Differential Mechanical Analysis Research Articles

Influence of the Addition of Alumina Nanofibers on the Strength of Epoxy Resins

The paper describes the effect of the addition of alumina nanofibers on the mechanical properties of the epoxy resin. Alumina nanofibers functionalized with epoxypropyl functional groups are used in this work. The dependence of the mechanical characteristics on the amount of the additive, as well as the features of its distribution in the material, is investigated. In the work, nanocomposites were obtained, which are epoxy resin with aluminum oxide nanofibers. The mechanical properties of the samples were studied by bending tests and differential mechanical analysis (DMA). It has been shown that the addition of alumina nanofibers leads to an increase in ultimate flexural strength. The maximum of this increase is near the percolation threshold of alumina nanofibers in epoxy resin. With the addition of 0.2% alumina nanofibers, the ultimate flexural strength increases from 41 to 71 MPa. It is shown that after exceeding the percolation threshold of nanofibers, the ultimate strength decreases. In this case, the elastic modulus increases from 0.643 to 0.862 GPa. DMA is shown that the glass transition temperature decreases with increasing amount of the additive. This indicates a decrease in the molecular weight of the polymer. By implication, this suggests that the hardener connects the epoxypropyl functional groups on the nanofibers and the epoxy groups in the resin, and as a result of this process, the nanofibers become natural polymer chain length limiters. The data obtained from mechanical testing and differential mechanical analysis can be used to strengthen epoxy resins in polymer composite materials and molding compositions.

The Activation Energy of Strain Bursts during Nanoindentation Creep on Polyethylene.

In the present investigation, statistical characterization of strain bursts observed during the load-controlled deformation of high-density polyethylene (HDPE), which arise within the crystalline phase during plastic deformation, was carried out via high-resolution nanoindentation creep experiments. Discrete deformation processes occurred during the nanoindentation creep tests, which indicated that they arose from the break-off of dislocation avalanches, i.e., dislocation climb is a possible mechanism for indentation creep deformation. Characterization of the strain bursts, in terms of the associated height and number, demonstrated that these quantities followed a Gaussian distribution depending on the load and loading rate. This analysis enabled the accurate measurement of creep activation energy. Our method used nanoindentation tests to measure the creep activation energy of HDPE within both the crystalline and amorphous phases. The activation energy of the creep process within the crystalline phase was evaluated using two methods. The frequency of jumps within the crystalline phase, as a function of the strain rate, showed two peaks related to the 5 nm and 10 nm jump sizes that corresponded to the block size within the crystalline lamellae. The results indicated that the intervals coincided with the mean free path of dislocations and the block grain boundaries acted as dislocation barriers. From the dependence of burst frequency on the strain rate and temperature, the activation energy and thermally activated length of the dislocation segment for the plastic slip activation were determined to be 0.66 eV and 20 nm, respectively. Both numbers fit well to the Peterson's model for the nucleation and motion of thermally activated dislocation segments. A similar activation energy resulted from the differential mechanical analysis of the literature for the αI-transition, which occurred near room temperature in polyethylene. The transition was described as the generation of screw dislocation and its motion along a block grain boundary; therefore, this process is suggested to be the basic mechanism underlying the strain bursts observed in this study.

Effect of the Ratio of Acetylacetate Groups on the Properties of a Novel Plant-Based Dual-Cure Coating System.

A novel plant-based dual-cure coating system based on a Michael addition reaction between bismaleimide (BDM) and modified acetoacetylated castor oil was developed. The BDM has a high reactivity toward acetylacetate groups, and the catalyst 1,4-diazabicyclo[2.2.2]octane (TEDA) was optimized by the rheological viscosity. The gel was characterized by Fourier transform infrared (FTIR) spectroscopy. Then, three films were prepared with the TEDA catalyst and analyzed with solid-state 13C NMR and FTIR spectroscopy. The thermal and mechanical properties of the three films were characterized by differential mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. We found that the cross-linking density, glass transition temperature (Tg), and Young’s modulus of the coating films increased with an increase in the ratio of acetylacetate groups from the modified acetoacetylated castor oil. This is the first study of the reaction of BDM with plant-based acetylacetate groups. Importantly, a quantitative ratio of acetylacetate groups can be obtained by a thiol–ene coupling reaction and a transesterification reaction, resulting in the formation of films having excellent performance.

Abstract LB-061: Systematic, network-based, comparative analysis of differential mechanisms of action of lanreotide and octreotide in neuroendocrine tumor derived cell lines

Abstract Lanreotide and octreotide are somatostatin receptor (SSTR) agonists thought to exhibit overlapping Mechanism of Action (MoA), despite small differences in their SSTRs affinity and differential PK response in vivo [1]. To systematically and quantitatively assess both concentration- and time-dependent MoA differences at the molecular level —by characterizing the full protein repertoire that mediates the compound's pharmacological effects— we assessed the protein-specific activity of lanreotide and octreotide in two gastroenteropancreatic neuroendocrine tumor (GEP-NET) derived cell lines (H-STS and KRJ-1). We performed RNASeq profiling at 4 different time points (24h -96h), following cell perturbation at 4 non-toxic doses (2 nM - 1 μM). RNASeq profiles were used to assess compound activity on 6,276 regulatory proteins, using VIPER, an experimentally-validated algorithm to infer protein activity based on the expression of its targets [2]. The analysis was performed using a GEP-NET-specific regulatory model inferred from a collection of 212 primary and metastatic human samples. Concentrations above the EC50 of the drugs were selected to (a) assess potential off-target effects and (b) discount potential effects from differential compound degradation. Confirming the robust nature of our approach, short-term (24h and 48h) transcriptional and protein activity profiles, following compound perturbation, were virtually identical across both cell lines and drug concentration (FET p-value < 10-12). However, the sensitivity and reproducibility of VIPER analysis, which represents the foundation for two NYS CLIA approved tests, allowed identification of 367 proteins affected differentially by these drugs (FDR < 0.05), which were enriched in cancer-relevant functional categories, including apoptosis, immune response, cell differentiation, cell proliferation and DNA-repair (FDR < 10-5). Most critically, while lanreotide-modulated proteins were virtually unchanged over time (from 24h to 96h, p < 0.05), the effect of octreotide on the same proteins was transient and virtually lost at 72h. This discrepancy cannot be attributed to concentration-related effects, since it was manifested identically across all tested concentrations. This work constitutes the first systematic, genome-wide characterization of the MoA of two clinically relevant SSTR agonists, showing both common as well as differentially affected pathways. Two key elements which may account for differential clinical response in patients emerged from the analysis: (1) Differences in the repertoire of affected proteins (MoA) by each compound, and (2) different response kinetics, with sustained lanreotide response from 24h to 96h vs. transient octreotide response with subsequent adaptive cell response after 48h. [1] Enzler et.al (2017) Sem. Oncol. 44:141.[2] Alvarez et.al (2016) Nat. Genet. 48:838. Citation Format: Mariano J. Alvarez, Gideon Bosker, Roswitha Pfragner, Mark Kidd, Irvin Modlin, Andrea Califano. Systematic, network-based, comparative analysis of differential mechanisms of action of lanreotide and octreotide in neuroendocrine tumor derived cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-061.

Effect of Montmorillonite on the Crystallization, Rheological and Physical Behavior of Polyamide-6/Polylactic Acid Blends

Organic montmorillonite (OMMT)/polyamide-6 (PA6)/polylactic acid (PLA) composites were prepared via a step melt compounding process using a twin screw. The effect of OMMT content on the crystallization behavior, as well as rheological and mechanical properties of the composites was carried out by differential scanning calorimetry, differential mechanical analysis, and using an advanced rheometer and a material testing machine. The crystallization behavior of the polymers was studied using a dynamic rheology method, which allowed to determine the onset of nucleation and obtain semiquantitative data on the nucleation density. The results revealed that the interaction between the OMMT and the PA6/PLA inhibits the molecular chain segment motion, which reduces the nucleation temperature, the crystal growth temperature, the melting temperature and the glass transition temperature of the samples. However, the PA6/PLA/OMMT composites showed better mechanical properties than the PA6/PLA composites.

Effect of Modified Red Pottery Clay on the Moisture Absorption Behavior and Weatherability of Polyethylene-Based Wood-Plastic Composites.

Red pottery clay (RPC) was modified using a silane coupling agent, and the modified RPC (mRPC) was then used to enhance the performance of high-density polyethylene-based wood-plastic composites. The effect of the mRPC content on the performances of the composites was investigated through Fourier transform infrared spectrometry, differential mechanical analysis (DMA) and ultraviolet (UV)-accelerated aging tests. After adding the mRPC, a moisture adsorption hysteresis was observed. The DMA results indicated that the mRPC effectively enhanced the rigidity and elasticity of the composites. The mRPC affected the thermal gravimetric, leading to a reduction of the thermal degradation rate and a right-shift of the thermal degradation peak; the initial thermal degradation temperature was increased. After 3000 h of UV-accelerated aging, the flexural strength and impact strength both declined. For aging time between 0 and 1000 h, the increase in amplitude of ΔL* (luminescence) and ΔE* (color) reached a maximum; the surface fading did not became obvious. ΔL* and ΔE* increased more significantly between 1000 and 2000 h. These characterization results indicate that the chromophores of the mRPC became briefly active. However, when the aging times were higher than 2000 h, the photo-degradation reaction was effectively prevented by adding the mRPC. The best overall enhancement was observed for an mRPC mass percentage of 5%, with a storage modulus of 3264 MPa and an increase in loss modulus by 16.8%, the best anti-aging performance and the lowest degree of color fading.

Transparent thermoplastic polyurethanes based on aliphatic diisocyanates and polycarbonate diol

Segmented thermoplastic polyurethanes (PUs) were synthetized using polycarbonate diol as soft segment with a molar mass of 500 and as a hard segment 1,5-pentanediol with a combination of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, haze, transmittance, hardness, tensile properties and retention of tensile properties tests were employed to characterize the different PUs. The results of this study show that IPDI/HDI relation has a significant impact on the phase mixing, crystallinity and therefore on the PU’s properties. The variation of diisocyanate type ratio allows obtaining PUs of different nature from a high rubbery material with a high content in IPDI to high crystalline PU increasing the HDI content. Material transparency was also modified by decreasing the amorphous nature of the materials with the increase in the HDI content. The weather resistance of the final PU is related with the different isocyanate relation.

Properties of PP/MWCNT-COOH /PP composites made by melt mixing versus solution cast /melt mixing methods

An approach on improvement of the properties of polypropylene / carbon nanotube (PP/CNT) composites is reported. PP blend compositions with carboxylic acid functionalized multi-walled carbon nanotubes (MWCNT-COOH) at filler content 1.0 wt.% were researched. One part of the composites was manufactured by direct thermoplastic mixing PP with the filler, but the other one was made from solution casted masterbatch with the following thermoplastic mixing. An increase of mechanical properties (Young's modulus, storage modulus and tensile strength), compared to an increase of glass transition temperature indicated a reinforcement effect of CNTs on PP matrix, determined from the tensile tests and differential mechanical analysis (DMA), while the elongation was reduced, compared to PP matrix. By differential scanning calorimetry (DSC) analysis, the effect of nanofiller on the reorganization of PP crystallites was observed. A noticeable enhanced effect on increase of the crystallization temperature was indicated for masterbatch manufactured composite. An increase of thermal stability was also observed, compared to pristine PP and the composite made by direct thermoplastic mixing PP with the filler.

Enhanced polyurethanes based on different polycarbonatediols

Segmented thermoplastic polyurethanes (PUs) were prepared from 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD) and different macrodiols with a molar mass of 1000. Properties of those PUs based on polycarbonatediol (PCD) were compared with their homologous based on polyesterdiol and polyetherdiol as macrodiols. The proportion used in this study was macrodiol:BD:MDI = 1:2:3, in mole ratio. The hard segment weight percentage is 48 wt% for different PUs. Thermogravimetric analysis, differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, as well as mechanical properties and retention on flexural properties tests were employed to characterize the physicochemical, thermal and mechanical properties of different PUs. Comparison of PUs based on PCD, ester and ether macrodiols indicates a better miscibility, higher hard segment–soft segment interactions and durability for the ones based on PCD. It is especially noticeable that the transparency of the films obtained with PCD as macrodiols as well as their good tensile strength and performance to standard durability tests, in comparison with those based on polyester and polyether. This trend could be related with a better miscibility caused by the highest hard segment–soft segment interactions favored by the presence of the carbonate groups.

Effects of Rice Husk Filler on the Mechanical and Thermal Properties of Liquid Natural Rubber Compatibilized High-Density Polyethylene/Natural Rubber Blends

Natural rubber/high-density polyethylene (NR/HDPE) blend with rice husk (RH) filler and liquid natural rubber (LNR) as the compatibilizer was prepared using an internal mixer at 140°C and 50 rpm. The reinforcing effect and compatibilizing performance of the added reagents in the composites were evaluated from the mechanical and thermal properties, and blend homogeneity. The tensile and impact strength decreased with RH loadings in the matrix, while the tensile modulus and hardness showed an opposite trend. The weak filler–matrix interaction, resulting in poor filler dispersion and large agglomerated particle size, caused those properties to decrease. However, the mechanical properties of the composites improved with the addition of NR or LNR into the matrix. The dissolution effect caused interactions between the phases, leading to an improvement in the compatibility in the blend. Changes in morphology resulted in the shift of T g of the amorphous part of NR to higher temperatures, as observed in differential mechanical analysis (DMA) thermograms. Scanning electron microscopy (SEM) micrographs of the fractured surface had also revealed the good RH–matrix interaction and, thus, the dispersion of particles in samples with added LNR.