Materials and Properties
Chenxi BI, Aimin LI
Abstract (
1319 )
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The degradation behavior of poly(lactic acid) (PLA) was investigated at a high temperature of 180 °C under the circulating hydrothermal condition, and their weight variation, generation of lactic acid, thermal weight?loss process, and chemical structure were evaluated by mass?loss rate, high performance liquid chromatography, thermogravimetric analysis, Fourier?transform infrared spectroscopy and liquid chromatography?mass spectrometry. The results indicated that the greater the cycle number, the faster the weight loss of PLA. The weight loss process was completed within 40 minutes by a hydrothermal reaction at 180 ° C. The production rate of lactic acid was accelerated with an increase of cycle number, but there was almost no variation in final volume. The PLA conversion rate was not reduced by the chemical cycling process, indicating a good cycle stability. The stability of PLA was enhanced with the progress of hydrothermal process, and the more cycles resulted in a much better stability. In the hydrothermal process, the hydroxyl index and carbonyl index of PLA exhibited an increasing trend with an increase of cycle number, suggesting that the chemical cycle process could accelerate the degradation of PLA.
Yanxiao LI, Yan ZHANG, Xuelian HE
Abstract (
1022 )
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897
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Ultra high molecular weight polyethylene (PE-UHMW) and high density polyethylene (PE-HD) have a similar molecular composition and structure, and therefore they have relatively good compatibility. In this paper, the PE-HD/PE-UHMW blends were prepared by ultrasonic-assisted twin-screw extrusion, and the effect of PE-UHMW content on the crystallization behavior, compatibility and final mechanical properties of the blends was investigated. The results indicated that the PE-UHMW phase achieved a uniform dispersion without phase separation in the PE-HD matrix at the content lower than 2.0 wt%. As the content of PE-UHMW increases, there is a significant increase in nucleation number for the PE-UHMW domain, which is beneficial to crystallization. Moreover, the degree of entanglement also increases gradually with an increase of PE-HD content. This makes more PE-HD molecules involved in the chain?folding crystallization with the nucleus formed by PE-UHMW, leading to a gradual increase of crystallinity. As a result, the yield strength, breaking strength and elongation at break of the blends were improved significantly with an increase of PE-UHMW content.
Sen WANG, Jiamei LAI, Jinqi RUAN, Yibiao WAN, Zhichao HUANG
Abstract (
755 )
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1126
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Epoxy resin was modified with single-layered graphene oxide and then used to prepare the carbon-fiber-reinforced composite (CFRP) laminates by a vacuum-assisted resin transfer molding process under the [45/0/90] 2S ply angle. A series of performance characterizations including drop hammer impact test, ultrasonic C scan test and post-impact compression test were conduct to investigate the modified epoxy-based CFRP laminates as well as the unmodified epoxy-based laminates as a control. The results indicated that both the modified epoxy-based CFRP laminates and the unmodified ones had inflection points in damage resistance and damage tolerance curves, and the inflection points appeared at the same depth position. Furthermore, the modified epoxy-based CFRP laminates and the unmodified ones exhibited the inflection points at 0.43 and 0.51 mm, respectively. Compared to the unmodified epoxy-based laminates, the modified ones achieved a significant improvement in impact resistance and post-impact compression performance. The damage prediction of composites can be realized by the fitting formula through the data simulation of pit depth and pit area after impact.
Jie WANG, Jibin HAN, Weidong WU, Hui LI, Jun LI, Hongshi JIANG
Abstract (
802 )
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839
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12 )
Maleic?modified polypropylene was used as a compatibilizer to prepared ACM/PP thermoplastic vulcanizates (TPV), and the effects of trithiocyanuric acid (TCY) and dicumyl peroxide (DCP) as vulcanizaters and dioctyl phthalate (DOP) as a plasticizer on the microstructure and physical properties of TPV were investigated. The results indicated that DCP exhibited a better vulcanizing effect than TCY, and the obtained TPV presented a desired microstructure and phase structure. The TPV achieved the optimum tensile and tear properties when 2 phr of DOC was incorporated, and it also showed the excellent compression set and oil resistance. The introduction of DCP decreased the hardness of TPV but enhanced its elasticity. A fine microstructure and good physical properties and elasticity were achieved for the TPV when 30 phr of DOP was added, and meanwhile the hardness was reduced effectively.
Weina CAO, Yahao ZHAO, Mengjie ZHOU, Jingwen ZHAI, Xiang YU
Abstract (
1468 )
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1579
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26 )
In this study, PET blends were prepared by a melt blending method, and their hydrophilic, thermal and mechanical properties were investigated by contact angle meter, DSC and electronic universal material testing machine, etc. The results indicated that the hydrophilic properties of the blends were improved by incorporating hydrophilic reagents like PEG, PAAS and PVP. However, there was little influence from hydrophilic reagents on the mechanical properties of the PET blends. The PET/PEG blends presented the greatest hydrophilicity among these hydrophilic reagents, and the hydrophilicity of PET/PEG blends increased gradually with an increase of PEG content. However, the hydrophilicity of the blends kept stable when the PEG content exceeded 5 wt%. Moreover, the crystallinity of PET increased at first and then tended to decrease with an increase of PEG.
Jianfen KANG, Yanfeng GUO, Yungang FU, Qing WEI, Meijuan JI
Abstract (
810 )
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622
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15 )
Aimed at the cushioning and protective functions of composite-layered structures of paper honeycomb and polyethylene closed-cell foam, the influence of honeycomb thickness on their acceleration response, compression deformation and cushioning energy absorption under different drop impact conditions were studied. One layer of honeycomb corresponded to a stress wave peak in the static compressions, and a small stress wave peak of sub-collapse behavior occurred in the larger thickness honeycomb in the dynamic compression of drop impacts. The impact resistance of polyethylene foam and its composite-layered structures were improved with the increase of honeycomb thickness. For the composite-layered structures of paper honeycomb and polyethylene foam with the honeycomb thicknesses of 10, 15, 20 and 25 mm, the increase of honeycomb thickness reduced the cushioning energy absorption at low impact energy but enhanced the energy absorption capability at high impact energy. However, the cushioning energy absorption of composite-layered structures with a large honeycomb thickness of 70mm was relatively poor. For the structures with the same honeycomb thickness, the strain energy, specific energy absorption and stroke efficiency of single-sided composite-layered structures were improved by 11.5 %, 39.1 % and 16.2 %, respectively, compared to the double?sided composite layered structures under the same impact mass or drop impact energy, indicating better cushioning energy absorption.
Processing and Application
Yiren GAO, Minjie WANG, Hongxia LI
Abstract (
889 )
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675
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In the injection molding process of the thin-walled part based on glass-fiber-reinforced polyetherimide, the core of the mold is easily worn, which seriously affects the quality of the part. Taking the thin-walled part of certain mobile phone as an example, and the micro wear characteristics of the core surface were analyzed in view of the practical production, and the melt flow behavior near the wall of the cavity and the erosion failure form and wear law of the surface material of the core were studied by a numerical method. The results indicated that during the injection process, the surface material of the core was eroded to form a crescent shaped groove, and the melt velocity near the wall of the cavity determined the shape and size of the crescent shaped groove. The incidence angle and dip angle of the glass fiber particles determined the erosion failure form of the material on the surface of the core. The wear amount increased with an increase of the roll angle of glass fiber particles, and the increment was exponential with an increase of the incidence speed.
Dayou DING, Yulu MA, Linsheng XIE, Huihao ZHU, Xiliang SHAN
Abstract (
833 )
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794
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17 )
Carbon fiber (CF)-reinforced poly(phenylene sulfide) (PPS) composites were prepared by a twin-rotor continuous mixing extruder, and their morphology, dynamic mechanical properties, mechanical performance and electrical properties were studied. The results indicated that the mechanical and electrical properties of PPS/CF composites could be improved by appropriately reducing the rotation speed of the extruder rotor and increasing the CF content. The composites achieved the impact strength of 49.94 J/m and the volume resistivity of 60.65 Ω·cm when the rotor speed was set to 200 r/min and the CF content was set as 20 %. These results suggested that the composites had better mechanical and electrical properties than pure PPS.
Jian TENG, Dongyang WANG, Xiangzhe ZHU
Abstract (
784 )
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742
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15 )
The mixing characteristics in the flow field of three eccentric twin?screw extruders with the eccentricities of 4 mm, 2 mm and 0 mm were comparatively investigated by use of a finite?time Lyapunov exponent (FTLE) and a Lagrangian coherent structure (LCS) combined with the mixing index and instantaneous mixing efficiency. The results indicated that when the eccentricity was 4mm, the fluid particles had a traversal range in the eccentric twin?screw extruder, and their Lagrangian coherent structure was relatively complete. There were some hyperbolic fixed points in the flow field, and the fluid particles underwent relatively good stretching and compressing actions. The analysis of instantaneous mixing efficiency parameters revealed that the mixing efficiency of the eccentric twin?screw extruder with an eccentricity of 4 mm was superior to the other two models.
Aoxiang CHEN, Zhihong WANG, Hang GAO
Abstract (
780 )
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591
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A good appearance and high quality were achieved for the welding accessory products through the analysis and verification of failure modes such as welding cracks, insert deformation and running glue during the injection molding process of the fuel filler assembly, the fuel pump flange assembly, and the drain assembly of plastic fuel tank. This lays the solid foundation for ensuring the high quality of plastic fuel tanks.
Xinlong CHENG, Lin GAO, Junmin LI, Ye MEI
Abstract (
757 )
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530
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Taking a BA01-type vehicle radiator support frame as an example, the effect of the polypropylene/glass fiber proportion in the composites was analyzed by a combination of computer software simulation and the relevant tests. The structural analysis and multi-objective optimization were also performed by constructing a Kriging model through the iSIGHT software. The results indicated that the comprehensive mechanical properties of polypropylene/glass fiber composites were most suitable for the production of vehicle radiator support frame at the glass fiber content of 42 wt%. The main beam and wing plate thicknesses exhibited the greatest influence on the fatigue life of vehicle radiator support frame. The structural parameters including the main beam and wing plate thicknesses were optimized by the Kriging model, and the multipurpose optimization design was realized for the enhancement of fatigue life and the weight reduction of this vehicle radiator support frame.
Additive
Xiang YU, Huanhuan TAN, Zhuo WANG, Yukun ZHANG, Yanfei AN, Junjie ZHAO
Abstract (
873 )
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701
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13 )
In this study, PA6/Aerogel (AG) composite powders were prepared by the porous material adsorption and solvent precipitation methods, and their coating properties, flowability and durability were investigated by DSC, XRD, and laser particle size analyzer. The results indicated that the PA6/AG composite powders were successfully prepared as a type of phase change materials with excellent durability performance. When the paraffin/AG mass ratio was set to 1∶1 for the AGbased phase change composite materials and the mass ratio of PA6/AGbased phase change composite materials was set to 2∶1 for the composite powders, the AGbased phase change composite materials in the composite powders were completely covered by PA resin, and therefore an excellent durability was achieved. Moreover, the particle size of the composite powders increase to 85.62 μm at this mass ratio, and an optimal flowability was obtained.
Standard and Test
Chen CHEN, Bin JIANG, Zhuming LV, Zeyu LV, Hui SUN, Tingting WEN
Abstract (
817 )
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723
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According to the requirements of EN71-3 and REACH regulation (EC 1907/2006)，ten types of plastic toys were sampled, and the chemicals within them were tested. Phthalates was detected as the chemicals with the highest detection rate, and the short-chain chlorinated paraffins and p-tetrocylphenol ethoxylate were also detected. A focused chemical candidate list was established for plastic toys at first, and then a primary election was conducted for the management lists by an exclusion method. Afterward, a recheck was performed by the ranking method of the sum of harmfulness and exposure weights. Finally, the top 6 chemicals including short-chain chlorinated paraffins, butyl benzyl phthalate, p-aminoazobenzene, lead and its compounds, cadmium and its compounds, and diisobutyl phthalate were filtered as the focused chemicals for plastic toys. A risk assessment on human health and ecological environment was suggested to carry out for these focused chemicals.
Yan LI, Kejie YANG, Shan ZHANG, Tingyong HU
Abstract (
3758 )
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945
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62 )
This article analyzed and compared the differences between GB/T 1.1—2020 and GB/T 1.1—2009 from the aspects of the document structure, general principles, standardization objective, names, the organization and subdivision of the subject matter, and the verbal forms for expressions of provisions. This article also studied the impact of changes in the main technical content of GB/T 1.1—2020 and GB/T 1.1—2009 on the standard-drafting work, and discussed the changes in the new and old versions of the standard for the improvement of quality on the standard-drafting work. All of the standardization technical committees and standardization drafters are recommended to learn and master the main content of the new version of GB/T 1.1—2020 and carry out the standard-drafting in accordance with the regulations of GB/T 1.1—2020 to improve the standard drafting quality.
Machinery and Mould
Ligang DING, Guofei CHENG, Wenqiang WEI, Siqiao HU, Kaixiang GUO
Abstract (
874 )
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677
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According to the structural characteristics of plastic parts and the requirements of production batch, the overall layout of the mold was determined. On the basis of mold flow analysis, a pouring system combining hot runner and common runner was designed to ensure the balanced filling of each mold cavity and the automatic separation of the cold material between the plastic part and the pouring system. By designing the side core-pulling mode of the half?slider structure, a compression spring and a limiting mechanism were assembled to realize the front membrane core pulling of the mold. The small push plate pushing mechanism was designed to simplify the overall structure of the mold to ensure a reasonable and reliable ejection action. The practical production confirmed that the die structure was reasonable, and the automatic production could be realized. This design meets the requirement for the molding cycle and the quality of plastic parts.
Review
Lin ZONG, Chenwei CHEN, Zhijie CHEN, Jing XIE
Abstract (
1656 )
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1372
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35 )
The research progress in the starch/poly(vinyl alcohol)(PVA) active packaging film and its application in food packaging were reviewed in this paper. The paper first introduced the researches on the blending modification at different proportion of starch and PVA, the hydrophobic modification and the reinforcement modification for the starch/PVA active film, and then the functional characteristics of the film and the influence of active substances on the performance of the films were discussed. Finally, the applications of the film in food packaging were summarized. The purpose of this paper is to provide a reference for the study of the starch/PVA?based active packaging films.
Baogou WU, Piming MA, Pengwu XU, Yong ZHANG, Ruyin WANG
Abstract (
1537 )
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1119
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44 )
This paper reviewed the latest research progress in the modification of poly(lactic acid) PLA for nucleation?induced crystallization, stereocomplexation, toughening and heat resistance. The effects of the chemical structure of nucleating agents, rapid stereocomplexation, reactive compatibilization and annealing technology on the physical and mechanical properties of PLA were discussed. Moreover, the applications and development of PLA were prospected.
