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2020, Volume 34 Issue 1 Publication date: 26 January 2020 Previous Issue Next Issue

Effect of Stretching Process on Structure and Properties of Polytetrafluoroethylene

2020, 34 (1): 1-5; DOI: 10.19491/j.issn.1001-9278.2020.01.001

Abstract ( 1166 ) PDF (2355 KB)( 769 )

A series of polytetrafluoroethylene (PTFE) drawn samples were prepared by uniaxial stretching at different stretching temperatures, rates and lengths, and the effects of stretching process on the structure and properties of the drawn samples were investigated systematically. The results indicated that the density and porosity of the drawn samples were effectively reduced by increasing the stretching temperature, rate and length, and their mechanical properties varied obviously with an increase of stretching length. The tensile strength increased from 28.72 MPa to 46.13 MPa, but the elongation at break decreased from 145 % to 85 %. Moreover, the compression rate of the drawn samples increased from 6.17 % to 16.21 % at different stretching lengths, whereas the elastic recovery rate increased from 3.90 % to 6.42 %, indicating that the obtained drawn samples are more suitable for use as sealing materials.

Effects of Rheological and Crystalline Properties of PE?HD on Its Foaming Process

2020, 34 (1): 6-10; DOI: 10.19491/j.issn.1001-9278.2020.01.002

Abstract ( 655 ) PDF (2249 KB)( 421 )

The thermal performance and rheological properties of PE?HDs were measured by DSC and Hakke rotational rheometer, and then its foaming properties were investigated through the batch foaming experiments. The result indicated that there was a significant effect on the foaming performance of PE?HD from its crystallization rate and viscoelastic properties. The rheological properties and molecular weight distribution of HDPE6098 were found to be suitable for the foaming process along with its fast crystallization rate. These advantages could help to obtain an expansion ratio of 17.69 times and a cell density of 1.30×10^6 cell/cm3 for the foamed PE?HD samples. However, HDPE7000F was found to have a broad high molecular?weight range and high modulus, leading to a limitation in cell growth during foaming and a poor foamed product.

Effect of Composition Ratio on Properties of PS/PA Parts Formed by Selective Laser Sintering

2020, 34 (1): 11-16; DOI: 10.19491/j.issn.1001-9278.2020.01.003

Abstract ( 570 ) PDF (3732 KB)( 269 )

The polyamide(PA) and polystyrene (PS) powders are compounded to prepare a series of experimental samples by a selective laser sintering machine, and the microstructure, dimensional accuracy, density, bending strength and surface roughness of the samples were characterized to explore the effect of composition ratio on the performance of the PS/PA samples. The results indicated that the bonding degree of PS and PA powders in the samples increased with an increase of PA content, and the bending section of the samples became flatter. The dimensional accuracy of the samples was better than other experimental groups at the PS/PA weight ratio of 1/4. The density of the samples also increased gradually with an increase of PA content. The density of the samples became larger and closer to each other at the PS/PA weight ratios of 1/2, 1/3, 1/4, and 1/5. The bending strength of the samples presented an upward trend with an increase of PA content and increased at the PS/PA weight ratios of 1/2, 1/3, 1/4 and 1/5. In addition, the samples exhibited a minimum in surface roughness at the PS/PA weight ratio of 1/4.

Effect of Lap Length on Bonding Properties of Titanium Alloy/Aramid Fiber Composites Single Lap Joints

2020, 34 (1): 17-21; DOI: 10.19491/j.issn.1001-9278.2020.01.004

Abstract ( 688 ) PDF (6528 KB)( 343 )

The single lap joints with different overlap lengths were fabricated by titanium alloy/aramid fiber composites, and their tensile strains and ultimate loads were characterized by DIC and universal testing machine. The effect of overlap length on the bonding properties and failure modes of the single lap joints of dissimilar materials was investigated. The results indicated that the ultimate load of single lap joints increased with an increase of overlap length, but their bonding strength decreased. The joints of high overlap length were damaged progressively. The joints rotation caused by the eccentric bending moment decreased, and the proportion of longitudinal strain area in overlap region was also reduced. Moreover, the fiber?tear failure of the composites increased, but the adhesive failure between the titanium alloy and adhesive layer decreased. In addition, the layer number of the stripped composites increased.

Effects of Molecular Weight and Chain Structure of Ethylene?propylene Block Copolymers on Structure and Performance of PP/EPR Blends

2020, 34 (1): 22-28; DOI: 10.19491/j.issn.1001-9278.2020.01.005

Abstract ( 697 ) PDF (4545 KB)( 311 )

A series of ethylene?propylene block copolymers (EP) with different molecular weights and average sequence length of ethylene monomer units were designed and synthesized by using slurry polymerization process and then used as a compatibilizer for polypropylene (PP)/ethylene?propylene rubber (EPR) blends. The effects of the content and molecular weight of block copolymer on the performance and the evolution of dispersed phase of the blends were investigated. The results indicated that there was an optimum content of EP for compatibilization in the PP/EPR blending system. The addition of EP in a small amount could efficiently control the size and morphology of dispersed phase and therefore enhanced the impact strength of the blends significantly. Meanwhile, the higher molecular weight for EP was beneficial to the impact performance of the blends. The similarity in the composition of EP and EPR was crucial to the compatibilization effect for PP/EPR blends.

Study on Creep Behavior of Annular Specimens of Continuous?fiber?reinforced Composites

2020, 34 (1): 29-33; DOI: 10.19491/j.issn.1001-9278.2020.01.006

Abstract ( 620 ) PDF (2545 KB)( 294 )

This paper reported a study on the tensile creep behavior of continuous?glass?fiber composites. To simulate the stress state of the composites in the pressure vessel and reduce the influence of clamping force, a tensile creep test method for annular specimens was developed. The tensile strength and tensile creep under different stress levels of composites were investigated. Based on the time?stress equivalence principle, the maximum creep stress of the composites with 50 years service life was fitted by a double logarithm method, which provides a technique support for the design of composite pressure vessels. Based on the time?stress equivalence principle, the maximum creep stress of composite is fitted by double logarithm method. In order to guarantee the service life of pressure vessel for 50 years, the maximum creep stress should be lower than 44.4 % of its tensile strength.

Toughening Modification of PHBV with Boltorn Hyperbranched Polyester

2020, 34 (1): 34-42; DOI: 10.19491/j.issn.1001-9278.2020.01.007

Abstract ( 646 ) PDF (4917 KB)( 289 )

Boltorn hyperbranched polyester (HBPE) was synthesized by a “one?step” method with trimethylolpropane as a core, 2,2?dimethylol propionic acid as an AB2?type monomer and p?toluenesulfonic acid as a catalyst. Poly(3?hydroxybutyrate?co?3?hydroxyvalerate) (PHBV) was modified by solution method using HBPE as modifier and chloroform as solvent, and it was characterized by differential scanning calorimetry, mechanical property test, polarization microscope, thermogravimetric analyzer, scanning electron microscope and other analytical methods. The results indicated that the glass transition of PHBV becomes more significant with an increase of HBPE content, suggesting that the addition of HBPE significantly enhances the segmental movement capability of PHBV. The degree of crystallinity of PHBV decreased from 64.77 % to 27.68 % with the addition of 4 phr of HBPE. In this case, the tensile strain at break increased by 194.04 %, tensile strength increased by 27.22 %, and the tear strength increased by 56.28 %. Moreover, the addition of HBPE increased the tensile strength of PHBV slightly but improved the toughness of PHBV significantly. HBPE can be considered as an excellent impact modifier for PHBV.

Scale Inhibition Performance of Amino?terminated Hyperbranched Polyamides for Calcium Sulfate from Circulating Water

2020, 34 (1): 43-50; DOI: 10.19491/j.issn.1001-9278.2020.01.008

Abstract ( 612 ) PDF (1758 KB)( 412 )

An amino-terminated hyperbranched polyamide copolymer was successfully prepared by the Michael addition and amidation using diethylenetriamine and methyl acrylate as comonomers, and its chemical structure was characterized by FTIR. The resultant copolymer was used for the scale inhibition of industrial circulating water, and the effects of the copolymer dosage, pH value of water environment and water temperature on calcium sulfate inhibition were investigated. The results indicated that the amino-terminated hyperbranched polyamide not only had a good dispersibility for Fe2O3 but also exhibited good scale inhibition for CaSO4, and it achieved a scale inhibition efficiency of 96.37 % at the dosage of 12 mg/L. Moreover, the amino-terminated hyperbranched polyamide also showed an excellent inhibition efficiency under a wide temperature range. The XRD and SEM analyses demonstrated that the amino?terminated hyperbranched polyamide not only could effectively inhibit the growth of scale crystals CaSO4 and reduce its crystallinity, but also could destroy the crystalline regularity to inhibit the scaling capability.

Study on Shielding and Mechanical Properties of High Density Polyethylene /Lead-boron Composite

2020, 34 (1): 51-57; DOI: 10.19491/j.issn.1001-9278.2020.01.009

Abstract ( 732 ) PDF (2135 KB)( 266 )

The shielding properties and mechanical properties of high density polyethylene/lead-boron composite were studied. The effects of density and B4C content on shielding performance are compared by shielding simulation, and the effects of B4C content on shielding performance, bending strength and impact strength are compared by experiments. The simulation results showed that the thermal neutron shielding performance and gamma shielding performance increases ,yet the fast neutron shielding performance decreases with the improved of the density of polyethylene / lead?boron composite. The neutron shielding performance decreases with the increase of B4C content while keeping the density of composite unchanged. The experimental data show that with the increase of B4C content, the fast neutron shielding performance and thermal neutron shielding performance of polyethylene/lead-boron composite decrease, while the gamma shielding coefficient increases, but the overall change is not obvious; the impact strength and the bending strength of the material decreases obviously. The simulation results and experimental data show that the high density polyethylene/lead-boron composite containing about 2 % B4C has better shielding performance and mechanical properties meanwhile.

Process Analysis of Layered?counter?pressure Injection Molding for Thick?wall Optical Lens

2020, 34 (1): 58-63; DOI: 10.19491/j.issn.1001-9278.2020.01.010

Abstract ( 573 ) PDF (1392 KB)( 268 )

In order to study the influence of back pressure on the formation of thick-walled optical lens, an experimental scheme for the layered-back-pressure injection-molded thick-walled optical lens was developed in this work, and an optimization experiment for the process parameters was conducted by the orthogonal experiment optimization design. The effect of the inner and outer back pressures on the optical properties of the thick-walled optical lens in an layer mode was investigated so as to fabricate an ideal thick-walled optical lens with excellent optical properties on the basis of the orthogonal optimization parameters. The orthogonal experimental results indicated that the shrinkage of the thick-walled optical lenses could be reduced effectively by use of PMMA as a raw material during the layered back-pressure injection molding process. The light transmittance and refractive index of the thick-walled optical lens were improved with an increase of the back pressure of the inner and outer layers, indicating excellent optical properties.

In?situ Fabrication and Patterning of Polyaniline Nanofiber?array Coatings

2020, 34 (1): 64-68; DOI: 10.19491/j.issn.1001-9278.2020.01.011

Abstract ( 562 ) PDF (3727 KB)( 299 )

Polyaniline nanofiber coating possesses antistatic properties, electromagnetic shielding, gas sensing, and etc, thus it is of great significance for improving product performance to construct large-area polyaniline nanofiber interface with controlled morphologies on general plastic surfaces. We report a combined method based on in-situ polymerization and lithography, i.e. constructing large-area polyaniline nanofiber arrays on polyethylene terephthalate surfaces. The results reveal that the obtained polyaniline coating prepared via the in-situ polymerization possess large-area and uniform nanofiber array structures. Compared with the drop-casting method, the micro-patterns of polyaniline nanofiber prepared via in-situ polymerization have superior precision and binding capacity with the substrates. Meanwhile, the polyaniline nanofiber sensors via in-situ polymerization show better humidity sensing performance and superior repeatable stability.

Interface Peeling Failure and Prevention of Metal?based Polymer Lined CompositePressure Vessel

2020, 34 (1): 69-75; DOI: 10.19491/j.issn.1001-9278.2020.01.012

Abstract ( 539 ) PDF (2282 KB)( 356 )

Based on the simulation method of crack peeling propagation failure process, a prediction method for critical load was proposed, and an equivalent critical vacuum pressure load control line and design criteria for preventing interfacial crack peeling and propagation failure were constructed by means of the critical strain energy release rate and damage initiation stress of the lining interface. The results indicated that the critical pressure load was controlled by the initial pre-crack length, critical strain energy release rate and initial damage stress at the composite interface. It was negatively correlated with the initial pre-crack length, but positively correlated with the critical strain energy release rate (GIC) and the initial damage stress (T0). When the initial pre-crack length increased from 11.11 % to 15.55 %, the critical pressure load (Pc) decreased by 34.9 % from 87.6 kPa to 57 kPa. The coordinate points of interface peeling toughness parameters (T0, GIC) were located above the control line of equivalent critical vacuum pressure load, which could effectively prevent the failure of lining interfacial crack peeling and propagation.

Analytical Solution of Heat Transfer Model for Heating Phase in RotationalMolding Process

2020, 34 (1): 76-82; DOI: 10.19491/j.issn.1001-9278.2020.01.013

Abstract ( 575 ) PDF (1032 KB)( 227 )

In this work, we established a heat transfer model for heating phase in the rotational molding process from mold heating to powder melting. In this model, the temperature gradients of the mold, internal air and powder were ignored, and their average temperatures only varied with time. The space inside the mold was divided into the internal air region and powder region. Heat was transferred from the mold to both internal air and powders by convection, and meanwhile, heat was also transferred from internal air to powders by convection when they were mixing. The heat equilibrium equations for the mold, internal air and powders were presented on the basis of the principle of energy conservation. Furthermore, the analytical solutions for their average temperatures were obtained by simplifying and solving the differential equations. The internal air temperatures calculated from the analytical solutions were in good agreement with the experimental results, thus proving the validity of the heat transfer model and its analytical solutions..

Study on Gas Volume of Plastic Foaming Agent in Closed Container under Fixed Volume

2020, 34 (1): 83-86; DOI: 10.19491/j.issn.1001-9278.2020.01.014

Abstract ( 668 ) PDF (1032 KB)( 311 )

The traditional method of drainage gas collecting is affected by human and environment, which is easy to produce errors and is not convenient for automation. In this study, the gas volume of a foaming agent can be calculated by measuring the gas pressure change of the foaming agent in a fixed volume closed container. At the same time, the starting temperature, jumping temperature, ending temperature, maximum gas volume and other parameters of foaming agent can be obtained by measuring the gas pressure in a fixed volume closed container, so as to monitor the whole foaming process of the foaming agent. The gas pressure of a foaming agent measured in a fixed volume closed container can be converted into the gas volume of foaming agent measured by the drainage gas collecting method, by establishing the functional relationship between the gas pressure in a fixed volume closed container and the gas volume of a foaming agent. The gas volume curve of a foaming agent measured by the drainage gas collecting method can also be transformed (change with temperature) to the pressure curve in a fixed volume closed container (change with temperature). In this paper, Azodicarbonamide (ADC) was selected to verify the feasibility of the formula.

Geometric Study on Fully Wiped Triangular Prism Mixing Components for Twin-Screw Equipment

2020, 34 (1): 87-91; DOI: 10.19491/j.issn.1001-9278.2020.01.015

Abstract ( 611 ) PDF (1186 KB)( 267 )

This paper explores a full-mesh triangular prism mixing element for twin-screw extruders to solve the production process problem of new glass fiber reinforced materials, explains its full meshing design theory, and proposed an eccentric design method which makes the component have better mixing effect and better interchangeability, and it is clear that the range of eccentricity and screw radius is 0~0.423. Then the geometric properties of the components are analyzed in detail according to the geometric principle. The expressions of the design parameters and the volume of the mixing cavity are derived. The numerical fitting method is used to simplify the expression to be applied to the actual design. Finally, the analysis of mixed surface normal shows the relationship between the conveying capacity and the component spiral parameters, and gives that the reasonable range of parameter selection is 2~8 which can not only maintain good mixing effect, but also have better conveying capacity. The necessary theoretical preparations are provided for the design and manufacture of the component and the hybrid experiment.

A Review on PTFE Composites Filled with Inorganic Materials

2020, 34 (1): 92-101; DOI: 10.19491/j.issn.1001-9278.2020.01.016

Abstract ( 1103 ) PDF (4137 KB)( 897 )

This paper reviewed the development status of three modification methods for the PTFE composites filled with inorganic materials including fibers, granule and fiber-granule composite fillers. The effects of inorganic fillers on the mechanical and tribological properties of PTFE composites were discussed, which involved the friction coefficient, tensile strength and material hardness. It was founded that many of inorganic fillers such as copper powders, molybdenum disulfide and glass fibers had a lower cost and a good modification effect on the improvement of mechanical properties and tribological properties of PTFE, and these fillers were more suitable for practical engineering applications. Moreover, the problems existed in the foreign and domestic researches in recent years were analyzed, and a solution direction was proposed.

Research Progress in Development and Application of Heat-resistant Epoxy Resins

2020, 34 (1): 102-111; DOI: 10.19491/j.issn.1001-9278.2020.01.017

Abstract ( 678 ) PDF (2026 KB)( 541 )

This paper introduced the elementary properties of epoxy resin and reviewed the development methods for new types of the high heat-resistant epoxy resins such as the blending modification with small organic molecules, organic resins and nano particles as well as the chemical methods for the synthesis of heat-resistant epoxy resins with new molecular structures. The paper also summarized the application research on high heat-resistant epoxy resins in different fields such as wear-resistant materials, coating coatings, electronic packaging materials, etc, and the development direction in future was prospected.