Table of Contents
Chapter 1.
Introduction………………………………………………………….........1
1.1. General Introduction……………………………………………………………….....1
1.2. Objectives…………………………………………………………………………….3
1.3. References…………………………………………………………………………….4
Chapter 2.
Bamboo Chemical Composition.………………………….………..….5
2.1. Introduction …………………………………….…………………………….……....5
2.2. Materials and
Methods…………………………….……………………………….....6 2.3. Results and
Discussion………………………………………………….……….….12 2.3.1
Hot Water and Alcohol Benzene Extractives………………….…………….….12 2.3.2 Holocellulose Content and Alpha-cellulose
Content…………………………...16 2.3.3 Lignin
Content……………………………….………………………...…..……20 2.3.4
Ash Content……………………………….………………………………...…..21 2.4.
Summary…………………………………………………………………………….23 2.5.
References…………………………………………………………………………..24
Chapter 3.
Anatomic, Physical and Mechanical Properties of Bamboo….....27
3.1
Introduction………………………………………………….……………………….27 3.1.1 Anatomical
Structures………………………………….……………..………….27
3.1.2 Physical and Mechanical
Properties………...………….………………………..28
3.2. Materials and
Methods…………………………….………………………………...30 3.2.1 Vascular Bundle Concentration
…………………………………...…………….30
3.2.2 Contact Angle
…………………………….…………...…..…………………….32
3.2.3 Fiber Characteristics…………………………………………...………………...32
3.2.4 SG, Bending and
Compression Properties …………………….……….…….....33
3.3. Results and
Discussion……………..……………….……………………………....34 3.3.1 Vascular Bundle Concentration
…………………………………………………34
3.3.2 Moisture Content
…….……………….…….……………….…...……………...34
3.3.3 Fiber Length Characteristics …………………………………………………….35
3.3.4 Contact Angle
………………………………………………………………..…38
3.3.5 Specific Gravity
………………………………….……………….……………..38 3.3.6 Bending Properties
…………………………….……………..………………….39
3.3.7 Compressive Properties ……………………………………...………………….42
3.4.
Summary…………………………………………………………………………….46
3.5. References…………………………………………………………………………...46
Chapter 4.
Medium Density Fiberboards from Bamboo……………………….50
4.1.
Introduction………………………………………………………………………..50 4.2. Materials and
Methods…………………………………………………………..…52 4.3. Results and
Discussion…………………………………………………………….54 4.3.1 Fiber Size
Distribution……………………………………………………………54
4.3.2 Physical and Mechanical
Properties of the Fiberboard. …………………...…….56
4.4.
Summary…………………………………………………………………………...62 4.5.
References…………………………………………………………………………62
Chapter 5.
Conclusions……………………………………………………………...66
Vita……………………………………………….……………………………..……....68
Abstract
This study investigated the chemical, physical, and
mechanical properties of the bamboo
species Phyllostachys pubescens
and its utilization potential to manufacture medium
density fiberboard (MDF).
The result showed holocellulose and alpha-cellulose content increased from the
base to the top portion. There was no significant variation in Klason lignin
content or ash content from the base to the top portion of the bamboo. The
outer layer had the highest holocellulose, alpha cellulose, and Klason lignin
contents and the lowest extractive and ash contents. The epidermis had the
highest extractive and ash contents and the lowest holocellulose and
alpha-cellulose content. Specific gravity (SG) and bending properties of bamboo
varied with age and vertical height location as well as horizontal layer. All
mechanical properties increased from one year old to five year old bamboo. The
outer layer had significantly higher SG and bending properties than the inner
layer. The SG varied along the culm height. The top portions had consistently
higher SG than the base. Bending strength had a strong positive correlation
with SG. In order to industrially use bamboo strips efficiently, it is
advisable to remove minimal surface material to produce high strength bamboo
composites. Compression properties parallel to the longitudinal direction was
significantly higher than perpendicular to the longitudinal direction. As
expected, at the same panel density level, the strength properties of the
fiberboard increased with the increasing of resin content. Age had a
significant effect on panel properties. Fiberboard made with one year old
bamboo at 8% resin content level had the highest modulus of rupture (MOR) and
modulus of elasticity (MOE) among the bamboo panels, which was largely
attributed to a higher compaction ratio as well as a higher percentage of
larger fiber size. Fiberboard made with five year old bamboo at 8% resin level
had the highest internal bond strength.
1.
Introduction
1.1 General
Introduction
Bamboo is
a naturally occurring composite material which grows abundantly in most of the
tropical countries. It is considered a
composite material because it consists of cellulose fibers imbedded in a lignin
matrix. Cellulose fibers are aligned
along the length of the bamboo providing maximum tensile flexural strength and
rigidity in that direction [Lakkad and Patel 1980]. Over 1200 bamboo species have been identified
globally [Wang and Shen 1987]. Bamboo
has a very long history with human kind.
Bamboo chips were used to record history in ancient China. Bamboo is also one of the oldest building
materials used by human kind [Abd.Latif 1990].
It has been used widely for household products and extended to
industrial applications due to advances in processing technology and increased
market demand. In Asian countries,
bamboo has been used for household utilities such as containers, chopsticks,
woven mats, fishing poles, cricket boxes, handicrafts, chairs, etc. It has also been widely used in building
applications, such as flooring, ceiling, walls, windows, doors, fences, housing
roofs, trusses, rafters and purlins; it is also used in construction as
structural materials for bridges, water- transportation facilities and skyscraper
scaffoldings. There are about 35 species
now used as raw materials for the pulp and paper industry. Massive plantation of bamboo provides an
increasingly important source of raw material for pulp and paper industry in
China [Hammett et al. 2001]. Table 1-1 provides a detailed description of
diversified bamboo utilization.
There are
several differences between bamboo and wood.
In bamboo, there are no rays or knots, which give bamboo a far more
evenly distributed stresses throughout its length. Bamboo is a hollow tube, sometimes with thin
walls, and consequently it is more difficult to join bamboo than pieces of
wood. Bamboo does not contain the same
chemical extractives as wood, and can therefore be glued very well [Jassen
1995]. Bamboo’s diameter, thickness, and
internodal length have a macroscopically graded structure while the fiber
distribution exhibits a microscopically graded architecture, which lead to
favorable properties of bamboo [Amada et al. 1998].
1
Table
1-1 Various uses of bamboo [Gielis 2002].
|
Use of bamboo as plant
|
Use of bamboo as material
|
|
|
Ornamental
horticulture
|
Local
industries
Artisanat
Furniture
|
|
|
Ecology
|
A variety of
utensils
|
|
|
Stabilize of the soil
|
Houses
|
|
|
Uses on marginal land
|
Wood
and paper industries
|
|
|
Hedges and screens
|
Strand boards
|
|
|
Minimal land use
|
Medium density
fiberboard
Laminated lumber
Paper and rayon
|
|
|
Agro-forestry
|
Parquet
|
|
|
Natural stands
|
Nutritional
industries
|
|
|
Plantations
|
Young shoots
for human consumption
|
|
|
Mixed agro-forestry
systems
|
Fodder
Chemical
industries
Biochemical products
Pharmaceutical industry
Energy
Charcoal
Pyrolysis
Gasification
|
|
With the
continued rapid development of the global economy and constant increase in
population, the overall demand for wood and wood based products will likely
continue to increase in the future.
According to a FAO (Food and Agriculture Organization) global outlook
study on the trends of demand for wood products, there will be an increase in
demand of the order of 20% by 2010. The
current concern is whether this future demand for forest products can be met
sustainably [FAO 1997].
As a
cheap and fast-grown resource with superior physical and mechanical properties
compared to most wood species, bamboo offers great potential as an alternative
to wood. Since bamboo species are
invasive and spread very fast uncared bamboo species also cause environmental
problems. Increased research during the recent years has considerably
contributed to the understanding of bamboo as well as to improved processing
technologies for broader uses.
2
The chemistry of bamboo is important in
determining its utilization potential.
Several studies have investigated the chemical composition of
bamboo. But systematic and thorough
research on a commercially important bamboo species is needed to determine
utilization potential for the products such as medium density fiberboard
(MDF). Most of previous studies provide
either only general information of several bamboo species or focuses on only
one aspect of one species. Chapter 2
presents the effect of age (1, 3, and 5 year old material), horizontal layer
(epidermis, outer, middle,
and inner
layer), and height location (bottom, middle, and top portion) of
Phyllostachys
pubescens
in detail.
Physical and mechanical properties of
several bamboo species have been studied
extensively. Chapter 3 presents the fiber length
distribution of Phyllostachys pubescens
at
different age, layer and location.
Contact angle of different layers of the bottom portion of three year
old bamboo were measured by dynamic contact angle measurement. Specific gravity and bending properties of
bamboo at different ages, horizontal layers, and height locations were also
determined. Also compressive strength at
different ages
and height locations were determined.
MDF is
the most commonly industrially produced type fiberboard and often has excellent
physical mechanical properties, and perfect surface properties. As an ideal board for furniture production
and other interior applications, MDF has gained much popularity around the
world. Chapter 4 focuses on the
utilization of bamboo fibers to MDF.
This chapter investigated the effects of age of bamboo fibers and the
resin content level on the physical and mechanical properties of the
manufactured fiberboards.
Chapter 2. Bamboo
Chemical Composition
2.1 Introduction
The
chemical composition of bamboo is similar to that of wood. Table 2-2 shows the chemical composition of
bamboo [Higuchi 1957]. The main
constituents of bamboo culms are cellulose, hemi-cellulose and lignin, which
amount to over 90% of the total mass.
The minor constituents of bamboo are resins, tannins, waxes and
inorganic salts. Compared with wood,
however, bamboo has higher alkaline extractives, ash and silica contents
[Tomalang et al. 1980; Chen et al. 1985].
Yusoff et al. [1992] studied the chemical
composition of one, two, and three
year old bamboo (Gigantochloa scortechinii).
The results indicated that the holocellulose
content did not vary much among different
ages of bamboo. Alpha-cellulose, lignin,
extractives, pentosan, ash and silica content increased with increasing age of
bamboo. Bamboo contains other organic composition in addition to cellulose and
lignin.
It
contains about 2-6% starch, 2% deoxidized saccharide, 2-4% fat, and 0.8-6%
protein. The carbohydrate content of
bamboo plays an important role in its durability and service life. Durability of bamboo against mold, fungal and
borers attack is strongly associated with its chemical composition. Bamboo is known to be susceptible to fungal
and insect attack. The natural
durability of bamboo varies between 1 and 36 months depending on the species
and climatic condition [Liese 1980]. The
presence of large amounts of starch makes bamboo highly susceptible to attack
by staining fungi and powder-post beetles [Mathew and Nair 1988]. It is noteworthy that even in 12 year old
culms starch was present in the whole culm, especially in the longitudinal
cells of the ground parenchyma [Liese and Weiner 1997]. Higher benzene-ethanol extractives of some
bamboo species could be an advantage for decay resistance [Feng et al. 2002].
The ash
content of bamboo is made up of inorganic minerals, primarily silica, calcium,
and potassium. Manganese and magnesium
are two other common minerals. Silica
content is the highest in the epidermis, with very little in the nodes and is
absent in the internodes. Higher ash
content in some bamboo species can adversely affect the processing machinery.
5
The internode of solid bamboo has
significantly higher ash, 1% NaOH, alcohol- toluene and hot water solubles than
the nodes [Mabilangan et al. 2002].
However, differences between the major chemical composition of node and
internode fraction of bamboo are small [Scurlock 2000]; neither the number of
nodes nor the length of internode segments would be critical to the utilization
of bamboo for energy conversion, chemical production, or as a building
material.
Fujji et al. [1993] investigated the
chemistry of the immature culm of a moso-
bamboo ( Phyllostachys
pubescens Mazel ). The results indicated that the contents of
cellulose,
hemicellulose and lignin in immature bamboo increased while proceeding downward
of the culm. The increase of cellulose
in the lower position was also accompanied by an increase in crystallinity.
The culm
of the bamboo is covered by its hard epidermis and inner wax layer. It also lacks ray cells as radial
pathways. Several results have revealed
that bamboo is difficult to treat with preservatives [Liese 1998; Lee 2001]. An oil-bath treatment can successfully
protect against fungal attack, but severe losses in strength have to be
expected [Leithoff and Peek 2001].
Since the
amount of each chemical composition of bamboo varies with age, height, and
layer, the chemical compositions of bamboo are correlated with its physical and
mechanical properties. Such variation
can lead to obvious physical and mechanical properties changes during the
growth and maturation of bamboo. This
chapter concentrates on a detailed analysis of chemical composition at
different age, height, and horizontal layer of bamboo in order to have a better
understanding of the effect of these factors on the chemical composition of
bamboo. It can also provide chemical
composition data for the pulp and paper industry which may have interest to
better utilize bamboo.
2.2 Materials and
Methods
The
bamboos for this study were collected on June, 2003 from the Kisatchie National
Forest, Pineville, La. Two
representative bamboo culms for each age group (one, three, and five years of
age) were harvested. The internodes of
each height location
and age group for chemical analysis were
cut into small strips with razor blade.
The
strips
were small enough to be placed in a Wiley Mill.
All of this material was ground in 6
the Wiley Mill. The material was then placed in a shaker with
sieves to pass through a No. 40 mesh
sieve (425-µm) yet retained on a No. 60
mesh sieve (250-µm). The resulting
material was placed in glass jars labeled with appropriate code for chemical
analysis.
Table 2-1 Chemical analysis of bamboo
[Higuchi 1955].
|
Species
(%)
ash
|
(%) Ethanol-
toluene
extractives
|
(%)
lignin
|
(%)
cellulose
|
(%)
pentosan
|
|
|||||||
|
Phyllostachys heterocycla
|
1.3
|
4.6
|
26.1
|
49.1
|
27.7
|
|
||||||
|
Phyllostachys nigra
|
2.0
|
3.4
|
23.8
|
42.3
|
24.1
|
|
||||||
|
Phyllostachys reticulata
|
1.9
|
3.4
|
25.3
|
25.3
|
26.5
|
|
||||||
To
prepare the samples of different horizontal layers of bamboo, bottom portion of
three year old bamboo was used. The
epidermis of the strips was first removed with a fine blade. The epidermis was kept for chemical analysis
and the rest of the strips were divided evenly based on volume into inner,
middle and outer layers along the radial direction by a fine blade. The grinding process was the same as above
described.
All tests
were conducted under the standards of American Society for Testing and
Materials (ASTM) except for alcohol-toluene solubility of bamboo. There was a minor modification for extractive
content test. Instead of benzene solutions, toluene solution was used. The exact standard that was followed for each
chemical property performed is presented in Table 2-2.
Table 2-2. Standards followed for chemical analysis
|
Property
|
Standard
|
|
|
Alcohol-toluene
solubility *
|
ASTM D 1107-56 (Reapproved 1972)
|
|
|
Hot-water
solubility
|
ASTM
1110-56 (Reapproved 1977)
|
|
|
Klason
lignin
|
ASTM D 1106-56 (Reapproved 1977)
|
|
|
Holocellulose
|
ASTM D 1104-56 (Reapproved 1978)
|
|
|
Alpha-cellulose
|
ASTM D
1103-60 (Reapproved 1978)
|
|
|
Ash
Content
|
ASTM D
1102-84 (Reapproved 1990)
|
|
7
Each test was conducted using 3
replications. It was necessary to
conduct additional experimentation when analyzing for alcohol-toluene
extractive content and holocellulose content.
The alcohol-toluene test is the starting material for many of the other
experiments. Both the lignin and
holocellulose content test are performed with extractive-free bamboo that is
derived from the alcohol-toluene extractive test. Additionally, holocellulose is a necessary
preparatory stage in order to determine the alpha-cellulose content.
Alcohol-toluene Solubility of Bamboo
The
extraction apparatus consisted of a soxhlet extraction tube connected on the
top end of a reflux condenser and joined at the bottom to a boiling flask. A two-gram oven-dried sample was placed into
a cellulose extraction thimble. The
thimble was plugged with a small amount of cotton and placed in a soxhlet
extraction tube. The boiling flasks
contained a 2:1 solution of 95 percent ethyl alcohol and distilled toluene
respectively and were placed on a heating mantle. The extraction was conducted for eight hours
at the rate of approximately six siphonings per hour.
When the
extraction was completed, all of the remaining solution was transferred to the
boiling flask which was heated on a heating mantle until the solution was
evaporated. The flasks were oven-dried
at 103±2oC, cooled in a desiccator, and weighed until a constant weight was
obtained.
The following formula was used to obtain
the alcohol-toluene solubility content of bamboo:
Alcohol-toluene
solubles (percent)= where,
W
W
W
1
2
×
100
[1]
1=weight
of oven-dry test specimen (grams).
W
2=weight
of oven-dry extraction residue (grams).
A minor change was made since it was
necessary to conduct additional
experiments
in order to provide sufficient extractive-free bamboo for other chemical 8
property experiments. Therefore, the sample size was increased to
20 grams and the extraction time to forty-eight hours.
Hot-water Solubility of Bamboo
A
two-gram sample was oven-dried and placed into a 250 mL Erlenmeyer flask with
100 mL of distilled water. A reflux
condenser was attached to the flask and the apparatus was placed in a gently
boiling water bath for three hours.
Special attention was given to insure that the level of the solution in
the flask remained below that of the boiling water. Samples were then removed from the water bath
and filtered by vacuum suction into a fritted glass crucible of known weight. The residue was washed with hot tap water
before the crucibles were oven-dried at 103±2oC. Crucibles were then cooled in a desiccator
and weighed until a constant weight was obtained.
The following formula was used to obtain
the hot-water solubility of bamboo:
W − W
Hot-water solubles (percent)=
1
W
1
2
×
100
[2]
where,
W
1=weight
of oven-dry test specimen (grams).
W2=weight of oven-dry
specimen after extraction with hot water (grams).
Klason Lignin in Bamboo
A
one-gram, oven-dried sample of extractive-free bamboo was placed in a 150 mL
beaker. Fifteen mL of cold sulfuric acid
(72 percent) was added slowly while stirring and mixed well. The reaction proceeded for two hours with
frequent stirring in a water bath maintained at 20 o C.
When the two hours had expired, the specimen was transferred by washing
it with 560 mL of distilled water into a 1,000 mL flask, diluting the
concentration of the sulfuric acid to three percent.
An allihn
condenser was attached to the flask. The
apparatus was placed in a boiling water bath for four hours. The flasks were then removed from the water
bath and
the insoluble material was allowed to
settle. The contents of the flasks were
filtered by
vacuum
suction into a fritted-glass crucible of known weight. The residue was washed 9
free of acid with 500 mL of hot tap water
and then oven-dried at 103±2oC.
Crucibles were then cooled in a desiccator and weighed until a constant
weight was obtained.
The following formula was used to obtain
the lignin content of bamboo:
W4 − W
Klason lignin content in bamboo (percent)= 3 × ( 100 − W )
100
×
1
W
2
where,
W
1=alcohol-toluene
extractive content (percent).
W
2=weight
of oven-dried extractive-free sample (grams).
W
3=weight
of oven-dried crucible (grams).
W4=weight of oven-dried
residue and crucible (grams).
Holocellulose in Bamboo
A
two-gram sample of oven-dried extractive-free bamboo was weighed and placed
into a 250 mL flask with a small watch glass cover. The specimen was then treated with 150 mL of
distilled water, 0.2 mL of cold glacial acetic acid, and one gram
of NaClO
2 and placed into a water bath maintained
between 70 oC -- 80 oC. Every hour
for five hours 0.22mL of cold glacial acetic acid and one gram of
NaClO 2 was
added and the contents of
the flask were stirred constantly. At the
end of five hours, the flasks were placed in an ice water bath until the
temperature of the flasks was reduced to 10 o C.
The contents of the flask were filtered
into a coarse porosity fritted-glass
crucible of
known weight. The residue was washed
free of ClO 2 with 500
mL of cold
distilled
water and the residue changed color from yellow to white. The crucibles were then oven-dried at 103 ±
2oC, then cooled in a desiccator, and weighed until a constant weight was
reached.
The following formula was used to
determine the holocellulose content in bamboo:
W4 − W
Holocellulose content in bamboo (percent) = 3 × ( 100 − W ) [4]
100
×
1
W
2
where,
10
W
1=alcohol-toluene
extractive content (percent).
W2=weight of oven-dried
extractive-free sample (grams).
W
3=weight
of oven-dried crucible (grams).
W
4=weight
of oven-dried residue and crucible (grams).
Alpha-cellulose in Bamboo
A three
gram oven-dried sample of holocellulose was placed in a 250 mL Erlenmeyer flask
with a small watch glass cover. The
flasks were placed into water bath that was maintained at 20 o C. The sample was then treated with 50 mL of
17.5 percent NaOH and thoroughly mixed for one minute. After the specimen was allowed to react with
the solution for 29 minutes, 50 mL of distilled water was added and mixed well
for another minute. The reaction
continued for five more minutes.
The
contents of the flask were filtered by aid of vacuum suction into a fritted-
glass crucible of known weight. The
residue was washed first with 50 mL of 8.3 percent NaOH, then with 40 mL of 10
percent acetic acid. The residue was
washed free of acid with 1,000 mL of hot tap water. The crucible was oven-dried in an oven at 103±2oC,
then cooled in a desiccator, and weighed until a constant weight was reached.
The following formula was used to obtain
the alpha-cellulose content in bamboo:
W4 − W
Alpha-cellulose (percent) = 3 × W [5]
100 × W2 1
where,
W
1=Holocellulose
content (percent).
W2=weight of oven-dried
holocellulose sample (grams).
W
3=weight
of oven-dried crucible (grams).
W
4=weight
of oven-dried residue and crucible (grams).
11
Ash
Content in Bamboo
Ignite an
empty crucible and cover in the muffle at 600 o C, cool in a dessicator, and
weigh to the nearest 0.1 mg. Put about 2
gram sample of air-dried bamboo in the crucible, determine the weight of
crucible plus specimen, and place in the drying oven at 103±2oC with the
crucible cover removed. Cool in a
desiccator and weigh until the weight is constant. Place the crucible and contents in the muffle
furnace and ignite until all the carbon is eliminated. Heat slowly at the start to avoid flaming and
protect the crucible from strong drafts at all times to avoid mechanical loss
of test specimen. The temperature of
final ignition is 580 o C to 600oC.
Remove the crucible with its contents to a dessiccator, replace the
cover loosely, cool and weigh accurately.
Repeat the heating for 30 min periods until the weight after cooling is
constant to within 0.2 mg.
The following formula was used to obtain
the ash content in bamboo:
Ash content (percent) =
W
W
1
2
×
100
[6]
where,
W
1=weight
of ash (grams).
W2=weight of oven-dried
sample (grams).
The effects of age, height, layer on
bamboo chemistry were evaluated by analysis of variance at the 0.05 level of
significance.
2.3 Results and
Discussion
The results of the bamboo chemistry
testing are listed in Table 2-3. For
specific chemical component the result is discussed in detail in the following.
Table 2-4 shows the results of analysis of variance and Table 2-5 shows the
Tukey comparison results.
2.3.1 Alcohol-toluene
and Hot Water Extractives
The
alcohol-toluene extractives of bamboo consists of the soluble materials not
generally considered part of the bamboo substance, which are primarily the
waxes, fats,
resins, and some gums, as well as some
water-soluble substances. The
alcohol-toluene
extractive
content of different age and height locations is presented in Figure 2-1. Age 12
had a significant effect on
alcohol-toluene extractive content. With
the increase of age, alcohol-toluene extractive content increases
steadily. Five year old bamboo had the
highest extractive content. There was
some variation among vertical sampling locations. The top portion had the highest extractive
content. The bottom and middle had not
significantly different in alcohol-toluene extractive content.
Table 2-3. Chemical composition of bamboo
Age Location Ash Hot
Water Alcohol- Holo- α-cellulose
toluene
Solubles
Solubles
Lignin
cellulose
% %% % % %
|
Bottom 1.82
|
68.92
|
|
|
5.83
3.32
21.98
46.52
One
Middle
1.94
70.84
5.07
2.86
22.11
47.30
|
Top 1.95
|
71.95
|
|
|
5.14
3.48
21.26
47.51
|
Bottom 1.30
|
68.58
|
|
|
6.33
4.17
23.21
46.21
Three
Middle
1.36
72.69
6.91
4.38
23.95
46.82
|
Top 1.41 7.43
|
5.21 23.71
|
73.82
|
46.99
|
|
|
|
Bottom 1.26 4.89
|
6.61 22.93
|
69.94
|
46.08
|
|
|
Five
Middle
1.30 5.19
Top
1.35 5.84
6.81
22.97
7.34
23.02
72.50 73.65
47.65 47.91
Three1
Epidermis
Outer Middle Inner
4.09 0.54 0.65 0.88
9.19 5.26 7.25 9.33
5.99 3.15 4.25 5.78
22.41 24.30 21.79 22.57
63.14 69.94 65.84 64.54
41.71 49.02 45.08 42.84
1
The
bottom portion of three year old bamboo was used to determine the effect of
horizontal layer on the
chemical
composition of bamboo.
Table 2-4. Analysis of variance table for
bamboo chemical composition.
Pr>F
Source DF Ash
Hot Water Alcohol- Holo- α-cellulose
Solubles
Solubles
toluene
Lignin
cellulose
Year
2
<0.0001
<0.0001
<0.0001
<0.0001
0.0005
0.025
Height
2
0.001
<0.0001
<0.0001
0.3760
<0.0001
<0.0001
|
Year*Height
|
4
|
0.700
|
<0.0001
|
0.0105
|
0.3379
|
0.0493
|
0.1625
|
|
|
Layer
|
3
|
<0.0001
|
<0.0001
|
<0.0001
|
0.0029
|
<0.0001
|
<0.0001
|
|
13
Table
2-5. Tukey comparison table for bamboo chemical composition.
Source Location Ash Hot
Water Alcohol- Holo- α-cellulose
toluene
Solubles
Solubles
Lignin
cellulose
1
A
C
C
B
B
AB
Year
3 5 Bottom
B B B
A B B
B A B
A A A
A A C
B A C
|
Height
|
Middle
|
A
|
B
|
B
|
A
|
B
|
B
|
|
|
Layer
|
Top
|
A
|
A
|
A
|
A
|
A
|
A
|
|
|
|
Outer
|
B
|
C
|
C
|
A
|
A
|
A
|
|
|
|
Middle
Inner
|
B
B
|
B
A
|
B
A
|
B
B
|
B
C
|
B
C
|
|
|
|
Epidermis
|
A
|
A
|
A
|
B
|
C
|
C
|
|
Bottom
Middle Top
) 8
ne lue nt (% 67
to co 45
o tive 3
h a
2
o Alc
l
c extr
1 0
135
Bamboo age (years)
Figure 2-1. Alcohol-toluene extractive content of bamboo
at different age and location.
The alcohol-toluene extractive content of
different horizontal layers of the
bottom
portion of three year old bamboo was presented in Figure 2-2. Epidermis and inner layer had significant
higher alcohol-toluene extractive content.
The outer layer had the lowest alcohol-toluene extractive content.
The
epidermis of bamboo has an attractive green color due to the chlorophyll in its
epidermis. After extraction with
alcohol-toluene, the color of the extraction solution
turned to a dark green color due to the
extraction of chlorophyll. Also several
studies
have
revealed that the chlorophyll in the epidermis is very easily degraded and thus
14
treatment with inorganic salts such as
chromates, nickel salts, and copper salts have been used to conserve the green
color of bamboo surfaces [Chang et al. 1998,2001; Wu 2002]. Wax material attached to the inner layer also
contributed to the higher alcohol-toluene extractive content relative to the
middle and outer layers.
7.00
ive 6.00
actxtr ) 5.00
|
ne e nt (%
|
4.00
|
|
|
lue nte
|
3.00
|
|
to
c o
2.00
o h
o
Alc
1.00 0.00
Epidermis
Outer
Middle
Inner
Horizontal layer of bamboo
Figure
2-2. Alcohol-toluene extractive content
of three years old bamboo of different horizontal layers.
Hot water extractives in the bamboo
include tannins, gums, sugars, coloring matter, and starches.
Age had
some effect on hot water extractive content of bamboo. Three year old bamboo had the highest hot
water extractive content. There was no
significant difference between one and five year old bamboo. This indicates that hot water extractive
increased from year one to year three and then decreased gradually.
Height
also had some effect on the variation of hot water extractive content. Bamboo top portions had a significantly
higher hot water extractive content than middle and bottom portions. There was no significant difference between
the middle and bottom portion.
The hot water extractive content in each
layer showed a similar trend as that of
alcohol-toluene
extractive content. The outer layer had
the lowest hot water extractive 15
content.
The epidermis and inner layer had significantly higher extractive
content, which can be explained similarly as was detailed for alcohol-toluene
extractives.
Bottom
Middle Top
e 10.00
ctiv ) 8.00
traex nt (% 6.00
ater nteco 4.00
t w Ho
-
2.00
135
Bamboo age (years)
Figure 2-3. Hot water extractive content of bamboo at
different age and height location.
12.00
)
|
nt (
|
%
|
10.00
|
|
|
nte
|
|
8.00
|
|
|
es co
|
|
|
|
ctiv 6.00
raxate 4.00
t w Ho
2.00 -
Epidermis Outer Middle Inner
Horizonal layer of three year old bamboo
Figure 2-4. Hot water extractive content of bamboo of
different horizontal layers.
2.3.2 Holocellulose
Content and Alpha-cellulose Content
Holocellulose include alpha-cellulose and
hemicellulose. Alpha-cellulose is the
main
constituent of bamboo. Approximately
40-55% of the dry substance in bamboo is 16
alpha-cellulose. Cellulose is a homopolysaccharide composed of
β-D-glucopyranose
units which
are linked together by (1 →4)-glycosidic bonds.
Cellulose molecules are
completely
linear and have a strong tendency to form intra- and intermolecular hydrogen
bonds. Bundles of cellulose molecules
are thus aggregated together in the form of microfibrils, in which crystalline
regions alternate with amorphous regions.
Hemicelluloses are heterogeneous polysaccharides, like cellulose, most
hemicelluloses function as supporting materials in the cell walls [Sjostrom
1981]. Alpha-cellulose is the main
source of the mechanical properties of bamboo and wood [Janssen 1981].
Figure 2-5 presents the holocellulose
content of bamboo at different ages and locations. There is no significant difference between
three and five year old bamboo in holocellulose content. One year old bamboo
had relatively lower holocellulose content. Height had a significant effect on
holocellulose content. Top portion had
the highest holocellulose content; bottom portion had the lowest holocellulose
content.
Bottom
Middle Top
)
ten
on
se c
l
o
ell u
t (%
75 70 65 60 55
l oc
Ho
50
13
Bamboo age (years)
5
Figure 2-5. Holocellulose content of bamboo at different
ages and heights.
Holocellulose
content of different layers of the bottom portion of three year old bamboo is
presented in Figure 2-6. Outer layer had
the highest holocellulose content, and the epidermis had the lowest. Although holocellulose content seems to
decrease from the
outer layer to the inner layer, it was
not significantly different between the middle and
inner
layers. Low holocellulose content in the
epidermis is partly due to its high 17
extractive and ash contents. Previous research has shown that the epidermis
wall consisted of an outer and inner layer; the inner layer appears to be
highly lignified. The cutinized layer is
composed of cellulose and petin [Liese and Hamburg 1987]. Since the outer layer had a significantly
higher extractive content and ash content, it seriously reduced the
holocellulose content in bamboo epidermis.
Alpha-cellulose
content of bamboo at different age and height is presented in Figure 2-7. Analysis of variance showed that age had no
significant effect on alpha- cellulose content. There was a significant difference in
alpha-cellulose content along the height of the bamboo culm. It increased gradually from the bottom to the
top portion.
) 75.00
t (% 70.00
one c 65.00
los 60.00
cellu l
55.00
o Ho
50.00
Epidermis Outer Middle Inner
Horizonal layer of three
year old bamboo
Figure
2-6. Holocellulose content of three
years old bamboo of different horizontal layers.
Alpha-cellulose
content had a significant difference across the bamboo culm of the bottom
portion of three year old bamboo (Figure 2-8).
It consistently decreased from the outer layer to the inner layer. The epidermis of bamboo had the lowest alpha-
cellulose content.
In general, the alpha-cellulose content
in bamboo is 40-50%, which is
compatible
to the reported cellulose content of softwoods (40-52%) and hardwoods (38- 18
56%).
Cellulose contents in this range make bamboo a suitable raw material for
the paper and pulp industry.
Bottom
Middle
Top
55
)
t (% 50
|
nten
|
45
|
|
|
co
|
|
|
|
lul
|
40
|
|
ha c
|
elAlp
|
35
|
|
|
|
|
|
30
|
|
|
|
|
13
|
5
|
|
||
|
Bamboo age (years)
|
|
|
||
Figure 2-7. Alpha-cellulose content of bamboo at
different age and height location.
|
)
|
55.00
|
|
|
t (%
|
49.00
|
|
|
nten
|
|
|
|
|
43.00
|
|
oseclul 37.00
ha c
31.00
e l
Alp
25.00
Epidermis Outer Middle Inner
Horizonal layer of three year old bamboo
Figure
2-8 Alpha-cellulose content of three years old bamboo of different horizontal
layers.
19
2.3.3 Klason Lignin Content
Lignin is
polymer of phenylpropane units. Many
aspects in the chemistry of lignin still remain unclear. Lignin can be isolated from extractive free
wood as an insoluble residue after hydrolytic removal of the
polysaccharides. Klason lignin is
obtained after removing the polysaccharides from extracted (resin free) wood by
hydrolysis with 72% sulfuric acid [Sjostrom 1981]. Bamboo lignin is built up from three
phenyl-propane units, p-coumaryl, coniferyl and sinapyl alcohols interconnected
through biosynthetic pathways [Liese 1987].
The
lignin present in bamboos is unique. The
lignification process undergoes changes during the elongation of the culm, the
full lignification of the bamboo culm is completed within one growing season,
showing no further ageing effect [Itoh and Shimaji 1981].
The
lignin content of one year old bamboo is significantly lower than that of three
and five year old bamboo (Figure 2-9).
Three year old bamboo seems to have higher lignin content than five year
old bamboo, but the magnitude of the difference is not statistically
significant.
Bottom Middle Top
|
13
|
5
|
|
|
Bamboo age (years)
|
|
|
Figure 2-9. Klason Lignin content of
bamboo at different age and height locations.
The Klason lignin content of the
different layers of the bottom portion of three year old bamboo was presented
in Figure 2-10. The outer layer had the
highest lignin content. There was no
significant difference among epidermis, inner layer and middle layer of
bamboo. The higher lignin content
contributes greatly to the higher strength properties of the outer layer.
The
lignin values of 20-26% place bamboo at the high end of the normal range or
11-27% reported for non-woody biomass [Bagby 1971] and closely resemble the
ranges reported for softwoods (24-37%) and hardwoods (17-30%) [Fengel 1984;
Dence 1992]. The high lignin content of
bamboo contributes to its high heating value of bamboo, and its structural
rigidity makes it a valuable building material [Scurlock 2000].
Epidermis Outer Middle Inner
Horizonal
layer of three yearold bamboo
Figure
2-10. Klason lignin content of three
years old bamboo of different horizontal layers.
2.3.4 Ash content
Ash is a term generally used to refer to inorganic
substances such as silicates, sulfates, carbonates, or metal ions [Rydholm
1965].
The ash content of bamboo at different
age and height is presented in Figure 2-11.
The
ash
content of one year old bamboo was significantly higher than that of three and
five 21
year old bamboo. Three and five year old bamboo had no
significant difference in ash content.
Analysis of variance also showed there was no difference between top and
middle portions for ash content; the ash content in the bottom portion of the
culm was the lowest.
Figure
2-12 showed the ash content at different layers. We can see that the epidermis had
significantly higher ash content, which is three times of other three
layers. It has been suggested that the
higher ash content in the epidermis is mainly due to the fact that almost all
the entire silica is located in the epidermis layers, with hardly any silica in
the rest of the wall [Satish et al. 1994].
Table 2-7 also shows the ash content data for several common wood
species. It is clear that bamboo has
significantly higher ash content than these common woods but generally lower
than that of bark of most wood species.
Bottom Middle Top
Bamboo age (years)
Figure 2-11. Ash content of bamboo at different age and
height location.
Epidermis Outer Middle Inner
Horizonal
layer of three year old bamboo
Figure 2-12. Ash content of three years old bamboo of
different horizontal layer.
Table 2-6. Low temperature ash content of different
wood
species [MISRA 1993].
|
Aspen
|
0.43
|
|
|
Yellow poplar
|
0.45
|
|
|
White oak
|
0.87
|
|
|
White oak bark
|
1.64
|
|
|
Douglas-fir bark
|
1.82
|
|
Wood species
Ash cont
Ash cont
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