Materials and Properties
ZHU Yuting, GU Lin, HE Jialong, JI Huajian, WANG Yu, ZHU Huihao, MA Yulu, XIE Linsheng
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564 )
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Polypropylene （PP）/polyamide 6 （PA6）/carbon nanotubes （CNTs） composites were prepared using a twin?rotor continuous mixing extruder and their in?situ microfiber composite films were further fabricated using a micro?nano laminated co?extrusion molding machine. Their microstructure and rheological， crystalline， mechanical， and electrical properties were investigated using scanning electron microscope， rheometer， differential scanning calorimeter， universal tensile tester， and resistance tester. The results showed that PA6/CNTs as a dispersion phase was subjected to form microfibers through a laminated co?extrusion method. The composites not only achieved an improvement in dynamic rheological properties due to the formation of microfibers， but also obtained an increase in the crystallinity and crystallization temperature of the PP phase. The composite films exhibited maximum tensile strength of 42.17 MPa at a CNT content of 0.5 wt%. Their elongation at break reached a maximum value of 857.82 %， but their volume resistivity decreased to 104 Ω·cm. In this case， the composite films showed optimal comprehensive mechanical properties and electrical conductivity.
CHEN Kexin, CHEN Shuning, LIN Jianrong
Abstract (
433 )
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Janus nanosheets （JNSs） were prepared through one?pot synthesis， and the surface morphology and chemical compositions were characterized using scanning electron microscope and electric cooling X-ray energy spectrometer. The effect of JNSs on the rheological， dynamic mechanical properties and mechanical properties of polystyrene（PS）/TiO2 blends as well as their morphology were investigated using dynamic hybrid rheometer， dynamic mechanical thermal analyzer and universal material testing machine. The results indicated that the prepared JNSs showed different rough levels on their two sides. The rough concave and smooth convex surfaces were found to contain amino groups and double bonds， respectively. The JNSs can be used as a compatibilizer for the PS/TiO2 blending system to enhance interfacial interaction， thus improving the compatibility between the inorganic particles and organic polymers. Compared to pure PS， the glass transition temperature of the PS/TiO2 composites with 0.5 phr JNSs was increased from 100 to 107 °C. Owing to the enhancement of interfacial interaction， the JNSs can dissipate energy in the direction of the force under the action of external force， resulting in an increase in tensile strength by 13.43 %. The elongation at break also increased from 12 % to 18 %.
WEN Hui, MA Yufei, XIN Chunling, HE Yadong
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688 )
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In this study， an epoxy?type chain extender （KL-E4370） was used to modify the thermoplastic polyamide elastomer （TPAE）. The rheological， crystalline， and foaming properties of TPAE before and after the chain extension were investigated using a rotating rheometer， differential scanning calorimeter and scanning electron microscope， and the corresponding chain extension reaction was studied， too. The results indicated that the molten TPAE has poor thermal and foaming properties. The introduction of chain extender can effectively increase the branching level of TPAE. After modification， the complex viscosity of TPAE was increased by more than one order of magnitude， the foaming rate was increased， the foaming temperature zone was widened， and the bubble rupture and merging problems were effectively overcome. However， the crystallization performance of TPAE decreased， and the initial crystallization temperature decreased by about 20 °C， resulting in obvious shrinkage of the bubble. When the content of chain extender was 1 wt%， the foaming rate of TPAE increased from 5.5 times to approximately 9 times， and the diameter of the bubble reached 50 μm.
BI Xinyuan, YAO Jianmin
Abstract (
617 )
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To solve the problems from the white pollution in farmlands， macromolecular poly（propylene carbonate） （PPC） and poly（butylene adipate-co?butylene terephthalate） （PBAT） were selected as two types of biodegradable materials together with powerful water permeability additives to prepare the PPC biodegradable water-permeable mulch films. The formulation and processing technology of the mulch films were optimized using the multi?blow film method， and their mechanical properties and degradation performance were characterized using a universal tensile tester and ultraviolet aging test box. The results indicated that according to the optimized formulation and processing technology of the preferred scheme A9 and A2， a thin PPC-based biodegradable water-permeable mulch film with a thickness of （0.007±0.002） mm was successfully prepared using a water-permeable mulch film processing technology. The mechanical properties of six products trial-produced based on the schemes A9 and A2 could meet the requirements of GB/T 35795-2017. The membrane surface of the mulch film with a thickness of 0.007 mm began to crack within 60 days， and its degradation degree was 77.06 % and 95.72 % within 180 and 360 days， respectively.
WU Tengda, ZHUANG Jibin, DIAO Xuefeng, WANG Qingwen
Abstract (
603 )
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The stereocomple poly（lactic acid） （SC?PLA） powders were prepared through melt blending using poly （L?lactic acid） and poly（D?lactic acid） as raw materials and then were injection molded to form SC?PLA parts. The melting， crystallization and thermal properties of SC?PLA powders and parts were characterized using a differential scanning calorimeter and a thermal deformation temperature tester. The results indicated that the crystallization ability of SC?PLA was related to the initial melting state. The melting stabilization time of SC?PLA increased in the melting temperature range of 220~230 °C， which facilitated the crystallization and was suitable for injection molding of SC?PLA. The better the crystallization ability of SC?PLA with low crystallinity of homopolymer PLA， the higher was the heat distortion temperature of the injection?molded parts of SC?PLA. The crystallization ability of SC?PLA could be increased through decreasing injection temperature and using the formulation based on SC?PLA powders and PLLA/PDLA mixture. The injection?molded parts of SC?PLA achieved a maximum heat distortion temperature of over 150 °C after annealing. During injection molding， the heat distortion temperature of the samples after annealing could be improved through retaining more SC?PLA crystals and increasing the crystallinity of SC?PLA.
YANG Xiuqin, LIU Yihe, MIAO Shicheng, ZHU Dengchang, YU Xiang
Abstract (
484 )
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In this study， PA6/CaSO4 composite powders were prepared using a solvent precipitation method. Their microstructure， thermal properties， particle size distribution， crystal structure， and flowability were investigated by SEM， DSC， XRD and laser particle size?distribution analysis. The results indicated that the PA6/CaSO4 composite powders transformed from a loose spherical structure to the dense spherical one with the addition of CaSO4. The introduction of CaSO4 increased the degree of crystallinity （Xc） of the composite powders and broadened their sintering temperature window. When the CaSO4 content was 5 wt%， the Xc reached maximum value of 61.84 % and the sintering temperature window reached a maximum value of 18.95 °C. Moreover， the particle size and repose angle of the composite powders decreased at first and then tended to increase with an increase in the CaSO4 content. However， their bulk density showed an increasing trend at first and then tended to decrease. The composite powders exhibited optimal flow performance at the CaSO4 content ranging from 3 to 5 wt%， which was most suitable for selective laser sintering.
LI Meilan, DOU Xiaoyu, HE Jiao, GONG Wei, XIE Chengcheng, LIU Bailing
Abstract (
562 )
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Fe3O4 magnetic particles were prepared by co?precipitation and then surface?treated through silanization and amidation reactions to obtain a carboxylated composite （Fe3O4?SiO2?NH?COOH）. The structure of Fe3O4?SiO2?NH?COOH， the effect of reaction condition on the Pb2+ adsorption of the Fe3O4?SiO2?NH?COOH and its repetitive utilization efficiency was analyzed by FTIR， SEM， TEM， VSM and XRD. The results indicated that the Fe3O4?SiO2?NH?COOH were successfully prepared with a desired structure and could be obtained through a rapid magnetic separation. Meanwhile， the static adsorption experiment showed that the adsorption kinetics belonged to the second order. The adsorption system reached an equilibrium with a maximum adsorbent capacity of 207.8 mg/g with a pH 4.5， a temperature of 55 ℃， a contact time of 100 min， and an Fe3O4?SiO2?NH?COOH concentration of 1.0 g/L. The Langmuir equation is able to better describe the adsorption isotherm， indicating an endothermic process for the adsorption of Pb2+. The adsorption capacity of Fe3O4?SiO2?NH?COOH toward Pb2+ showed an increase at first and then tended to stabilize with an increase in time. However， it increased at first and then decreased with an increase in pH. Compared to monovalent cations， the presence of divalent Ca2+ and Mg2+ in the solution could generate a certain inhibitory effect on the adsorption reaction. The Pb2+ removal rate was still above 50 % after regeneration of Fe3O4?SiO2?NH?COOH for six times.
LEI Jingfa, DUAN Huantian, LIU Tao, WEI Zhan, SUN Hong
Abstract (
571 )
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To study the dynamic mechanical properties of melt deposited poly（lactic acid）（PLA） materials， their dynamic compression experiments were carried out using a split Hopkinson pressure bar （SHPB） experimental device with loading strain rates of 880， 1 230， 1 650 and 2 230 s-1. The deformation images of PLA materials were obtained under different strain rates using a high frame rate image acquisition instrument. A digital image correlation （DIC） method was adopted to analyze the strain field along the loading direction， and the strain rate analysis was carried out. The results indicated that the melt deposited PLA present elastic， plastic and unloading stages in the deformation process under a dynamic loading. With an increase in strain rate， a significant plastic flow region appears in the plastic stage of PLA， and the compressive strength and maximum strain also tended to increase. The strain distribution in the sample was almost uniform over the whole dynamic impact experiment， and the strain range increased with an increase in strain rate. The strain rate kept almost a constant value during the whole loading process. According to the SHPB experiment， the strain rate error measured by the DIC method was less than 3 %. This indicates that the DIC method can be applied to the SHPB experiment.
LI Shaoyuan, SUN Ling, CAI Hengfang
Abstract (
519 )
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The diffusion behavior of CO2 and O2 molecules in the poly（lactic acid） （PLA）/polyvinylidene fluoride（PVDF） blends was studied using a molecular dynamics simulation method. The free volume fraction of the blending system model and the diffusion coefficient of CO2 and O2 molecules in the system were calculated through the Fick’s first law using the Einstein relational formula. The relationships between free volume fraction and probe radius and the between the free volume fraction and diffusion coefficient were explored. The results indicated that the CO2 and O2 molecules exhibited the smallest diffusion coefficients at mass ratio of PLA to PVDF of 9 to 1. The blends exhibited optimal barrier performance. The smaller the dynamic radius of small molecules in the blending system， the larger was the diffusion coefficient. The free volume fraction decreased with an increase in probe radius according to the hard?ball probe model. In different blending systems， the free volume fraction showed a variation trend consistent with the diffusion coefficient. This result was in good agreement with the Fox's and Flory's theories in free volume.
CHEN Shiqi, WANG Xuanlun
Abstract (
578 )
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Polypropylene random copolymer （PP?R）/nano?SiO2 composites were prepared through a melt blending method， and their mechanical properties， crystallization thermodynamics， crystalline morphology and micromorphology were characterized using an electronic universal tensile testing machine， differential scanning calorimeter， polarizing microscope and scanning electron microscope. The results indicated that the addition of nano?SiO2 resulted in an increase in the crystallization temperature of PP?R from 93 to 105.6 °C and in the melting temperature from 141.6 to 142.8 °C. The nano?SiO2 plays a role of heterogeneous nucleation in improving the crystallization rate of PP?R and refining its crystal grain. The composites containing 2 wt% nano?SiO2 achieved a maximum value in impact strength at -15 °C. This result was more than 2 times higher than that of pure PP?R. On the other hand， the composites containing 1 wt% nano?SiO2 achieved a maximum value in impact strength at 23 °C， which is nearly 2 times higher than that of pure PP?R. Moreover， the bending strength， tensile strength and elongation at break of the composites were improved as well.
TIE Rui, WU You, HAN Xiaolong, SONG Jiajie, WANG Yuchen, KAN Chunyi, YUAN Mengju, JIN Yujuan
Abstract (
408 )
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Poly（3-hydroxybutyrate-co-3-hydroxyvalerate） （PHBV）/ethylene-vinyl acetate elastomer （EVA）/organically modified montmorillonite （OMMT） blends were prepared through melting blending using OMMT as a modifier. Their rheological， crystalline， mechanical， and thermal properties as well as morphology were characterized using a rotational rheometer， differential scanning calorimeter， infrared spectrometer， universal testing machine， thermal weight loss analyzer， polarized light microscope and scanning electron microscope. The results indicated that the blends achieved an increase in loss modulus and complex viscosity with an increase in the OMMT content. OMMT can induce an intercalation structure in the blends. The addition of OMMT deteriorated the crystallization of the blends， resulting in a decrease in crystallinity. The blends exhibited the lowest degree of crystallinity of 43.4 % at an OMMT content of 7 phr. Their elongation at break and impact strength increased at first and then decreased with an increase in the OMMT content. Compared to the PHBV/EVA binary blends， the ternary blends with 3 phr of OMMT achieved an increase in elongation at break by 38.3 % and in impact strength by 52.5 %. Their impact facture surface became rougher with the addition of OMMT.
LIU Zili, WU Chenying, LIU Xiqin, WEI Dongbo, BAO Jinfang, ZHU Jun, CHEN Xinxiang
Abstract (
511 )
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Polyethylene vinyl acetate/low-density polyethylene/aluminum hydroxide compounds were prepared using whisker as an impact modifier. Their microstructure， flame retardant properties， mechanical properties and electrical properties were characterized using scanning electron microscope， thermogravimetric analyzer， oxygen index meter， cone calorimeter， universal tensile machine and high resistance meter. The results indicated that aluminum hydroxide particles were well dispersed in the matrix without obvious agglomeration， and the whiskers were staggered in the compounds with tightly bonding onto the matrix interface. The flame retardancy of the compounds was improved due to the enhancement of carbon layer resulting from the network skeleton of the pyrolysis products of whiskers. When the addition amount of magnesium hydroxide sulfate hydrates whisker（MHSH）， aluminum borate whisker， and calcium sulfate whisker（CSW） was set to be 13.5 phr， 6.75 phr， and 6.75 phr， respectively， the compound sample exhibits optimal flame retardant performance with a mass retention rate of 32.7 wt% at 800 °C. With this formulation， the compound achieved a limiting oxygen index of 26.8 vol%， a peak heat release rate（pHRR） of 364.4 kW/m2， a total heat release of 20.8 MJ/m2， and a total smoke release（TSR） of 187.2 m2/m2. MHSH can reduce the pHRR and TSR and enhance the tensile strength of the compounds. CSW can delay the time to ignition， reduce the flashover trend， increase the TSR， and increase the elongation at break of the compounds. However， whiskers generated a limited influence on the tensile strength， shore hardness， and electrical insulation properties of the compounds.
Processing and Application
XUE Maoyuan, MEI Yi, LUO Ningkang, TANG Fangyan, XIAO Zhankai
Abstract (
432 )
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The problems of warpage and deformation occurring in the injection?molded car lift switch panel were investigated. The warpage deformation of the molded products was obtained through selecting the packing curve model and parameters for the orthogonal experimental design and also simulating and analyzing with the Moldflow software. The optimal process parameter combination of the range analysis and optimization method was obtained from the range analysis of the warpage deformation. The Vague set was employed to optimize the standard deviation of volume shrinkage rate and the maximum volume shrinkage rate through multi?objective optimization. The optimal process parameter combination of Vague set optimization method was obtained. Then， the warpage quantities obtained from different optimization methods were compared. The results indicated that the uneven shrinkage was the main factor causing the warpage of the part. The warpage deformation corresponding to the range analysis and optimization method was 1.5 %， which was lower than the minimum warpage deformation in the orthogonal experiment. The optimization effect was not evident. The warpage deformation corresponding to the Vague set optimization method was reduced by 26.5 % compared to the minimum warpage deformation in the orthogonal experiment. There is no significant difference in the internal pressure distribution of the mold. The Vague set optimization method exhibited a better optimization effect than the range analysis one. This indicates that the Vague set optimization method can greatly reduces the warpage deformation of the mold.
LI Shao, WANG Xiaoxin, ZHOU Lehui, FU Nuofeng, ZHONG Jianquan
Abstract (
382 )
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A sandwich injection?simulation analysis was carried out for a barrel?shaped plastic part using the Moldflow software. The effects of the material viscosity ratio of core to shell and the product wall thickness on the core penetration length， core thickness， and core distribution uniformity of the sandwich injection?molded products were investigated. The results indicated that under the same molding process parameters， the core penetration length ratio decreased in a rate of 1.41 %~1.67 % with an increase in a viscosity ratio of core to shell. Meanwhile， the average value of the core melt thickness ratio increased at a rate of 1.76 %~2.28 %， and the core melt thickness ratio deviation increased at a rate of 1.91 %~2.66 %. As the product wall thickness increased by 1 mm， the core melt penetration length ratio decreased by 1 %~2 %， the average value of the core melt thickness ratio increased by about 6 %， and the core melt thickness ratio deviation increased by about 10 %.
CHEN Lijuan, LIU Pu, DONG Lei, LIU Chang, FAN Xuehua, ZHANG Sheng, SUN Jun, WANG Jingbao, ZHAO Jingmao
Abstract (
453 )
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To explore the applicability of heat-resistance non-crosslinked polyethylene （PE-RT） in the salt water at three different temperatures of 80， 85 and 90 °C， an immersion experiments was conducted to simulate the real working condition. The water absorption， tensile strength， elongation at break and molecular structure of PE?RT before and after immersion were characterized using a universal tensile testing machine and infrared spectrometer. The result indicated that although PE?RT absorbed water， resulting in an increase in weight after immersion， the maximum water absorption was about 0.65 %. This result is far less than the range specified in the ISO 23962?1 standard. After immersion for 28 days， the PE?RT present a variation rate of tensile strength between -15 % and -9 % and a variation rate of elongation at break between -30 % and -24 %. This meets the requirements of ISO 23962?1. The PE?RT underwent oxidation and chain scission at an immersion temperature of 90 °C. Therefore， the material developed in this study is recommended to use in salt water at a temperature lower than 85 °C.
WU Hu, LI Xinning, YANG Xianhai, YANG Liyong
Abstract (
468 )
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Aiming at the problems in the physical processing protocol of 2，2'?azobis（2，4?dimethylvaleronitrile） （ABVN）， a solution was proposed by means of a connecting rod robot to crush the remaining materials at the bottom of the barrel. Based on the Lie group and Lie algebra theory， the configuration of the connecting rod robot was designed， and a variety of equivalent kinematic chains were generated and optimized. The results indicated that selecting the RRR?type connecting rod robot for processing was an optimal physical processing protocol. The RRR?type linkage robot was easy to manufacture due to its simple structure， and it could run stably when used to disperse the remaining materials. It took 127.1， 129.1， 143.1 and 109.6 s for the current protocol， RRP?type， RPP?type， and RRR?type protocols to crush the remaining materials， respectively. The RRR?type protocol can save about 13.77 % of the processing time compared to the current protocol.
CHEN Chenwei, ZHU Kexin, CHEN Lijun, YANG Shaohua, XIE Jin
Abstract (
755 )
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This paper introduced the anti-fogging principles and preparation methods of anti?fog packaging films and anti-fog antibacterial packaging films. Three preparation methods of anti?fog packaging materials were introduced in detail， which included the modification of anti?fogging agents， the covering of photosensitive material coatings， and the use of hydrophilic base materials. The research progress in the applications of anti?fog packaging film and anti-fog antibacterial packaging film in the preservation of fruits and vegetables were reviewed. The development and applications of anti?fog antibacterial packaging materials were prospected.
Additive
LU Yuxin, LU Lingang
Abstract (
820 )
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This paper reported a study on the change process of the macro?carbon formation of tea polyphenols. Thermogravimetry was conducted for tea polyphenols using a synchronous thermal analyzer in different atmospheres and at different heating rates. The Kissinger’s and Ozawa’s methods were employed to calculate the activation energy of tea polyphenols in different atmospheres. The results indicated that an expanded carbon layer was formed for tea polyphenols after heated， and it could retain a complete carbon skeleton at high temperatures. Tea polyphenols exhibited a good thermal stability. There is a rapid weight loss only when heating temperature exceeds 200 °C. The carbon residue rate of tea polyphenols reached 29.69 wt% in nitrogen at a heating temperature of 800 °C， and the carbon residue rate reached 9 wt% in air. The average activation energy of tea polyphenols in nitrogen was greater than that in air. However， the activation energy in air was greater than that in nitrogen in the initial heating stage.
WU Tingting, DENG Jianneng, LI Daobin, CAI Guoquan, DENG Shaoxin
Abstract (
463 )
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Epoxidized neopentylglycol dioleate （ENDO） was prepared as a novel eco?friendly plasticizer through an esterification reaction and an epoxidation reaction between oleic acid and neopentylglycol， and its chemical structure was characterized through Fourier?transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The rheological properties， low temperature embrittlement properties， solvent extraction resistance， and aging resistance of the polyvinyl chloride （PVC） compounds plasticized with ENDO， dioctyl phthalate （DOP）， dioctyl adipate （DOA） or trioctyl trimellitate （TOTM） were investigated using a torque rheometer， ultra?low temperature embrittlement tester， aging tester and universal testing machine. The results indicated that ENDO was successfully synthesized with a desired chemical structure. The TOTM?plasticized PVC compound exhibited greater torque and energy consumption than the ENDO， DOP， and DOA?plasticized one. The low?temperature embrittlement property of the plasticized PVC by ENDO could pass?30 ℃ test. In the extraction resistance test of n?hexane，the residual rates of elongation at break of the plasticized PVC by DOP，ENDO，DOA and TOTM were 88.24 %，87.99 %，1.69 % and 0.71 %，respectively. And in the extraction resistance test of anhydrous ethanol，they were 79.00 %，96.22 %，72.76 % and 74.52 %，respectively. The change rate of elongation at break and tensile strength，the mass loss of thermal aging of the plasticized PVC by ENDO were all lower than those of the plasticized PVC by TOTM.
Standard and Test
LI Yan, ZHANG Weijie, TANG Xiaoxu, JIANG Lei, HUANG Jiawen, CHENG Debao
Abstract (
807 )
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This paper compared three test methods and standards of carbon black content at home and abroad and discussed the differences among the three test methods， including the tubular electric furnace method， muffle furnace method， and thermogravimetric analysis method. Based on the comparative studies， some suggestions were provided for the revision the GB/T 13021—1991 standard. The results indicated that the determination method included in the GB/T 13021—1991 standard was relatively simple. To revise the GB/T 13021—1991 standard， some regulations were recommended to be included. For example， if the nitrogen with an oxygen content of less than 0.002 %， oxygen removal may not be carried out in the tubular electric furnace method. The other regulations were also suggested to use， including the requirement for cleaning and weighting the sample prior to the formal test， appending a muffle furnace method （either a traditional muffle furnace method or a microwave muffle furnace method） and a thermogravimetric analyzer method. In muffle furnace method， weighing steps were recommended to adopt according to the provisions of the ISO 6964?2019 standard. In the thermogravimetric analyzer method， the sampling position and value description were recommended to be included in addition to the provisions of ISO 6964?2019.
Machinery and Mould
SHI Wentian, SUN Wenlong, YUAN Meixia, LIU Yude
Abstract (
491 )
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This paper reviewed the research progress in the special cutting tools for processing fiber?reinforced composite materials （FRP）. The current research status in tool materials， tool surface coatings， tool special structures and processing auxiliary processes was also introduced in detail. Some typical FRP special processing tools at home and abroad developed in recent years were summarized. In addition， the tool path and process parameter optimization method were introduced briefly. Finally， the overall design ideas and principles of the FRP special processing tool were proposed and discussed.
Review
TAN Bowen, SUN Zhaoyang, JI Yang
Abstract (
1640 )
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This paper reviewed the synthesis routes of poly（glycolic acid） （PGA） and its monomers and compared the mechanical properties， barrier properties， biodegradability， and thermal stability of PGA with other traditional plastics. The development of PGA for the scaled?up production line was also introduced. The modification methods for PGA?based materials were summarized and discussed to provide a critical suggestion on the technical challenges and opportunities for PGA?based materials. With diversity and advanced properties， PGA exhibit great potential to substitute tradition petrochemical?based polymers for high strength and high barrier applications.
WANG Qian, LIU Qing, MO Shunpin, CHEN Xuehua, LYU Wenyan
Abstract (
2618 )
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This paper reviewed the recent research progress in gel polymer electrolyte （GPE） at home and abroad. The paper also introduced the research status in the preparation method， modification method and performance of GPE based on polyoxyethylene， polyvinylidene fluoride-hexafluoropropylene， polyacrylonitrile， and polymethyl methacrylate. Finally， the future research direction of GPE was prospected.
WANG Huitian, YIN Sha, CHEN Zhengwei, ZHAO Haibin, LOH Chaliang
Abstract (
910 )
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This article introduced the definition and advantages of microcellular foamed plastics and compared the two microcellular foaming injection molding processes， including physical microcellular foaming and chemical microcellular foaming. The latest research progress in microcellular foam injection molding technology was introduced in terms of process optimization， mold opening secondary foaming， surface quality improvement， and mechanical performance prediction. Finally， the future research direction of microcellular foam injection molding technology was prospected.
