Studies of Dimensional Stability, Thermal Stability and Biodegradation Resistance
Capacity of Chemically Treated Bamboo
Runumee D. Borthakur
Bamboo is the worlds fast growing and widely used lignocellulosic versatile
material. Like other biological materials, bamboo is susceptible to environmental
degradation such as moisture, heat, rain, insects etc. as well as dimensional
variation when exposed to natural environmental conditions although, with the
use of appropriate treatments, the shelf-life of these materials can be prolonged.
Chemical modification of split bamboo with a bulk Monomer like Methyl Methacrylate
(MMA) or butyl methacrylate (BMA) in the presence of a dithioligand was studied.
Polymerisation of MMA and BMA was possible by heat treatment as the catalyst.
The dimensional stability efficiency of the treated sample in terms of Anti-shrink
Efficiency (ASE%) was improved compared to untreated samples, as were the mechanical
strength properties modulus of rupture and modulus of elasticity. The efficacy
of the preservative chemicals for the treatment of bamboo samples was evaluated
in ground contact against termite and fungus and found to be improved on treatment.
The penetration of the preservative chemicals and deterioration of the bamboo
samples after burial test was evident from Scanning Electron Micrograph (SEM).
From the thermal analysis data of the treated and untreated samples, it was
observed that the percentage of weight loss decreases in treated samples compared
to untreated sample. The interaction of the bamboo component and chemicals was
confirmed by FTIR spectroscopy.
Received: March 26, 2013;
Accepted: May 06, 2013;
Published: March 04, 2014
Bamboo, commonly termed poor mans timber in India, is a fast
growing lignocellulosic and versatile bio-resource with numerous uses in rural
and urban sectors as a raw material due to its fibrous nature, excellent strength,
easy workability and availability (Liese and Kumar 2003).
Bamboos are also used as craft and building materials in many parts of the world
apart from their use as raw material for paper industry. However, some properties
restrict the wider use of the lignocellulosic material like dimensional changes
due to fluctuating humidity and moisture, biodegradability and photosensitivity
etc. (Ozmen, 2007).
Even though bamboos have a hard and highly refractive outer rind, the presence
of rich source of potential nutrients and lack of resistive chemical characteristics
makes it highly biodegradable. The main components of bamboo are cellulose as
a skeleton (40%), hemicellulose as a matrix (~25%) and lignin as an incrusting
material (20-25%) (Tamolang et al., 1980; Kumar
et al., 1994; Liese and Kumar, 2003). Most
of the physical and chemical properties exhibited by lignocellulosics are attributed
to these natural polymers and their matrix arrangement. All these polymers are
hydrophilic in nature due to the presence of hydroxyl and other oxygen-containing
groups (Pandey et al., 2009). Since these groups
absorb moisture through hydrogen bonding, the moisture content of lignocellulosic
material changes as the surrounding humidity and temperature change, which causes
swelling of the cell wall of bamboo. On drying, the cell wall shrinks again
causing dimensional instability (Ozmen, 2007; Das
and Chakrabarty, 2008). Bamboo is also susceptible to degradation by fungus,
bamboo borer and certain types of termites. Termites with their cellulose-decomposing
bacteria in the gut can easily digest the cellulosic part of bamboo and as a
result, the strength of the bamboo reduced drastically which in turn makes it
unfit as a construction material. The dimensional instability and biodegradation
of bamboo and other lignocellulosic materials can be minimized by modifying
the hydroxyl groups found in cell wall polymers by using suitable preservatives
(Deka et al., 2003; Singh
et al., 1979; Rowell, 1975). To protect the
lignocellulosic material from degradation and enhance its service life, various
treatment methods have been employed during last few decades such as treating
with mineral oil, coal tar ; heating in hydrocarbon oil, smoking, treating with
various etherifying and esterifying agents, acetals, alkylene oxide and alkoxysilane-coupling
agents and have been documented by several researchers (Rowell,
1975, 2005; Rowell and Gutzmer,
1975; Kumar et al., 1991; Singh
et al., 1992; Deka et al., 2003).
Studies were also carried out to improve physical strength and other performance
properties of wood was done by impregnated with suitable polymers for end use
(Hill, 2006). Improvement of moisture resistance and hardness
of wood using vinyl monomers followed by curing (radiation or catalyst) was
described (Meyer, 1984). Polymer system cross linked
by Methyl Methacrylate (MMA) alone or in combination with other monomers for
enhanced the dimensional stability was reported (Ng et
al., 1999). It has been reported that a combined treatment of boron
and MMA could extend the durability of treated wood (Musta
et al., 1999). Wood Polymer Composite (WPC) had improved physical
and mechanical properties more than untreated wood (Rowell
and Konkol, 1987). Improved dimensional stability, strength and stiffness
of the wood was achieved when rubber wood is impregnated with styrene in combination
with a crosslinker (glycidal methacrylate) (Devi et al.,
2003). However, studies on polymer (MMA and BMA) treated bamboo for improving
its dimensional and other performance properties are lacking. Therefore, the
present study was carried out by treating bamboo with conventional chemicals
such as boric acid, copper acetate, trimethyltetramine dithiocarbamate prior
to impregnation with Methyl Metha Crylate (MMA) and Butyl methacrylate (BMA)
polymer for arresting dimensional change and biodegradation.
MATERIALS AND METHODS
Raw material: The experiment was carried out during 2007-2010 to study
the durability and dimensional stability of bamboo. Bambusa balcooa Roxb.
(Bhaluka) was selected for this experiment due to its wider application in construction
of houses, bridge, fencing, agricultural implements and easily available bamboo
species of Assam. The internodes portion of a four years old bamboo was collected
for the experiments from a homestead garden of Assam, India. Rectangular strips
of approximately 10.00x2.15x1.23 cm3 (lengthxbreadthxthickness) were
prepared from bamboo culms for treatment. The samples were pretreated by refluxing
in acidic methanol for three hours to elute some lignin, starch, waxes and soluble
compounds, thereby facilitating the increase penetration of chemicals. The pretreated
samples were then oven dried at 100±5°C so that at least 20% moisture
remains inside the samples because microbial degradation can occur if moisture
is more than 20% of the dry weight. The remaining 20% moisture is essential
to facilitate movement of water soluble chemical preservatives. The treatment
was carried out as per BIS (BIS, 1977).
Treatment of the samples: To carry out this study two polymer namely Methyl Methacrylate (MMA) and butyl methacrylate (BMA) are used. Other chemicals used in this study are Boric Acid (BA), Copper Acetate (CA), trimethyltetramine dithiocarbamate (Triendtc). The treatment of the bamboo samples were carried out as follows:
||The samples were first treated with (5% each) boric acid followed
by copper acetate and triethylenetetramine dithiocarbamate (Triendtc)
||The chemically treated samples (a) were soaked in (5%) MMA and BMA solutions
and subsequent in situ polymerization were carried out by heat treatment
using benzoyl peroxide as catalyst
After completion of chemical treatments, all the samples were treated with
kerosene for seven days and air dried.
Evaluation of properties of treated and untreated bamboo: The dimensional
parameters such as Anti Shrink Efficiency (ASE),volumetric swelling coefficient
(S), Bulk Coefficient (BC) were determined by repeated water soaking method
(Rowell and Ellis, 1978) using the following relations.
Wight percent gain (WPG): The WPG or chemical loading was calculated as:
where, Wt is OD weight of the treated sample in g. Wu is OD weight of the untreated sample in g.
Volumetric swelling co-efficient (S) and anti shrink efficiency (ASE): The S and ASE were calculated following the relations:
where, Vw is swollen volume of bamboo sample after treatment in cm3, V u,t is OD volume of either untreated and treated samples in cm3:
where, Su is volumetric swelling of the untreated sample, St is volumetric swelling of the treated sample.
Bulk co-efficient (BC): Bulk (BC) was calculated as:
where Vu and Vt are oven-drying volumes of untreated and treated samples, respectively.
Infra-Red (IR) spectroscopic studies of treated and untreated bamboos: The IR spectra of treated and untreated bamboo powder were recorded as KBr (potassium bromide) pallet in a Perkin Elmer Spectrophotometer, Model 580 B, in the range of 4000-200 cm-1.
Scanning electron micrograph (SEM) study: To study the adherence of chemicals onto bamboo cell wall, the SEM of treated and untreated samples were taken in Scanning Electron Microscope. The observations were made in JEOL, JSM-35M-35 CF electron microscope at Indian Institute of Technology, Guwahati, Assam, India.
Thermal analyses: For thermal analyses of treated and untreated bamboo samples, the samples were first ground to powder form (+40 and-60 British Standard Sieve) and then simultaneous thermogravemetric (TG) and Differential Thermogravemetric (DTG) analyses were carried out using Perkin Elmer Pyris Diamond Instrument at heating rates of 20°C min-1 in the temperature range 40-650°C in air atmosphere. The weight of the sample powder was in the range of 5.88-8.44 mg and α alumina was used as reference material.
Evaluation of physical and mechanical properties of the bamboo samples: The physical and mechanical properties of the treated and untreated bamboo samples were evaluated by using Universal Testing Machine at NEIST, Jorhat, Assam, India.
Determination of modulus of rupture (MOR): The MOR of the specimens was reported using the following mathematical expression:
where, P = Maximum load applied in kg., L = Length span of the tested specimen in cm., b = Width of the specimen in cm, d = Depth of the specimen in cm.
Determination of modulus of elasticity (MOE): The modulus of elasticity of the test specimen were determined using the relation:
where, P1 is load in kg at proportionality limit, Y is central deflection at the limit of proportionality load in cm, L is length span of the test specimen in cm, b is width of the test specimen in cm, d is depth of the specimen in cm.
Determination of termite resistance capacity: The termite resistance
capacities of treated and untreated bamboo samples were determined visually.
For this, the treated bamboo samples along with untreated control samples were
subjected to termite attack in a termite colony under ambient environmental
condition (average temperature of 28°C and average relative humidity of
72%). After six months of exposure to termite, the samples were exhumed for
visual observation and recorded the damage level.
Cellulase inhibition test: To carry out the cellulase inhibition test,
five 250 mL beaker was taken (marked 1 to 5). In each of five 250 mL beakers
60 mL of phosphate buffer (pH 6.47) were taken, to each of which 1 gm of bamboo
powder (BP) was added. In each of the beaker (No. 2-5), 5% (w/v) of Boric Acid
(BA), Copper Acetate (CA), sodium salt of triethylenetetramine dithiocarbamate
(Triendtc.) and a mixture of 5% (w/v) each of BA, CA, Triendtc. were added.
To each of the five beakers 6 mL (300 units) of cellulase enzyme (Aldrich) were
added. After adding chemicals and cellulase enzyme, the beakers were covered
for 24 h at room temperature along with remaining beaker without adding the
chemicals. After which they were heated at 60°C for 1 h in water bath to
stop the cellulase activity. After cooling at room temperature, the solution
were filtered and made up the volume to 100 mL and glucose was estimated by
Fehling solution using methylene blue indicator relative to a standard glucose
RESULTS AND DISCUSSION
The dimensional variations of bamboo samples treated with different chemicals
and their combinations in terms of antishrink efficiency (ASE), bulk coefficient
(BC) and Weight Percent Gain (WPG) shows in Table 1. The bamboo
samples treated with BA, CA, Triendtc followed by MMA and BMA showed comparatively
higher antishrink efficiency (ASE) with increase in Bulk Coefficient (BC). In
the present study maximum ASE (59.39%) value at the level of 26.11% WPG shown
by the sample treated with boric acid, copper acetate, triendtc followed by
MMA and kerosene. An ASE of 46% was reported when oil palm wood treated with
MMA without cross linking agents (Ibrahim, 1989). Musta
et al. (1999) reported improved dimensional stability and moisture
excluding efficiency of boric acid and MMA treated Japanese cedar wood. Geraldes
et al. (2004) did a series of studies and reported that acrylates crosslinking
agents capable to impart a more effective cross linking on poly (MMA) matrix.
Hill (2006) studied the dimensional stability of Mahang
wood treated with MMA without cross linking agents and reported that though
there is no significant changes in dimension of the wood after MMA treatment,
this treatment showed very effective in reducing water or moisture uptake. Similar
results have been observed in the present study also. In this study MMA and
BMA treatment without any cross linker showed very effective in reducing water
or moisture uptake. The results of the present study suggest that in presence
of polymer and chemicals, the cell wall of bamboo showed less shrinkage and
swelling in contact with moisture than the untreated samples. The added polymer
MMA and BMA absorbed by the remaining pores of the cell in bamboo after the
impregnation of the chemicals such as BA, CA, Triendtc. The presence of kerosene
creates a hydrophobic environment inside and on the surface of the samples as
well as prevents the leaching of preservatives by moisture penetration. This
treatment also showed higher weight percent gain (WPG 26.11%) value than the
other treatments as well as untreated samples. Increase of WPG indicates the
presence of added chemicals in to the bamboo samples. The dimensional stability
in terms of antishrink efficiency was determined and found to be improved on
treatment. However, these samples also exhibits total protection from termite
compared to simple MMA and BMA treatment (Table 1).
The assignment of the major FTIR absorption bands of modified and unmodified
bamboo samples were shown in Fig. 1. The appearance of a strong
absorption band at 3425-3340 cm-1 ascribed due to the v O-H
as well as the presence of H- bonding network.
|| Dimensional characteristics of the treated and untreated
|*Combined treatment of BA, CA, Triendtc, MMA and Kerosene
showing highest WPG, BC and ASE, value
|| IR spectra of (1) MMA, (2) BMA and (3) Untreated bamboo
However, two bands in the 2929-2960 cm-1 were also prominent in
all spectra, these being attributed to C-H stretching vibration in methyl and
methylene groups of lignin and extractives. Strong absorption band at around
1740 cm-1 ascribed due to carbonyl group C = O and 1270 cm-1
due to C-O group. Two small bands at 1600 and 1637 cm-1 are assigned
to the absorbed water and β -glucosidic linkages between the sugar units,
respectively (Owen and Thomas, 1989). Weak absorptions
between 1500 and 1400 cm-1 arise from the aromatic ring vibrations
and ring breathing with C-O stretching of lignin. Increase in the intensity
of vO-H in plane bending vibrations at 1385 cm-1, a band
was observed, which is specific to the bamboo components, cellulose and hemicellulose.
The major chemical components of wood degrade at different temperatures. Hemicelluloses
and lignin are amorphous and start to degrade before cellulose (Hill,
2006). Hemicelluloses are the least thermally stable wood components due
to the presence of acetyl group (Bourgois et al.,
1989). In the present study two significant weight losses has been observed.
The first weight loss is attributed due to the decomposition of hemicelluloses
(Nguyen et al., 1981) and the second weight
loss is attributed to cellulose decomposition (Nguyen et
al., 1981; Bouchard et al., 1986). From
the experimental results of thermo gravimetric analyses, it was observed that
the major weight losses due to thermal degradation for treated and untreated
bamboo samples were found at the stage II, which supports the present findings.
These weight losses were followed by lignin at a temperature above 370°C.
In contrast to the other weight loss, the polymerised bamboo material shows
minimum weight loss (53.82). This could be due to the greater stability of the
hemicellulose after polymerisation with MMA and BMA. Amongst the treated samples
BA+CA+Triendtc+MMA and kerosene showed the highest thermal stability. It was
also observed that the temperature at which moisture started to be liberated
was higher (235°C) for treated samples. This observation can be explained
on the basis of changes occurring in the fine structure and morphology of bamboo
fibers due to treatment. On modification, the tendency to liberate absorbed
moisture upon heating was decreased, as moisture is strongly held within a tightly
packed structure, leading to a higher finished temperature (Bouchard
et al., 1986), similar results have been found in the present study.
Variations of weight loss and decomposition temperatures of the treated and
untreated bamboo samples are shown in Table 2. From TG curves,
(Fig. 2, 3) it was observed that the first
weight loss in the range of 120-150°C corresponds to water evaporation.
The active decomposition temperature that caused the major weight loss were
started from 245°C and it was highest (247-359°C) for BA, CA, Triendtc
followed by MMA and kerosene treated (Fig. 3) sample indicating
increased bulking and -OH group modification to give good dimensional stability.
The result showed that there is a substantial decrease of weight loss in the
treated samples and it was minimum(53.82%) for BA, CA, Triendtc followed by
MMA and kerosene treatment, which also revealed that enhanced ASE and BC gave
better thermal stability of bamboo samples.
From the measurement of strength (MOR) and stiffness (MOE) of both treated
and untreated samples, it was observed that there is increase in the Modulus
of Rupture (MOR) and compressive stress. No significant difference in MOE was
found between the simple MMA and BMA treated and untreated bamboo samples, although
14% improvement was observed in BA, CA, Triendtc, MMA, BMA and kerosene treated
samples (Table 3).
|| Weight loss and active decomposition temperature of untreated
and treated bamboo sample
|Combination of BA, CA, Triendtc, MMA and Kerosene treatment
showing minimum weight loss
|| Thermogram of untreated bamboo sample
|| Thermogram of BA, CA, Triendtc and MMA treated bamboo sample
|| Effect of chemicals on strength (MOR) and stiffness (MOE)
of bamboo sample
|*Combination with BA, CA, Triendtc, BMA and Kerosene treatment
showing highest strength (MOR) and stiffness (MOE)
The insignificant change in MOE suggest that the polymer itself was not elastic
enough which could enhance the elasticity of bamboo. Schneider
et al. (2003) also reported the same for basswood when treated with
MMA and the treated material with addition of 1% TMPTMA showed highest MOR value
(88.87%). In the present study bamboo samples treated with BA, CA, Triendtc,
MMA and kerosene showed highest MOR (61.06 N mm-2) and MOE (7543
N mm-2). It could be due to the chemical modification of cellulose
by MMA and physical bulking of copper acetate, boric acid, triendtc and kerosene
oil. Wahab et al. (2006) studied the strength
properties of Gigantochloa scortechinii treated with Ammonium Copper-Quaternary
(ACQ), Copper Chrome Arsenic (CCA) and Borax Boric Acid (BBA) and reported that
the strength properties of the treated bamboo dependent on the type of preservative
applied, concentration and their retention in the bamboo. Impregnation of
Dyera costulata wood with phenol formaldehyde resin mixed with urea showed
higher MOR, MOE and dimensional stability (Izreen et
al., 2011).This treatment also rendered higher anti swelling efficiency
The incorporation of the preservatives constituent in to the internal configuration
of the bamboo samples were studied by Scanning Electron Micrograph (SEM). The
penetration of the chemicals resulted in bulking of the cell wall to give dimensionally
stabilized bamboo. The SEM of the untreated sample (Fig. 4)
showed a diffused configuration, while the white patches seen in the micrograph
(Fig. 5-7) were the penetration of the chemicals
observed on the cell walls of the bamboo.
|| SEM of untreated bamboo sample
|| SEM of MMA penetration in bamboo sample
After one year of graveyard (termite mound) test (Fig. 8) it was observed that compared to untreated samples, the samples treated with only MMA and BMA was slightly damaged by termite (Fig. 9). On the other hand, the samples treated with BA, CA and triendtc showed good biodegradation inhibition but the dimensional stability was not optimum.
The bio-resisting property of this treatment may be due to the antibacterial
and antifungal activity of the boric acid, copper acetate and dithiocarbamate.
Boric acid has been reported as stomach poison for insects (Yamaguchi,
2003). Similarly transition metal compounds of dithiocarbamate and dithiophosphinates
are known antifungal and antibacterial agents and the mode of action being of
certain vital enzymes by the sulphur donors, the Cu2+ also can inhibit
action of several biomolecules (Kalita et al., 2002).
Dithiocompounds also inhibit the enzyme actycholinesterase (Gruzdyev
et al., 1980). Further petroleum oil like kerosene has low toxicity
to warm blooded animals but prevents metabolism in egg or insect body. The oil
can easily penetrate through the wax scale and cuticles, can cause coagulation
of the cytoplasma and inhibit the course of enzyme process (Gruzdyev
et al., 1980).
|| SEM of BMA treated bamboo sample
|| SEM of BA, CA, Triendtc and MMA treated bamboo sample
Lignocellulosic materials are degraded by fungus and termites which contain
cellulose enzyme. In the mechanisms of the cellulase action, it is found that
the Tricoderma Cellulase consists of three enzymes systems, (a) endoglucanase
(EG), (b) Cellulohydrolase (CBH) and (c) β-glucosidase (β-G) (White,
1982). The inhibition of cellulase activity and dimensional stabilization
may be concurrently considered from two angles: (1) Application of cellulase
activity inhibitor and (2) Chemical modification of the-OH group of the non
reducing chain end, the site of CBH attack. The -OH groups are not only enzyme
attack sites but also water absorption sites through hydrogen bonding, which
facilitate swelling. In the cellulase activity inhibition experiment (Table
4) it was observed that in presence of boric acid and copper acetate the
cellulase activity (amount of glucose released) is slightly reduced.
|| Termite mound test of bamboo samples
||Deterioration of the treated (G1,G2,G3)and Untreated(C) bamboo
samples after Graveyard test
The combined treatment of boric acid, copper acetate, triendtc and cellulose
showing least amount (0.154 g mole-1) of glucose liberation, which
showed that these chemicals are effective as enzyme inhibitor.
|| Cellulose inhibition activity data in absence and in presence
|Combination of BP+BA+CA+Triendtc+cellulase showing least amount
of glucose liberation
The present finding was supported by Vyas et al.
(2005), that in alkaline media cellulase activity is enhanced compared to
acidic media. The presence of boric acid and copper acetate hydrolyze to give
slightly acidic medium due to the presence of acetic acid. However, the presence
of boric acid, copper acetate and dithiocarbamate, there is a substantial decrease
in the cellulase inhibition activity as seen from the amount of glucose released.
Dimensional stability and resistance to biodegradation by chemical treatment of lignocellulosic materials depends upon the type of chemicals, their penetration and how much hydroxyl groups are modified to give adequate cross linking and bulkiness. From the present studies, it may be concluded that treatment of bamboo samples with boric acid followed by copper acetate, triethylenetetramine dithiocarbamate, methyl methacrylate and kerosene can be used for achieving dimensional stability and prevent biodegradation. The strength and stiffness properties of bamboo can also be improved by this treatment. Compared to other chemical methods of treatment of bamboo, the present method appears to be better in the sense that the chemicals are cost effective, can be handle and applied easily and less toxic at low concentration and at the same time give very good results.
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