Polymer Degradation and Stability最新文献_第5页

Favorable compatibility efficiency and thermal stability of PLA/P4HB/PGMA blends contributed by phase interface-located chain expansion reaction

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111159

Yitong Ding , Mingjiao Li , Wenjing Dong, Ze Kan, Zhibo Li

{"title":"Favorable compatibility efficiency and thermal stability of PLA/P4HB/PGMA blends contributed by phase interface-located chain expansion reaction","authors":"Yitong Ding , Mingjiao Li , Wenjing Dong, Ze Kan, Zhibo Li","doi":"10.1016/j.polymdegradstab.2024.111159","DOIUrl":"10.1016/j.polymdegradstab.2024.111159","url":null,"abstract":"<div><div>Chemically synthesized poly(4-hydroxybutyrate) (P4HB) serves as an alternative material for toughening poly(lactic acid) (PLA), but the two materials exhibit poor compatibility, and most compatibilizers fail to localize at the phase interface, resulting in inefficient toughening. In this study, a phase interface-located reactive compatibilizer, poly (glycidyl methacrylate) (PGMA), is synthesized to enhance the interfacial adhesion between PLA and P4HB, thereby improving their compatibility. The PGMA compatibilizer demonstrates a tendency to selectively disperse at the phase interface of PLA and P4HB supported by thermodynamic calculations. Compared to the PLA/P4HB blend, the PLA/P4HB/PGMA blend exhibits enhanced molecular chain entanglement and a blurrier phase interface. Consequently, the mechanical and shape memory behavior of the PLA/P4HB/PGMA blend are improved. For example, the elongation at break of the PLA/P4HB/PGMA blend increased from 20.8 % to 265.1 %, marking an increase of 12.7 times compared to the PLA/P4HB blend. Due to its small molecular weight, the <span><math><msub><mi>T</mi><mrow><mi>o</mi><mi>n</mi><mi>e</mi><mi>s</mi><mi>e</mi><mi>t</mi></mrow></msub></math></span> (onset degradation temperature) of PGMA is only 180.3 °C. Fortunately, the <span><math><msub><mi>T</mi><mrow><mi>o</mi><mi>n</mi><mi>e</mi><mi>s</mi><mi>e</mi><mi>t</mi></mrow></msub></math></span> of the PLA/P4HB/PGMA system exceeds 220 °C after the chain expansion reaction, indicating a significant improvement in thermal stability. Thus, the phase interface-located chain expansion reaction offers an effective approach to improving the compatibility of PLA/P4HB blends while maintaining their high thermal stability.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111159"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143183390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Alcohol degradation of anhydride-cured epoxy resin insulations and the properties of recycled materials 酸酐固化环氧树脂绝缘材料的酒精降解和再生材料的性能

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111134

Xu Zhang , Yiran Hu , Guoli Wang , Chao Gao , Jiahe Yu , Xiaoxing Zhang , Yunjian Wu

{"title":"Alcohol degradation of anhydride-cured epoxy resin insulations and the properties of recycled materials","authors":"Xu Zhang , Yiran Hu , Guoli Wang , Chao Gao , Jiahe Yu , Xiaoxing Zhang , Yunjian Wu","doi":"10.1016/j.polymdegradstab.2024.111134","DOIUrl":"10.1016/j.polymdegradstab.2024.111134","url":null,"abstract":"<div><div>Epoxy resins are widely used as electrical insulation materials due to their excellent properties. However, the three-dimensional network structure of epoxy resin makes it difficult to be degraded and recycled, and incineration or landfill will cause environmental pollution as well as waste of resources. In order to study the degradation technology of epoxy insulating materials (EIM) under mild conditions, the degradation of EIM was achieved under mild conditions using K<sub>3</sub>PO<sub>4</sub> as a catalyst in ethylene glycol at 120 °C for 3 h Degradation products of epoxy resin insulation materials (DEM) were used to partially replace bisphenol A diglycidyl ether (DGEBA) in the preparation of recycled epoxy resin insulation materials (RIM). The results showed that RIM could maintain good insulating properties when the DEM content was lower than 38.4 wt.%, the tensile strength and T<sub>g</sub> were also held up will when the DEM content was 22wt.%. This study provides new ideas and methods for the recycling of epoxy resin insulating materials, which can help the resourceful reuse of epoxy cast electrical equipment after decommissioning.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111134"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142823426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Impact of phosphonate and phosphoramidate in Si/P/triazine hybrid flame retardants on cotton flammability

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111107

Valbone Shabani , Wael Ali , Bassem Assfour , Raphael Otto , Dennis Killa , Seden Caglar , Ying Feng , Eui-young Shin , Jochen S. Gutmann , Thomas Mayer-Gall

{"title":"Impact of phosphonate and phosphoramidate in Si/P/triazine hybrid flame retardants on cotton flammability","authors":"Valbone Shabani , Wael Ali , Bassem Assfour , Raphael Otto , Dennis Killa , Seden Caglar , Ying Feng , Eui-young Shin , Jochen S. Gutmann , Thomas Mayer-Gall","doi":"10.1016/j.polymdegradstab.2024.111107","DOIUrl":"10.1016/j.polymdegradstab.2024.111107","url":null,"abstract":"<div><div>Phosphorus and nitrogen-containing flame retardants are well-known for their high efficacy when used in combination, either as separate compounds or within the same molecule. However, a detailed examination of the chemical bonding of phosphorus is needed to understand the flame behavior. To this end, two different scenarios were examined and compared with a phosphorus-free benchmark. Both scenarios contain a triazine ring and a silane-based precursor. The first scenario involves a direct bond between phosphorus and triazine (phosphonate), while the second involves a bridging of phosphorus and triazine via nitrogen (phosphoramidate). This allowed to investigate the structural effect of phosphoramidate and phosphonate of triazine derivatives on the thermal and flame retardant behavior. The flame-retardant performance and mechanism of the treated samples were investigated by means of the vertical flame test (DIN EN ISO 15025), thermogravimetric analysis and microscale combustion calorimetry, amongst others. Our research shows that triazine-based phosphonate has a better flame retarding effect on cotton than phosphoramidate at the same phosphorus concentration. Self-extinguishing characteristics was observed at a low add-on value of 0.23 mmol/g for phosphonate-based flame retardant, while a higher add-one value of 0.24 mmol/g was required in the case of phosphoramidate. The comprehensive analysis demonstrated that both flame retardants undergo mechanisms in both the gas phase and condensed phase by releasing incombustible gases and promoting the carbonization of cotton fabrics.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111107"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143183396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Construction of durable biomass-based flame retardant with high phosphorus and nitrogen contents for wood coatings

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111160

An Wei , Shunxiang Wang , Xulan Lu , Yongjin Zou , Cuili Xiang , Fen Xu , Lixian Sun , Yunhao Lu

{"title":"Construction of durable biomass-based flame retardant with high phosphorus and nitrogen contents for wood coatings","authors":"An Wei , Shunxiang Wang , Xulan Lu , Yongjin Zou , Cuili Xiang , Fen Xu , Lixian Sun , Yunhao Lu","doi":"10.1016/j.polymdegradstab.2024.111160","DOIUrl":"10.1016/j.polymdegradstab.2024.111160","url":null,"abstract":"<div><div>As a commonly used material, wood's inherent flammability poses a significant fire safety hazard to people, and it is necessary to improve the flame-retardant performance of wood. This study prepared a novel lignin-based intumescent flame-retardant (PGL) using phosphorus-rich phytic acid, nitrogen-rich guanazole, and carbon-rich lignin as raw materials. Subsequently, PGL was infiltrated into the urea-formaldehyde resin as a flame-retardant component, and a series of PGL-modified urea-formaldehyde resin wood coatings (PGLUF) were prepared. The wood coated with PGLUF exhibited high flame retardancy and passed the UL-94 V-0 level test with a limit of oxygen index (LOI) of 36.5 %. The total heat release (THR) and peak heat release rate (PHRR) were reduced by 92.73 % and 93.58 %, respectively, compared to pure wood. Moreover, when the PGL content was 3 wt.%, the PGLUF could achieve comparable flame retardancy to the coating containing 5 wt.% commercial flame-retardant (triphenyl phosphate, TPP). PGL also exhibited a plasticizing effect on the coatings. The impact strength of PGLUF-coated wood increased with the increase of PGL content. PGL can simultaneously enhance the flame retardancy and mechanical properties of materials, and the preparation process is green and safe. Therefore, the PGL shows excellent potential in practical applications.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111160"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Enhancing flame-retardant and mechanical properties of epoxy composites through bio-based flame retardant treated cotton fabric reinforcement 通过生物基阻燃处理棉织物增强环氧树脂复合材料的阻燃性和机械性能

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111109

Maksym Li , Prabhakar M．N． , Jong-kyu Park , Jung-il Song

{"title":"Enhancing flame-retardant and mechanical properties of epoxy composites through bio-based flame retardant treated cotton fabric reinforcement","authors":"Maksym Li , Prabhakar M．N． , Jong-kyu Park , Jung-il Song","doi":"10.1016/j.polymdegradstab.2024.111109","DOIUrl":"10.1016/j.polymdegradstab.2024.111109","url":null,"abstract":"<div><div>Due to tightening fire safety regulations and environmental concerns, eco-friendly natural fiber-reinforced composites (NFRCs) are increasingly popular for their biodegradability, renewability, low cost, and high specific mechanical properties. However, ensuring fire safety in NFRCs is challenging, as conventional synthetic flame retardants can reduce mechanical properties due to particle agglomeration and poor compatibility with the matrix. Therefore, in this study, the flame-retardant epoxy composite (EP/FR) was fabricated by using cotton treated with novel dual complex solutions containing phytic acid, chitosan, and urea. Remarkably, applying just one bilayer of this treatment led to significant improvements in flame retardancy, as evidenced by a reduction of up to 44.8 % in the peak heat release rate and a 23.7 % decrease in total heat release during cone calorimeter testing. Additionally, the horizontal burning rate was reduced by up to 16.8 %. Analysis of solid residue after fire test and gas product liberated during pyrolysis demonstrated an intumescent mechanism of flame retardancy. Mechanical property studies showed better performance for EP/FR, with SEM of the fractured surface proving better interfacial adhesion between fiber and matrix because of the fiber treatment. Overall, this study offers a novel and greener approach to improving the flame-retardant and mechanical properties of NFRC, paving the way for more sustainable composite materials.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111109"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Raman spectroscopic observation of conformational changes during thermal exposure and its effects on melting and crystallization behavior of high-density polyethylene 拉曼光谱观测热暴露期间的构象变化及其对高密度聚乙烯熔化和结晶行为的影响

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111152

Yusuke Hiejima , Hikaru Kawada , Takumitsu Kida , Koh-hei Nitta

{"title":"Raman spectroscopic observation of conformational changes during thermal exposure and its effects on melting and crystallization behavior of high-density polyethylene","authors":"Yusuke Hiejima , Hikaru Kawada , Takumitsu Kida , Koh-hei Nitta","doi":"10.1016/j.polymdegradstab.2024.111152","DOIUrl":"10.1016/j.polymdegradstab.2024.111152","url":null,"abstract":"<div><div>In the present study, we used Raman spectroscopy to reveal conformational changes of high-density polyethylene (HDPE) during long-time thermal exposure in air at 110 °C. In the early stage, we observed an increase in crystallinity complemented by a decrease in the number of non-crystalline short <em>trans</em> sequences owing to structural rearrangement, which is the typical effect of annealing. Deterioration of the mechanical properties, such as a decrease in the strain at break, gradually proceeded, even before chemicrystallization. This will be ascribed to conformational reordering of the crystalline structure, i.e., a gradual increase in crystallinity accompanied by a decrease in both non-crystalline short and long <em>trans</em> sequences. During chemicrystallization, a further increase of crystallinity accompanied by elimination of the non-crystalline short and long <em>trans</em> sequences resulted in embrittlement of the HDPE specimen. Conformational changes in the HDPE specimen after thermal exposure were monitored in situ during heating and cooling. The <em>trans</em> sequence formed during thermal exposure was highly stabilized, resulting in higher crystallinity and <em>trans</em> fractions up to the vicinity of the melting temperature. The detection of non-crystalline short <em>trans</em> sequences can be used to predict the degree of deterioration of thermally exposed HDPE owing to the strong correlation between the decrease in the number of non-crystalline short <em>trans</em> sequences and the strain at break.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111152"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Preparation of perovskite catalysts and their mechanism of catalytic degradation and regeneration of waste polyisocyanurate 过氧化物催化剂的制备及其催化降解和再生废弃聚异氰脲酸酯的机理

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111138

Xiaohua Gu , Shangwen Zhu , Siwen Liu , Chin Hao Chong

引用次数: 0

New modification strategy for thermoplastic polyurethane with high hygrothermal ageing resistance and flame retardancy 具有高耐热老化性和阻燃性的热塑性聚氨酯改性新策略

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111140

Lvxing Wang , Saifei Xiang , Guangpu Ling , Jianbo Ying , Jiahui Zhou , Jintao Yang

{"title":"New modification strategy for thermoplastic polyurethane with high hygrothermal ageing resistance and flame retardancy","authors":"Lvxing Wang , Saifei Xiang , Guangpu Ling , Jianbo Ying , Jiahui Zhou , Jintao Yang","doi":"10.1016/j.polymdegradstab.2024.111140","DOIUrl":"10.1016/j.polymdegradstab.2024.111140","url":null,"abstract":"<div><div>Thermoplastic polyurethane (TPU) has been extensively used in many industrial communities, such as aerospace, electronics, and automotive manufacturing due to its remarkable mechanical strength, elasticity, and excellent chemical resistance. However, flammability and performance deterioration under high-temperature and high-humidity of TPU greatly limit its wider application. Herein, TPU composites with high hygrothermal ageing resistance and flame retardancy are prepared by introducing a molecularly engineered fluorinated thermoplastic polyurethane (FTPU) and synergistic flame retardant. The results show that the presence of FTPU greatly enhances the hydrophobicity of the matrix, impeding the diffusion of the water molecules into the composite, and alleviating the decrease of glass transition temperature and the rise of loss factor resulted from water plasticization effect. As a result, the TPU/FTPU composite shows a much higher mechanical property retention rate after immersing in water of 80 °C for 7 days, as compared to the pristine TPU. In addition, FTPU also exhibits synergistic effect with aluminum diethylphosphinate (ADP) and melamine cyanurate (MCA). The composite containing FTPU, ADP, and MCA (8 %, 4.5 %, and 4.5 %, respectively) can meet UL94 V-0 flame-retardant standard while the counterpart without FTPU shows UL94 V-2 flame retardancy. At the same time, such composite still exhibits tensile strength retention rate of 84.3 % after hygrothermal ageing treatment. This work provides a new modification strategy to simultaneously improve the hygrothermal ageing resistance and flame retardancy of TPU, which also can hopefully inspire the design of other polymers for high performance purpose.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111140"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143181562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Measurement of monomers and oligomers (≤20mer) as intermediates using LC–Orbitrap MS from marine biodegradation of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in laboratory

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111166

Makoto Yasojima , Kana Kuroishi-Kawabe , Chihiro Nouda-Ibushi , Ryo Fujita , Takaki Mine , Hiroaki Takemori , Masao Kunioka

{"title":"Measurement of monomers and oligomers (≤20mer) as intermediates using LC–Orbitrap MS from marine biodegradation of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in laboratory","authors":"Makoto Yasojima , Kana Kuroishi-Kawabe , Chihiro Nouda-Ibushi , Ryo Fujita , Takaki Mine , Hiroaki Takemori , Masao Kunioka","doi":"10.1016/j.polymdegradstab.2024.111166","DOIUrl":"10.1016/j.polymdegradstab.2024.111166","url":null,"abstract":"<div><div>Degraded intermediates in the marine biodegradation of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), a microbial polyester, were detected and quantified using LC<img>Orbitrap MS. Intermediates were extracted from a biofilm (BF) attached to the biodegraded film using solvent extraction. Monomers and oligomers up to 11mer were identified on the surface of a marine biodegraded PHBH film and in the associated BF. The biodegradability and intermediate amounts of three films (ca. 90 mg) on day 9 were 13 % and 9.2 μg in the first test, 30 % and 13 μg in the second test, and 52 % and 19 μg in the third test, respectively. Differences in biodegradability and intermediate amounts between the biodegradation tests suggest that variation in the microbial community and quantity in seawater affect enzymatic degradation and mineralization rates. The amounts of 3-hydroxybutyric acid (3HB) monomer, 3-hydroxyhexanoate (3HH) monomer, and oligomers (3HB equivalent) were 67:5:28 (9.2 μg) in the first test, 69:5:26 (13 μg) in the second test, and 79:7:14 (19 μg) in the third test, respectively. The substantial occupancy of monomers in the intermediates suggests that the oligomers are rapidly enzymatically degraded into monomers, which are slowly mineralized and metabolized. Monomers were the only species identified in the pore water (free water within the BF), and the concentrations of intermediates in seawater were below the detection limit. The monomer composition (3HB:3HH) in the intermediate was consistent with the copolymer composition, indicating no selective accumulation of specific monomers.</div></div>","PeriodicalId":406,"journal":{"name":"Polymer Degradation and Stability","volume":"232 ","pages":"Article 111166"},"PeriodicalIF":6.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143183391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Analysis of high-molecular weight polyethylene glycol degradation by Pseudomonas sp.

IF 6.3 2区化学

Polymer Degradation and Stability Pub Date : 2025-02-01 DOI: 10.1016/j.polymdegradstab.2024.111144

M. Geisler , J. Khan , T. Heine , M.B. Ansorge-Schumacher , J. Thiele , A. Kaufmann

引用次数: 0