Dynamic Mechanical Spectra Research Articles

Enhance Slower Relaxation Process of Poly(ethyl acrylate) through Internal Plasticization

Abstract In this paper, we report a chemical way to resolve longer motions units in the glass-rubber transition region of poly (ethyl acrylate) (PEA), so called internal plasticization. The ethyl acrylate (EA) monomers were copolymerized with little amount of isoprene (IP) monomers. We propose that the single bonds adjunct to double bonds would have better flexible activity than usual single bonds, so the motion units located between two adjunct double bonds would be enhanced. The dynamic mechanical spectra of internally plasticized PEA (IPPEA) and PEA show that the tan δ of IPPEA is asymmetric, while the tan δ of PEA is symmetric. Furthermore, the results of 2D-DMAS show that the LSM, SRM and RM of IPPEA are located at 7 °C, 12 °C and 36 °C. The shoulder peak of tan δ of IPPEA at higher temperature side was confirmed that it contains sub-rouse mode (SRM) and rouse mode (RM). Thus, internal plasticization is an effective way to resolve modes above Tg.

Curing Process of Epoxy Resin Using Low Molecular Polyamide 651 as Curing Agent

In this paper low molecular polyamide 651(PA651) is used as the curing agent of epoxy resin. The optimum curing conditions and dosage of the curing agent are obtained by DMA and FT-IR analysis. Based on the dynamic mechanical temperature spectra of samples test, the best curing conditions are room temperature 2 hours, 70°C 2 hours, 125°C 2.5 hours and 150°C 1 hours (RT / 2 h + 70 °C / 2 h +125°C / 2.5 h + 150 °C / 1 h). The best dosage of curing agent PA651 is 50 wt %. Since the analysis of Fourier Infrared spectral verified that epoxy groups react completely, the curing conditions are the best curing process.

Influences of ethylene–butylacrylate–glycidyl methacrylate on morphology and mechanical properties of poly(butylene terephthalate)/polyolefin elastomer blends

ABSTRACTElastomer ethylene–butylacrylate–glycidyl methacrylate (PTW) containing epoxy groups were chosen as toughening modifier for poly(butylene terephthalate) (PBT)/polyolefin elastomer (POE) blend. The morphology, thermal, and mechanical properties of the PBT/POE/PTW blend were studied. The infrared spectra of the blends proved that small parts of epoxy groups of PTW reacted with carboxylic acid or hydroxyl groups in PBT during melt blending, resulting in a grafted structure which tended to increase the viscosity and interfere with the crystallization process of the blend. The morphology observed by scanning electron microscopy revealed the dispersed POE particles were well distributed and the interaction between POE and PBT increased in the PBT/POE/PTW blends. Mechanical properties showed the addition of PTW could lead to a remarkable increase about 10‐times in impact strength with a small reduction in tensile strength of PBT/POE blends. Differential scanning calorimetry results showed with increasing PTW, the crystallization temperature (Tc) and crystallinity (Xc) decreased while the melting point (Tm) slightly increased. Dynamic mechanical thermal analysis spectra indicated that the presence of PTW could improve the compatibility of PBT/POE blends. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40660.

Dynamics of Poly (butyl acrylate) and Poly (ethyl acrylate) with internal double bonds

In this paper, the changes in dynamics of Poly (butyl acrylate) (PBA) and Poly (ethyl acrylate) (PEA) after introducing internal double bonds (through copolymerizing with isoprene (IP)) were studied through sight of fragility theory. The dynamic fragility was determined. And the result shows that dynamic fragility indexes of PBA-co-IP and PEA-co-IP are smaller than PBA and PEA. Furthermore, the scaled dynamic mechanical spectra show that PBA-co-IP and PEA-co-IP have longer length of glass–rubber transition region. In one side, our work is well fitted to the universal theory that smaller fragility leads to longer soft dispersing in glass–rubber transition region. In the other side, adding internal double bonds is an effective way to weak fragility of polymers, which results in a broader transition region.

Acrylonitrile–butadiene rubber functionalization for the toughening modification of recycled poly(ethylene terephthalate)

ABSTRACTThe incorporation of functionalized acrylonitrile–butadiene rubber (NBR) into recycled poly(ethylene terephthalate) (PET) was introduced as an effective route for modifying the properties of PET and as a new method for PET recycling as well. To achieve modified NBR, glycidyl methacrylate (GMA) was grafted onto NBR with optimized reactive mixing, in which the highest grafting degree and lowest gel content were generated. PET/NBR blends with and without GMA functionalization were produced by melt mixing, and the mechanical properties, dynamic mechanical thermal properties, and phase morphologies of the systems were determined and compared. We found that low amounts of peroxide initiator (dicumyl peroxide) and high levels of the GMA monomer in the presence of the styrene comonomer led to the maximum grafting degree and suppressed the competing rubber crosslinking and GMA homopolymerization reactions. The blend compatibility with PET determined from dynamic mechanical thermal analysis spectra and scanning electron microscopy images was greatly improved when the NBR‐grafted GMA was used instead of the neat NBR in the blend recipes. As a result, the rubber phase dispersed in the PET matrix more finely, and the impact strength of the blend advanced very significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40483.

The effect of temperature on creep behavior of wood-plastic composites

The creep properties of wood-plastic composites limit their application, particularly in temperature variations affecting long-term performance. In this study, the effect of temperature was studied based on dynamic mechanical analysis spectra and isochrones and a newly developed stress-temperature incorporated creep equation. According to the dynamic mechanical analysis spectra, the addition of a higher content of wood flour resulted in higher moduli, indicating increased stiffness and lower mechanical loss factor. According to the isochrones, the creep strain of wood-plastic composites increased with elevated temperatures and stresses at the same time point. Moreover, the strain increased almost linearly with increasing stress at lower temperatures but became nonlinear with elevated temperature. With these findings, a stress-temperature incorporated creep equation was developed based on short-term creep tests. This empirical equation incorporates the effect of temperature in a power law equation. Good agreement was observed between the equation and experimental results.

High performance natural rubber composites with a hierarchical reinforcement structure of carbon nanotube modified natural fibers

A simple and facile method for depositing multiwall carbon nanotubes (MWCNTs) onto the surface of naturally occurring short jute fibers (JFs) is reported. Hierarchical multi-scale structures were formed with CNT-networks uniformly distributed and fully covering the JFs (JF–CNT), as depicted by the scanning electron microscopy (SEM) micrographs. The impact of these hybrid fillers on the mechanical properties of a natural rubber (NR) matrix was systematically investigated. Pristine JFs were cut initially to an average length of 2.0 mm and exposed to an alkali treatment (a-JFs) to remove impurities existing in the raw jute. MWCNTs were treated under mild acidic conditions to generate carboxylic acid moieties. Afterward, MWCNTs were dispersed in an aqueous media and short a-JFs were allowed to react with them. Raman spectroscopy confirmed the chemical interaction between CNTs and JFs. The JF–CNT exposed quite hydrophobic behavior as revealed by the water contact angle measurements, improving the wettability of the non-polar NR. Consequently, the composite interfacial adhesion strength was significantly enhanced while a micro-scale “mechanical interlocking” mechanism was observed from the interphase-section transmission electron microscopy (TEM) images. SEM analysis of the composite fracture surfaces demonstrated the interfacial strength of NR/a-JF and NR/JF–CNT composites, at different fiber loadings. It can be presumed that the CNT-coating effectively compatibillized the composite structure acting as a macromolecular coupling agent. A detailed analysis of stress-strain and dynamic mechanical spectra confirmed the high mechanical performance of the hierarchical composites, consisting mainly of materials arising from natural resources.

The proper glass transition temperature of amorphous polymers on dynamic mechanical spectra

Glass transition is crucial to the thermal and dynamical properties of polymers. Thus, it is important to detect glass transition temperature (T g) with a sensitive and proper method. Dynamic mechanical analysis (DMA) is one of the most frequently used methods to determine T g due to its advantage of high sensibility. However, there is controversy in the past literatures to determine the proper glass transition temperature among three transition temperatures, i.e., T g1, T g2 and T g3 in the dynamic mechanical spectra, which correspond to the temperature abscissa of intersect value of two tangent lines on storage modulus (E′), the peak of the loss modulus (E″) and the peak of the loss tangent (tan δ). In this work, these three transition temperatures were compared with the glass transition temperature determined by DSC (T gDSC). Based on the discussion of different modes of molecular motion around the glass transition region, it is demonstrated that T g1 and T g2 have the same molecular mechanism as T gDSC, i.e., local segmental motion which is enthalpic in nature and determines the proper glass transition temperature, while T g3 is assigned to the transition temperature of entropic Rouse modes, thus cannot be used as the proper glass transition temperature.

Mechanical and Optical Properties of Polycarbonate Containing p-Terphenyl

Mechanical and optical properties of polycarbonate (PC) containing p-terphenyl (p-tPh) are studied. It is found from the dynamic mechanical spectra that the addition of p-tPh greatly enhances the modulus in the glassy state due to the antiplasticizing effect. Moreover, p-tPh molecules dissolved in PC show marked intermolecular orientation correlation with PC chains during hot-stretching. As a result, p-tPh orients to the stretching direction accompanying the orientation of PC chains. Because p-tPh shows a high level of optical anisotropy, the oriented p-tPh molecules enhance the orientation birefringence. The enhancement of both modulus and optical anisotropy leads to a thinner retardation film, which will be a great benefit in the industry.

Effect of EPDM as a compatibilizer on mechanical properties and morphology of PP/LDPE blends

Blends of polypropylene (PP) and low-density polyethylene (LDPE) with and without ethylene-propylene-diene (EPDM) terpolymer as a compatibilizer were studied. Mechanical properties were chosen to estimate the compatibilization efficiency of EPDM. The interactions between phases were valued through glass transition shifts in dynamic mechanical spectra, and morphology of the blends was obtained using scanning electron microscopy. Interfacial adhesion was improved by EPDM addition. Addition of EPDM to PP/LDPE blends improved mechanical properties, especially Izod impact strength in LDPE-rich blends and with higher EPDM content.

Accelerated cell sheet detachment by copolymerizing hydrophilic PEG side chains into PNIPAm nanocomposite hydrogels

One-end-connected short poly(ethylene glycol) (PEG) side chains were facilely introduced into the poly(N-isopropylacrylamide) (PNIPAm) nanocomposite hydrogel (NC gel) via in situ copolymerization of NIPAm monomer and PEG macromonomer in the aqueous suspension of hectorite clay Laponite XLS. The NC gels were characterized with Fourier transform infrared and x-ray photoelectron spectroscopy for the composition, DSC and transmittance for the phase separation temperature, dynamic mechanical spectra and swelling ratio for the interaction. Increasing the PEG content led to a small increase in the storage modulus and the lower critical solution temperature (LCST) of the copolymerized NC gels, and the LCST of the copolymerized NC gels was still below 37 °C. The L929 cell adhesion and proliferation on the surface of these NC gels were not suppressed by the incorporation of hydrophilic PEG side chains. By lowering temperature below the LCST, the cell sheet spontaneously detached from the copolymerized NC gels. The surface morphology and surface wettability of the NC gels were detected by atom force microscope and contact angle measurement. A rough and hydrophilic surface induced by a small amount of PEG side chains was found to be favorable to accelerate the cell sheet detachment, probably due to the enhanced water permeation into the gel–cell sheet interface.

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

Glassy PMMA samples are plastically deformed at room temperature in the uniaxial compression regime to residual strains of e res = 25%. Dielectric spectra of the initial and deformed samples are recorded via the method of broadband dielectric spectroscopy in the frequency range f = (5 × 10−4) − 107 Hz. The results are compared with the dynamic mechanical spectra of samples deformed under the same conditions. Dielectric and mechanical spectra are noticeably distorted by deformation. As a result, dielectric permittivity ɛ′ increases, shear modulus G′ decreases, and the intensity of dielectric β losses slightly increases, while dielectric and mechanical α losses increase appreciably. In addition, the “anomaly” of total dielectric Δɛtot and total mechanical ΔG tot dispersions (Δɛtot = ɛ0 − ɛ∞ ≈ Δɛα + Δɛβ and ΔG tot = G 0 − G ∞ ≈ ΔG α + ΔG β) occurs, that is, the polymer is transformed from the state with Δɛα ≪ Δɛβ and ΔG α Δɛβ and ΔG α > ΔG β. The described phenomenon is related to a strong gain in α dielectric and mechanical losses in the deformed material. It is found that α losses increase owing to an anelastic deformation component arising during glass loading. This component is responsible for an increase in the internal energy of the glass during its anelastic deformation. Possible causes of the observed effects are discussed.

The origin of a new transition in dynamic mechanical spectra of multilayer polymeric composite

An additional damping transition at −25 °C, which has never been reported in blended system, is observed in dynamic mechanical spectra (DMS) of isotactic polypropylene/ethylene 1-octene copolymer (iPP/POE) composites with alternating multilayered structure. With increasing layer number, this additional transition becomes larger followed by the decrease of the damping peak of iPP. Through mechanical analysis, the maximum of interfacial stress is found at −25 °C, where the new damping peak appears coincidentally. Hence, the origin of the additional transition is ascribed to the advanced defreezing of chain segments of iPP for balancing difference of the mechanical response between adjacent layers.

Synthesis and characterization of photoactive polyurethane elastomers with 2,3-dihydroxypyridine in the main chain

Photoactive polyurethane elastomers with pyridine derivatives in the polymer backbone were synthesized by chain-extending isocyanate end-capped prepolymers with 2,3-dihydroxypyridine. The isocyanate-terminated prepolymers were obtained from poly(tetramethylene oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6-hexamethylene diisocyanate. The properties of the linear heterocyclic polyurethane were compared with properties of the crosslinked heterocyclic polyurethane obtained by chain extension with various crosslinkers. Heterocyclic polyurethane elastomers were characterized using Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), dynamic mechanical analysis (DMA), contact angle measurements, and mechanical analysis. Static mechanical measurements showed greater elongation and tensile strength for polyurethanes with a lower content of heterocyclic groups in the hard segment. The static contact angles of the cast films of these polymers indicated that the nature of the hard segment influences the surface polarity. The dynamic mechanical spectra revealed that linear polymers have two transition temperatures as results from a clear phase separation caused by high-intermolecular hydrogen bonds in the regions of pyridine units and urethane groups. Polyurethane elastomer films with pyridine moieties in the main chain form a photosensitive material. If stored in laboratory conditions (light, ambient air atmosphere), the color of the films changes from white to black. These photo-induced structural changes are studied by H NMR measurements.

Rheological Properties of Soybean β-Conglycinin in Aqueous Dispersions: Effects of Concentration, Ionic Strength and Thermal Treatment

Steady shear and dynamic oscillatory measurements were used to investigate the effect of concentration, ionic strength and thermal treatment on rheological properties of soybean β-conglycinin in aqueous dispersions. SDS-PAGE and Differential Scanning Calorimetry (DSC) showed that β-conglycinin exhibited partial denaturation and formation of aggregates during isolation. Under steady shear flow, strong shear-thinning behavior was observed with increasing shear rate from 0.001 to 1200 s−1. A dispersion of β-conglycinin (≥5% w/v, without applying thermal treatment) exhibited gel-like dynamic mechanical spectra at 20°C. This suggested that β-conglycinin in aqueous dispersions showed rheological properties of typical weak gel-like (entanglement) or semi diluted polymeric solution. Weak gel network of β-conglycinin was susceptible to ionic strength, suggesting that electrostatic forces play an important role in the formation of weak gel network. These properties of β-conglycinin have practical significance for the food processors in the formulation of new products.

Renewable biocomposites of dimer fatty acid-based polyamides with cellulose fibres: Thermal, physical and mechanical properties

Dimer fatty acid-based polyamides (DAPA) are reinforced with cellulose fibres (CF) from 5 to 20 wt.%. Thermal, morphological, dynamic mechanical and mechanical properties of the corresponding biocomposites (DAPAC) are investigated. They exhibit a high increase in glass transition temperature ( T g ) and a decrease in the crystallisation temperature and crystallinity degree. This can be attributed to carbonyl (DAPA) and hydroxyl (CP) groups’ interactions. These hydrogen bonds reduce the polymer mobility. For instance, the dynamic mechanical spectra of these biocomposites reveal an increase in the stiffness and higher thermal–mechanical stability. Morphological observations reveal a moderate interfacial adhesion between the fibres and the matrix. With the increase of the fibre content, tensile tests show a high increase in Young modulus and yield stress, and a decrease of elongation at break. Predicted modulus results based on micromechanical models, Voigt and Reuss bounds and Halpin–Tsai approaches, are compared with the experimental values. They show that the Halpin–Tsai model can be used to quantify the mechanical properties for DAPA/CF biocomposites.

Enhancement to the rate-dependent mechanical behavior of polycarbonate by incorporation of triptycenes

The tensile and compressive properties of triptycene-polycarbonates were tested over 6 orders of magnitude in strain rate. Initially we studied a low molecular weight, low triptycene content PC blended with Iupilon® PC and then a series of higher molecular weight, higher triptycene content polymers. The PC blend with only 1.9wt% triptycene displayed up to 20% increase in modulus and up to 17% increase in yield strength with elongations over 80% as compared to the Iupilon® PC. The higher molecular weight T-PCs (up to 26wt% triptycene) exhibited improvements in modulus by over 20% and improvements in compressive strengths by nearly 50% at both low and high strain rates without any apparent sacrifice to ductility, as compared to Iupilon® PC. All samples containing triptycene units retained transparency and exhibited no signs of crystallinity or phase separation. Moreover, both the blends and triptycene-PC copolymers displayed significantly altered dynamic mechanical spectra, specifically, the emergence of a pronounced, new β′ relaxation approximately 75°C above the traditionally observed β relaxation in PC (approximately −100°C). The enhancement of the mechanical properties observed provides valuable insights into the unique packing and interactions during plastic flow induced by the presence of triptycene units.

Phase separation in the polyurethane/poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks synthesized by different ways

AbstractThe thermal, dynamic mechanical analysis, morphology and mechanical properties of semi‐interpenetrating polymer networks based on crosslinked polyurethane (PU) and poly(2‐hydroxyethyl methacrylate) (PHEMA) synthesized by photopolymerization and by thermopolymerization have been investigated. The thermal analysis has evidenced the two glass temperature transitions in the semi‐IPNs and this is confirmed by the thermodynamic miscibility investigation of the systems. The Dynamic Mechanical Analysis spectra have shown that the phase separation is more significant in the thermopolymerized semi‐IPNs: the tan δ peaks of constituent polymers are more distinct and the minimum between the two peaks is deeper. The calculated segregation degree values of semi‐IPN's components are significantly higher for thermopolymerized semi‐IPNs, thereby the process of phase separation in the thermopolymerized semi‐IPNs is more developed. The structures of two series of samples investigated by SEM are completely different. The mechanical properties reflect these changes in structure of semi‐IPNs with increasing amount of PHEMA and with the changing of the method of synthesis. The results suggest that the studied semi‐IPNs are two‐phase systems with incomplete phase separation. The semi‐IPN samples with early stage of phase separation demonstrate higher mechanical characteristics. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Thermomechanical properties of biodegradable films based on blends of gelatin and poly(vinyl alcohol)

The aim of this work was to study the effect of the poly(vinyl alcohol) (PVA) concentration on the thermal and viscoelastic properties of films based on blends of gelatin and PVA using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). One glass transition was observed between 43 and 49 °C on the DSC curves obtained in the first scanning of the blended films, followed by fusion of the crystalline portion between 116 and 134 °C. However, the DMA results showed that only the films with 10% PVA had a single peak in the tan δ spectrum. However, when the PVA concentration was increased the dynamic mechanical spectra showed two peaks on the tan δ curves, indicating two T gs. Despite this phase separation behavior the Gordon and Taylor model was successfully applied to correlate T g as a function of film composition, thus determining k=7.47. In the DMA frequency tests, the DMA spectra showed that the storage modulus values decreased with increasing temperature. The master curves for the PVA–gelatin films were obtained applying the TTS principle ( T r=100 °C). The WLF model was thus applied allowing for the determination of the constants C 1 and C 2. The values of these constants increased with increasing PVA concentrations in the blend: C 1=49–66 and C 2=463–480. These values were used to calculate the fractional free volume of the films at the T g and the thermal expansion coefficient of the films above the T g.

Mechanical properties of epoxy networks based on DGEBA and aliphatic amines

AbstractThe mechanical properties of epoxy networks based on diglycidyl ether of bisphenol A epoxy resin cured with various linear aliphatic amines, such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and cyclic amines such as 1‐(2‐aminoethyl)piperazine and isophorone diamine, were studied. General characteristics such as Tg, density, and packing density, were determined and related to the structure and funcionality of the curing agent. Dynamic mechanical spectra were used to study both the α and β relaxations. Tensile and the flexural tests were used to determine the Young's and flexural modulus, and fracture strength all in the glassy state. Furthermore, linear elastic fracture mechanics was used to determine KIC. As a rule, isophorone diamine network presented the higher tensile and flexure modulus while 1‐(2‐aminoethyl)piperazine gave the highest toughness properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007