A co-training style semi-supervised artificial neural network modeling and its application in thermal conductivity prediction of polymeric composites filled with BN sheets

Predicting the thermal conductivity of polymeric composites filled with BN sheets is helpful for fabricating ther-mal management material.In this study,a co-training style semi-supervised artificial neural network model(Co-ANN)was proposed to take advantage of unlabeled data to refine the prediction.The thermal conductivity of polymer matrix,the diameter,aspect ratio,and volume fraction of the BN sheets are considered as the input variables of the thermal conduction model.Two artificial neural network(ANN)learners with different archi-tecture will label the unlabeled examples.Through estimating the labeling confidence from the mathematical influence and thermal conductive behavior,the most confidently labeled example will be used to augment the training dataset.The lower limit of the labeling confidence is introduced to reduce the data noise.After learn-ing the augmented training information,a combination of two ANN regressors will construct the final Co-ANN thermal conduction model.Compared to other models,the newly developed Co-ANN thermal conduction model remarkably improves the thermal conductivity prediction and exhibits the best accuracy and generalization per-formance.The proposed method shows a vast potential in thermal conductive material design.

Supposition of graphene stacks to estimate the contact resistance and conductivity of nanocomposites

In this study,the effects of stacked nanosheets and the surrounding interphase zone on the resistance of the contact region between nanosheets and the tunneling conductivity of samples are evaluated with developed equations superior to those previously reported.The contact resistance and nanocomposite conductivity are modeled by several influencing factors,including stack properties,interphase depth,tunneling size,and contact diameter.The developed model's accuracy is verified through numerous experimental measurements.To further validate the models and establish correlations between parameters,the effects of all the variables on contact resistance and nanocomposite conductivity are analyzed.Notably,the contact resistance is primarily dependent on the polymer tunnel resistivity,contact area,and tunneling size.The dimensions of the graphene nanosheets significantly influence the conductivity,which ranges from 0 S/m to90 S/m.An increased number of nanosheets in stacks and a larger gap between them enhance the nanocomposite's conductivity.Furthermore,the thicker interphase and smaller tunneling size can lead to higher sample conductivity due to their optimistic effects on the percolation threshold and network efficacy.

Highly Elastic,Bioresorbable Polymeric Materials for Stretchable,Transient Electronic Systems

Substrates or encapsulants in soft and stretchable formats are key components for transient,bioresorbable electronic systems;however,elastomeric polymers with desired mechanical and biochemical properties are very limited compared to nontransient counterparts.Here,we introduce a bioresorbable elastomer,poly(glycolide-co-ε-caprolactone)(PGCL),that contains excellent material properties including high elongation-at-break(<1300%),resilience and toughness,and tunable dissolution behaviors.Exploitation of PGCLs as polymer matrices,in combination with conducing polymers,yields stretchable,conductive composites for degradable interconnects,sensors,and actuators,which can reliably function under external strains.Integration of device components with wireless modules demonstrates elastic,transient electronic suture system with on-demand drug delivery for rapid recovery of postsurgical wounds in soft,time-dynamic tissues.

Influence of UVB-Irradiation on the Structures and Solid Particle Erosion Resistance for CF/PC Composites

The service life and properties of Carbon fiber reinforced polycarbonate (CF/PC) composites are seriously affected by ultraviolet radiation from outdoor exposure during aging. In this work, the changes of structure and solid particle erosion resistance for CF/PC composites after ultraviolet irradiation were studied. It was shown that ultraviolet irradiation causes photo-oxygen aging and photo-fries re-arrangement of the composite, and the result was confirmed by FTIR. We correlated the solid particle erosion resistance with aging time, and found that the solid particle erosion resistance of CF/PC composites greatly decreased by UVB irradiation during 15 hours. Furthermore, the eroded material surface was analyzed using scanning electron microscope (SEM). It suggests that ultraviolet aging leads to plasticization and degradation, resulting in reduction of erosion resistance of the composite.

A Perspective for Developing Polymer-Based Electromagnetic Interference Shielding Composites

The rapid development of aerospace weapons and equipment,wireless base stations and 5G communication technologies has put forward newer and higher requirements for the comprehensive performances of polymer-based electromagnetic interference(EMI)shielding composites.However,most of currently prepared polymer-based EMI shielding composites are still difficult to combine high performance and multi-functionality.In response to this,based on the research works of relevant researchers as well as our research group,three possible directions to break through the above bottlenecks are proposed,including construction of efficient conductive networks,optimization of multi-interfaces for lightweight and multifunction compatibility design.The future development trends in three directions are prospected,and it is hoped to provide certain theoretical basis and technical guidance for the preparation,research and development of polymer-based EMI shielding composites.

Breaking Through Bottlenecks for Thermally Conductive Polymer Composites:A Perspective for Intrinsic Thermal Conductivity,Interfacial Thermal Resistance and Theoretics

Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.

Structural Design Strategies of Polymer Matrix Composites for Electromagnetic Interference Shielding:A Review

With the widespread application of electronic communication technology,the resulting electromagnetic radiation pollution has been significantly increased.Metal matrix electromagnetic interference(EMI)shielding materials have disadvantages such as high density,easy corrosion,difficult processing and high price,etc.Polymer matrix EMI shielding composites possess light weight,corrosion resistance and easy processing.However,the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance.This review firstly discusses the key concept,loss mechanism and test method of EMI shielding.Then the current development status of EMI shielding materials is summarized,and the research progress of polymer matrix EMI shielding composites with different structures is illustrated,especially for their preparation methods and evaluation.Finally,the corresponding key scientific and technical problems are proposed,and their development trend is also prospected.

Thermal conductivity model of filled polymer composites

Theoretical and empirical models for predicting the thermal conductivity of polymer composites were summarized since the 1920s.The effects of particle shape,filler amount,dispersion state of fillers,and interfacial thermal barrier on the thermal conductivity of filled polymer composites were investigated,and the agreement of experimental data with theoretical models in literatures was discussed.Silica with high thermal conductivity was chosen to mix with polyvinyl-acetate （EVA） copolymer to prepare SiO2/EVA co-films.Experimental data of the co-films＇ thermal conductivity were compared with some classical theoretical and empirical models.The results show that Agari＇s model,the mixed model,and the percolation model can predict well the thermal conductivity of SiO2/EVA co-films.

Highly Thermally Conductive Polymer/Graphene Composites with Rapid Room‑Temperature Self‑Healing Capacity

Composites that can rapidly self-healing their structure and function at room temperature have broad application prospects.However,in view of the complexity of composite structure and composition,its self-heal is facing challenges.In this article,supramolecular effect is proposed to repair the multistage structure,mechanical and thermal properties of composite materials.A stiff and tough supramolecular frameworks of 2-[[(butylamino)carbonyl]oxy]ethyl ester(PBA)–polydimethylsiloxane(PDMS)were established using a chain extender with double amide bonds in a side chain to extend prepolymers through copolymerization.Then,by introducing the copolymer into a folded graphene film(FGf),a highly thermally conductive composite of PBA–PDMS/FGf with self-healing capacity was fabricated.The ratio of crosslinking and hydrogen bonding was optimized to ensure that PBA–PDMS could completely self-heal at room temperature in 10 min.Additionally,PBA–PDMS/FGf exhibits a high tensile strength of 2.23±0.15 MPa at break and high thermal conductivity of 13±0.2 W m^(−1)K^(−1);of which the self-healing efficiencies were 100%and 98.65%at room temperature for tensile strength and thermal conductivity,respectively.The excellent self-healing performance comes from the efficient supramolecular interaction between polymer molecules,as well as polymer molecule and graphene.This kind of thermal conductive self-healing composite has important application prospects in the heat dissipation field of next generation electronic devices in the future.

Photoconductive Properties of MEH-PPV/CuS-Nanoparticle Composites

Photoconductive properties of photodiodes based on composites of CuS nanoparticles and Poly[2-methoxy,5- （2＇-ethylhexyloxy）-p-phenylenevlnylene] （MEH-PPV） are investigated. By comparing composite devices with different MEH-PPV：CuS weight ratios of l：l （D2-1）, 1：1.25 （D2-2）, 1：2.5 （132-3） and 1：5 （D2-4）, it is found that the device D2 3 exhibited the best performance： the short-circuit current density of 17μA/cm^2 with the light intensity of 16.7mW/cm^2, the highest open-circuit voltage of 0,83 V, and the photosensitivity of 132 at reverse bias of - 1 V. The photosensitivity is improved by a factor of 5 compared with the undoped MEH-PPV device.

Preliminary Study on Tensile and Impact Properties of Kenaf/Bamboo Fiber Reinforced Epoxy Composites

The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.

Highly Flexible Fabrics/Epoxy Composites with Hybrid Carbon Nanofillers for Absorption-Dominated Electromagnetic Interference Shielding

Epoxy-based nano-composites can be ideal electromagnetic interference(EMI)-shielding materials owing to their lightness,chemical inertness,and mechanical durability.However,poor conductivity and brittleness of the epoxy resin are challenges for fast-growing portable and flexible EMI-shielding applications,such as smart wristband,medical cloth,aerospace,and military equipment.In this study,we explored hybrid nanofillers of single-walled carbon nanotubes(SWCNT)/reduced graphene oxide(rGO)as conductive inks and polyester fabrics(PFs)as a substrate for flexible EMI-shielding composites.The highest electrical conductivity and fracture toughness of the SWCNT/rGO/PF/epoxy composites were 30.2 S m^(−1)and 38.5 MPa m^(1/2),which are~270 and 65%enhancement over those of the composites without SWCNTs,respectively.Excellent mechanical durability was demonstrated by stable electrical conductivity retention during 1000 cycles of bending test.An EMI-shielding effectiveness of~41 dB in the X-band frequency of 8.2-12.4 GHz with a thickness of 0.6 mm was obtained with an EM absorption-dominant behavior over a 0.7 absorption coefficient.These results are attributed to the hierarchical architecture of the macroscale PF skeleton and nanoscale SWCNT/rGO networks,leading to superior EMI-shielding performance.We believe that this approach provides highly flexible and robust EMI-shielding composites for next-generation wearable electronic devices.

A comprehensive review on material selection for polymer matrix composites subjected to impact load

Polymer matrix composites(PMC)are extensively been used in many engineering applications.Various natural fibers have emerged as potential replacements to synthetic fibers as reinforcing materials composites owing to their fairly better mechanical properties,low cost,environment friendliness and biodegradability.Selection of appropriate constituents of composites for a particular application is a tedious task for a designer/engineer.Impact loading has emerged as the serious threat for the composites used in structural or secondary structural application and demands the usage of appropriate fiber and matrix combination to enhance the energy absorption and mitigate the failure.The objective of the present review is to explore the composite with various fiber and matrix combination used for impact applications,identify the gap in the literature and suggest the potential naturally available fiber and matrix combination of composites for future work in the field of impact loading.The novelty of the present study lies in exploring the combination of naturally available fiber and matrix combination which can help in better energy absorption and mitigate the failure when subjected to impact loading.In addition,the application of multi attributes decision making(MADM)tools is demonstrated for selection of fiber and matrix materials which can serve as a benchmark study for the researchers in future.

Dynamic Mechanical Behavior of a Novel Polymeric Composite Damping Material

The dynamic mechanical behavior of a novel polymeric composite damping material has been investigated in this article. The composite consists of chlorinated polyethylene （CPE）, N,N-dicyclohexyl-2-benzothiazolylsufenamide （DZ）, 4,4＇-thio-bis（3-methyl-6-tert-buthylphenol） （BPSR） and vapor-grown carbon fiber （VGCF）. It is found that either the position or the intensity of damping peak can be controlled by changing the composition of CPE/DZ/BPSR composite. Within a certain composition region, damping peak maximum depends on CPE/DZ ratio, whereas damping peak position is controlled by BPSR content. Moreover, the improvement of storage modulus can be achieved by incorporation of VGCF. These results may imply that a damping material possessing both good damping properties and high strength can be designed and obtained.

Tailoring polymeric composite gel beads-encapsulated microorganism for efficient degradation of phenolic compounds

Phenol and its derivatives are highly toxic pollutants in industrial wastewater for the ecological environments,so there is essential attention to develop effective means of removing these harmful substances from water.In this work,the microorganism was immobilized into polymeric composite gel beads prepared by the effective recombination of natural abundant chitosan(CS)and industrial polyvinyl alcohol(PVA)for treating phenolic compounds.The degradation rate of 99.5%can be achieved to treat 100 mg·L^(1)of phenol at 30℃using the fresh resultant immobilized microorganism,where only 21.1%degradation rate was obtained by the free microorganism under the identical conditions.The recycling experiments of repeated 90 times to treat 100 mg·L^(1)of phenol displayed that the degradation rate of phenol was stable to 99%with the appearance of beads unchanged significantly,indicating the immobilized microorganism possessed excellent operating stability.Moreover,while the phenol derivatives of 100 mg·L^(1)were treated catalytically including pmethylphenol,catechol,and oaminophenol for 24 h by the immobilized microorganism,the degradation rates were all above 95%.The immobilized microorganism into PVACS polymeric composite with excellent operating stability and degradation activity would provide a feasible solution for treating phenolic compounds in water in industrial applications.

Performance study of jute-epoxy composites/sandwiches under normal ballistic impact

This study is undertaken to explore the use of natural fiber Jute-epoxy(JE),Jute-epoxy-rubber(JRE)sandwich composite for ballistic energy absorption.Energy absorbed and residual velocities for these composites are evaluated analytically and through Finite Element Analysis(FEA).FE analysis of JE plates is carried out for different thicknesses(3,5,10 and 15 mm).JE plates and JRE sandwiches having the same thickness(15 mm) are fabricated and tested to measure residual velocity and energy absorbed.The analytical results are found to agree well with the results of FE analysis with a maximum error of 9%.The study on JE composite plate reveals that thickness influences the energy absorption.Experimental and FE analysis study showed that JRE sandwiches have better energy absorption than JE plates.Energy absorption of a JRE sandwich is about 71% greater than JE plates.Damages obtained from FEA and testing are in good agreement,SEM analysis confirms composites failed by fiber rupture and fragmentation.

Effective viscoelastic behavior of particulate polymer composites at finite concentration

Polymeric materials usually present some viscoelastic behavior. To improve the mechanical behavior of these materials, ceramics materials are often filled into the polymeric materials in form of fiber or particle. A micromechanical model was proposed to estimate the overall viscoelastic behavior for particulate polymer composites, especially for high volume concentration of filled particles. The method is based on Laplace transform technique and an elastic model including two-particle interaction. The effective creep compliance and the stress and strain relation at a constant loading rate are analyzed. The results show that the proposed method predicts a significant stiffer response than those based on Mori-Tanaka＇s method at high volume concentration of particles.

A Novel Method for Preparing Polyurethane Based Conductive Composites with Low Percolation Threshold

A novel method for preparing conductive carbon black fllled polymer composites with low percolation threshold from polyurethane emulsion are reported in this paper. The experimental results indicate that with a rise in carbon black concentration the insulator-conductor transition in the emulsion blended composites occurs at 0.8-1.4vol%. In contrast, the solution blended composites exhibit drastic increase in conductivity at conducting filler fraction as high as 12.3-13.3vol%. It is demonstrated that the composites microstructure rather than chemical structure of the matrix polymer predominantly determines the electrical conduction performance of the composites.

Ceramification of Composites of MgO-Al_(2)O_(3)-SiO_(2)/Boron Phenolic Resin with Different Calcine Time

The ceramifiable polymer composite of MgO-Al_(2)O_(3)-SiO_(2)/boron phenolic resin(MAS/BPF)with 40wt%of inorganic fillers was calcined at 1200℃for different time to promote ceramification of ceramifiable composite and improve heat resistance.The effects of different calcine time on the macroscopical morphology,mass loss,phase evolution,microstructure and chemical bond evolution of MAS/BPF composites were characterized by XRD,XPS,and SEM analyses.The experimental results reveal that the increase of calcine time result in the fewer holes,relatively denser and smoother top layer of MAS/BPF composites and protect the interior from deeper decomposition.The final residues of composites are amorphous carbon and C-O-Si-Al-Mg ceramic.And MAS/BPF composites show excellent mass stability,low shrinkage and self-supporting features after 2 h holding compared with BPF composites without 40wt%of inorganic fillers.

Production and characterisation of new bioresorbable radiopaque Mg–Zn–Y alloy to improve X-ray visibility of polymeric scaffolds

For the medical diagnosis,radiopaque materials(RM)made from high specific gravity elements like Pt,Au,Ta,Iodine,Bromine are either attached or blended or coated on an implant to makes it detectable under X-ray/Fluoroscopy/CT-Scan.RM facilitate the surgeon in an operation theatre to position an implant during the surgery.Mainly,RM are non-degradable,thus in case of biodegradable implants,it may detach from the body and accumulate in vital organ cause serious health issue.Therefore,a new bioresorbable radiopaque material(BRM)was produced by alloying the high specific gravity elements Zn(35%w/w)and Y(4%w/w)with Mg metal.In this alloy,three main phases were identified,alpha Mg,Mg_(7)Zn_(3)and icosahedral quasicrystalline I-phase Mg3Zn6Y,which reinforce the Mg matrix.Hereafter,BRM was powdered to a size of less than 25 microns and blended in different ratios with bioresorbable poly-L-lactic acid(PLLA)for fabricating PLLA/BRM bio-composite.BRM microparticles were uniformly distributed and interfacial bonded with the matrix.The X-ray was passed through bio-composite to captureμCT radiograph for evaluating linear attenuation co-efficient(μ)and optical density(OD).Thermal analysis reveals that BRM particles act as a nucleating site and enhance the crystallinity of the polymeric chain.During the In Vitro accelerated degradation study,the alkaline nature of BRM neutralise the acidity of PLLA and balance the pH of the body fluid to reduce the inflammatory reactions,but this compromises the stability of the polymer as it increases the decomposition rate.