Low dielectric loss BST/PTFE composites for microwave applications

Ba_0.3Sr_0.475Ce_0.03La_0.12Ti_0.997Mn_0.003O₃/Polytetrafluoroethylene (PTFE) composites were prepared using powder processing technique. The effects of the ceramic filler volume fraction and the coupling agent on the phase composition, microstructure, dielectric and thermal properties of the composites were investigated in this paper. The ceramic filler dispersion in the PTFE matrix, thus the dielectric loss, permittivity, and dimensional thermal stability of the composite was considerably improved by the modification of BST filler surface using phenyl trimethoxy silane (PTMS) coupling agent. Variation of the dielectric permittivity of the composite with composition was well fitted by the effective medium theory (EMT) model in the experimental compositional range. The obtained silane-treated composite with 0.5 V_f BST exhibits extremely low dielectric loss: ε_r = 16, tan δ = 5.4 × 10⁻⁴ @1 MHz and 5.16 ± 0.6 × 10⁻³ @ 10 GHz. The CTE of the composites was reduced to 43 ppm/°C.     

Correlation among crystalline morphology of PEEK,interface bond strength,and in‐plane mechanical properties of carbon/PEEK composites

The effect of the cooling rate on in‐plane and interlaminar properties of carbon fiber/semicrystalline PEEK matrix composites was studied. Strengths and moduli were measured in tension, flexure, and interlaminar shear, all of which were shown to correlate, to different degrees, with the fiber–matrix interface adhesion and the bulk matrix properties. The in‐plane and interlaminar properties, in general, increased with a decreasing cooling rate, which was attributed to changes in the failure mechanism from adhesive failure involving fiber–matrix interface debonding at high cooling rates to matrix‐dominant cohesive failure at low cooling rates. The present study demonstrates that the mechanical properties of semicrystalline thermoplastic composites can be tailored for desired applications by controlling the processing conditions, especially the cooling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1155–1167, 2002; DOI 10.1002/app.10406     

Hyperbranched-polysiloxane-based hyperbranched polyimide films with low dielectric permittivity and high mechanical and thermal properties

A series of hyperbranched polysiloxane (HBPSi)-based hyperbranched polyimide (HBPI) films with low dielectric permittivity and multiple branched structures are fabricated by copolymerizing 2,4,6-triaminopyrimidine (TAP) with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 4,4′-diaminodiphenyl ether, and HBPSi via the two-step polymerization method. The dielectric permittivity of HBPSi hyperbranched polyimide films decreases with increasing TAP fraction, namely, from 3.28 for sample PI-1 to 2.80 for PI-4, mainly owing to the enlarged free volume created by the incorporation of multiple branched structures. Moreover, HBPSi HBPI possesses desirable solubility and good mechanical properties and thermal stability. PI-4 not only has low dielectric permittivity (2.80, 1 MHz), excellent solubility (soluble in several common organic solvents), and remarkable thermal properties (glass-transition temperature of 273 °C, 5% weight loss temperature of 498 °C in N₂ and 486 °C in O₂), but it also demonstrates admirable mechanical properties with a tensile strength of 103 MPa, elongation at break of 7.3%, and a tensile modulus of 2.16 GPa. HBPSi HBPI might have potential applications in interlayer dielectrics and other microelectronics fields. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47771.     

Polyethylene/silica nanorod composites with reduced dielectric constant and enhanced mechanical strength

Reinforcement of materials with low dielectric constant by nanofillers has attained more and more attention. Conventional 1D nanofillers, such as carbon nanotubes, significantly enhance mechanical properties of polymers; however, they do not reduce dielectric constant. In this study, silica nanorods (SNR) were used to prepare polyethylene composites by mechanical blending followed by hot pressing. It was found that the incorporation of SNRs enables enhancement of strength and elastic modulus. Dielectric constant did not increase as predicted when SNRs were incorporated into polyethylene (PE); on contrary, it considerably decreased from ~2.4 to around ~2.2 at SNR loading of 5 wt %. However, when glass fibers were used as fillers, we did not observe such decrease. SEM image and density measurement indicated that the composites were compact with very low porosity. We believe that the incorporation of SNRs alters crystalline and chain arrangement of PE, thus reduces the polarization and dielectric constant. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47143.     

Silacyclobutane-functionalized cyclosiloxanes as photoactive precursors for high thermal stability,low dielectric constant and low dielectric loss polymers

Low dielectric photoactive materials have significant potential as components in future microelectronics. Although a number of photosensitive groups have been used to construct photopatternable materials, it remains challenging to introduce these groups into polymer chains via facile yet controlled polymerization techniques. The present work demonstrates the synthesis of a new class of photoactive cyclosiloxane monomers having hybrid siloxane-carbosilane main chains. These compounds can be cured by applying ultraviolet radiation and heat to promote the reaction of the silacyclobutene units and form hyper-cross-linked cyclosiloxanes. The cured resins show high thermal stability (with T_5% values in the range of 460–550°C), low dielectric constants (2.36–2.76 at 10 MHz) and low dielectric losses (10⁻³ at 10 MHz). Thus, these polymers could possibly be used as high-performance dielectric materials.     

Influences of porous reduction graphene oxide/molybdenum disulfide as filler on dielectric properties,thermal stability,and mechanical properties of natural rubber

A ternary composite system consisting of natural rubber (NR), porous reduced graphene oxide (rPGO), and molybdenum disulfide (MoS₂) was introduced for applying in the dielectric field, of which rPGO and MoS₂ hybrid conductive filler (rPGM) was prepared by an effective and environmentally friendly method-microwave reduction. And the well-dispersed NR composites (NGM) were made by the latex co-precipitation method. Due to the large specific surface area of rPGM itself and the synergistic dispersion of rPGO and MoS₂, it formed many stable interface structures with the NR matrix, which not only made the blend exhibit high elasticity and withstood large deformation as NR but also greatly improved the dielectric, mechanical and thermal stability of the NR matrix. Compared with neat NR, the dielectric constant of nanocomposite increased by 11 times in the presence of rPGM conductive filler, and the leakage current generated by direct contact of fillers was reduced due to the attachment of MoS₂ to the surface of rPGO; when 2% rPGM was added, the NR exhibited the highest tensile strength (21.3 MPa), elongation at break (495%), and abrasion resistance (0.165 cm⁻³); in addition, the thermal stability of the nanocomposite was also improved. These phenomena indicate that rPGM had great potential in conductive fillers and provided a reliable way for NR applications in the field of dielectric elastomers.     

Mechanical,dielectric, and thermal properties of fluorosilicone rubber composites filled with silica/multiwall carbon nanotube hybrid fillers

In this work, hybrid fillers consist of modified silica (SiO₂) and multiwalled carbon nanotube (MWCNT) were used to improve the mechanical, dielectric, and thermal properties of fluorosilicone (FSR) composites via a direct mechanical mixing method. With the increase of CNT loading in SiO₂/CNT hybrid loading ratio, the tensile properties, dielectric constant, electrical conductivity, and thermal properties all increase without a sharp sacrifice of flexibility. The dielectric constant of FSR-S15/C5 achieved 7,370 @1 kHz, which is about four orders of the FSR-S20, and the dielectric loss remains as low as 0.676 @1 kHz. Therefore, the linkage of SiO₂ and FSR chains not only enhances the interfacial interaction between the fillers and FSR matrix but also decreases the agglomeration of the fillers in matrix. What is more, modified SiO₂ and CNT were designed as the effective hybrid filler to improve the performance of the polymeric matrix through synergic effect.     

Effects of different compatilizers on mechanical,crystallization and thermal properties of polypropylene/magensium oxysulfate whisker composites

Two kinds of compatilizers, maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and maleic anhydride grafted polypropylene (PP-g-MAH), were incorporated into a polypropylene/magnesium oxysulfate whisker (PP/MOSw) composite. Scanning electron microscopy pictures presented a clear interface between MOSw and the PP matrix in the PP/MOSw composite, while vague interfaces appeared in the PP/iPOE-g-MAH/5MOSw and PP/iPP-g-MAH/5MOSw composites. Dynamic mechanical thermal analysis results indicated that PP-g-MAH was highly compatible with the PP matrix while POE-g-MAH was not. Impact strength results showed that POE-g-MAH had a superior toughening effect on PP/MOSw composites, since the proper interfacial interaction and appearance of β-crystal PP. However, incorporating PP-g-MAH seemed to be conducive to increasing strength and modulus (both for tensile and flexural tests), as evidenced by the greatly raised interfacial adhesion between the PP matrix and MOSw. Quantitative characterization carried out by Turcsányi equation for ternary composites also confirmed that PP-g-MAH efficiently enhanced interfacial interaction, by the proof of higher B values. Therefore, the thermal stability of PP-g-MAH treated composites was far superior to that of PP/iPOE-g-MAH/5MOSw composites. Differential scanning calorimetery and polarized light microscopy results showed that POE-g-MAH promoted PP nucleation, with effects further enhanced with the presence of PP-g-MAH.     

Multifunctional epoxy resin/polyacrylonitrile‐lithium trifluoromethanesulfonate composites films with very high transparency,high dielectric permittivity,breakdown strength and mechanical properties

Multifunctional transparent composite films with high dielectric permittivity (high‐k), breakdown strength, and mechanical properties are urgently required by cutting‐edge fields. Herein, novel multifunctional films were facilely prepared through building unique cross‐linked structure based on epoxy resin (EP) and polyacrylonitrile (PAN)‐lithium trifluoromethane sulfonate (LiTf) complex. Compared with high‐k materials reported previously, EP/(PAN‐LiTf) films simultaneously show very high transparency, good flexibility, high tensile, and breakdown strengths. For 0.22EP/(PAN‐LiTf) film with 22 wt % EP, its average transmittance and elongation at break are as high as 91% (600–800 nm) and 12.7%, respectively; moreover, its dielectric permittivity, AC breakdown strength and the maximum energy density are severally about 4.9, 1.8, and 15.2 times of those of EP resin, completely overcoming the sticky problems in conductor/polymer composites. The origin behind these attractive properties is intensively discussed, and believed to be attributed to the unique structure of EP/(PAN‐LiTf) films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45218.     

Epoxy/benzoxazinyl POSS nanocomposite resin with low dielectric constant and excellent thermal stability

Benzoxazinyl modified polyhedral oligomeric silsesquioxane (BZPOSS) is successfully synthesized and used to prepare nanocomposites with bisphenol A type epoxy resin (E51). The differential scanning calorimetry results showed the curing peak temperature of E51/BZPOSS blend decrease to 242°C, suggesting the high catalytic activity of BZPOSS to the polymerization of E51. The scanning electron microscope micrographs of poly(E51/BZPOSS)s and silicon element distribution maps given by EDS both demonstrated homogeneous dispersion of BZPOSS. Dielectric properties tests confirmed the dielectric constant can be reduced by the introduction of BZPOSS, which is attributed to the nano-pores from the cage structure of POSS. When 20 wt% BZPOSS was added, the dielectric constant decreased to 2.28 at 1 MHz. Meanwhile, DMA and TGA results indicated the thermal stability and heat resistance of poly(E51/BZPOSS)s at high temperature increased with the increase of BZPOSS, which is due to the increase of the crosslinking density and the change of crosslinking structure of copolymer.     

Mechanical,thermal, and dielectric properties of SiCf/SiC composites reinforced with electrospun SiC fibers by PIP

Electrospun unidirectional SiC fibers reinforced SiC_f/SiC composites (e-SiC_f/SiC) were prepared with ∼10% volume fraction by polymer infiltration and pyrolysis (PIP) process. Pyrolysis temperature was varied to investigate the changes in microstructures, mechanical, thermal, and dielectric properties of e-SiC_f/SiC composites. The composites prepared at 1100 °C exhibit the highest flexural strength of 286.0 ± 33.9 MPa, then reduced at 1300 °C, mainly due to the degradation of electrospun SiC fibers, increased porosity, and reaction-controlled interfacial bonding. The thermal conductivity of e-SiC_f/SiC prepared at 1300 °C reached 2.663 W/(m∙K). The dielectric properties of e-SiC_f/SiC composites were also investigated and the complex permittivities increase with raising pyrolysis temperature. The e-SiC_f/SiC composites prepared at 1300 °C exhibited EMI shielding effectiveness exceeding 24 dB over the whole X band. The electrospun SiC fibers reinforced SiC_f/SiC composites can serve as a potential material for structural components and EMI shielding applications in the future.     

Effect of nano aluminum nitride filler on mechanical,thermal, and dielectric properties of the glass/mullite composites for low-temperature co-fired ceramic applications

Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low-temperature co-fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X-ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co-fired ceramics products.     

X‐ray irradiated LDPE/PP blends with high mechanical and dielectric performance

In this study, the influences of polypropylene (PP) additive (varying from 20% to 80% wt) and low dose X‐ray irradiation (changing from 25 to 100 Gy) on the mechanical and dielectric properties of low‐density polyethylene (LDPE) were investigated. LDPE/PP film blends were prepared by hot press technique. While the highest Young modulus and tensile strength were observed for the 20%LDPE/80%PP blend at 25 Gy X‐ray irradiation, the same blend had the highest energy at break and percentage strain at break values for 50 Gy X‐ray exposure. These results also indicated a chain scission in the material. The differential scanning calorimetry curves also indicated a chain scission and crosslinking effects in the blends due to X‐ray irradiation. Hence, the higher concentration of PP additive and exposure of low dose X‐ray resulted in a polymer composite with high mechanical performance. On the other hand, the dielectric investigations revealed that the 25 Gy X‐ray irradiated 20%LDPE/80%PP blend may also attract attention for capacitor applications due to its increased static dielectric constant and reduced dielectric loss. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46571.     

Mechanical and thermal properties of polypropylene/sugarcane Bagasse composites

To determine the possibility of using sugarcane bagasse (SCB) waste as reinforcing filler in the thermoplastic polymer matrix, SCB‐reinforced polypropylene (PP) composites were prepared. The PP and SCB composites were prepared by the extrusion of PP resin with 5, 10, 15, and 20 wt % of SCB filler in a corotating twin screw extruder. The extruded strands were cut into pellets and injection molded to make test specimens. These specimens were tested for physicomechanical properties such as tensile, flexural, Izod, and Charpy impact strengths, density, water absorption, and thermal characteristics, namely, heat deflection temperature (HDT), melt flow index, and thermogravimetric analysis. It was found that the flexural strength increased from 23.66 to 26.84 MPa, Izod impact strength increased from 10.499 to 13.23 Kg cm/cm, Charpy impact strength increased from 10.096 to 13.98 Kg cm/cm, and HDT increased from 45.5 to 66.5°C, with increase in filler loading from 5 to 20% in the PP matrix. However, the tensile strength and elongation decreased from 32.22 to 27.21 MPa and 164.4 to 11.20% respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3827–3832, 2007     

Thermal,dielectric, and mechanical properties of SiC particles filled linear low‐density polyethylene composites

A thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm^?1 K^?1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<10² Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High‐performance hyperbranched poly(phenylene oxide) modified bismaleimide resin with high thermal stability,low dielectric constant and loss

High‐performance hyperbranched poly(phenylene oxide)‐modified bismaleimide resin with high thermal stability, low dielectric constant, and loss was developed, which is made up of hyperbranched poly(phenylene oxide) (HBPPO), 4,4′‐bismaleimidodiphenylmethane (BDM), and o, o′‐diallylbisphenol A (DBA). The curing reactivity, morphology, and performance of BDM/DBA/HBPPO resin were systemically investigated, and similar investigations for BDM/DBA resin were also carried out for comparison. Results show that BDM/DBA/HBPPO and BDM/DBA resins have similar curing mechanism, but the former can be cured at lower temperature than the later; in addition, cured BDM/DBA/HBPPO resin with suitable HBPPO content has better thermal stability and dielectric properties (lower dielectric constant and loss) than BDM/DBA resin. The difference in macroproperties between BDM/DBA/HBPPO and BDM/DBA resins results from the different chemical structures and morphologies of their crosslinking networks. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

双隔离结构聚乙烯/石墨烯导热复合材料的研究

采用聚二烯丙基二甲基氯化铵改性石墨烯纳米片、聚苯乙烯磺酸钠改性聚乙烯颗粒,通过静电诱导自组装和热压成型工艺制备了具有蜂窝状石墨烯框架的聚乙烯复合材料(N?PE?HD/P?GNPs).利用红外光谱仪、扫描电子显微镜、导热系数测试仪、电子拉力试验机对复合材料的改性状态、微观形貌、导热性能和力学性能等进行分析表征.结果表明,...     

Effect of tensile rates on thermal and mechanical properties of porous PTFE composites

To achieve polymer-matrix composites for sealing materials with thermostability and toughness, PTFE composites filled with short glass fibers (SGFs) were hyperthermal stretched to prepare a substrate material with high thermal stability and porosity. The effects of various tensile rates on the thermal and mechanical properties and morphologies were investigated. The results revealed that the thermal stability could be improved slightly and the thermal expansion coefficient of composites increased by the tensile rate. Through observing the morphologies, tensile process produced cavities and the increased tensile rate had negligible effects on porosity, which also could be proved by density test. From mechanical properties analysis, stretched composites exhibited that the tensile strength increases first and then decreases with the increased tensile rate. Although the variation tendency of Young's modulus is similar to that of tensile strength, which is smaller than that of unstretched composite. When the tensile rate reached 50 mm·min⁻¹, the tensile strength and Young's modulus of the stretched composites increased by 65 and 9% to maximum, respectively. Meanwhile, elongation at break and shore hardness decreased. The thermal and mechanical properties improvement could be ascribed to the strain-induced crystallization and crystal alignment. In addition, the interplanar spacing and grain size were inversely proportional to the tensile rate. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48175.     

Synthesis,characterization and dielectric properties of nickel-based polyoxometalate/polyurethane composites

The aim of this study was to synthesis, characterization and investigation of the influence of the polyoxometalate concentrations (1, 3, 5 and 10 wt%) on chemical, thermal, physical and morphological properties of nickel-based polyoxometalate/polyurethane composite (Ni-POM/PU) materials. Firstly, nickel-based polyoxometalate (Ni-POM) compound has been synthesized and characterized through various spectroscopic techniques. Synthesized Ni-POM compounds have been used for preparation of polyurethane composites as a reinforcement. Three different Ni-POM/PU composites containing Ni-POM were prepared by solution mixing and casting techniques. The chemical structure and morphology of prepared Ni-POM/PU composite samples were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis and SEM techniques. Effects of Ni-POM on thermal stability, glass transition temperature, optical transparency, hydrophilicity and physical properties of polyurethane composites were examined. Thermal stabilities and glass temperatures of the materials have been checked by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The SEM results confirmed the highly porous structure and the formation of Ni-POM structures in the polymer matrix. Synthesized composites showed high chemical stability, good processability, and low Tg values. The dielectric properties of the prepared Ni-POM/polyurethane composites were also investigated at room temperature. These results displayed that the dielectric constant of the POM/polyurethane composites decreased with the increase of the Ni-POM content in polymeric matrix.     

Study on properties of low dielectric loss resin matrix

Allyl phenyl compounds, allyl epoxy resins, and epoxy acrylate resins are adapted to copolymerize with bismaleimide (BMI) resins and to modify mechanical properties and processing properties. Reaction activity, physical properties, mechanical properties, dielectric properties, and thermal stability were investigated. Impact strength and flexural strength of modified BMI resin are increased about twice and 42% than that of pure BMI resin, respectively. Fracture elongation is from 1.6 to 2.3%. The fracture surfaces of the broken specimens are examined by scanning electron microscopy (SEM). As a result, modified BMI resins put up typical toughness rupture. The modified BMI resins possess excellent dielectric properties, and dielectric constant and dielectric loss almost hold the line with increasing epoxy concentration. When the test frequency scope is from 1 to 20 GHz, the dielectric constant and dielectric loss of modified BMI resins is 3.05–3.12 and 0.0089–0.012, respectively. The modified BMI resins still possess fine properties after hydrothermal aging. After 100 h in boiling water, the reservation ratios of both the impact strength and flexural strength of modified system exceeded 90%, and the water absorption and heat distortion temperature (HDT) is 2.6% and 235°C, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 315–319, 2006