Dynamic Mechanical Thermal Analysis Results Research Articles

Interaction between wood and polyvinyl acetate glue studied with dynamic mechanical analysis and scanning electron microscopy

AbstractThe long‐term properties of bonds are those that are of special interest. To achieve good bonds, the wood polymers and the adhering polymers must be compatible. This paper describes studies of the interaction of wood (Pinus sylvestris) with commercial polyvinyl acetate (PVAc) glue, polymethylmethacrylate (PMMA), and a more hydrophilic acrylate. Interaction was studied with a dynamic mechanical thermal analyzer (DMTA) operating in tensile mode in the tangential direction of wood. DMTA results were correlated with scanning electron microscopy (SEM) fractography studies of adhesion between polymers and wood on a cell wall level. The hypothesis put forward is that a good adhesion on the cell wall level results in a decrease in the glass transition temperature (Tg) measured with DMTA. A decrease in Tg for the hydrophilic acrylate was shown when it was impregnated in wood. The decrease of Tg was correlated with good adhesion to wood on the cell wall level. For PVAc and PMMA no decrease in Tg was measured when glued or impregnated in wood. SEM study also showed that the adhesion on a cell wall level was poor. The results show that DMTA can be a useful technique to study adhesion between wood and glue on a molecular level. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3009–3015, 2004

Effect of polydimethylsiloxane macrodiol molecular weight on properties and morphology of polyurethane and polyurethaneurea

AbstractTwo series of polyurethanes and polyurethaneureas were prepared using a two‐step bulk‐solution polymerization procedure. Each series consisted of three polymers based on three molecular weights of α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS): 940, 1913, and 2955. The soft segment in all cases was an 80:20 mixture of PDMS and poly(hexamethylene oxide) (MW 700), and the hard segment was based on 4,4′‐methylenediphenyl diisocyanate and mixed chain extenders (40 wt %). In the polyurethane (PU) series the chain extender was a 60:40 (mol) mixture of BDO and 1,3‐bis(4‐hydroxybutyl)1,1,3,3‐tetramethyldisiloxane (BHTD), whereas in the polyurethaneurea (PUU) series it was a 60:40 (mol) mixture of BHTD and 1,2‐ethylenediamine. The polymerization was carried out by preparing a prepolymer using a bulk polymerization procedure followed by chain extension in a solution of N,N‐dimethylacetamide. Polymers were characterized by size‐exclusion chromatography, tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The number‐average molecular weights of the polymers in the PU series were in the range of 114,300–124,500, whereas they were in the 78,400–103,300 range for the PUU series. Polymers with good clarity and mechanical properties were obtained with PDMS‐940 and PDMS‐1913, but those obtained from PDMS‐2955, despite having good tensile strength, had a low percentage of elongation, high modulus, and poor clarity. DSC and DMTA results indicated that regardless of the PDMS molecular weight, the siloxane segments existed as a highly phase‐separated state. This poor compatibility was consistent with the low solubility of PDMS compared to that of the hard‐segment‐forming components. The polymers in the polyurethane series exhibited multiple melting endotherms, attributed to the melting of ordered domains from different hard segments. The combined heats of fusion were similar for the materials in the PU series. In contrast, the polymers in the PUU series showed a hard‐segment order that was significantly less defined, with the heat of fusion approximately a third to a half that of the materials in the polyurethane series. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1565–1573, 2003

An investigation into the relationship between the impact performance of rotationally molded polyethylene products and their dynamic mechanical properties

AbstractIn this paper, a study of the relationship between the impact performance of rotationally molded polyethylenes and their dynamic mechanical properties is carried out. A wide range of conventional linear low density polyethylene powders and met‐allocene catalyzed linear low density polyethylene powders were rotationally molded and tested. Instrumented falling weight impact tests were carried out over a temperature range of −60°C to 20°C. Dynamic Mechanical Thermal Analysis (DMTA) tests were also carried out between −100°C and 90°C, at a frequency of 100 Hz. Comparisons between the impact performance of metallocene catalyzed LLDPEs and Ziegler‐Natta LLDPEs are made. The transitions evident in the DMTA results are related to changes in impact performance with temperature. The beta transition is found to fall in the transition region between high impact performance at low temperatures and lower impact performance at ambient temperatures.

Molecular dynamics of elastomers investigated by DMTA and the NMR-MOUSE ®

A series of elastomers, consisting of different polymers and crosslink densities, is investigated by dynamic-mechanical thermal analysis (DMTA) and NMR relaxation in an inhomogeneous field by the NMR-MOUSE®. A broad range of molecular mobilities and therefore variation in the glass transition temperature is covered by use of polymers with different side groups. The molecular mobility of every system is also investigated by the frequency-temperature superposition principle. Reduced variables are deduced from analysis of the DMTA results. Comparison of both DMTA and NMR results leads to consistent conclusions. The temperature dependence of the transverse relaxation time can be predicted by the use of an empirical power law presented in this paper and the WLF-equation.

Multivariate analysis of spectra of cyanate ester/bismaleimide blends and correlations with properties

A multivariate approach to the analysis of cured resin blends comprising cyanate ester and bismaleimides is reported. An analysis of samples subjected to accelerated ageing tests by immersion in water at temperatures up to 70°C shows that simple near infrared spectroscopic measurements on virgin materials can predict dynamic mechanical thermal analysis results, and provide correlations with thermogravimetric analysis. This suggests a rapid screening method for a range of materials, perhaps in conjunction with a combinatorial approach to advanced composites manufacture.

Use of hygrothermal decomposed polyester–urethane waste for the impact modification of epoxy resins

Hygrothermally decomposed polyurethane (HD-PUR) of a polyester type was used as an impact modifier in tri- and tetrafunctional epoxy (EP) resins. Between 5 and 80 wt % of the PUR modifier was added to the EP prior to its crosslinking with a diamine compound (diaminodiphenyl sulfone, DDS). The mean molecular weight between crosslinks (Mc ) was determined from the rubbery plateau modulus of the dynamic mechanical thermal analysis (DMTA) spectra. The fracture toughness (Kc) and energy (Gc) of the modified resins were determined on static-loaded compact tension (CT) specimens at ambient temperature. The change in the Kc and Gc as a function of Mc followed the prediction of the rubber elasticity theory. The efficiency of the HD-PUR modifier was compared with that of a carboxyl-terminated liquid nitrile rubber (CTBN). Attempts were also made to improve the functionality of the modifier by hygrothermal decomposition of PUR in the presence of glycine and ε-caprolactam, respectively. DMTA and fractographic results showed that HD-PUR functions as an active diluent and a phase-separating additive at the same time. As HD-PUR can be regarded as an amine-functionalized rubber, it was used as the hardener (by replacing DDS) in some EP formulations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1139–1151, 2000

Use of hygrothermal decomposed polyester-urethane waste for the impact modification of epoxy resins

Hygrothermally decomposed polyurethane (HD-PUR) of a polyester type was used as an impact modifier in tri- and tetrafunctional epoxy (EP) resins. Between 5 and 80 wt % of the PUR modifier was added to the EP prior to its crosslinking with a diamine compound (diaminodiphenyl sulfone, DDS). The mean molecular weight between crosslinks (Mc) was determined from the rubbery plateau modulus of the dynamic mechanical thermal analysis (DMTA) spectra. The fracture toughness (Kc) and energy (Gc) of the modified resins were determined on static-loaded compact tension (CT) specimens at ambient temperature. The change in the Kc and Gc as a function of Mc followed the prediction of the rubber elasticity theory. The efficiency of the HD-PUR modifier was compared with that of a carboxyl-terminated liquid nitrile rubber (CTBN). Attempts were also made to improve the functionality of the modifier by hygrothermal decomposition of PUR in the presence of glycine and «-caprolactam, respectively. DMTA and fractographic results showed that HD-PUR functions as an active diluent and a phase-separating additive at the same time. As HD-PUR can be regarded as an amine-functionalized rubber, it was used as the hardener (by replacing DDS) in some EP formulations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1139 -1151, 2000

Phase behaviour of ternary blends of poly(ethylene naphthalate), poly(ether imide) and poly(ether ether ketone)

The phase behaviour of melt mixed binary and ternary blends of PEN, PEI and PEEK were investigated using differential scanning calorimetry (d.s.c.) and dynamic mechanical thermal analysis (DMTA) techniques. Both PEN/PEI and PEN/PEEK binary blends exhibit single glass transition temperatures ( T gs) in full composition range and PEN and PEEK were found to be immiscible particularly at mid-concentration range. When PEI is added to the immiscible PEN/PEEK system, first the blends form two separate PEN-rich and PEEK-rich phases below about 40% PEI concentration, and above this concentration, these three homopolymers form a miscible phase in the amorphous state exhibiting a single T g. Based on the d.s.c. and DMTA results, an approximate ternary phase diagram is drawn. Three component Fox equations were found to describe the T gs of the ternary blends in the miscible regions quite well.

Thermoplastic Elastomeric Blends of Nylon-6/Acrylate Rubber: Influence of Interaction on Mechanical and Dynamic Mechanical Thermal Properties

Abstract Nylon-6 and acrylate rubber (ACM) were melt blended in a Brabender Plasticorder at 220 °C and 40 rpm rotor speed. The reactive nature of the blend is reflected in the mixing torque behavior of the blends at different compositions. The solubility characteristics of the blends in formic acid solution gives an approximate idea of the amount of nylon-6 grafted onto ACM and vice-versa. A reaction mechanism is proposed based on the well known epoxy—amine and epoxy—acid reactions and is confirmed by infrared spectroscopic studies of the blends. The influence of interaction between the two polymers on the mechanical and the dynamic mechanical properties of the blends is analyzed in detail, and the results are interpreted on the basis of the formation of nylon—ACM graft copolymer at the interfaces. The dynamic mechanical thermal analysis (DMTA) reveals a two phase morphological structure, indicating incompatibility of the blend components. The grafting reaction results in dramatic increase in both the storage modulus and the Young's modulus of blends. The presence of grafted rubber chains is reflected in the secondary transition of the rubber loss peak at higher temperature. Also, a substantial improvement in the damping properties of the blends in the service temperature range (i.e., 25 to 175 °C) is revealed from the DMTA results. The dynamic vulcanization of the ACM phase during melt mixing improves the elongation at break values of the blends.

Blends of polycaprolactone-poly(dimethylsiloxane)-polycaprolactone triblock copolymer with poly(vinyl chloride): preparation and characterization

Miscibility, thermal, mechanical, gas permeation, morphological and surface properties of poly(vinyl chloride) (PVC) blends containing 1–10% triblock polycaprolactone—poly(dimethylsiloxane)—polycaprolactone (PCL-PDMS-PCL) copolymer were investigated by using several techniques. Fourier transform infra-red analysis of blends reveal the existence of specific interactions via hydrogen bonding between the α-hydrogen of PVC and the carbonyl group of PCL in the triblock copolymer. This PCL-PDMS-PCL/PVC blend system exhibited a single glass transition according to differential scanning calorimetry and dynamic mechanical thermal analysis results. Stress—strain results showed that PCL-PDMS-PCL triblock copolymer is a very effective plasticizer for PVC. Gas permeability of the blends increased with the copolymer content. Morphological and surface properties of the blend system were examined by scanning electron microscopy and contact angle measurements.

Thermomechanical Behavior of Concentrated Starch‐Water Preparations

ABSTRACTThe rheological behavior of concentrated starch preparations from various origins was studied by dynamic mechanical thermal analysis (DMTA). Four types of starch were used: wheat, potato, normal, and waxy corn adjusted to moisture contents in the 42–49% (w/w) range. The thermal treatments of the starch‐water mixtures consisted of heating to 85°C and cooling to room temperature, both at a rate of 1°C/min. During heating, the storage modulus (E′) appearance was first characterized by an increase with a maximum at ≈70°C (or potato starch at 63°C) followed by a decrease to 85°C. During cooling, storage modulus increased steadily down to room temperature. The magnitude of these variations depended on the starch type. Despite some differences, all the loss tangent curves showed a decrease during heating from 60–70°C to 85°C, followed by a plateau during cooling. To propose an interpretation for the DMTA results, we measured, by laser‐light diffraction, the influence of heating (up to the maximum E′ peak) on the distribution of the granule sizes of the different starches. Moreover, differential scanning calorimetry (DSC) was used to measure the temperature range where the melting of starches ordered regions occurred. Partial melting enthalpies were plotted against temperature. The hypothesis of a relationship between swelling and an increase in rigidity during heating seemed to be confirmed by laser‐light diffraction, whereas DSC indicated the decrease in rigidity was caused predominantly by order‐disorder transitions. During cooling, amylose gelation plays a major role in the rigidity increase, but a contribution of amylopectin is not excluded.

Poly(ether urethane)/poly(ethyl methacrylate) interpenetrating polymer networks: Morphology, phase continuity and mechanical properties as a function of composition

The composition range of polyurethane (PUR)/poly(ethyl methacrylate) (PEMA) interpenetrating polymer networks was investigated with respect to morphology and phase continuity using mechanical and dynamic mechanical methods and transmission electron microscopy (TEM). Dynamic mechanical data revealed one main tanδ transition with a shoulder for the intermediate compositions from 70:30 to 40:60 indicating a semi-miscible system. For the remaining compositions only one peak, indicating a higher degree of miscibility was observed. The storage and elastic moduli were related to the Davies, Kerner and Budiansky modulus-composition models. The Budiansky modulus-composition model, which indicates phase inversion at the mid-range composition, resulted in the best fit. However, it was found that the shape of the modulus versus composition curves was strongly temperature-dependent. In previous studies, not much attention had been given to the temperature at which the modulus-composition studies were conducted. Tensile testing revealed a strong synergistic effect at the 70:30 PUR/PEMA composition with maxima occurring at this composition for both the elongation at break and the toughness index. The tensile strength increased in a three-step regime corroborating the dynamic mechanical thermal analysis results. TEM micrographs confirmed a co-continuous system at the 70:30 to 40:60 PUR/PEMA mid-range compositions.

Techniques to monitor the UV curing of potential solvent-free film-coating polymers

A methodology has been established for systematically evaluating polymer films produced by UV curing. Cast films of 1,3-bis[(p-acryloxymethyl)phenethyl] tetramethyldisiloxane (I) and norborenylpolydimethylsiloxane (II) were cured by UV irradiation. The films were evaluated from real-time FTIR studies, a non-rheologically destructive method for determining microviscosity, dynamic mechanical thermal analysis (DMTA) and leaching and swelling studies. Real-time FTIR indicated that while conversion from prepolymer to network was complete for II, conversion was only 80% for I with 0.05% benzoin methyl ether (BME), an initiator, and only 60% with 0.5% BME. Results of DMTA show the glass transition temperatures (T g values) of the films to have an inverse rank order correlation with conversion. Along with microviscosity results, this is indicative of a diffusion rate-limited curing reaction. Results of leaching and swelling studies demonstrated greater rates and extents of leaching and swelling from films prepared with a lower concentration of initiator (0.05% BME). These observations were in good agreement with the results from the microviscosity and DMTA studies which showed larger free volumes and lower T g values as well as slightly lower crosslinking densities in films prepared with less initiator. The methods presented in this paper have been shown to be useful in quantifying the reaction of this new class of film formers and in identifying the mechanisms of film formation.

Blends of thermotropic polyester with poly(phenylene oxide)

AbstractA thermotropic liquid crystalline polymer (LCP) based on wholly aromatic copolyesters based on hydroxynaphthoic and hydroxybenzoic acid was melt‐blended with a thermoplastic poly(phenylene oxide) by corotating twin screw extruder. Rheological properties, temperature transitions, dynamic and mechanical properties, and electron microscopy study have been performed. Rheological study indicated significant viscosity reductions with increasing LCP content leading to ease of processing. From the differential scanning calorimeter (DSC) and dynamic mechanical thermal analyzer results, these blends showed incompatibility for the whole range of concentrations. Mechanical properties were found to be slightly improved at low LCP and dramatically improved at above 50% LCP contents. In addition, impact strength was significantly increased up to two times after adding 10% LCP into the matrix. The morphology of blends was affected by composition. Droplets and stubby fibrils structures caused lower tensile strength, whereas fibrillar structure improved this property.