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Journal ArticleDOI

A delineating procedure to retrieve relevant publication data in research areas: the case of nanocellulose

01 May 2016-Scientometrics (Springer Netherlands)-Vol. 107, Iss: 2, pp 627-643
TL;DR: It is investigated how a bibliometric analysis could provide interesting insights into research about this sustainable nanomaterial nanocellulose and how a delineation procedure enables us to retrieve relevant publications from research areas involving nano cellulose.
Abstract: Advances concerning publication-level classification system have been demonstrated striking results by dealing properly with emergent, complex and interdisciplinary research areas, such as nanotechnology and nanocellulose. However, less attention has been paid to propose a delineating method to retrieve relevant research areas on specific subjects. This study aims at proposing a procedure to delineate research areas addressed in case nanocellulose. We investigate how a bibliometric analysis could provide interesting insights into research about this sustainable nanomaterial. The research topics clustered by a Publication-level Classification System were used. The procedure involves an iterative process, which includes developing and cleaning a set of core publication regarding the subject and an analysis of clusters they are associated with. Nanocellulose was selected as the subject of study, but the methodology may be applied to any other research area or topic. A discussion about each step of the procedure is provided. The proposed delineation procedure enables us to retrieve relevant publications from research areas involving nanocellulose. Seventeen research topics were mapped and associated with current research challenges on nanocellulose.

Summary (2 min read)

Introduction

  • Bibliometrics has been used to monitor and quantitatively assess scientific fields within the context of science policy and research management (Moed, Glänzel, & Schmoch, 2004; Okubo, 1997; Raan, 2014; Zitt, 2015).
  • They can simplify literature search and information retrieving procedures (Glanzel & Schubert, 2003; Ruiz-Castillo & Waltman, 2015; Waltman & van Eck, 2012).
  • Nanocelluloses have been a research area for many countries, including the major producers of cellulose worldwide, such as the USA, Canada, Finland, Sweden and Brazil (Milanez et al., 2013).
  • In the next section, the authors describe the overall delineating procedure and its general issues.

Overall delineation procedure

  • To delineate the field, i.e., to collect a relevant set of publications to represent nanocellulose, clusters (research areas) were selected from the CWTS publication level classification system.
  • Predefined nanocellulose publications are indicated as black circles and the first step is retrieving all research area that contains at least one of them.
  • Moreover, in these two clusters, more than 80% overlapped with the initial set.
  • Analysis of retrieved research area and cleaning of the initial set An analysis of the content of publications in the peripheral research areas was conducted.
  • The authors introduce here the Pareto Principle (or 80/20 rule).

Independency test

  • An independency test was conducted to evaluate the effectiveness of the procedure proposed.
  • The test involved retrieving the number of publication from the top five authors before and after cleaning the initial set of nanocellulose publications, obtaining the percentage of decrease and the position on a ranking of authors.
  • The map positions the research topics on the basis of their citation relations, i. e the closer two topics, the more frequent the citation traffic between them.
  • The node labels also match the main content of the clusters.
  • The map compares the topics that characterize each nuclei cluster and provide themes that they share.

Results and discussion

  • Effect of cleaning the initial set of nanocellulose publications.
  • To the other half, none term could reduce the coverage in more than 5%.
  • Considering the only first and the last moment, the number of nanocellulose-focused publication diminished 52.6% while the number of clusters decreased 96.8%.
  • Moreover, it is important to highlight that the top authors from cluster 13.6.3 are not the same top authors from the cluster 13.6.11 due to the fact that they simply did not overlap.
  • The cleaning step did not affect the publications from author E.

Map of the nanocellulose research topics

  • The delineating approach was able to retrieve two nuclei research areas, one associated with cellulose nanocrystals and nanofibrils and other to bacterial cellulose.
  • At the bottom right of the map, electrospinning process, conductive polymers, and electro-active cellulose-based papers are positioned together.
  • The other three research areas (cellulose dissolution, cellulose surface, and tempo mediated oxidation) are the smallest ones and their development must be monitored as they are associated to some issues concerning nanocellulose.
  • An analysis from the topics shared by the nuclei areas was performed with support of VOSviewer.
  • The more the noun-phrase is located in the left part of the map the more it appeared on titles and abstracts from papers addressed to cluster 13.6.3 (red).

Conclusion

  • The proposed delineation procedure enabled us to retrieve relevant publications from research areas involving nanocellulose.
  • Seventeen research topics were identified, mapped and associated with current research challenges on nanocellulose.
  • The independency test showed that the cleaning procedure did affect the number of publication from most of the top author.
  • Delineating scientific fields is a complex task as boundaries are not frequently well established since scientific studies have become more complex and interdisciplinary.
  • The investigation will evaluate the added value of peripheral clusters to the nuclei and what type of analyses they are necessary and in which cases they can be ignored.

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A DELINEATING PROCEDURE TO RETRIEVE RELEVANT PUBLICATION DATA IN RESEARCH
AREAS: THE CASE OF NANOCELLULOSE
1
Douglas Henrique Milanez
a,c,*
Ed Noyons
b,*
Leandro Innocentini Lopes de Faria
a,c
a
Federal University of Sao Carlos, Materials Engineering Dept, Centre for Information Technology in Materials
(NIT/Materiais), Washington Luis Highway, km 235, São Carlos SP (Brazil)
b
Leiden University, Centre for Science and Technology Studies (CWTS), PO Box 905, 2300 AX Leiden (The
Netherlands)
c
Federal University of Sao Carlos, Science Information Dept, Labmetrics, Washington Luis Highway, km 235,
São Carlos SP (Brazil)
*Corresponding authors:
Telephone: +55 16 3351 8551
Email address: douglas@nit.ufscar.br
Telephone: +31 71 527 3928
Email address: noyons@cwts.leidenuniv.nl
Abstract
Advances concerning publication-level classification system have been demonstrated striking results by dealing
properly with emergent, complex and interdisciplinary research areas, such as nanotechnology and nanocellulose.
However, less attention has been paid to propose a delineating method to retrieve relevant research areas on
specific subjects. This study aims at proposing a procedure to delineate research areas addressed in case
nanocellulose. We investigate how a bibliometric analysis could provide interesting insights into research about
this sustainable nanomaterial. The research topics clustered by a Publication-level Classification System were
used. The procedure involves an iterative process, which includes developing and cleaning a set of core publication
regarding the subject and an analysis of clusters they are associated with. Nanocellulose was selected as the subject
of study, but the methodology may be applied to any other research area or topic. A discussion about each step of
the procedure is provided. The proposed delineation procedure enables us to retrieve relevant publications from
research areas involving nanocellulose. Seventeen research topics were mapped and associated with current
research challenges on nanocellulose.
Keywords: bibliometrics; research topics; science classification; nanotechnology.
MSC Classification 68P20
JEL Classification D83
Introduction
Bibliometrics has been used to monitor and quantitatively assess scientific fields within the context of
science policy and research management (Moed, Glänzel, & Schmoch, 2004; Okubo, 1997; Raan, 2014; Zitt,
2015). Partly, it is a consequence of the increased use of Internet since the early 1990s and the development of
information technologies. Together, they made a huge volume of scientific databases available. Meanwhile,
scientific studies have become more complex and interdisciplinary, involving the exchange of knowledge between
scientists from different disciplines in specific subject of research. Nanotechnology-focused research is a good
example. Bibliometric indicators and tools are useful instruments to study and gain insight in science and, in
particular, complex fields or research areas, c.f., van Raan (2004). Therefore, many studies on nanotechnology
relied on bibliometric approaches (Hullmann & Meyer, 2003; Igami, 2008; Kostoff, Koytcheff, & Lau, 2009;
Milanez, Faria, Amaral, Leiva, & Gregolin, 2014; Mogoutov & Kahane, 2007; Wang, Notten, & Surpatean, 2012).
Nonetheless, the problem often is: how to delineate a field or research area; how to retrieve the relevant data;
which publications to include and which not; what insights can be obtained from the set of publication retrieved.
1
Earlier version presented at the 15
th
International Society of Scientometrics and Informetrics Conference in Istanbul (Turkey),
Jun 29
th
July 4
th
, 2015.

In this sense, classification systems are an indispensable tool to study the structure and dynamics of
scientific fields (Boyack, Klavans, & Börner, 2005; Glanzel & Schubert, 2003; Leydesdorff, Carley, & Rafols,
2013; Leydesdorff, de Moya-Anegón, & Guerrero-Bote, 2014; Ruiz-Castillo & Waltman, 2015; Y. Zhu & Yan,
2015; Waltman & van Eck, 2012; Zitt, 2015). They can simplify literature search and information retrieving
procedures (Glanzel & Schubert, 2003; Ruiz-Castillo & Waltman, 2015; Waltman & van Eck, 2012). Zitt (2015)
provides an interesting overview of current field delineation procedures and challenges of information retrieval.
According to Glanzel and Schubert (2003), classification of science into a disciplinary structure can be as old as
science and Ruiz-Castillo and Waltman (2015) highlighted that the assignment of individual publications or
journals to research areas still remains an open question in Scientometrics. Currently, most of classification
systems are based on journal assignment, such as the Web of Science and Scopus systems. The drawback of these
journal-based classification systems is the fact they do not deal properly with multidisciplinary journals or
interdisciplinary research (Neuhaus & Daniel, 2009; Ruiz-Castillo & Waltman, 2015; Waltman, van Eck, &
Noyons, 2010; Waltman & van Eck, 2012). Some studies question the appropriateness of the database journal-
based classification system, such as for the purpose of normalizing citation impact indicators (Ruiz-Castillo &
Waltman, 2015), assignment of individual publications (Neuhaus & Daniel, 2009) or evaluating complex and
emerging domains (Zitt, 2015).
The development of publication-level classification systems is currently a subject of research. Boyack et
al. (2011) clustered a corpus of 2.15 million biomedical publications from Medline database (2004-2008) which
generated coherent and concentrated cluster solution of text-based similarity approaches based on keywords
extracted from titles and abstracts. They found their approach more precise than the Medical Subject Headings.
Waltman and van Eck (2012) proposed a methodology to cluster a large-scale set of scientific publication indexed
on Thomson Reuters’ Web of Science database. Each publication was assigned to a single research area, which
was organized in a three-level hierarchical structure. Their methodology took into account direct citation to cluster
the publication and they labelled each research area with discriminative keywords extracted from titles and
abstracts. Such publication-level classification systems will be used to gain insights on research areas involved in
specific subjects.
In the present study, we intended to map research areas associated with nanocelluloses. These cellulose-
based nanomaterials are sustainable and has a great potential for innovation (Isogai, 2013; Mariano, Kissi, &
Dufresne, 2014; Milanez, Amaral, Faria, & Gregolin, 2013; Moon, Martini, Nairn, Simonsen, & Youngblood,
2011). Nanocelluloses have been a research area for many countries, including the major producers of cellulose
worldwide, such as the USA, Canada, Finland, Sweden and Brazil (Milanez et al., 2013). Different disciplines are
involved with nanocellulose research since its properties and behaviour have allowed applications as reinforcement
agent in composite materials, packing material, optically transparent paper for electronic devices, texturizing agent
in cosmetics and food, bio-artificial implants and bandages (Isogai, 2013; Klemm et al., 2011; Mariano et al.,
2014; Moon et al., 2011; Siqueira, Bras, & Dufresne, 2010).
Nanocelluloses is a generic term referring to cellulose nanofibrils on the one hand and cellulose
nanocrystals on the other (Dufresne, 2013; Klemm et al., 2011; Moon et al., 2011; Siqueira et al., 2010; TAPPI,
2011). The main difference between these two types of cellulose in nanoscale dimensions relies on the degree of
crystallinity. Cellulose nanocrystals are basically shorter and rod-like crystalline cellulose, whereas cellulose
nanofibrils are long chains of alternate amorphous and crystalline cellulose. Consequently, they differ on their
mechanical and functional properties (Eichhorn et al., 2010; Mariano et al., 2014; Moon et al., 2011). Both types
of nanocellulose can be obtained from renewable sources, including natural fibres, plants, pulp and forest and
agricultural residues. In this case, mechanical process and chemical/enzymatic approaches are used to obtain
cellulose nanofibrils and cellulose nanocrystals, respectively. Moreover, cellulose nanocrystals can be
biosynthesized by bacteria, resulting in the also called bacterial cellulose (Klemm et al., 2011; Milanez et al., 2013;
Moon et al., 2011).
Checking the research topics associated with nanocelluloses can provide insights into current technical
challenges concerning this nanomaterial, such as increasing the scale of production minimizing costs,
characterization of sources and mechanical properties. Surface modifications to reduce moisture adsorption and
improve the adhesion between the nanomaterial and the polymeric matrix, thermal degradation, and
biocompatibility with living tissues has also been target of research (Gardner, Opo, Oporto, Mills, & Samir, 2008;
Isogai, 2013; Klemm et al., 2011; Mariano et al., 2014; Milanez et al., 2013; Moon et al., 2011; Siqueira et al.,
2010).
This study aims at proposing a delineation procedure to retrieve relevant research areas addressed to a
specific topic. Nanocellulose was selected as a case, but it may be used for other subjects, of course. The approach
involves research areas identified in the CWTS Web of Science Publication-level Classification System, a 2014
update of the version introduced by Waltman & van Eck (2012). This paper is structured as follows. In the next
section, we describe the overall delineating procedure and its general issues. Next, we discuss details concerning
specific parts and tasks. We present and discuss results in Section 3 and finally in Section 4 we draw our
conclusions.

Methodology
Overall delineation procedure
To delineate the field, i.e., to collect a relevant set of publications to represent nanocellulose, clusters
(research areas) were selected from the CWTS publication level classification system. By this method, papers that
were not easily picked up by keyword or journal based search strategies could be identified. Figure 1 presents a
schematic representation of the distribution of the clustered Web of Science publications according to CWTS
Publication-level classification system (Waltman & van Eck, 2012). Predefined nanocellulose publications are
indicated as black circles and the first step is retrieving all research area that contains at least one of them.
Source: authors.
Fig. 1 Schematic representation of Web of Science publications clustered according to the CWTS
Publication-level Classification System. The black nodes represent the publications focused on
nanocellulose.
Figure 2 depicts the proposed procedure as an iterative process which can be described in four main steps:
1. Determine an initial set of publication concerning the theme of interest. In this first step, a set of
publication which well represents the theme of interest (nanocellulose) is retrieved via the online Web of
Science database, using a straightforward search strategy. This set of publication is a starting set and will
be refined as well as expanded through the next steps;
2. Prior retrieval of nanocellulose research areas. The second step involves locating the research areas
(publication clusters) with at least one publication from the initial set of nanocellulose. The bottom level
of the classification scheme was used in this study (Waltman & van Eck, 2012);
3. Analysis of retrieved research area and cleaning of the initial set. The content of each research area was
analyzed pragmatically. A cleaning task was developed by selecting terms to eliminate part of the initial
set of nanocellulose publication. This step provided a final set of nanocellulose publication clusters and
enhanced the precision of research area assigned to nanocellulose;
4. Final retrieval and selection of relevant nanocellulose research areas. After cleaning the initial set of
nanocellulose publication, the research areas (publication clusters) were retrieved again. Finally, as the
number of topics retrieved was high, a selection that relies on the 80/20 rule was conducted reaching the
final research areas associated with nanocelulose.
After performing the delineation, an independency test was conducted to verify how the steps from
process affected the number of publication from the main authors in nanocellulose. We also had a look on the
arrangement of the selected research topics on a map and discussed how relevant they are to support nanocellulose
developments.
Web of Sciencedatabase clustered
Regular publication
Nanocellulose focused publication

Source: authors.
Fig. 2 Iterative process of the overall procedure proposed.
Determine an initial set of publication on nanocellulose
A search expression was developed considering several terms and synonyms found in nanocellulose
literature and recommended by experts (Klemm et al., 2011; Milanez et al., 2013; Siqueira et al., 2010; Siró &
Plackett, 2010), as can be seen from Table 1. The search expression encompassed different words that refer to
cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose as well as other generic forms, such as
nanocellulose, cellulose nanoparticles, and cellulose nanofiller.
Besides the fact that there are two main types of nanocellulose (Klemm et al., 2011), the variety of search
terms is partially consequence of research initiatives scattered across the twentieth century, especially in the 1980s,
when researcher from the International Telephone and Telegraph Corporation patented a mechanical method to
produce microfibrillated cellulose (Klemm et al., 2011; Tubark, Snyder & Sandberg, 1983). Bacterial cellulose
was an object of research at least since its first documentation in a paper describing cellulose as result of bacterial
fermentation (Brown, 1886). Among other initiatives, the international organization Technical Association of the
Pulp and Paper Industry (TAPPI) performed, in 2011, a roadmap to standardize the nanocellulose terms to cellulose
nanofibrils and cellulose nanocrystals (TAPPI, 2011).
There are some words on Table 1 using the prefix “micro”, which could indicate an idea of micrometric
scale; however, according to some experts in nanocellulose (Isogai, 2013; Klemm et al., 2011; Siqueira, Bras, &
Dufresne, 2010), these materials are cellulose in nanoscale due to the fact that there is at least one dimension that
scale. In fact, the use of prefix “nano” as part of nanocellulose set of terms started only in 2001, concurrently with
the unfolding of many nanotechnology research initiatives (Milanez et al., 2014).
The search was conducted in March 31
th
2014 in the online Web of Science database (topic search) using
the search expression from Table 1. Only articles that were contained in the CWTS Web of Science publication-
level classification system criteria were used. The classification system takes into account only article, letter and
review published from 2000 to 2013 and indexed in the Science Citation Index Expanded and the Social Science
Citation Index. Moreover, to be part of one research area, a publication must be related, either directly or indirectly,
to at least 49 other publications in terms of citation (Waltman & van Eck, 2012).
Table 1 Boolean search expression to retrieve the initial set of nanocellulose publications.
("bacterial cellulos*") OR ("cellulos* crystal*") OR ("cellulos* nanocrystal*") OR ("cellulos* whisker*")
OR ("cellulos* microcrystal*") OR ("cellulos* nanowhisker*") OR ("nanocrystal* cellulos*") OR
("cellulos* nano-whisker*") OR ("cellulos* nano-crystal*") OR ("nano-crystal cellulos*") OR ("cellulos*
micro-crystal*") OR ("cellulos* microfibril*") OR ("microfibril* cellulos*") OR ("cellulos* nanofibril*")
OR ("nanofibril* cellulos*") OR ("micro-fibril* cellulos*") OR ("nano-fibril* cellulos*") OR ("cellulos*
micro-fibril*") OR ("cellulos* nano-fibril*") OR ("cellulos* nanofiber*") OR ("nanocellulos*") OR
("cellulos* nanoparticle*") OR ("nano-cellulos*") OR ("nanoparticl* cellulos*") OR ("nanosiz* cellulos*")
OR ("cellulos* nanofill*") OR ("nano-siz* cellulos*") OR ("cellulos* nano-fiber*") OR ("cellulos* nano-
particle*") OR ("cellulos* nano-fill*") OR ("nano-particl* cellulos*"))
Source: Developed considering nanocellulose-focused terms found in the literature (Klemm et al., 2011;
Milanez, Amaral, Faria, & Gregolin, 2013; Milanez et al., 2014; Siqueira, Bras, & Dufresne, 2010; Siró &
Plackett, 2010) and expert opinions.
Establishing a
search expression
Web of Science
online database
Initial set of
publication
CWTS Publication-
level classification
system
Lowest level
Prior research
areas retrieving
Cluster content
analysis
Cleaning terms
establishment
Cleaning initial
set of publication
Final set of
publication
Selecting relevant
research areas
Final retrieving
and selection

Prior retrieval of nanocellulose research areas
Research areas that contained at least one publication from the nanocelulose set were retrieved from the
CWTS Web of Science Publication-level database. In total, 533 research topics (clusters from the classification
system) were found. These clusters showed large differences in terms of volume (number of publications included).
The largest cluster contains 2,751 publications whereas the smallest one covers only 50 publications. Almost 80%
of these clusters contained less than three publications from the initial set.
Interestingly, we found that two research areas (clusters) included 56.3% of the initial nanocellulose set
of publications. Moreover, in these two clusters, more than 80% overlapped with the initial set. Their descriptive
labels also pointed towards nanocellulose research. Therefore, they were considered as nuclei of research in
nanocellulose. Other clusters in which the representation of the initial set was much lower, were considered
peripheral research areas and their relevance to nanocellulose research was evaluated (see next section).
Analysis of retrieved research area and cleaning of the initial set
An analysis of the content of publications in the peripheral research areas was conducted. We wanted to
check whether these articles focused on the nanomaterial as an object of research. If not, they were considered
noise. Because an evaluation of all research area retrieved would be too labour intensive, we made a selection. The
checking task was performed only on those clusters that matched one of the following criteria:
Research topics that contained at least 20 publications from initial dataset;
Research topics of which at least 5% overlapped (percentage proportion) with the initial set.
A total of 20 (peripheral) clusters were evaluated. The analysis regarded only articles from the initial
dataset of nanocellulose publications assigned to these clusters. The task involved reading each title to decide
whether the article was a study focused upon nanocellulose or not. When the title was not clear, the abstract was
also consulted.
Once the checking process was completed, specific terms were identified and considered to clean the
initial set of nanocelulose publications. Only research topics with high percentage of “noise publication” were
used. The presence ofnoise publications” is usual in bibliometric analysis because there is no exhaustive search,
but the idea is to gain more precision during the cluster retrieving.
Noun-phrases were obtained with support of VOSviewer corpus map analysis applied to titles and
abstracts from publications belonging to these clusters, which were processed separately. The cleaning-terms
extraction took into account only high frequency terms from clusters contents. However it is important to highlight
that not every highly frequent words found were used. For instance, “ethanol” (alone) is one of the most frequently
word from cluster 16.3.2, but it was not incorporated on the set of cleaning terms from Table 2 due to the fact that
nanocellulose is a sub-product of ethanol produced from cellulose enzymatic fermentation, also called, second
generation ethanol (Kangas et al., 2014; Song, Winter, Bujanovic, & Amidon, 2014; Tsukamoto, Durán, & Tasic,
2013; J. Y. Zhu, Sabo, & Luo, 2011). Thus, excluding publications containing “ethanol” would have an undesired
effect on the final set of nanocellulose publications. This not happened with the word “ethanol yield”, though. In
order to avoid such undesired effects, we studied the effect of each potential cleaning-term on the nuclei clusters
before selecting the final ones.
Table 2 presents the final terms used to clean the nanocellulose-focused publications retrieved using the
search expression from Table 1. They were applied on the title, abstract, author’s keyword and keyword plus search
field. The effect of this cleaning task on the nuclei clusters and the peripheral clusters we used will be discussed
in the results.
Table 2. Boolean expression of terms used to clean the nanocellulose-focused publications.
"gene" OR "xyloglucan" OR "microtubule" OR "*cyto*" OR "kinesi" OR "tubulin" OR "*cell wall*" OR
"spindle" OR "phragmoplast" OR "mitosis" OR "preprophase" OR "phenotype" OR "*plant growth*" OR
"meiosi" OR "*lignin distribution*" OR "delignification" OR "hemicellulose" OR "saccharification" OR
"ethanol yield" OR "lignocellulos*" OR "glucosidase" OR "xylanase"
Source: Authors.
Final retrieving and selection of relevant research areas
The final set of nanocellulose publication comprised 2,600 nanocellulose publications (named now as
core-nanocellulose) and they were assigned to 428 research areas, which still would be a highly number of cluster
to be evaluated. In fact, 81.0% of these clusters included only one or two publications from the core-nanocellulose
publication, which raised questions about their actual relevance to the advances on nanocelulose studies: the

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TL;DR: This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them, and summarizes cellulOSE nanoparticles in terms of particle morphology, crystal structure, and properties.
Abstract: This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).

4,920 citations

Journal ArticleDOI
TL;DR: Some of the empirical evidence for the existence of power-law forms and the theories proposed to explain them are reviewed.
Abstract: When the probability of measuring a particular value of some quantity varies inversely as a power of that value, the quantity is said to follow a power law, also known variously as Zipf's law or the Pareto distribution. Power laws appear widely in physics, biology, earth and planetary sciences, economics and finance, computer science, demography and the social sciences. For instance, the distributions of the sizes of cities, earthquakes, forest fires, solar flares, moon craters and people's personal fortunes all appear to follow power laws. The origin of power-law behaviour has been a topic of debate in the scientific community for more than a century. Here we review some of the empirical evidence for the existence of power-law forms and the theories proposed to explain them.

4,734 citations

Journal ArticleDOI
TL;DR: This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.
Abstract: Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.

3,452 citations

Journal ArticleDOI
TL;DR: In this article, a review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocells.
Abstract: Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.

2,546 citations


"A delineating procedure to retrieve..." refers background in this paper

  • ...…it was not incorporated on the set of cleaning terms from Table 2 due to the fact that nanocellulose can be a sub-product of ethanol produced from cellulose enzymatic fermentation—also called, second generation ethanol (Kangas et al. 2014; Song et al. 2014; Tsukamoto et al. 2013; Zhu et al. 2011)....

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Journal ArticleDOI
TL;DR: An overview of recent progress in the area of cellulose nanofibre-based nanocomposites is given in this article, with particular emphasis on applications, such as reinforced adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocom composites.
Abstract: This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.

2,214 citations


"A delineating procedure to retrieve..." refers background in this paper

  • ...The main difference between these two types of cellulose in nanoscale dimensions relies on the degree of crystallinity, which impacts on mechanical and functional properties of final products (Eichhorn et al. 2010; Mariano et al. 2014; Moon et al. 2011)....

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  • ...These themes appear frequently in nanocellulose-focused studies (Azizi Samir et al. 2005; Charreau et al. 2013; Chirayil et al. 2014; Dai et al. 2014; Domingues et al. 2014; Durán et al. 2012; Eichhorn et al. 2010; Isogai 2013; Klemm et al. 2011; Moon et al. 2011; Orts et al. 2005; Pääkkö et al. 2007; Siqueira et al. 2010; Siró and Plackett 2010)....

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  • ...…studies (Azizi Samir et al. 2005; Charreau et al. 2013; Chirayil et al. 2014; Dai et al. 2014; Domingues et al. 2014; Durán et al. 2012; Eichhorn et al. 2010; Isogai 2013; Klemm et al. 2011; Moon et al. 2011; Orts et al. 2005; Pääkkö et al. 2007; Siqueira et al. 2010; Siró and…...

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Frequently Asked Questions (2)
Q1. What are the contributions in "A delineating procedure to retrieve relevant publication data in research areas: the case of nanocellulose" ?

This study aims at proposing a procedure to delineate research areas addressed in case nanocellulose. The authors investigate how a bibliometric analysis could provide interesting insights into research about this sustainable nanomaterial. A discussion about each step of the procedure is provided. 

In future research, the authors intend to develop new research aiming at excluding the manual checking on the peripheral clusters and include a procedure more automated. This clear separation provides suggestions for further research, putting the nuclei research in context. The investigation will evaluate the added value of peripheral clusters to the nuclei and what type of analyses they are necessary and in which cases they can be ignored.