Present Situation of Wood / Inorganic Nanocomposites
Abstract:Scholars both at home and abroad have done lots of primary studies in wood-inorgani-nano-composite field！which bases on the research on the
characterization of nano-materials！nano-composite and the methods of
making nano-composites. The resu1ts show that there is some nano-space
inside wood in which nano-particles can be accepted,and the nano-space exist in wood, such as those between the micro fibrils on the wall of wood-cells; and then combined with the wood’s main components！and a1so some active keys
and groups in wood which can compound with nano-particles. And in methods
so-called sol-ge1.intercalation or immersing under pressur etc, some of wood's
properties,especially mechanism ones will be improved in a great deal, and
may even gain some new properties of the composites. The paper aims at the industrialization of wood-inorganic-nano-composites and considering the characteristics of wood, making use of the related studying results of
nano-science & nano-technology (NST) into the wooden composite field. This paper analyzes and researches on the composite’s preparation and measurement and characterization of the construction, and arises some supposals and prospect of the research including the choice of suitable nano-materials, surface-modifying, or pre-treated with some surface-activated materials, wood-inorganic-nano-composite will be gained; the present studv covers the nano-particles’compounding with wood, the characterization of the structure of
wood-inorganic-nano-composites！the measure of their properties and the
Key words(wood；inorganic nano-material；composite；surface
modifying；structural characterization；present situation of study.
Because of its excellent use of features, Wood has been widely uesed in various fields as a renewable natural polymer composites; but some of the inherent shortcomings greatly restrict its use effects and application quality. people have gradually accepted nano-composite materials which are made of Nano-modifier and other matrix materials (such as resin, rubber, ceramics and metal, etc.);besides ,binary interface for collaborative
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nanotechnology including the super-double-sparse nature and super-amphiphilic interface
material are the nano-materials which has entered the practical stage. Composited with
wood,they become wood nano-composite materials which may produce peculiar properties. Moreover, Wood-nano-composite must meet two basic conditions: First, at least one of the relative sizes of the dispersed phase (nano-particles) and the continuous phase (wood), is between 1 ~ 100 nm .
Due to the nano-phase, the performance of wood has improved a lot and the composites may have new features.
1.The Research of Nano-materials and Nano-compositeMaterials 1.1 Nano-materials
1.1.1 Characteristics of nano-materials
Nano materials have a size or features on the scale of around 1nm to 100nm nanometers. nanotechnology refers to a range of techniques used to manipulate matter at the scale of atoms and molecules. The word ‘Nano’ is a size scale, rather than a material, one nanometre being one billionth of a metre. The matter being manipulated can be any material organic or inorganic. Then, as a new state of matter,Nano-materials is being gradually accepted. Beacuse its size is smilar with the Wavelength of de Broglie Wave ,the nano-materials have certain unique properties！such as size effect！surface effect, quantum effect, macroscopic
quantum tunneling effect etc.At the same time , the nano-materials has the new effect
caused by combination of nano-structures,such as Quantum coupling effect and so on.
Nano-materials have two parts with approximately equal volume fraction.One is the particle with diameter of several or dozens of nanometers; another is the interface between nano-particles. The former is a long-range ordered crystal structure .The latter is neither a
long-range order nor a short-range order structure.
1.1.2 Classification and Preparation of Nano-materials
Nano-materials can be divided into six categories ,for example, nano-powder (zero-dimensional), nano-fiber (one-dimensional), nano-film (two-dimensional), nano-block (three-dimensional), nano-composite materials and nano-structure .The preparation is associated with the type of nano-materials.It has been the longest for the study on nano-powder (body) , the technology is sophisticated,and it is also the basis for preparation
of other nano-materials. However , in some articles , nano-materials is divided into 7
With unique performance ,Nano-structured materials include mineral matters such as
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montmorillonite(MMT)and illite and natural pearls, shells and animal teeth and tendons in fliers . Besides the leaves and organizations of plants are usually ordered assembly of nano-structured materials.
Preparation of nano-particles mainlyexists 4 kinds, containing wet, solid-coherent method, gas phase method, gravity separation method and so on .However , there are 10 kinds of Preparation of nano-particles in the review about preparation of nano-materials and the latest
progress written by Liu Zhen .
1.2 Surface Modification of Nano-powder
In air environment nano-materials has a large number of soft and hard reunions which will result in performance degradation powder . In order to show its singular performance, nano-powder materials must be uniformly dispersed, fully open its aggregates, and reduce in powder and the surface tension between the media.
Some important researches include surface modification of nanoscale particles, modification to control the nanoparticle size, shape, and the prevention of the agglomeration of nanoparticles to enhance its composite system's ability to uniformly dispersed nano-composite materials.There are two types of nano-particle surface treatment , they are physical-coated and chemical modification methods. Its role is: ? to improve or change the
dispersion of nano-particles; ? to improve the surface activity of particles; ? to produce
new particles in the surface of the performance and new features; ? to improve the
compatibility between particles and other substances .
Luo Zhongfu found that after treatment with surface-active agents , the mechanical
properties of nano-sio / epoxy resin composites significantly improved . 2
Wei Wu and others analysed the effects of micro-structure, particle dispersion,and adsorption between interfaces after the differdent surface treatment of nano-sio, as well as mechanical 2
properties of composite materials of PP / nano-sio. 2
There are mainly some composite methods of nano-composite materials, such as sol-gel method, in situ (molecular and ionic) intercalation synthesis, blending, injection-filling and etc.; besides , there are composite alkoxide method, microemulsion, deposition, and
Ye Linzhong studied the toughening effect of light CaCO on PVC. The results showed that, 3
CaCO of 10 nm has a good toughening effect on PVC; Zeng Xiao-fei, etc. found CaCO 33
nano-particles and CPE elastomer particles can simultaneously strengthening and toughening
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Tang Yi and others found that nano-SiO, nano-AlO can greatly increase the coating bond 223
strength, abrasion resistance and resistance to stripping .
Using nano-materials in the coating in the sanitary ware, interior decoration materials, furniture, which can produce sterilization, cleaning effect. Adding nano-materials in the paint can play a role in a fire-retardant, heat insulation and fireprotection . At present, nano-coatings research focused on improving weather resistance of building exterior and antibacterial property of building interior. However there is a little research on functional coatings of wood surfaces .
2 Wood/Inorganic Nanocomposites
2.1 Present Situation of Wood / Inorganic Nanocomposites Researches For example , teak has a beautiful wood color and texture, a hard material and good durability in the nature, because inorganic minerals in the form of nano-particles penetrate the wood matrix, forming a natural wood / inorganic nano-composite material .
Saka. S and others deposited SiO and other inorganic particles with the size of about 100 2
nm in wood cell wall by the sol-gel method (sol-ge1) , mading wood / inorganic
nanocomposites. Furno. T, etc. used "double diffusion method to make wood-based
inorganic composite materials of boron silicate . Saka. S, Miyafuji. H and Ueno. T and
other people using gels, and sol-gel method ,successly prepared SiO.andTiO. 22
Wood-inorganic composites has good mechanical strength, dimensional stability, flame
retardancy, etc.; Wimmer and others used nano-materials to increase the penetration of
wood vertical wood hardness; Since 1999 Hiroyuki Matsumura and W olfgang Glasser
has developed a one-step to prepara thermoplastic nano-composite materials from the
cellulose fiber .
 In China, Wang Xi-Cheng using sol-gel method and a method of in situ composite
method made the wood-based silica composite material at the level of cellular , its mechanical properties, dimensional stability and corrosion-resistant properties of
flame-retardant were increased in various degrees; Sun Li etc. injected the precursor
solution with the main components of silicon alkoxide into the wood by conventional pretreatment or by coupling agent (GPTMS) pretreatmentIn the heat treatment conditions of the reaction , silica nucleated in the wood cells , gathered and grew up, and then it became
wood / silica nanocomposites; Cai Ning, etc. injected the precursor of ceramic precursor solution with the main components of TEOS into the wood by the method of sol-gel ,then by hydrolysis, condensation reaction to form SiO2. Gel, one part bonds with the cellulose
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occurs, others fill in the rest of micro-capillary in the way of physical presence , those three constitute the cell wall skeleton, at the level of molecular, which constitute a composite material with wood .
Li Jian, Jian Qiu and others major studied nano-materialst for preparing nano-composite materials by the injection method, sol-gel method, supercritical extraction of timber ; Zhao Guangjie etc. has studied on the choice of modifier of Wooden Layered Montmorillonite (MMT) nano-intercalation (also said embedding method, Intercalation) , and the "one step injection method "and "two steps injection method" used to prepare wood matrix montmorillonite (MMT) nano-intercalation composites. They also researched on montmorillonite (MMT) intercalated nano-composite structure and performance evaluation. But in the all, we have yet not to seen comprehensive and systematic study on the wood / inorganic nano-composite materials .
2.2 Mechanism of Wood / Inorganic Nano Composites
2.2.1 Micro-structure and nano-space of wood
Wood is a natural polymer melting insoluble composite materials , and has a variety of
active groups. It is the premise and base to study the micro-structure of wood itself that its biological synthesis, structure, the major components of the sediment distribution. The gaps in the wood can be divided into permanent gaps and transient gaps . According to their size scale ,it is divided into three levels : macro, meso and micro-voids .Nano-space exists in wood and the wood have a capacity of accepting zero-dimensional,
one-dimensional nano structural .
For example ,in the tracheids of wood and wood fiber , the intercellular layer I and the primary wall P and the secondary wall thickness of the inner S3 of the cell wall are
2.2.2 Mechanism of Wood / Inorganic Nano Composites
When designing the composite material , we mainly focus on its functional , composite and the exceptional stability of composite system design . When combining,we pay more attention to component selection, mix and disperse, and complex technology, the interface
[ 24]role of composite materials and the physical stability of the composite materials
Inorganic nano-powder materials usually have very strong surface activity and powerful capacity of adsorption, which is easy to in the oxygen bond to wood components .Some also have special optical properties .And the reflectance of the L-band ultraviolet is very high . It can greatly enhance the wood aging . In addition, with the small size effect of the surfaceof some inorganic nano-particles (such as nano-SiO) , it may produce the effect of 2
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infiltration ,which is conducive to inorganic nano-particles into the micro-structure of wood. Because there are a large number of keys and different unsaturated residual hydroxyl bonding states in the surface of nano-particles,it can be associated with the wood components in the group to form a solid combination.
If the wood-SiO nano-composite materials produced through the way of sol-gel , 2
nano-SiO particles is uniform distribution in the cell walls and cell gaps , and it formed in 2
the wood cell walls in-situ, which range of size is from 60 to 80 nm, while it still maintain the porous structure of characteristics of wood itself .
2.2.3 Factors of Wood / Inorganic Nano Composites
The performance properties of Wood / inorganic nano-composites depends on the performance properties of the matrix of wood itself and nano-materials (including particle size, preparation method, phase, etc.) as well as the interfacial properties between the those two. At present researches on the latter are less.
In general, with the reduction of the nano-particle size , the strength of composite materials increased .
2.3 Wood/Inorganic Nanocomposites composite method
The composite of wood and inorganic nanocomposites will expand the traditional use realm of wood.
2.3.1 The nanoparticles filling method
This method is simple to use and has been widely used. But it’s hard to make sure the space distribute parameter of the nanometer units of the composite system, and the nanoparticles are easy to cluster, this will has influence on the property of composite material. We can overcome this through surface modification on nanoparticles. However, the interface functions between different parts are waiting for further research.
2.3.2 The nanoparticles In situ composite
The use of wood-specific functional groups on the nano-materials in the complexation of metal ions adsorption and macromolecule matrix’s steric clash to reactant, or the nanoscale
limited space provided by matrix wood, in response to reaction in situ to generate nanoparticles and then constitute nanocomposites. This is usually used in wood manufacture and Nano-oxide composite materials.
2.3.3 Two phase synchronization In situ composite
The use of nano materials and wood matrix form nanocomposites synchronously, including intercalation in-situ polymerization, Sol-gel method and so on. This method overcomes the
shortcomings of nano-particle phase separation.
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2.4 Structure and Characterization of Wood/ Inorganic Nano-composites Composite material structure analysis and characterization are the basic guarantee to obtain its best performance. The woods based on quantum effects of nanoparticles and nanocomposites should not only have a structure, but also nano-particle size and particle size distribution should be uniform. We can take advantage of X-ray diffraction (XRD) test to
determine the microstructure of Si0、CaC0; X-ray diffraction can be carried out 223
quantitative analysis of crystalline material, grain size measurement and analysis of grain orientation; it can also be used to observe the dispersion of inorganic nano-particles in the nano-space of timber-related cases.
Atomic force microscopy (AFM) Could study the surface structure of various materials、
hardness、 elasticity、plasticity and other mechanical properties and surface friction nature of the micro-area.
X-ray photoelectron spectroscopy or Electron Spectroscopy for Chemical Analysis (XPS or ESCA) can be used to qualitative analysis the chemical compositions of samples and valence state , and to observe the structural characteristics of nano-units (including the surface atomic layer structure); it also can be used to research, and characterize nano-particles / polymer (such as timber) interaction via Auger electron spectroscopy (AES), laser Raman
spectroscopy, infrared spectroscopy, etc.
Applying scanning probe microscopy techniques, including scanning electron microscopy (SEM), we can obtain the sample system, surface topography and near-atomic-resolution level of the fine structure of information and nano-scale mechanical properties and nano-particles and polymer matrix ( such as plastic, wood micro-fibrils) of the contact angle and so on. By these technology ,we also can observe microfibril structure in different levels of wood fiber cell walls .SEM image three-dimensional senses are strong, while its imaging process is a function of time ,it can be easily to carry out image information processing. And combined with wave dispersive spectrometer (WDS) and energy dispersive spectrometer ( EDS) , at the same time you can observe the morphology of composite materials and carry
out micro-analysis, a comprehensive analysis of the regional composition ; We can also
use transmission electron microscopy (TEM) to observe the arrangement of layers of width of the cell wall of wood fiber cross-section , etc. .
Because of good natural properties of wood and the unique properties of nano-material itself, there will be huge research and application prospects in wood and nano-materials composite .we can improve it from below aspects : (a) Integrated the synergistic effect of
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wood and inorganic nano-particles and other components ; (2) According to the performance requirements of wood / inorganic nano-composite material to make a design.
In the theory,it is possible to composite wood and inorganic nano-particles . However,As the wood itself, because of complexity of the structure and composition of wood, and nano-materials,and micro-, small size, coupled with the quantum effects, surface effects, etc.,it is difficult to composite wood and inorganic nano-particles.So we can do more researches by methods of mechanism of biosynthesis and wood .
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