基于科学计量的天然橡胶学科领域前沿热点分析

2020-02-22 03:19李一萍茶正早王大鹏
热带作物学报 2020年12期

李一萍 茶正早 王大鹏

摘  要:当前天然橡胶产业持续低迷,追踪国际天然橡胶研究前沿热点对于我国天然橡胶产业发展和升级具有重要参考价值。本研究采用科学计量方法结合CiteSpace技术,对Web of Science数据库的天然橡胶文献进行共被引、共词和聚类分析,概述了该领域重要的基础文献,揭示其学科领域研究前沿和热点。结果表明,共探测出6个前沿热点,高度聚合在三大学科领域。其中,在化学与材料科学领域,领先优势十分明显,共遴选出4个前沿热点:(1)功能化改性石墨烯或氧化石墨/天然橡胶纳米复合材料;(2)生物基体/天然橡胶纳米复合材料;(3)弹性体或天然橡膠纳米复合材料的应变诱导结晶行为;(4)废旧橡胶的自修复与回收加工。在生物科学领域,遴选出1个前沿热点,即橡胶树基因组测序、橡胶生物合成路径与关键基因。在生态与环境科学领域,遴选出1个前沿热点,即橡胶林的扩张及其对生态环境的影响。高频和高突现关键词在三大学科呈现由多到少分布,反映了当前天然橡胶研究领域发展趋于多方向性,但其前沿热点相对集中在天然橡胶全产业链的下游。

关键词:天然橡胶;学科领域;科学计量;前沿热点

中图分类号:S794.1;G353.1      文献标识码:A

Abstract: At present, the natural rubber industry has fallen into continuous tremor. Consequently, tracking and analyzing the hotspots in the fields of international natural rubber research is of important referring values for developing and upgrading the natural rubber industry of China. Based on the database from Web of Science, scientometrics methods and CiteSpace were used to analyze the co-citation, co-word and clustering of natural rubber literature. The basic articles were summarized to track and reveal the future fronts and hotspots in this field. The results showed that six hotspots were detected, which were highly concentrated in the three fields. Of the fields of chemistry and material science, the leading advantage was very obvious, and four hotspots were protruded: (1) functionally modified grapheme or graphene oxide/natural rubber nanocomposites; (2) biobased/natural rubber nanocomposites; (3) strain-induced crystallization behavior of elastomers or natural rubber; (4) self-healing and recycling of waste rubber. Of the field of biological science, there was one hotspot: rubber tree genome sequencing, rubber biosynthesis pathway and key genes. Of the field of ecological and environmental science, the expansion of rubber plantation and its impact on the ecological environment is becoming important research hotspots in this field. High-frequency and high-emergency keywords showed a distribution trend of gradually less in the three major disciplines, which reflecting that the current research field of natural rubber intends to be multi-directional, but its frontier hotspots are relatively concentrated in the downstream link of the whole natural rubber industry chain.

Keywords: natural rubber; discipline field; scientometrics; fronts and hotspots

DOI: 10.3969/j.issn.1000-2561.2020.12.028

天然橡胶是由含橡胶的植物中采割其胶乳加工而成。据统计[1-2],世界上能产胶的植物约有2 000多种,其中重要的有大戟科的巴西橡胶树(Hevea brasiliensis),菊科的橡胶草(Taraxacum brevicorniculatum)和银色橡胶菊(Parthenium argentatum),杜仲科的杜仲(Eucommia ulmoides Oliver)等。巴西橡胶树(又称橡胶树)由于其产量高、品质好、经济寿命长、生产成本低等优点,成为人工栽培中最为重要的产胶植物,其产量占世界天然橡胶总产量的99%以上。橡胶是热带地区典型的经济林作物,是重要的战略物资。在热带农林业中,橡胶具有特殊和重要的地位。迄今为止,天然橡胶在航天、军工及医疗等高端和特殊用途领域中仍具有不可替代性。当前,天然橡胶产业持续低迷,国际天然橡胶产品供大于求,但我国天然橡胶的自给率仍不到20%。而与此同时,国内高端和特殊用途的高性能胶却仍然几乎完全依赖进口。我国天然橡胶产业发展中的一些重大问题已逐渐发生转变,如从早期的追求高产转变为高产与优质并重、胶木兼优品种的选育和推广、劳动力成本的不断上升、加工领域工艺改进和技术创新等。从我国天然橡胶产业发展历程来看,科学技术的提升是推动橡胶产业升级的重要动力。当前一些高新尖的技术领域,如天然高分子或纳米微粒补强天然橡胶合成纳米复合材料、橡胶微生物降解、产胶植物橡胶生物合成与调控等,未来很可能极大地影响天然橡胶产业的发展。

科学知识图谱是进行领域分析和可视化的通用过程,其分析范围可以是一门学科、一个研究领域、或特定研究问题的主题领域。换句话说,知识图谱的分析单元是科学知识的一一个领域,它通过一个科学团体或更精确定义的专业成员的智力贡献集合来反映[3-4]。常用的科学文献数据来源有Web of Science、Scopus、Google Scholar和PubMed等。科学计量方法包括作者共引分析、文献共引分析、共词分析和共现分析等[5-6]。知识图谱工具通常将一组文献作为输入,生成具有复杂结构的交互式图像用于定量分析和视觉探索。许多知识图谱技术起源于共被引分析理论,这一理论描述了知识基础在共被引文献网络中的结构特征[7-8]。本研究依据科学计量学理论,基于CiteSpace可视化分析工具,对近15年天然橡胶学科领域的研究成果和重要文献进行识别和可视化,建立学科领域知识图谱,跟踪和揭示国际天然橡胶学科领域的前沿热点,以期为科研管理者、政策制定者、相关科研人员及天然橡胶产业发展提供科学参考和借鉴。

1  材料与方法

1.1  数据来源

数据来源于Web of Science核心合集的SCI-EXPANDED和SSCI。本文定义的天然橡胶,是指从巴西橡胶树(Hevea brasiliensis)提取的天然胶乳。为了确保天然橡胶文献数据集的查全率,采用表1制定的检索策略进行主题检索。检索词主要有天然橡胶、天然胶乳、橡胶胶乳、橡胶树、橡胶林、橡胶种植园、胶园、植胶区、橡胶间作、橡胶生物合成、橡胶产量、割胶、产胶、排胶等。经检索得到9960条记录,除重后获得9579篇文献,这些文献共引用了179 317篇引文(检索日期:2019-09-17,数据库更新日期:2019-09-16)。

1.2  研究工具和方法

采用CiteSpace(5.5.R2)进行天然橡胶文献数据集的可视化分析。CiteSpace使用时间切片技术构建随时间变化的时间序列网络模型,并综合这些单独的网络形成一个概览网络,以便系统地回顾相关文献。以每年引用次数排序前100的文献构建当年共被引网络,然后合成各个网络。合成的网络被划分为多个共被引文献聚类。相似的论文和相关的聚类被定位在接近的位置,而不同论文和聚类则相距较远。采用文献[4]中的方法,排除检索结果中的干扰文献:基于CiteSpace技术特点,对检索策略的持续精炼以及对检索结果文献的手工剔除,在一定程度上会导致相关研究文献的缺失并影响文献的关联。通过对原始检索结果所生成的图谱,辨别分析有效文献所生成的大型活跃聚类,而对无效文献生成的聚类则加以识别和排除,能够有效地保证文献查全率,同时能够排除与研究无关的干扰文献。每个聚类成员(被引文献)代表研究領域的知识基础,引用这些文献的施引文献是与这些聚类相关的研究前沿[3-4]。由于文章篇幅所限,只列出前5~10篇被引文献和施引文献进行陈述和解读。一个节点的引文历史描述为若干个引用年轮,每一个引用年轮代表共被引网络中相应年份的引用次数。

2  结果与分析

合成的网络包含1499篇引文。4个最大的连接网络包括1272个节点,占整个网络的84%。该网络具有非常高的模块化值,为0.8307,表明各学科领域在共被引聚类中有明确的定义。图谱展示了4个主要学科领域(图1):左侧区域涉及化学与材料科学,右上方涉及生物科学、生态与环境科学,右下方涉及免疫学。不同颜色区域表示这些区域共被引连接首次出现的时间,紫色区域比粉色区域生成的时间早,黄色区域是在粉色区域之后生成。黄色区域是仍在持续发展的聚类,目前仍在活跃的大型聚类象征着学科的前沿方 向,也是本文重点分析的部分。每个聚类都可以通过标题术语、关键字和引用聚类文献的抽象术语进行标记。如最右侧黄色区域被标记为橡胶人工林与生态环境,表明关于橡胶人工林与生态环境的论文引用了#8聚类。表2按照核心论文数量列出了前13个聚类。轮廓值是衡量聚类同质性或一致性的指标,同质聚类的平均轮廓值趋于1[3-4]。

2.1  化学与材料科学活跃聚类的研究前沿探测

2.1.1  功能化石墨烯纳米复合材料——#2聚类  #2是活跃的大型聚类,关注功能化改性石墨烯或氧化石墨烯补强天然橡胶制备纳米复合材料(表3),由121篇共被引文献组成。聚类中引用次数较高的文章[9-12],展示了超声辅助胶乳共混法和原位还原法等将氧化石墨烯均匀分散于天然橡胶基体,显著提高材料的拉伸强度、机械、电热和屏蔽性能等。Wu等[13]系统研究了石墨烯/天然橡胶纳米复合材料的硫化动力学特性的变化。覆盖率前5的施引文献[14-18],引用了该聚类8%~12%的引文。Papageorgiou等[14]、Srivastava等[17]和Mensah等[18]的文章综述了不同类型石墨烯应用于补强天然橡胶或弹性体纳米复合材料,及其对复合材料的拉伸强度、热稳定性、气体屏蔽、电学、机械和动态力学性能等的影响。其他施引文献[15-16]也在关注改进的方法制备功能化改性石墨烯或氧化石墨烯/天然橡胶纳米复合材料及其性能的增强。

2.1.2  生物基纳米复合材料——#10聚类  #10聚类代表了聚乳酸、纳米微晶纤维素等生物基体补强天然橡胶制备纳米复合材料活跃的施引文献和被引文献(表4)。该聚类引用次数第一的文章由Bitinis等[19]发表,关于聚乳酸/天然橡胶共混物的微观结构、结晶行为和机械性能研究。其他共被引文献代表了聚乳酸基或形状记忆聚乳酸基与天然橡胶或环氧化天然橡胶制备共混物及其韧性、晶体稳定性增强的知识基础[20-23]。覆盖率前5的施引文献[24-28],引用了该聚类6%~7%的引文。Cao等[24, 28]采用两2种方法制备海鞘纳米微晶纤维素/天然橡胶纳米复合材料,对其形态、力学性能和水膨胀行为进行了比较研究。Heuwers等[25]、Quitmann等[26]研究了不同形状记忆聚乳酸基天然橡胶纳米复合材料的储能、力学和机械应力性能。Chen等[27]研发了一种生物基动态硫化聚乳酸/天然橡胶共混物,其中交联NR相具有连续的网状分散。

3  討论与结论

一个领域的研究前沿体现的是该领域当前的科学发展水平。天然橡胶领域的跨学科、跨专业和学科交叉视角明显,使得新兴研究领域和主题不断出现。本研究借助知识图谱可视化分析概述了2004—2018年天然橡胶领域重要的基础文献,突出了持续发展的研究领域;并通过关键词共现分析寻找研究热点,探索活跃的研究方向。主要研究结果如下:

(1)在共被引文献和施引文献分析的基础上,按照学科探测研究前沿,在三大学科探测出6个研究前沿。①化学与材料科学领域识别出4个研究前沿:功能化改性石墨烯或氧化石墨烯补强天然橡胶制备纳米复合材料;生物基体补强天然橡胶制备纳米复合材料;弹性体或天然橡胶纳米复合材料的应变诱导结晶行为;废旧橡胶的自修复与回收加工。②生物科学领域识别出1个研究前沿:橡胶树基因组测序、调控橡胶树乳管橡胶生物合成路径与关键基因。③生态与环境科学领域识别出1个研究前沿:土地利用变化背景下橡胶人工林的扩张对生态环境的影响。

(2)在关键词共现频次和强度分析基础上,发现高频和高突现关键词主要分布在化学与材料科学领域,如“纳米复合材料”“共混”“改性”“石墨烯”“聚合物基体”“诱导结晶”“性能”等,其次分布在生态与环境科学领域,如“生物多样性”“热带雨林”“土地利用”等,分布在生物科学领域的关键词较少,主要有“基因表达”“乳管”“聚异戊二烯”等。这预示着当前天然橡胶研究趋于多方向性,但活跃的研究主题主要集中在天然橡胶全产业链的下游。伴随着天然橡胶产业发展带来的环境和社会问题,防止砍伐森林,保护生物多样性,确保天然橡胶产业的可持续生产非常值得关注。在基础研究领域,提高天然橡胶产量和质量,明确调控橡胶生物合成关键路径和基因,为橡胶树优异种质的发掘利用和高产优质抗逆遗传改良奠定基础,也是活跃的研究主题。

(3)本研究所指“研究前沿”是一簇共被引聚类形成的高被引论文及其后续的施引论文形成的一个“专业研究方向”,还不能完全等同于科学研究中的前沿科学问题和前沿研究领域,所以本方法只是监测分析科学研究发展态势的一种视角。另外,论文的写作、发表和被引用存在一定的滞后性,影响了研究前沿成果的及时揭示,因此需要补充各类相关信息,如施引论文,才能更为全面地监测和分析科学研究发展态势。

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