Production of Cement Bonded Boards (CBB) from untreated fibrous raw materials
is faced with the problem of inhibitory effects of sugars, extractives and lignin
in lignocellulosic materials (Moslemi and Lim, 1984;
Hong and Lee, 1986). The disadvantages of inhibition
include delayed setting, relatively lowered hydration temperature and prolonged
time to attain maximum temperature (Moslemi and Lim, 1984).
Addition of an accelerator into a mixture of cement-water paste could enhance
the speed of hydration process to occur earlier (Nazerian
et al., 2011). Several attempts have been made to overcome this challenge
using cold or hot water extraction and/or incorporation of chemical additives
such as calcium chloride (CaCl2), aluminium sulphate (Al2(SO4)3),
magnesium chloride (MgCl2) prior CBB production (Hong
and Lee, 1986; Olorunnisola, 2007). The chemical
additives are usually added in quantity of less than 4% (by cement weight) and
have been found to enhance many of the boards properties such as increased
density, improved appearance, bending and compressive strength, dimensional
stability and improved wood-cement bond due to its effect of accelerating the
hydration of wood-cement mixtures (Olorunnisola, 2007).
CaCl2 is the most commonly used among various available chemical
additives. It accelerates the hydration of cement particularly the tri-calcium
silicate phase (C3S), reduces the setting time and in some cases
increases the maximum hydration temperature (Biblis and
Lo, 1968; Moslemi et al., 1983; Lee
and Short, 1989; Ramachandran, 1994; Olorunnisola
and Adefisan, 2002). It improves the bending strength and dimensional stability
attributable to increased board density and improved bonding between particles
of lignocellulosics and cement (Badejo, 1989; Fabiyi,
2004; Olorunnisola, 2006). The internal bonding
and direct screw withdrawal increased by 166 and 67%, respectively with the
addition of CaCl2 to coconut cement boards while those of density
were 64 and 45%, respectively (Almwdia et al., 2002).
However, CaCl2 may not be effective in overcoming severe inhibitions
of cement hydration due to heartwood polyphenols of some certain wood species.
Compounds that can accelerate cement hydration and also chelate or chemically
modify polyphenols are more effective than CaCl2 at improving the
cement compatibility of inhibitory wood species (Semple and
Evans, 2000). Semple and Evans (2000) found that
although CaCl2 performed well as an accelerator in the presence of
wood-wool of Acacia mangium wood, it was not as effective as other compounds
like tin chloride (SnCl4), aluminium chloride (AlCl3)
and sodium silicate (Na2O.3SiO3). This finding suggests
that different lignocellulosics depending on their constituent would react differently
when incorporated in cement mixes. Therefore, it is important to understand
the effect of various chemical additives on different lignocellulosic fibres
sources for making CBB.
In Nigeria, several studies have been conducted on the hydration of rattan
canes (Dahunsi, 2000; Olorunnisola
and Adefisan, 2002; Olorunnisola, 2005; Adefisan
and Olorunnisola, 2007; Olorunnisola, 2007). The
reason for this is because rattans have short rotation and can be harvested
in less than seven years after planting and processed with simple and relatively
cheap technology. Also, the assembly line from rattan harvesting to CBB production
involves low capital investment (Olorunnisola and Adefisan,
2002; Olorunnisola, 2005; Olorunnisola,
2008). There are three major rattan species namely: Eremospatha macrocarpa,
Laccosperma secundiflorum and Calamus deerratus that are found in
Nigeria (Dahunsi, 2000). Adefisan
(1999) reported that E. macrocarpa has diameter of 10-17 mm and stem
length of 20-25 mm while L. secundiflorum has diameter of 10-20 mm and
stem length of 10 mm. The sugar contents of both species differed with L.
secundiflorum having the highest carbohydrate content (over 70%) which may
cause it to have the highest probability of inhibiting cement hydration (Dahunsi,
These rattan species respond to pre-treatments differently. Olorunnisola
and Adefisan (2008) reported that hot water extraction improved the compatibility
of the C. deerratus while L. secundiflorum was more amenable to
cold water extraction. Hot water extraction of C. deerratus cement mix
had higher hydration temperature and lower setting time than those soaked in
cold water. However, cold water extraction resulted in higher hydration temperature
and lower setting time in the L. secundiflorum cement mix than hot water
(Olorunnisola and Adefisan, 2008). Unfortunately, most
of the hydration studies conducted on rattan canes by several researchers have
centred on L. secundiflorum and C. deerratus while it is rare
to find information on E. macrocarpa. Since both E. macrocarpa
and L. secundiflorum are widely spread and common in Nigeria, it is very
important to investigate the hydration behaviour of both rattan species under
same laboratory conditions and experimental procedures. This step would enhance
comparative analysis of hydration behaviour between both species. Apart from
the traditional chemical pre-treatments that have been used so far, there is
no available information on the use of Al2(SO4)3
as chemical additive in relation to rattan canes.
The use of infrared spectroscopy to monitor the chemical structure of different polymers is widely explored. Its versatility is due to the fact that it requires minimum sample preparation, not tedious and not time consuming. However, its use for monitoring the changes that occur when cement, lignocellulosic fibres and chemical additives are mixed together is limited in literature. This study therefore aimed at investigating the effects of cold water extraction and incorporation of CaCl2 and Al2(SO4)3 on the hydration behaviour and infrared spectroscopy of E. macrocarpa and L. secundiflorum mixed portland cement.
MATERIALS AND METHODS
Matured stems of E. macrocarpa and L. secundiflorum canes were harvested from Gambari Forest Reserve located between longitude 50°44' E and latitude 7°14 N in Ibadan, Oyo state, Nigeria. The canes were converted into billets of about 6 cm and hammer milled. The milled particles were sieved using a set of 1.18, 0.85 and 0.60 mm sieves. Particles that passed through the 0.85 mm sieve and were retained in the 0.60 mm sieve were collected and dried to 10% moisture content. These particles were divided into four sets with the first set mixed with cement but no additive incorporation (henceforth called untreated), the second set was soaked in distilled water for 30 min at room temperature, drained and dried to 10% moisture content (henceforth referred to as cold water treated), the third set pre-treated with CaCl2 and the fourth set pre-treated with Al2(SO4)3 before mixed with cement.
Hydration test: For the hydration tests, 15 g of the E. macrocarpa
or L. secundiflorum particles, 200 g of Portland cement (purchased at
a local hardware store, Moscow, Idaho state, USA) and 93 ml of distilled water
were mixed in a polyethylene bag to form homogeneous slurry following the method
developed by Adefisan and Olorunnisola (2007). The neat
cement was mixed with 90 mL of distilled water while 3% CaCl2 or
Al2(SO4)3 (by cement weight) was added.
|| Cement compatibility assessment schemes
However, untreated and 30 min cold water extracted samples were mixed with
the neat cement and 90 mL of distilled water only prior hydration characterisation.
Hydration characterisation was performed in a set of well insulated thermos
flasks. The temperature rise was monitored for 24 h using thermocouples (J-type)
connected to an 8-channel datalogger (USB TC-08, Pico Technology). Three sampled
specimens of each mixture were prepared. The compatibility of E. macrocarpa
and L. secundiflorum with cement was assessed using the compatibility
indices (Table 1).
Chemical characterization: Specimens for the chemical analysis were obtained from each of the untreated and pre-treated rattan/cement mixes and ground into fine powder using pestle and mortar. Fourier Transform Infrared (FTIR) spectra were measured directly from the powder (1% w/w basis) thoroughly dispersed in KBr (99% w/w basis). Spectra were recorded using a Thermo Scientific Nicolet 8700 spectrometer equipped with a DTGS detector. Each spectrum was taken as an average of 64 scans at a resolution of 4 cm-1.
RESULTS AND DISCUSSION
Setting time of rattan-cement composites: The results of the hydration
tests are presented in Table 2 and Fig. 1.
The setting times of the E. macrocarpa and L. secundiflorum cement
mixes without pre-treatment were 12.4 and 11.9 h, respectively. Based on the
classification of Hofstrand et al. (1984), the
untreated E. macrocarpa and L. secundiflorum were very suitable
for Cement Bonded Board (CBB) production. Generally, the incorporation of chemical
additives and 30 min cold water extraction of the two fibrous materials resulted
in reduced setting time that ranged from 5.2 to 9.4 and 5.6 to 10.7 for the
E. macrocarpa and L. secundiflorum cement composites, respectively.
In addition, the setting time for 30 min. cold water extraction and 3% Al2(SO4)3
were very similar for the two rattan species (Table 2). The
greatest improvement in the setting time was observed for rattan/cement/water
mix treated with CaCl2.
Rattan species (E. macrocarpa and L. secundiflorum) did not significantly
affect the setting times of the rattan/cement/water mix but incorporation of
different chemical additives significantly influenced the setting time of the
rattan/cement/water mix (Table 3). CaCl2 significantly
reduced the setting time of the rattan/cement/water mix than Al2(SO4)3.
Olorunnisola (2008) reported the setting time of 10.3
h for 30 min cold water extracted L. secundiflorum (sieved) mixed with
cement. This is agreement with 10.7 h obtained in this study for same condition
Maximum hydration temperature of the rattan-cement composites: The maximum
hydration temperatures (Tmax) attained by the untreated E. macrocarpa
and L. secundiflorum cement mixes were 59.1 and 58.3°C (Table
2). The Tmax for CaCl2, Al2(SO4)3
and 30 min cold water extraction pre-treated E. macrocarpa/cement mix
were 83.7, 60.4 and 65.1°C, respectively. In addition, Tmax for
CaCl2, Al2(SO4)3 and 30 min cold
water extraction pre-treated L. secundiflorum/cement mix were 78.6, 57.7
and 63.3°C, respectively (Table 2). Based on the Sandermann
and Kohler (1964) index, the untreated E. macrocarpa and L. secundiflorum
could be classified as intermediately suitable for the production of CBB. The
chemical pre-treated E. macrocarpa and L. secundiflorum could
be classified as suitable except the Al2(SO4)3
pre-treated L. secundiflorum which ranked as intermediately suitable
for the production of CBB. Hence, the addition of chemical additives significantly
improved the Tmax of the rattan/cement mixes with those treated with
CaCl2 having highest maximum hydration temperature than those pre-treated
with Al2(SO4)3 and 30 min cold water extraction.
In addition, E. macrocarpa/cement mix had higher Tmax than L. secundiflorum/cement mix. This indicates that CaCl2 was more effective than Al2(SO4)3 or 30 min water extraction in minimising the inhibitory effects of sugars and extractives present in the rattan/cement mixtures. The practical implication of this study is that the use of Al2(SO4)3 to pre-treat E. macrocarpa or L. secundiflorum is not economical since 30 min water extraction gave the same Tmax; hence cold water extraction is preferred because water is readily available and affordable. In addition, L. secundiflorum particles however inhibited cement setting more than E. macrocarpa particles. Higher sugar contents in the L. secundiflorum canes may contribute to its low Tmax.
|| Hydration behaviour of Eremospatha macrocarpa and
Laccosperma secundiflorum/cement mixes
|| Hydration parameters of Eremospatha macrocarpa and
Laccosperma secundiflorum/cement mixes
|Means with the same letters in the same column for each of
the rattan species are not statistically different
|| Duncans multiple range tests of the effects of pre-treatment
and rattan species on the hydration parameters of rattan/cement mixes.
|Means with the same letters in the same column for either
pre-treatment or rattan species are not statistically different
Olorunnisola (2008) reported that the maximum hydration
temperature of 30 min cold water extracted L. secundiflorum (sieved)
mixed with cement was 51°C. This is contrary to 63.3°C obtained in this
study for same condition (Table 2). This contradiction may
be due to differences in the sources of Portland cement used. Olorunnisola
(2008) used Portland cement produced in Nigeria while Portland cement used
in the present study was purchased at a local hardware store, Moscow, Idaho
state, USA. The study conducted by Olorunnisola (2008)
ranked 30 min cold water extracted L. secundiflorum as intermediately
suitable while the present study conducted at Idaho ranked it suitable for CBB
The choice of any of these two rattan species (without pre-treatment) did not significantly affect the Tmax of the rattan/cement mixes. However, the application of chemical additives significantly influenced the maximum hydration temperatures of the E. macrocarpa and L. secundiflorum/cement mixes (Table 3). This implies that different chemical additives had different effects on the hydration behaviour of the rattan/cement mixes.
Time ratio indices of the rattan-cement composites: The time ratio indices
(tR) of the rattan/cement mixes are presented in Table
2. The time ratio indices for both untreated rattan species cement mixes
were the same (1.1). Similarly, the tR for CaCl2 pre-treated
E. macrocarpa/cement mix and L. secundiflorum/cement mix were
the same (0.5). The tR for Al2(SO4)3
and 30 min cold water were 0.9 and 0.9-1.0, respectively for pre-treated
E. macrocarpa/cement mix and L. secundiflorum/cement mix. Therefore,
pre-treating either of the two rattan species with CaCl2, Al2(SO4)3
or 30 min cold water extraction did not make any difference, hence tR
is not rattan species dependent but chemical additive dependent.
||FTIR spectra of two rattan species: Eremospatha macrocarpa
and Laccosperma secundiflorum. Each spectrum is an average of spectra
from two specimens
Based on the classification of Olorunnisola (2008),
the untreated rattans are suitable for CBB production. The incorporation of
chemical additives significantly improved the tR of the rattan/cement
mixes. The greatest improvement was observed for rattan/cement mixes pre-treated
with CaCl2 (Table 3). Therefore, it suggests that
CaCl2 improved the compatibility of the rattan/cement mixes more
than Al2(SO4)3 or 30 min cold water extraction.
Olorunnisola et al. (2005) reported that incorporation
of 3% CaCl2 to L. secundiflorum-cement system gave setting
time and maximum hydration temperature as 9 h and 53.3°C, respectively.
Their data showed that only the setting time support the suitability of 3% CaCl2
pre-treated L. secundiflorum-cement system but the present study show
that both the setting time and maximum hydration temperature ranked 3% CaCl2
pre-treated L. secundiflorum-cement system as suitable for CBB production.
The compatibility ranking of fibrous material based on the time ratio index
shows 30 min cold water extracted L. secundiflorum is suitable for CBB
production. Hence, the present study and the report of Olorunnisola (2008) support
Chemical characterisation: Figure 2 shows the FTIR
spectra of E. macrocarpa and L. secundiflorum without cement.
Infrared bands observed in the various treatments with their peak assignments
and structural polymers are presented in Table 4 and 5.
There are similarities and a few dissimilarities in the positions and intensities
of the infrared spectra of the two rattan species investigated. Peaks numbered
2, 6, 8, 10, 14, 15, 17 and 20 have the same band frequencies for both E.
macrocarpa and L. secundiflorum (Table 4, 5).
However, the band frequencies for peaks numbered 3, 4, 11, 12, 13, 17, 18, 21,
23, 24 and 25 for E. macrocarpa differed from that of L. secundiflorum.
Majorly, the carbonyl band for xylan differed by 3 cm-1 with
E. macrocarpa occurring at 1737 cm-1 and L. secundiflorum
at 1734 cm-1.
The lignin assigned peak for E. macrocarpa and L. secundiflorum
occurred around 1506/1608 cm-1. However, some peaks occurred at higher
frequency for E. macrocarpa than L. secundiflorum. Examples of
these are peaks at 698, 1113, 1162, 1463 and 3412 cm-1 for E.
macrocarpa compared with L. secundiflorum at 695, 1110, 1161, 1457
and 3407 cm-1. The band at 3540-3000 cm-1 which was assigned
to O-H groups in the rattans emerged due to the combination of cellulose, hemicelluloses
and lignin (Faix, 1992). This band is broader with higher
intensity for L. secundiflorum than E. macrocarpa. Likewise the
intensities for peaks numbers 10, 11, 12, 13, 15, 17, 19 and 20 are higher for
L. secundiflorum than E. macrocarpa. Generally, there is no difference
in the chemical functional groups that were present in both rattan species.
||Summary of infrared bands observed in Eremospatha macrocarpa
and the untreated and pre-treated E. macrocarpa/cement mixes. The
wavenumber of the 30 min cold water extraction is not presented because
they are similar to that of Al2(SO4)3
||Summary of infrared bands observed in Laccosperma secundiflorum
and the untreated and pre-treated L. secundiflorum/cement mixes.
The wavenumber of the 30 min cold water extraction is not presented because
they are similar to that of Al2(SO4)3
Therefore, the peak intensity, band width and b and frequency from the spectra
can only be used to differentiate the two rattan species under investigation.
Chemical changes that occurred due to the blending of untreated, 30 min cold
water extracted, Al2(SO4)3 or CaCl2
pre-treated E. macrocarpa or L. secundiflorum mixed with cement
after the hydration testing had been terminated are illustrated in Fig.
3 and 4. The addition of Portland cement caused the appearance
of some peaks in the spectra (numbers 1, 5, 7, 22 and 26).
||FTIR spectra of (A) Eremospatha macrocarpa, (B) E.
macrocarpa/cement mix, (C) E. macrocarpa/cement/CaCl2,
(D) E. macrocarpa/cement/Al2(SO4)3
and (E) E. macrocarpa/cement/30 min cold water extraction. Each
spectrum is an average of spectra from two specimens. Peak position and
assignment as well as structural polymer for each peak are presented in
||FTIR spectra of (A) Laccosperma secundiflorum, (B)
L. secundiflorum/cement mix, (C) L. secundiflorum/ cement/CaCl2,
(D) L. secundiflorum/cement/ Al2(SO4)3
and E) L. secundiflorum/cement/30 min cold water extraction. Each
spectrum is an average of spectra from two specimens. Peak position and
assignment as well as structural
The formation of the band at 3643 cm-1 in the untreated, 30 min
cold water extracted and chemically treated rattan/cement mixes remained unchanged;
indicating that its emergence is due to the chemical constituent of cement.
It was due to the metal-bonded hydroxide (Mollah et al.,
1992). This indicates the OH band from Ca(OH)2. The band at 3407/3414
cm-1 which was assigned to O-H groups in lignocellulosic materials,
was affected by the pre-treatment and incorporation of cement to the rattan
species. The blending of the rattan particles with cement and the incorporation
of chemical additives and 30 min cold water extraction caused the band to be
become narrower than in the ordinary rattan particles. In addition, peaks 23
and 24 at 2853 and 2926-2918 cm-1, respectively drastically decreased
due to the addition of cement. This implies that the cement suppressed the methylene
and methyl stretching frequencies that occurred in the rattan species.
The lignin assigned peaks (1506/1507 and 1608/1609 cm-1) did not
appear in the rattan/cement mix but were masked due to the presence of broader
band with peaks at 1426 and 1457 cm-1. In addition, the peak at 1047
cm-1 disappeared when cement was mixed with rattan particles. There
were many bands that disappeared due to the addition of cement namely: peaks
numbers 21, 15, 14, 13 and 6 which are xylan in hemicelluloses, cellulose, syringyl,
guaiacyl and arabinogalactan, respectively (Table 4, 5).
Addition of CaCl2 to L. secundiflorum particles helped expose
cellulose to advance participation probably by enlarging its surface area for
interpenetration networking with cement. Chemical reactivity of this peak (number
17) is rattan species dependent. The region between 1750 and 750 cm-1
was drastically affected (reduced the peaks intensities) by the incorporation
of CaCl2 while Al2(SO4)3 and 30
min cold water extraction had little effect on this region for E. macrocarpa.
However, 30 min cold water extraction drastically reduced the peaks intensities
in the region between 1510 and 1300 cm-1 for L. secundiflorum.
The effects of cold water extraction and chemical additives on the setting time (tmax), maximum hydration temperature (Tmax), time ratio (tR) and surface chemistry of Eremospatha macrocarpa and Laccosperma secundiflorum particles mixed with Portland cement was investigated. Hydration behaviour showed that E. macrocarpa and L. secundiflorum canes are suitable for CBB production based on its setting time and time ratio index. However, maximum hydration temperature only ranked E. macrocarpa and L. secundiflorum as intermediately suitable. Cold water extraction (for 30 min) and chemical additives improved the hydration behaviour of the rattan cement mixes. Calcium chloride was a better chemical accelerator for the rattan cement mixes than aluminium sulphate. Cold water extraction had little advantage over aluminium sulphate for the species. L. secundiflorum inhibited cement setting more than E. macrocarpa. The surface chemistry studied using infrared spectroscopy showed that addition of cement to rattan fibre caused the suppression of methylene and methyl stretching frequencies that occurred in the rattan species. Addition of CaCl2 to L. secundiflorum particles helped expose cellulose to advance participation probably by enlarging its surface area for interpenetration networking with cement.
This study was conducted at the Forest Products Laboratory, University of Idaho, Moscow, USA with a grant received from John D. and Catherine T. MacArthur Foundation through University of Ibadan, Nigeria. The support is acknowledged with thanks.