scholarly journals Improved Water-Tree Resistances of SEBS/PP Semi-Crystalline Composites under Crystallization Modifications

Molecules ◽  
2020 ◽  
Vol 25 (16) ◽  
pp. 3669
Author(s):  
Jun-Qi Chen ◽  
Xuan Wang ◽  
Wei-Feng Sun ◽  
Hong Zhao
Keyword(s):  
Accelerated Aging ◽  
Dynamic Mechanical Properties ◽  
Melt Crystallization ◽  
Dynamic Relaxation ◽  
Scanning Calorimetry ◽  
Polarizing Microscopy ◽  
Water Tree ◽  
Relaxation Loss ◽  
Pp Composites ◽  
Lower Size

Water-tree resistances of styrene block copolymer/polypropylene (SEBS/PP) composites are investigated by characterizing crystallization structures in correlation with the dynamic mechanical properties to elucidate the micro-structure mechanism of improving insulation performances, in which the accelerated aging experiments of water trees are performed with water-knife electrodes. The water-tree morphology in spherulites, melt-crystallization characteristics and lamella structures of the composite materials are observed and analyzed by polarizing microscopy (PLM), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. Dynamic relaxation and stress-strain characteristics are specifically studied by means of a dynamic thermomechanical analyzer (DMA) and electronic tension machine, respectively. No water-tree aging occurs in both the highly crystalline PP and the noncrystalline SEBS elastomer, while the water trees arising in SEBS/PP composites still has a significantly lower size than that in low-density polyethylene (LDPE). Compared with LDPE, the PP matrix of the SEBS/PP composite represent a higher crystallinity with a larger crystallization size in consistence with its higher mechanical strength and lower dynamic relaxation loss. SEBS molecules agglomerate as a “island” phase, and PP molecules crystallize into thin and short lamellae in composites, leading to the blurred spherulite boundary and the appreciable slips between lamellae under external force. The high crystallinity of the PP matrix and the strong resistance to slips between lamellae in the SEBS/PP composite essentially account for the remarkable inhibition on water-tree growth.

Enhancing the mechanical and water resistance performances of bamboo particle reinforced polypropylene composite through cell separation

Holzforschung ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Dan Ren ◽  
Xuexia Zhang ◽  
Zixuan Yu ◽  
Hankun Wang ◽  
Yan Yu
Keyword(s):  
Water Absorption ◽  
Cell Separation ◽  
Water Resistance ◽  
Dynamic Mechanical Properties ◽  
Simple Method ◽  
Interface Modification ◽  
Wood Particles ◽  
Bamboo Fibers ◽  
Pp Composites ◽  
Mechanical Performances

AbstractIt is frequently observed that bamboo particle composites (BPCs) do not show higher mechanical performances than the corresponding wood particles composites (WPCs), although bulk bamboo is much stronger than wood in mechanical performances. Herein this phenomenon was demonstrated from the cell compositions in the applied bamboo particles. To address that, a simple method to physically separate bamboo fibers (BFs) and bamboo parenchyma cells (BPs) from a bamboo particle mixture was developed. Polypropylene (PP) composites with pure BFs, BPs, a mixture of BFs and BPs (BFs + BPs), wood particles (WPs) as fillers were prepared. The flexural and dynamic mechanical properties, water absorption, and thermal properties were determined. The BF/PP composites showed the best mechanical performances (MOR at 35 MPa, MOE at 2.4 GPa), followed by WP/PP, (BF + BP)/PP, and BP/PP. They also exhibited the lowest water absorption and thickness swelling. Little difference was found for the thermal decomposition properties. However, a lower activation energy of BF/PP compared with BP/PP implied an uneven dispersion of BFs and weaker interfacial interaction between BF and PP. The results suggest that the mechanical performances and water resistance of bamboo particle/polymer composites can be significantly improved through cell separation. However, interface modification should be applied if higher performances of BF/PP composites are required.

scholarly journals Investigation of viscoelastic properties and thermal behavior of photocurable epoxy acrylate nanocomposites

2017 ◽  
Vol 24 (5) ◽  
pp. 691-697
Author(s):  
Behzad Shirkavand Hadavand ◽  
Hossein Hosseini
Keyword(s):  
Thermal Behavior ◽  
Dynamic Mechanical Properties ◽  
Mechanical Analysis ◽  
Cuo Nanoparticles ◽  
Epoxy Acrylate ◽  
Silane Coupling Agents ◽  
Scanning Calorimetry ◽  
Dynamic Mechanical ◽  
Acrylate Resin ◽  
Epoxy Acrylate Resin

AbstractIn this study, the dynamic-mechanical properties and thermal behavior of the nanocomposites of a photocurable epoxy-acrylate resin and CuO nanohybrid were determined. In order to improve the dispersion of CuO nanoparticles and prevention of nanoparticle migration to the surface coating, the surface of commercial nanoparticles was modified by triethoxymethylsilane (TEMS) and vinyltrimethoxysilane (VTMS) as silane-coupling agents. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) tests were then performed on CuO-filled epoxy-acrylate resins to identify the loading effect on the properties of material. The thermal stability of nanocomposites was affected slightly after incorporation of CuO nanoparticles. DMA studies revealed that filling the CuO nanoparticles into epoxy-acrylate resin can produce a significant enhancement in storage modulus, as well as a shift in the glass transition temperature. The films reinforced with the modified CuO exhibit the most significant enhancements in properties.

scholarly journals Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 22
Author(s):  
Artur Kościuszko ◽  
Dawid Marciniak ◽  
Dariusz Sykutera
Keyword(s):  
Mechanical Properties ◽  
Impact Strength ◽  
Injection Molding ◽  
Accelerated Aging ◽  
Mold Temperature ◽  
Degree Of Crystallinity ◽  
Injection Mold ◽  
Secondary Crystallization ◽  
Scanning Calorimetry ◽  
Injection Molded

Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding.

scholarly journals Thermal Kinetics of SiCp Reinforced Al-Zn-Mg-Cu Alloy Composite

2021 ◽  
Author(s):  
Saikat Das ◽  
R. Govinda Rao ◽  
Prasanta Kumar Rout
Keyword(s):  
Base Alloy ◽  
Accelerated Aging ◽  
Stir Casting ◽  
Hardness Profile ◽  
Scanning Calorimetry ◽  
Transmission Electron ◽  
The Matrix ◽  
Aging Kinetics ◽  
Aging Phenomena ◽  
Kinetics Of

Abstract In the present work, the artificial aging kinetics of SiCp particles reinforced AA7075-SiCp composite fabricated by stir casting method was investigated. The aging behavior of AA7075-SiCp composite was investigated by Rockwell hardness tests and differential scanning calorimetry (DSC). Results show there are no changes in the sequences of formation and dissolution of precipitate. Reinforced particles are uniformly distributed throughout the matrix. The hardness profile shows increase in hardness with the comparison of AA7075 base alloy. In addition to SiCp in the matrix, precipitation kinetics has changed compared with base alloy since higher dislocations present in composite, hence requires lower activation energy to form ή precipitate and takes less time to reach the maximum hardness. In contrast, the addition of SiCp at low volume percent also showing accelerated aging phenomena in the composite during the aging process. High-resolution transmission electron microscope (HRTEM) micrograph of peak age (T6) condition divulges that enormous fine and plate-like ή (MgZn2) precipitates are uniformly distributed in the composite.

scholarly journals Evaluation of graphene/crosslinked polyethylene for potential high voltage direct current cable insulation applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yuan Li ◽  
Guangya Zhu ◽  
Kai Zhou ◽  
Pengfei Meng ◽  
Guodong Wang
Keyword(s):  
Space Charge ◽  
High Voltage ◽  
Direct Current ◽  
Tensile Yield Strength ◽  
Scanning Calorimetry ◽  
Crosslinking Degree ◽  
High Voltage Direct Current ◽  
Water Tree ◽  
Mechanical And Electrical Properties ◽  
Aging Test

AbstractThis paper evaluates the potential usage of graphene/crosslinked polyethylene (graphene/XLPE) as the insulating material for high voltage direct current (HVDC) cables. Thermal, mechanical and electrical properties of blends with/without graphene were evaluated by differential scanning calorimetry (DSC), tensile strength, DC conductivity, space charge measurements and water tree aging test. The results indicate that 0.007–0.008% weight amount of graphene can improve the mechanical and electrical insulation properties of XLPE blends, namely higher tensile/yield strength, improved space charge distribution, and shorter/fewer water tree branches. The improvements mainly attribute to the high stiffness of graphene, deep traps introduced by the interaction zones of graphene and XLPE, and the blockage effect of graphene within XLPE. For thermal performance of XLPE blends, graphene nano-fillers have but limited improvement. The crystallinity of the blends barely changes with the addition of graphene. However, the crosslinking degree increases as the additive-like amounts of graphene doped. The above findings provide a guide for tailoring lightweight XLPE materials with excellent mechanical and electrical performances by doping them with a small amount of graphene.

Relationships between molecular structure and physical properties in bent-core mesogens

2006 ◽  
Vol 364 (1847) ◽  
pp. 2657-2679 ◽  
Author(s):  
Wolfgang Weissflog ◽  
H.N Shreenivasa Murthy ◽  
Siegmar Diele ◽  
Gerhard Pelzl
Keyword(s):  
Optical Measurements ◽  
Polar Phase ◽  
X Ray Diffraction ◽  
Aromatic Rings ◽  
Scanning Calorimetry ◽  
Polarizing Microscopy ◽  
X Ray ◽  
Smectic Phases ◽  
Collective Rotation ◽  
Clear Change

New five-ring bent-core mesogens that possess only ester connecting groups between the aromatic rings and different lateral substituents at the central phenyl ring are presented. The mesophases have been assigned by polarizing microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical measurements. It is shown that the mesophase behaviour depends strongly on the position of the lateral substituents. Compounds, which are derived from 4-cyano-, 4-chloro- and 4,6-dichloro-resorcinol, show polymorphism variants where polar phases (SmAP, SmCP) occur together with nematic and conventional smectic phases, e.g. SmA–SmAP, SmA–SmC S P A –Col ob –SmC S P A , N–SmA–SmCP A , SmA–SmC–SmCP A and SmC–SmCP A . On the basis of the behaviour of two series of materials, the occurrence of different polar-switching mechanisms could be demonstrated. Apart from the usual mechanism by director rotation around the tilt cone, the polar switching can also take place through collective rotation of the molecules around their long axes, which corresponds to a field-induced switching of the layer chirality. A remarkable finding is the polar switching in the crystalline modification of long-chain, bent-core compounds with a methyl group in 2-position, which is accompanied by a clear change of the optical texture and by a relatively high switching polarization (approx. 600 nC cm −2 ). It was found for selected bent-core compounds that, above the transition temperature of a polar to a non-polar phase, the non-polar phase can be transformed to the polar phase by application of an electric field, which was proved for the transitions isotropic–SmCP F , SmA–SmCP F and isotropic–CrII polar.

Thermotropic Copolyesters Based on Polyethylene Terephthalate and 4-Hydroxybenzoic Acid for High Modulus Fibers

2021 ◽  
Vol 887 ◽  
pp. 3-9
Author(s):  
T.R. Deberdeev ◽  
A.I. Akhmetshina ◽  
S.V. Grishin
Keyword(s):  
Dimethyl Ester ◽  
Hydroxybenzoic Acid ◽  
Gravimetric Analysis ◽  
Scanning Calorimetry ◽  
Polarizing Microscopy ◽  
Polymer Backbone ◽  
Molecular Compounds ◽  
Anisotropic Phase ◽  
Thermal Stability Of ◽  
Thermotropic Copolyesters

The copolyesters derived from dimethyl ester of terephthalic acid, ethylene glycol, and 4-hydroxybenzoic acid (HBA) have been synthesized via catalytically promoted polycondensation omitting the acetylation step. FTIR spectroscopy results have evidenced an insertion of HBA along a polymer backbone. Of note, thermal gravimetric analysis has shown that the HBA moieties substantially improved the thermal stability of polyesters. As found by differential scanning calorimetry and polarizing microscopy, the copolyesters are capable of forming an anisotropic phase in a temperature range of 150-170 °C. Additionally, the free surface energy of the samples was determined to evaluate the compatibility of thermotropic copolyesters with other high-molecular compounds.

scholarly journals Inhibition of Rejuvenation Liquid on Trees in XLPE Cables under Switching Impulse Voltages

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2133
Author(s):  
Guangya Zhu ◽  
Kai Zhou ◽  
Wei Gong ◽  
Min He ◽  
Jiaming Kong ◽  
...  
Keyword(s):  
Average Length ◽  
Substantial Reduction ◽  
Accelerated Aging ◽  
Inhibitory Effect ◽  
Control Group ◽  
Initiation Rate ◽  
Water Tree ◽  
Electrical Tree ◽  
Electrical Trees ◽  
Two Parameters

In this paper, the inhibitory effect of preinjected rejuvenation liquid on trees in cross-linked polyethylene (XLPE) cables was investigated. Experimental samples were prepared by inserting needles into XLPE samples, and many equally-spaced holes existed in the outer semiconductive layer. All cable samples were divided into two groups. One sample group was treated with rejuvenation liquid, while the other group was the control group. A tree accelerated aging system was used to obtain trees in the XLPE cable samples. During the aging experiment, an impulse voltage was applied to the samples repeatedly. The micromorphologies of the two groups were observed. Based on the micromorphologies, two parameters were determined: the initiation rate of electrical trees and the average length of trees. Furthermore, the electric field distribution was simulated to analyze the initiation of electrical trees. The results indicate that an electrical tree is much harder to initiate in the pretreated XLPE cables than in the untreated cables. This phenomenon is likely attributed to the dielectrophoretic forces in the pretreated cables. Moreover, rejuvenation liquid deposited in XLPE causes a substantial reduction in the Maxwell stress of molecular chains. Rejuvenation liquid inhibits electrical tree initiation and water tree growth to a great extent.

scholarly journals Influence of Thermally-Accelerated Aging on the Dynamic Mechanical Properties of HTPB Coating and Crosslinking Density-Modified Model for the Payne Effect

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 403 ◽  
Author(s):  
Yongqiang Du ◽  
Jian Zheng ◽  
Guibo Yu
Keyword(s):  
Mechanical Properties ◽  
Aging Time ◽  
Loss Modulus ◽  
Accelerated Aging ◽  
Crosslinking Density ◽  
Dynamic Mechanical Properties ◽  
Maximum Elongation ◽  
Solid Rocket Motor ◽  
Payne Effect ◽  
Dynamic Mechanical

Hydroxyl terminated polybutadiene (HTPB) coating is widely used in a solid rocket motor, but an aging phenomenon exists during long-term storage, which causes irreversible damage to the performance of this HTPB coating. In order to study the effect of aging on the dynamic mechanical properties of the HTPB coating, the thermally-accelerated aging test was carried out. The variation of maximum elongation and crosslinking density with aging time was obtained, and a good linear relationship between maximum elongation and crosslinking density was found by correlation analysis. The changing regularity of dynamic mechanical properties with aging time was analyzed. It was found that with the increase of aging time, Tg of HTPB coating increased, Tα, tan β and tan α decreased, and the functional relationships between the loss factor parameters and crosslinking density were constructed. The storage modulus and loss modulus of HTPB coating increased with the increase of aging time, and decreased with the increase of pre-strain. The aging enhanced the Payne effect of HTPB coating, while the pre-strain had a weakening effect. In view of the Payne effect of HTPB coating, the crosslinking density was introduced into Kraus model as aging evaluation parameter, and the crosslinking density modified models with and without pre-strain were established. The proposed models can effectively solve the problem that the Kraus model has a poor fitting effect under the condition of small strain (generally less than 1%) and on the loss modulus, which have improved the correlations between the fitting results and the test results.

Effect of MWCNT carboxyl functionalization on the shear rheological and electrical properties of HMS-PP/MWCNT foams

2020 ◽  
pp. 0021955X2094309
Author(s):  
Olavo S Bianchin ◽  
Guilherme HF Melo ◽  
Rosario ES Bretas
Keyword(s):  
Impedance Spectroscopy ◽  
Rheological Properties ◽  
Polarized Light ◽  
Multiwall Carbon Nanotubes ◽  
Dynamic Mechanical Properties ◽  
Dielectric Constants ◽  
Scanning Calorimetry ◽  
Cellular Density ◽  
Foaming Behavior ◽  
High Dielectric

Different concentrations of multiwall carbon nanotubes (MWCNT) and carboxyl functionalized MWCNT (MWCNT-COOH) were added to a high melt strength polypropylene (HMS-PP) to produce foams with high dielectric constants, using azodicarbonamide (AZO) as blowing agent. The AZO foaming behavior and the crystallization, thermal properties, steady state and oscillatory shear rheological properties of the nanocomposites were analyzed by polarized light optical microscopy (PLOM), differential scanning calorimetry (DSC), thermogravimetry analyses (TGA) and parallel plate rheometry. The morphology, the dielectric and dynamic mechanical properties (DMTA) of the foams were also studied by scanning electron microscopy (SEM), impedance spectroscopy and bending method, respectively. A decrease in crystallite size and an increase in the HMS-PP overall crystallinity promoted by the presence of both types of MWCNTs was observed, as well as an increase in the crystallization temperatures. From these results and from the analyses of the rheological properties, it was possible to predict that the 5 wt.% MWCNT foam would have the lowest bubble growth rate, the 1.5 wt.% MWCNT-COOH the highest, while the 3 wt.% MWCNT-COOH composition would have the slowest bubble stability (and consequently the highest cellular density) and the 1.5 wt.% MWCNT-COOH the fastest. Also, it was possible to predict that only the 5 wt.% MWCNT-COOH foam would have a percolated and electrically conductive structure. All these predictions were confirmed by the resultant morphology and impedance spectroscopy results. The highest mechanical damping was displayed by the 3 wt.% MWCNT-COOH foam, while the lowest by the 5 wt.% MWCNT-COOH foam. Regarding the dielectric properties, the 1.5 wt% MWCNT-COOH foam was found to be the most suitable to be used as a capacitor material; this foam was also the less dense of all the samples.

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