Dr. D. Jiang, Y. Wang, Prof. B. Li, Prof. C. Sun, S. Qi College of Science Northeast Forestry University Harbin 150040, P. R. China E-mail: libinzh62@163.com Prof. B. Li Post-Doctoral Mobile Research Station of Forestry Engineering Northeast Forestry University Harbin 150040, P. R. China Dr. Z. Wu Key Laboratory of Engineering Dielectrics and Its Application Ministry of Education Harbin University of Science and Technology Harbin 150040, P. R. China E-mail: zijian.wu@hrbust.edu.cn Prof. H. Yan School of Mechatronics Engineering Harbin Institute of Technology Harbin 150001, P. R. China Dr. L. Xing MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage School of Chemistry and Chemical Engineering Harbin Institute of Technology Harbin 150001, P. R. China Prof. Y. Li College of Materials Science and Engineering North University of China Taiyuan 030051, P. R. China

Flexible Sandwich Structural Strain Sensor Based on Silver Nanowires Decorated with Self-Healing Substrate

Nowadays, plastic products are closely related to human life. While it brings convenience to human beings, there are also great health and environmental threats. Most of the plastic products are polymer compounds obtained by addition polymerization or condensation polymerization. It will cause chronic poisoning to humans if long-term use plastic products are used. In addition, due to the relatively low production cost and short service life of plastic products, a large amount of waste plastics is discarded every year, which causes serious environmental problems. Traditional disposal technologies such as landfill and incineration not only waste a lot of resources but also accompany serious secondary pollution problems. In order to meet the needs of sustainable development and green environmental protection, various recycling methods have been explored for waste plastics, which have been used to develop economic and environmentally friendly value-added products. This paper reviews a range of management methods for the increasingly severe problem of discarded plastics and briefly summarizes the advantages and disadvantages of some methods, lists some examples of more valuable recycled products and materials, and finally puts forward the improvement direction and challenge to solve this problem.

Research progress for plastic waste management and manufacture of value-added products

In this study, we used the Takayanagi model expanded by Loos and Manas-Zloczower for the tensile modulus to assess the tensile strength of polymer/carbon nanotube nanocomposites (PCNTs).
 The new model assumes the strengthening and percolating efficiencies of the interphase between the polymer matrix and the nanoparticles. We evaluated the suggested model with the experimental data of two PCNTs and found that this model successfully calculated the average levels of the percolation threshold, interphase thickness (t), and interphase strength (σiN). The percolation threshold > 0.004, interphase volume fraction   30 nm caused the lowest relative tensile strength, less than the strength of the polymer matrix. Among the studied variables, the t and σiN parameters most significantly affected the tensile strength of PCNTs; when t = 25 nm and σiN = 17 GPa, there was 1300% improvement in the strength of the PCNT. This model can be applied in future studies to accelerate the material design process.

Evaluation of the Tensile Strength in Carbon Nanotube-Reinforced Nanocomposites Using the Expanded Takayanagi Model

Viscoelastic nature of polymers makes their properties strongly dependent on temperature and strain rate. Characterization of material properties over a wide range of strain rates and temperatures requires an expensive and time consuming experimental campaign. While viscoelastic properties of materials are widely tested using dynamic mechanical analysis (DMA) method, the frequency dependent component of the measured properties is underutilized due to a lack of correlation between frequency, temperature, and strain rate. The present work develops a method that can extract elastic modulus over a range of strain rates and temperatures from the DMA data for nanocomposites. Carbon nanofiber (CNF) reinforced high-density polyethylene (HDPE) matrix nanocomposites are taken as the study material. Four different compositions of CNF/HDPE nanocomposites are tested using DMA from 40 to 120 °C at 1–100 Hz frequency. First, time-temperature superposition (TTS) principle is used to develop an extrapolation for the results beyond the test parameter range. Then the TTS curve is transformed to a time domain relaxation function using integral relations of viscoelasticity. Finally, the strain rate sensitive elastic modulus is extracted and extrapolated to room temperature. The transform results are validated with tensile test results and the error found to be below 13.4% in the strain rate range 10−5 to 10−3 for all four nanocomposites. Since the materials are tested with the aim of finding a correlation among the test methods, the quality of the material is not a study parameter and the transform should yield accurate results for any material regardless of composition and quality.

Extracting elastic modulus at different strain rates and temperatures from dynamic mechanical analysis data: A study on nanocomposites

Piezoelectric hydrogel nanocomposites are being developed as interface for connecting biological organs and electronics because of their flexibility, biocompatibility, and electromechanical behaviours, which allow environmental stimulations to be converted into electronic signals. The vision of this work is to develop a series of piezoelectric hydrogel nanocomposites which is capable of generating electric current in aqueous condition. Conductive nanoparticles have been composited in the PHEMA-based hydrogel. Theoretical models and characterisations on the electromechanical properties of such hydrogel have been investigated to assist the understanding of the piezoelectric mechanisms. The hydrogel nanocomposite was demonstrated as a self-powered motion sensor to quantitatively detect human motion and can be considered as candidate material for soft energy harvesting electronics. Overall, the work presented in this paper provides theoretical basis, design guidelines, and technical support for the development of soft self-powered electronics, thus unlocking the potential of piezoelectric hydrogel nanocomposites.

Understanding piezoelectric characteristics of PHEMA-based hydrogel nanocomposites as soft self-powered electronics

Measuring the strain rate sensitivity of materials is desired to improve the design of polymeric parts in automotive and aerospace structures. In this work, we present a technique for determining the mechanical response of polymers at different temperatures and strain rates by converting frequency-domain dynamic mechanical analysis (DMA) data to the time domain. Two polymers of practical interest, vinyl ester and polycarbonate, are examined. The modulus of elasticity in the linear region is measured as a function of the applied strain rate and compared to predictions from the DMA transformation technique. Close agreement between the results obtained from the two techniques is observed over the studied range of strain rates. The transformation technique only relies on the assumptions of the linear theory of viscoelasticity and is expected to be applicable to a wide range of polymers and can also be extended to polymer-matrix composites.

Strain rate sensitivity of polycarbonate and vinyl ester from dynamic mechanical analysis experiments

Interest in designing lightweight structures has resulted in the adoption of polymers and particulate composites in numerous structural applications. Weight saving is extremely beneficial both in terms of increased payload and reduced fuel consumption in transportation sector. Major challenges to the adoption of composite materials for such applications include unavailability of predictive models for high strain rate response and creep life. Dynamic mechanical analysis (DMA) is a widely used technique in polymer science for determining transition temperatures and activation energies. However, DMA results are not directly applicable to the design of structures because only frequencydomain properties are reported from those measurements. This work develops a transformation method for converting the DMA data from frequency to the time domain by appropriate integral relations from viscoelasticity theory. The material relaxation function can then be determined in order to predict the response over varying strain rates and loading conditions. The procedure is demonstrated for three material systems: vinyl ester, polycarbonate and high density polyethylene/fly ash composites. Close matching between the DMA predictions and the results of separate tensile tests and literature data is observed at a wide range of strain rates.

Chrys Koomson

Papers

Extracting elastic modulus at different strain rates and temperatures from dynamic mechanical analysis data: A study on nanocomposites

Strain rate sensitivity of polycarbonate and vinyl ester from dynamic mechanical analysis experiments

Prediction of strain rate sensitivity of polymers by integral transform of DMA data