradiation observed by XRD, DSC and tan δ peaks were found for the PU samples extended with lower contents of chitin (chitin/BDO; 0/100). In comparison with irradiation times the 200 h irradiation showed maximum change in the crystalline behavior.

Viscoelastic Property Mapping along Encrusted Polymeric Urinary Catheters

Mapping of the material viscoelastic property variation along the length axis of polymeric stents. Five pigtail ureteral stents and five percutaneous stents placed in vivo for different periods were studied. Viscoelastic property changes along the length of polymeric stents were measured using the dynamic mechanical analysis technique. The type of encrustations was identified using FT-IR spectroscopy and their morphology by scanning electron microscopy (SEM). Variations in viscoelastic stiffness were confirmed for both types of stents. In a few cases, the variation was quite large (400%). Various encrustation types and/or organic sheathing of the salt were found to be responsible for this effect. In detail, calcium oxalate monohydrate (COM) plaques for percutaneous and COM/organic layer for pigtail stents were recognized by FT-IR spectroscopy and SEM observation to invoke reinforcing effects along the stent axes. The phenomenon of stiffness variation along the stent axes requires further study to understand the mechanism behind it and consequently to improve the biomaterial and design of specific areas of stents as well as to avoid encrustations. This further research might lead in the near future to the development of new types of polymer stents for drug-eluting specialized areas.

The use of dynamic mechanical thermal analysis technique for determining an uneven distribution of precipitated silica in CPE/NR blends

Precipitated silica is generally used as non-black reinforcing filler for light colored products. Compared with carbon black, the use of silica is subject to many problems, particularly poor silica dispersion and distribution. In silica filled CPE/NR blends, the uneven distribution of silica in each phase of the blend occurs mainly due to strong filler–polymer interaction between silanol groups on the silica surfaces and chlorine atoms on the CPE backbone. In order to investigate the uneven filler distribution in polymer blends, changes in damping behavior could be used to calculate the amount of silica localizing in each phase of the blends. The results reveal that, with small loading of silica, an even silica distribution is observed due to the counter-balancing effects of relatively low viscosity of the NR phase and strong silica–CPE interaction. As silica loading increases, the effect of strong silica–CPE interaction becomes dominant, leading to preferential migration of silica to the CPE phase. The uneven silica distribution at high silica loading is found to be reduced by addition of silane coupling agents. The effect of 3-thiocyanatopropyl triethoxy silane (Si-264) is more pronounced than bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) due to the superior wettability and, hence, the silanol deactivation efficiency. The determination of uneven silica distribution by dynamic mechanical properties is in good agreement with the phase morphology of blends.

Synthesis and characterization of novel, biodegradable, thermally stable chitin‐based polyurethane elastomers

AbstractBiodegradable polyurethane (PU) elastomers with potential for biomedical and industrial applications with tunable thermal properties were synthesized by the reaction of poly(ϵ‐caprolactone) and 4,4′‐diphenylmethane diisocyanate and extended with different mass ratios of chitin and 1,4‐butane diol (BDO). Their chemical structures were characterized with Fourier transform infrared, 1H‐NMR, and 13C‐NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical thermal analysis techniques. The incorporation of chitin contents into the PU backbone caused improvements in the thermal stability and degradation rate. Optimum thermal properties and degradation profile were obtained from elastomers extended with chitin, whereas elastomers extended with BDO displayed the worst properties. The investigation of the structure–property relationships of the prepared elastomers showed that the main determining factors for the observed properties were the physical effective crosslink density, hydrogen bonding, thermal stability, and content of chitin in the PU backbone. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and thermomechanical characterization of polyurethane elastomers extended with α,ω‐alkane diols

AbstractA series of polyurethane (PU) elastomers was prepared by the reaction of poly(ϵ‐caprolactone) and 4,4′‐diphenylmethane diisocyanate, which was extended with a series of chain extenders (CEs) having 2–10 methylene units in their structure. The completion of the reaction was confirmed by Fourier transform infrared spectroscopy. The chemical structures of the synthesized PU samples were characterized with Fourier transform infrared, 1H‐NMR, and 13C‐NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, DSC, and dynamic mechanical thermal analysis techniques. The mechanical properties were also studied and are discussed. The thermogravimetric analysis and DSC analysis showed that CE length had a considerable effect on the thermal properties of the prepared samples. The dynamic mechanical thermal analysis and damping peaks were also affected by the number of methylene units in the CE length. The elastomer extended with 1,2‐ethane diol exhibited optimum thermal properties, whereas the elastomer based on 1,10‐decane diol displayed the worst thermal properties. Tensile strength and elongation at break decreased with increasing CE length, whereas hardness showed the opposite trend. The glass‐transition temperature moved toward lower temperatures with increasing CE length. The decrease in the glass‐transition temperature and tensile properties were interpreted in terms of decreasing hard segments and increasing chain flexibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Molecular engineering and properties of chitin based shape memory polyurethanes

Shape memory polyurethanes (SMPUs) are playing a prominent role in biomedical, self repairing, aerospace and smart materials. Shape memory polyurethanes (SMPUs) were prepared from polycaprolactone diol 4000 (PCL4000), 1-4-butanediol (BDO), chitin, dimethylol propionic acid (DMPA), triethylamine (TEA), and 4, 4′-diphenylmethane diisocyanate (MDI). Trifunctional characteristics of chitin enhanced the thermal and mechanical properties of SMPUs. DMPA was used to obtain higher recovery and lower residual strain. The morphology, microstructure, mechanical, thermo-mechanical, and shape memory properties of synthesized SMPUs were investigated using Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA) and tensile testing techniques. The results showed that crosslinked SMPUs have better thermal and thermo-mechanical properties, and a good shape memory effect.

Effects of polymer–fiber interactions on rheology and flow behavior of suspensions of semi-flexible fibers in polymeric liquids

Rheological properties of suspensions of fibers in polymeric fluids are influenced by fiber–polymer interactions. In this paper, we investigate this influence from both experimental and modeling standpoints. In the experimental part of this investigation, we have changed the fiber–polymer interactions by treating the surface of the fibers. The resulting effects are observed using scanning electron microscopy and dynamic mechanical analysis techniques and quantified from the measurements of the viscosity in the start-up of shear flows and dynamic tests in the linear viscoelastic range region. The results are interpreted with the help of a mesoscopic rheological model developed for suspensions of fibers in viscoelastic fluids.

Physical and tribological properties of a new polycarbonate-organoclay nanocomposite

A new polycarbonate (LS2) nanocomposite containing a 3 wt% proportion of the organically modified montmorillonite bentone 2010 (B 2010) has been prepared by extrusion and injection moulding, and its tribological properties determined under a pin-on-disc configuration against stainless steel. The nanocomposite (LS2 + 3% B 2010) presents a 88% reduction in friction and up to two orders of magnitude reduction in wear rate with respect to the base polymer. The new nanocomposite has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), and its thermal and dynamic mechanical properties have been determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) techniques. The nanocomposite shows a uniform dispersion of the nanoclay as pointed out by two different statistical methods. The good tribological performance of the new nanocomposite is attributed to this uniform microstructure and to the increase in the nanoclay stacking distance.