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2018, Volume 32 Issue 05 Publication date: 26 May 2018 Previous Issue Next Issue

Progress in Intrinsic Heat-conductive Cross-linked Polymers

2018, 32 (05): 1-7; DOI: 10.19491/j.issn.1001-9278.2018.05.001

Abstract ( 469 )

This paper reviewed the latest research progress in heat-conductive crosslinking-polymers and analyzed the phonon heat transfer mechanism and influencing factors on heat conduction of intrinsic polymers. Furthermore, the paper mainly discussed the methodology for enhancing the thermal conductivity of cross-linked polymers, which included the introduction of the prepolymer and curing agent with ordered structure units, the incorporation of liquid crystal or mesogenic units into the cured networks to form local microscopically-ordered structures, and the construction of heat conductive pathways through nonbonding inter-chain interactions by choosing proper crosslinker for the networks. Finally, the further direction in development of the intrinsic heat-conductive cross-linked polymers was mentioned.

Research Progress on Modification of Micro-foamed PP

2018, 32 (05): 8-14; DOI: 10.19491/j.issn.1001-9278.2018.05.002

Abstract ( 626 )

This article overviewed the foaming mechanisms of polypropylene (PP) and internal structural characteristics of micro-foamed PP composites and also introduced the research status in the field of micro-foam PP composites. The effect of modification methods on the properties of microfoamed PP composites was discussed on the basis of foaming mechanism and cell structure. Finally, the research direction of micro-foamed PP composites was summarized and their application prospects were brought out.

Research Progress in Composite Separators for Power Lithium Ion Battery

2018, 32 (05): 15-27; DOI: 10.19491/j.issn.1001-9278.2018.05.003

Abstract ( 727 )

This paper introduced the main functions and properties of lithium ion battery separators and also described their production methods and preparation principles, which included coextrusion, coating, hot rolling, electrospinning and gel filling. To meet the high requirements in heat resistance, electrolyte wettability and mechanical properties in the power lithium ion battery, the research results from the co-extrusion, coating, hot-rolling, electrospinning and gel filling process for composite separators were overviewed. The features and applications of the composite separators were introduced. Finally, the development prospect of separators was brought out.

Study on Synergistic Effect and Foaming Behavior of PET Toughened with Nano-SiO2/POE

2018, 32 (05): 28-33; DOI: 10.19491/j.issn.1001-9278.2018.05.004

Abstract ( 541 )

Poly(ethylene terephthalate) (PET)/poly(ethylene-1-octene) (POE)/nano-SiO2 composites were prepared by a two-step melt blending process and then was foamed by a batch method with supercritical carbon dioxide as a foaming agent. The effects of nano-SiO2 and POE on the toughness and foaming behaviors of composites were investigated. The results indicated that the impact resistance of composites was enhanced significantly with the addition of nano-SiO2, and the impact strength increased by 150 % from 11.63 kJ/m2 to 29.15 kJ/m2 when 0.3 phr of nano-SiO2 was introduced. There is a synergistic toughening effect observed between Nano-SiO2 and POE. The storage modulus and complex viscosity of composites were found to decrease with an increase of nano-SiO2 content. Moreover, the cell size of composite foams was reduced from 75.39 to 50.49 μm with an increase of nano-SiO2 content from 0 to 1.0 phr, but their cell density increased from 6.67×107 to 9.61×107 cells/cm3 due to the heterogeneous nucleation effect of nano-SiO2.

Study on Structure and Properties of Epoxy Resin Modified with CTBN and PI

2018, 32 (05): 34-40; DOI: 10.19491/j.issn.1001-9278.2018.05.005

Abstract ( 790 )

A diglycidyl ether of bisphenol-A type epoxy resin (DGEBA) was modified by using liquid carboxyl-terminated butadiene acrylonitrile rubber (CTBN) and polyimide (PI) as combining impact modifiers, methylhexahydrophthalic anhydride (MeHHPA) as a curing agent and 2,4,6-tris(dimethylaminomethyl)phenol as a curing accelerator. The effects of CTBN and PI on the mechanical properties, dynamic mechanical properties and morphology of DGEBA were investigated. The results indicated that the Izod impact strength, fracture strength and elongation at break of DGEBA were significantly increased, while the modulus decreased slightly. The modified DGEBA achieved optimum mechanical properties when 20~30 phr of CTBN and 1.5~2.0 phr of PI were incorporated. Moreover, the presence of PI in an appropriate amount could enhance the storage modulus and heat resistance of DGEBA. The scanning electron microscopic observation indicated that the toughening effect was attributed to the plastic deformation of fracture surface.

Preparation and Properties of Silane-crosslinked EVA/PP/Magnesium Hydroxide Compounds

2018, 32 (05): 41-47; DOI: 10.19491/j.issn.1001-9278.2018.05.006

Abstract ( 520 )

Halogen-free flame-retardant compounds based on silane-crosslinked PP and EVA were prepared through a two-step melt blending method using magnesium hydroxide (MH) as a flame retardant, and the crosslinking efficiency of silane grafted onto EVA/PP compounds were investigated in terms of block-copolymerized PP (PP-B) and homo-PP(PP-H). The mechanical properties, hot elongation performance and flame-retardant properties of compounds were investigated by using universal testing machine, hot-set elongateion tester, limiting oxygen index and vertical burning experiments. The results indicated that the silane-crosslinked EVA/PP-B compounds achieved a higher crosslinking degree than the EVA/PP-H ones. The EVA/PP-B crosslinked compound could reach the crosslinking level required when the content of MH was lower than 120 phr. With increasing the MH content from 80 to 160 phr, the limiting oxygen index values of compounds increased from 25.0 to 32.2 vol %, which were improved by 0.5 %~1.5 % compared to the un-crosslinked ones. The flame retardancy of compounds was improved up to the V-0 grade of GB/T 2408—2008 when the MH content exceeded 120 phr. The compounds were found to undergo a two-stage thermal degradation, in which the first stage involved the dehydration of MH and decarboxylic reaction of EVA and the second one involved the thermal pyrolysis of polymer main chain and volatilization of residues.

Study on Foaming Behaviors of High Melt-elastic PLA/Coffee Ground Composites

2018, 32 (05): 48-54; DOI: 10.19491/j.issn.1001-9278.2018.05.007

Abstract ( 829 )

The preparation of PLA/coffee ground composites modified with diphenylmethane diisocyanate (MDI) was carried out by a melt-mixing method, and the resulting composites were formed by using supercritical CO2 as a foaming agent. The thermal, rheological and mechanical properties of composites were studied and their foaming behavior was investigated. The rheological results indicated that the melt elasticity of composites was improved in the presence of MDI due to a chain-extending reaction. The thermal and mechanical properties of composites were also influenced by MDI and coffee grounds. A bimodal behavior was observed in differential scanning calorimetric thermograms due to the melting and cold crystallization of PLA. The degree of cold crystallinity of PLA was improved up to 24.68 % due to the chain extension of MDI, which also resulted in an improvement in the impact resistance of the composites. Moreover, the composite foams achieved a cell density of 9.26×106 cell/cm3 and a foaming expansion ratio of 9.33. This indicated that the incorporation of MDI favored an improvement in melt elasticity for PLA/coffee ground composite and thus could well control the cellular structure of PLA foams.

Preparation and Properties of Composite Fiber Membranes Based on Poly(lactic acid)and Nano-gallium Oxide Through Electrospinning

2018, 32 (05): 55-61; DOI: 10.19491/j.issn.1001-9278.2018.05.008

Abstract ( 495 )

The poly (lactic acid) (PLA)/nano-gallium oxide (NGO) composite fiber membranes were prepared by an electrospinning technology and the morphology, crystalline properties and mechanical properties were inveistigated by scanning electron microscopy, differential scanning calorimetry and universal testing machine, respectively. Moreover, the antibacterial performance of the membranes was evaluated by an oscillation flask method. Morphological observation indicated that the diameter of composite fibers decreased with an increase of NGO content and their diameter distribution also became broad. Thermal analysis results indicated that the melt temperature and crystallinity degree of the membranes demonstrated an increasing trend at first and then began to decrease with an increase of NGO content. Mechanical evaluation indicated that the fracture strength and elastic modulus of the membranes increased at first and then decreased with an increase of NGO content, but their elongation at break showed a decrease at first and then an increase. The composite fiber membranes also presented a good antibacterial property against Staphylococcus aureus, and their antibacterial effect was enhanced gradually with increasing the NGO content.

Effect of Surface Photo-crosslinking on Mechanical Properties and Water Resistance of Thermoplastic Starch

2018, 32 (05): 62-66; DOI: 10.19491/j.issn.1001-9278.2018.05.009

Abstract ( 375 )

Thermoplastic starch (TPS) was prepared by extrusion and then injection molded into the test bars. The ethanol solution containing benzophenone was coated on the surface of TPS and the irradiated by UV light. The effect of UV irradiation time on the mechanical performance, dynamic thermomechanical properties and water resistance of TPS was investigated intensively. The results indicated that an optimum cross-linked network structure was formed with UV irradiation for 15 min, which led to an effective improvement in mechanical properties and water resistance. In this case, the resulting TPS achieved the maximum tensile strength of 5.28 MPa as well as the flexural strength of 5.83 MPa and impact strength of 73.99 kJ/m2. Moreover, the TPS presented two loss factor peaks at -45.40 and 60.60 ℃ with an improved storage modulus, and it also exhibited the highest surface contact angle of 96.8 °.

Effect of Filament Encapsulation on Flexural Properties of Epoxy/Carbon Fiber Composites

2018, 32 (05): 67-72; DOI: 10.19491/j.issn.1001-9278.2018.05.010

Abstract ( 509 )

A type of CF bundle wound with PBO(Poly-p-phenylene benzobisoxazole) filament was designed, and than the epoxy composites with the CF bundles were prepared by vacuum assisted resin transfer molding (VARTM). The flexural strength and modulus of the PBO-CF/epoxy composites were evaluated by a three-point bending test method, the bending failure modes were observed by a scanning electron microscope. The influence of filament winding methods on the failure process was studied. The result indicated that filament winding could effectively improve the flexural strength of epoxy/CF composites. The composites achieved an increase in flexural strength by 20 % through the unidirectional rotation-winding method and an increase by 36 % through the bi-directional rotation-winding mode. The damages of three point bending were all observed on the compression surface. The failure process of filament-winding carbon fiber-reinforced composites was resulted by the compressive yield of a single bundle rather than by a single fiber. Moreover the interfacial adhesion between the PBO-CF and epoxy matrix was poor, thus resulting in a limitation for the further improvement of flexural properties.

Study of Flame-retardant Polypropylene with Novel Organic-metal Hybrid Char-forming Agent

2018, 32 (05): 73-78; DOI: 10.19491/j.issn.1001-9278.2018.05.011

Abstract ( 394 )

A novel intumescent flame retardant (IFR) was prepared by combining ammonium polyphosphate (APP) with a self-made novel organic-metal hybrid char-forming agent (SCTCFA-ZnO), and then the intumescent flame retardant polypropylene (PP) composites were prepared by using this IFR through melting blending. The synergistic effects of APP and SCTCFA-ZnO on the flame retardancy and thermal degradation of PP composites were investigated by the means of limited oxygen index, vertical burning test, cone calorimeter test, thermogravimetric analysis and scanning electron microscopy. The results indicated that the PP composites achieved a UL 94 V-0 classification in the vertical burning experiment and an limited oxygen index of 31.1 % when 25 % of IFR was incorporated at an APP/SCTCFA-ZnO mass ratio of 2/1. Cone calorimetric results also indicated a reduction in flammability parameters due to a combination of APP and SCTCFA-ZnO for PP composites. Thermal analysis indicated that the presence of IFR improved the thermal stability and char-forming ability of the composite. Morphological observation demonstrated a compact and continuous intumescent char layer formed on the composites, which improved the flameretardant properties accordingly.

Preparation and Properties of Polyamide 6-based Fluorescent Material Through In-situ Polymerization

2018, 32 (05): 79-83; DOI: 10.19491/j.issn.1001-9278.2018.05.012

Abstract ( 480 )

The polyamide 6 (PA6)-based fluorescent materials were prepared by dispersing fluorescent powders in caprolactam (CL) aqueous solution, followed by the anionic ring-opening polymerization CL, and their properties were characterized. X-Ray diffraction characterizations indicated that there is no effect on crystallinity of PA6 in the presence of a small amount of fluorescent powders. Fluorescence emission spectroscopy analysis indicated that the prepared PA6-based fluorescent materials presented a higher photoluminescence intensity, and the photoluminescence intensity was also affected significantly by the content of fluorescent powders. The sample containing 0.15 wt % of fluorescent powders was found to exhibit the highest photoluminescence intensity. Morphological characterization revealed that the fluorescent powders were homogeneously distributed in the PA6 matrix, but the high concentration of fluorescent powders resulted in an aggregation. Thermal analysis indicated that, although the addition of fluorescent powders did not influence the thermal decomposition behavior of PA, the maximum decomposition temperature of PA6based fluorescent materials is lower than pure PA6. Moreover, the presence of fluorescent powders prevented the formation of γ-form crystals but promoted the α-form crystals for PA6.

Development of Direct-pressure Vulcanization Technology for High-performance Tires

2018, 32 (05): 84-91; DOI: 10.19491/j.issn.1001-9278.2018.05.013

Abstract ( 565 )

In this paper, a direct-pressure vulcanization technology for high performance tires was developed by utilizing a retractable high-rigid metal internal mold to replace the soft capsules. Due to the high rigidity and high structural accuracy of the metal mold, this new technology forced the tires to be highly uniform and symmetrical, thus enhancing the dynamic balance and uniformity of tires. The traditional steam-heating method is completely replaced by an electromagnetic inductionheating method. The molds became the heat source by themselves with this method and therefore the thermal energy could be conducted to the tires efficiently. The test results from the tire with the specification of 255/30R22 indicated that the dynamic imbalance, radial force variation and lateral force variation decreased by 22.52 %, 20.9 % and 43.9 %, respectively, with this new vulcanization technology. Moreover, the vulcanization temperature difference at the symmetry site of tires was reduced by about 7 ℃, and the energy consumption of a single tire was reduced by 86 %.

Security Assessment for Anti-falling and Anti-penetrating Performance of Cross-linked High-density Polyethylene High Integrity Container for Nuclear Power Station

2018, 32 (05): 92-96; DOI: 10.19491/j.issn.1001-9278.2018.05.014

Abstract ( 443 )

The cross-linked high-density polyethylene high integrity container (PE-XHD-HIC) has been applied to deal with low-and middle-radioactive wastes of nuclear power station. A security assessment for PE-XHD-HIC was performed by the nonlinear dynamics software LS-DYNA to simulate its anti-falling and anti-penetrating performance at a height of 1.2 m under the two typical actual accident conditions of nuclear power station. The simulation results indicated that the stress of PE-XHD-HIC was less than its ultimate strength, whereas its maximum strain was less than the damage strain. The PE-XHD-HIC was verified to meet all the requirements in operation and security.

Influence of Needle-punching Process on Basalt Nonwovens and Their Composites

2018, 32 (05): 97-102; DOI: 10.19491/j.issn.1001-9278.2018.05.015

Abstract ( 449 )

The needle felt reinforced composite plates were prepared by using basalt needle punched nonwoven fabric as a reinforcement and boron phenolic resin as a matrix through, and the effect of needle punching process on the mechanical properties of the composites was investigated. The tensile strength of composites exhibited an increasing trend at first and then decreased with an increase of lamination pressure. However, the flexural strength increased linearly with increasing the lamination pressure in the same needle-punching process. In a certain case, the porosity of reinforcement presented a more significant effect on mechanical properties of composites that its tensile strength.

Analysis of Optical Performance for Injection-compression-molded LED Lens

2018, 32 (05): 103-108; DOI: 10.19491/j.issn.1001-9278.2018.05.016

Abstract ( 568 )

The optimal processing parameters of A3B2C2D2E2F3G1 for the injection-compression molding of LED lens were obtained by simulating optimization using an orthogonal experiment matrix of L18(37), and the optical performance of the lens was evaluated. The results indicated that the reduction of interior residual stress and refractive index variation of lens is beneficial to the improvement of optical performance under the processing parameters of high compression speed and low injection rate. The refractive index variation of molded lens with hot runner was lower than that with cold runner. The light transmittance and maximum light intensity obtained with cold runner were 93.1 % and 590.3 cd, respectively, but both of them with hot runner were 4.4 % and 75 cd higher than those with cold runner. The injection-compression molding for LED lens with hot runner was superior to that with cold runner in the aspect of optical performance.

Applications of Trifunctional Epoxy Resin as Crosslinking Agent for PLA Extrusion Foaming

2018, 32 (05): 109-115; DOI: 10.19491/j.issn.1001-9278.2018.05.017

Abstract ( 574 )

A trifunctional epoxy resin was used as crosslinking agent for the chemical foaming and extrusion process of poly(lactic acid) (PLA). The effects of content of trifunctional epoxy resin on the melting and crystallization behavior, crosslinking degree and melt strength of PLA were investigated, and the cellular morphology of PLA foams was studied. The results indicated that the cold crystallization temperature increased with an increase of the content of trifunctional epoxy resin, and the presence of trifunctional epoxy resin also resulted in the appearance of multiple melting peaks. The crystallization and melting enthalpies and degree of crystallinity of PLA foams exhibited an increasing trend and then decreased with increasing the content of trifunctional epoxy resin. The degree crosslinking was found to increase with an increase of the content of trifunctional epoxy resin. The melt strength of PLA increased significantly with increasing the content of trifunctional epoxy resin. The incorporation of trifunctional epoxy resin also led to a decrease in void fraction and open cell, and however the cell size presented a decrease at first and an increase afterwards. The optimum temperature of extruder head was 170~175 ℃.

Study on Preparation and Antistatic Performance of Polyurethane Materials Modified with Reduced Graphene Oxide

2018, 32 (05): 116-119; DOI: 10.19491/j.issn.1001-9278.2018.05.018

Abstract ( 476 )

In this paper, graphite oxide was first prepared by the Hummers’ method, and then reduced graphene oxide (RGO) was obtained by ultrasonic exfoliation and thermal reduction. The resulting RGO was used as an antistatic agent to prepare the polyurethane-based composites, and the effect of RGO on the antistatic properties of the composites was investigated. The results indicated that RGO has a thin, transparent and amorphous structure, and the addition of RGO reduced the electrical resistivity of the composites significantly. The electrical resistivity was found to decrease with an increase of RGO content and was lower than 1010 Ω·cm at a RGO content of 1 wt%. Moreover, the composites achieved a fair improvement in compressive strength.

Effect of L-cysteine modification on properties of wheat-gluten based bioplastics

2018, 32 (05): 120-125; DOI: 10.19491/j.issn.1001-9278.2018.05.019

Abstract ( 433 )

The modification of wheat gluten with L-cysteine was studied to improve the properties of wheat-gluten-based bioplastics, and its effect on the properties of the resulting bioplastic panels was discussed in terms of the amount of L-cysteine, processing temperature and processing time. The optimal process conditions for the bioplastic panels were obtained from orthogonal experiments. The results indicated that the optimal modification condition was determined as an L-cysteine content of 6 wt %, a processing temperature of 40 ℃ and processing time of 50 min. The bioplastic panels obtained under this condition achieved the tensile strength of 37.68 MPa, elongation at break of 22.83 % and water absorption of 76.08 % when the tensile strength was considered as a main factor. However, if the elongation at break was taken as a main evaluation indicator, the optimum modification condition should be determined as an L-cysteine content of 4 wt %, a processing temperature of 30 ℃ and processing time of 30 min. The bioplastic panels obtained under such a condition exhibited the tensile strength of 13.24 MPa, elongation at break of 80.19 % and water absorption of 80.31 %.

Investigation on Rapid Flattening Test Method for Weldline Strength of Polyethylene Pipe Fittings

2018, 32 (05): 126-129; DOI: 10.19491/j.issn.1001-9278.2018.05.020

Abstract ( 787 )

This paper introduced the flattening test method for polyethylene (PE) pipe fittings and presented a comparative investigation on the experimental results and variation trends between the flattening test and hydrostatic strength test at 165 h and 80 ℃ through exact tests for the weldline strength of pipe fittings. The results indicated that there was no crack found in the flattening test of weld line, while the specimen was confirmed to be qualified in the hydrostatic strength test. However, when the specimen was determined as a qualified product in the hydrostatic strength test, there are two cases for the flattening test, i.e. with cracks and without crack. The flattening test was found to detect the weldline strength of PE pipe fittings quickly and effectively, and it could meet the requirement for injection molding so as to improve the product quality by adjusting the processing technology and modifying the mold schemes.

Design of Injection Mould for an SUV‘s Storage Box

Qing-Dong LIU

2018, 32 (05): 130-134; DOI: 10.19491/j.issn.1001-9278.2018.05.021

Abstract ( 525 )

The storage box used in sport utility vehicles has a complicated structure, and it is difficult to be ejected during the injection molding. The forming process of a storage box was analyzed, and a hot runner system was designed. In the injection molding system of this storage box, a two-step slide-pulling mechanism of lifter in slide was designed because of two neighboring perpendicular holds. Moreover, a two-step slide-pulling mechanism in slide was also designed, because the storage box was easy to be damaged when the slide was pulled. Considering of a difficulty in ejection due to overhigh columns and reinforcements, the lifter was designed. The results indicated that the mold designed in this work had a reasonable and reliable structure and it could meet the requirement of production.

Design of Three Ejection Reversing Circular Arc Stripping Mechanism Based on Mathematical Modeling

2018, 32 (05): 135-143; DOI: 10.19491/j.issn.1001-9278.2018.05.022

Abstract ( 516 )

Aiming at the demolding difficulty in sealing ring mounting groove buckle on both ends inside the product, a rotary demolding mechanism with three-time ejection was design in this paper, and a dynamic mathematic model for this mechanism was constructed. Based on this mathematical model, the template driven mechanism for realizing the rotary demolding of the sealing ring mounting groove buckle was confirmed to be entirely feasible. Moreover, a slider displacement control mechanism with three-order ejection was designed according to the requirement of demolding mechanism. This mold had two plates, one module and two cavities, and three-side gate runner ejection plate structure. The demolding mechanism, top-out sequence control mechanism and die structure designed in this paper can provide a useful reference for the mold design of similar products.