INTERNATIONAL CONFERENCE ON NANOMATERIALS: SCIENCE,
ENGINEERING AND TECHNOLOGY (ICoNSET) 2019

Effect of NCO/OH Ratio on Physical and Mechanical
Properties of Castor-Based Polyurethane Grouting Materials
N N Bonnia*1, N I A Mat Hussain1, R S F N Hirzin2 and E S Ali3
1

Materials Science Department, Faculty of Applied Sciences, Universiti Teknologi
MARA Shah Alam, Malaysia.
2
Polymer Science Department, Faculty of Applied Sciences, Universiti Teknologi
MARA Shah Alam, Malaysia.
3
Applied Physic Department, Faculty of Science and Technology, Universiti Sains
Islam, Malaysia.
E-mail: noornajmi@uitm.edu.my
Abstract. This research focused on fabrication of castor-based PU grout (CPUG) using castor
oil with OH value of 161 mg/KOH/g and MDI with NCO content of 31%. CPUG wereprepared based on different NCO/OH ratio. The effect of NCO/OH ratio on the foam reaction
time, density, rheology, morphological and mechanical properties were investigated. The result
obtained shows that the rise time of CPUG decreased with the increased of NCO/OH ratio
while tack free time increased with the increased of NCO/OH ratio. Morphological properties
shows that CPUG consist of closed cell of foams and the diameter of a single cell foam
decreased with the increased of NCO/OH ratio. The apparent density, rheology index, flexuralstrength, flexural modulus and compression strength of CPUG significantly increased with theincreased of NCO/OH ratio. CPUG’s apparent density was in the range of 230.23 kg/m3 whilerheology index of CPUG was between 1.74 to 2.43 cm/g. Both values obtained were in therange of industrial PU grout’s density and rheology index (214 kg/m3 & 1.48 cm/g). CPUG
with NCO/OH ratio of 2.6:1 give the best flexural and compression strength with a value of
11.01Mpa and 2Mpa respectively. Flexural and compression strength of CPUG weretantamount to the industrial PU grout’s properties which the average of flexural strength was
about 7.4MPa while the average of compression strength was about 2MPa.

1. Introduction
The existence of crack on concrete bridge deck have been raise the concern of the bridges users as thecrack can spread until a hole forming on concrete bridge deck which can cause traffic problem andalso decrease the bridge’s service life. Polyurethane grouting is a mature technology used to seal thecracks that occur on concrete bridge deck. Nowadays, polyurethane grouting material has been gaining
a lot of attention from manufacturers from all over the world due to its extraordinary properties suchas light weight, good permeability and good mechanical performance [1]. Polyurethane grouts is arigid, closed cell foam which produced from reaction of two main components which are isocyanate as
hard segment and polyols as soft segment [2]. Most of available polyurethane grout in the industry are
petrochemical-based polyurethane. However, petrochemical-based polyurethane is expensive due tothe increase in price of petrochemicals and crude oils. The high demand of petrochemicals and crude
oil in the industries and also the high cost of production of petrochemical-based polyurethane grouts
due to complex extraction process of petroleum contribute to the high price of petrochemical-based
polyurethane [3]. The production of petrochemical-based polyurethane increase the environmental

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concern as the extraction process of petrochemical-based polyol caused environment pollution due tothe released of waste product formed during extraction process to the surrounding. Therefore, green
grout polyurethane was developed to replace petrochemical-based polyurethane grout. Green grout
polyurethane can be produced from natural polyol such as vegetables-based polyol. A few types ofvegetables oil that is highly unsaturated and can be used as polyol are soybean oil, corn oil, linseed oil,sunflower oil, safflower oil, tung oil, olive oil and castor oil [4]. However, most of the vegetable oils
must be synthesized in order to get the polyol except for castor oil which is a very unique vegetable oilthat has hydroxyl group in its chemical structure which enable it to be use directly as a sole polyol
without any modification process. Castor oil has low hydroxyl number which led to a low reactivity
and with the use of castor oil as a sole polyol in production of PU, semi-flexible to semi-rigid PU
foams is formed [4]. It is hard to formulate rigid PU grout by using castor oil. Despite that, rigid
CPUG with excellent mechanical properties still can be fabricated which is by varying the NCO/OH
ratio of CPUG. NCO/OH ratio is defined as equivalent ratio between the materials containing NCO
and OH groups [5]. The increase of NCO/OH ratio led to an increase of isocyanate which can enhance
the formation of covalent crosslinking in CPUG samples resulting CPUG samples with excellent
mechanical properties [6]. In this study, the effects of NCO/OH ratio on foam reaction time, density,rheology, morphological and mechanical properties of CPUG were investigated.
2. Experimental
2.1. Materials
The chemicals used in this research were castor oil (hydroxyl value : 161.62 mg/KOH/g, equivalentweight : 347gmol-1) distributed by Progressive Scientific Sdn. Bhd, isocyanate (4,4-methylenediphenyl
diisocyanate) with NCO content : 31% , molecular weight : 360, supplied by Growchem Sdn. Bhd.,
surfactant (polyalkyleneoxidemethylsiloxane copolymer) manufactured by Momentive Amer Ind.,blowingagent(1,1-dichloro-1-fluoroethane)
suppliedby
AirgasUSA,
pentamethyldipropylenatriamine (PMDETA) act as blowing catalyst and dimethylcetylhexamine(DMCHA) act as gelling catalyst which both catalyst were supplied by Huntsman (Singapore) Pte Ltd.
2.2. Castor-based Polyurethane Grout Preparation
Four different compositions with varied ratios of castor oil and isocyanate were fabricated. The
compositions used were explained in Table 1. Castor oil (100pbw), blowing agent (1pbw), surfactant(2pbw), gelling catalyst (0.4pbw) and blowing catalyst (0.4pbw) were mixed in a plastic using
mechanical stirrer for about 2 minutes at 3000 rpm. Then, the hard part, isocyanate(NCO) was added
into the mixtures and mixed at 3000 rpm for about 20 seconds. After that, the samples was poured into
an acrylic mould and conditioned at room temperature for about 24 hours. Later, the samples were
demoulded and conditioned at room temperature for about 36 hours before being tested [7].
Table 1. CPUG formulations.
NCO/OH ratio
CPUG 1
CPUG 2
CPUG 3
CPUG 42:1
2.2 : 12.4 : 1
2.6 : 12.3. Characterizations and Testing
Foam reaction time such as cream time, rise time and tack free time were determined during the
fabrication of CPUG according to method ASTM D7487-13. The density of each CPUG samples were
determined according to method BS: Part 1 : 1988 Method 2 which involved the measurement of four
CPUG block samples from each composition with a dimension of 50 X 50 x 50mm. The rheology

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properties of CPUG was determined by pouring CPUG into a clear hose having a diameter of 10mm.
CPUG sample was poured in a direction which was opposite to the earth gravity and it was let to flow
down the hose until it stop flowing and expanding [7]. Then, the rheology index of CPUG was
calculated according to the recorded flow distance and total weight of CPUG used. Scanning electron
microscopy (SEM) was conducted on CPUG samples according to ASTM E 2089 method with 100X
magnification. CPUG’s surface was coated with about 10-20 nm of gold before the analysis started
and the cell morphology of CPUG was examined. Flexural properties was examined based on ASTM
D 790 method with a compression speed of 4.1mm/min and the sample dimension of 3.2 X 12.7 x125mm. Compression properties of CPUG was determined according to ASTM D 395 method B withcrosshead speed movement of 50mm/min and sample dimension of 50 X 50 X 50mm.
3. Results and Discussion
The foam reaction time, rheology index, apparent density and mechanical properties of CPUG were
presented in Table 2.
Table 2. The foam reaction time, rheology index, apparent density and mechanical properties of
CPUG
Samples

CPUG 1
CPUG 2
CPUG 3
CPUG 4

Foam reaction time (s)
Cream
time

Rise
time

3
4
4
4

340
320
300
280

Tack
free
time
430
435
470
475

Rheology
index(cm/g)

Apparent
density(kg/m3)

Flexuralstrength(MPa)

Flexural
Modulus(MPa)

Compressi
on strength
(MPa)

1.74
1.89
2.25
2.43

188.27195.21
268.56268.86

3.76
5.78
8.81
11.01

344.98549.25822.301069.50

1.68
1.86
2.00
2.00

3.1. Foam reaction time
Cream time is the time taken by CPUG to start foaming after the stirring of raw materials. Figure.1
shows that the cream time increased with the increased of NCO/OH ratio up to 2.2:1 which the creamtime increased from 3s to 4s. Then, it remain constant at 4s for CPUG with NCO/OH ratio of 2.2:1 up
to 2.6:1. The overall range of cream time for CPUG was 3-4s. The values obtained correlatesatisfactorily with previous finding which stated that rigid polyurethane foam can start foaming
between 2s to7s [8]. NCO/OH ratio did not much influence the cream time of CPUG as there was notmuch difference in the cream time of CPUG samples.
550
500
450
400
350
300
250
200
150
100
50
0

NCO/OH ratio :

2.0:1
2.2:1
2.4:1
2.6:1

cream timerise timetack free time

Figure 1. CPUG reaction time.

INTERNATIONAL CONFERENCE ON NANOMATERIALS: SCIENCE,
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The rise time is the time taken by freely rising foam of CPUG to expand. The rise time of CPUG
decreased with the increased of NCO/OH ratio as higher NCO/OH ratio appeared to enhance thefoaming reaction of CPUG [9]. As the NCO/OH ratio increased, the exothermic reaction that took
place in the system increased which triggered the foaming process as more gaseous from blowing
agent vapourize and trapped in closed cell of the foam which at the end resulted a faster foaming
reaction [10]. The overall range of rise time for CPUG was between 280-340s. The values obtained
was slightly differ from previous findings. This may caused by the use of castor oil as a sole polyol
which exhibit low OH value that affect the reaction rate of PU. On the other hand, the tack free time of
CPUG increased with the increased NCO/OH ratio. Tack free time is the time taken by CPUG to start
loses its stickiness on the outer skin of the foam which indicate the surface cure time of CPUG. The
overall range of tack free time for CPUG was 430-465s. The increased of NCO/OH ratio resulting inincreased of unreacted monomers (NCO) in CPUG sample which caused a stoichiometric imbalance
between the reacting groups. The unreacted NCO had a low free energy which make them to be
exposed on free surfaces and resulted a stickiness of CPUG samples that led to an increase of tack freetime [11].
3.2. Apparent density
Apparent density is the overall density which include the skin of CPUG. In figure 2, it is observed thatthe apparent density of CPUG samples increased with the increased of NCO/OH ratio. This is parallelto the previous research which stated that the increased of NCO/OH ratio resulted an increase ofdensity of PU foam [9]. The highest apparent density was achieved by CPUG produced using
NCO/OH ratio of 2.6:1 with a value of 268.86 kg/m3. High density of CPUG was directly related tocrosslinking and the foam rigidity as the increased of NCO/OH ratio led to the increased of hard
segment in CPUG samples [9]. The increased of hard segment (NCO) caused the formation of
intensive urethane and allophanate crosslinking in CPUG samples which led to increase of CPUG’s
density. The allophanate crosslinking is defined as a side reaction that occurred when the freeisocyanate or unreacted NCO groups in CPUG samples react with the urethane formed [11]. The
overall range of CPUG’ apparent density obtained was between 188.27-268.86 kg/m3. The value
obtained was consistent with previous research which stated that the density for PU grout was in range
between 80 to 500 kg/m3 [12].
300

Density, kg/m3

250
200
150
100
50
NCO/OH ratio

0
2.0:1

2.2:1

2.4:1

2.6:1

Figure 2. Density of CPUG samples.
3.3. Rheology properties
Rheology properties is one of the important properties that need to be measured in relation with thefinal application of CPUG. The rheology test was conducted in order to identify the ability of CPUG
to expand and flow which simulate the rheology of CPUG when being injected into the crack on
concrete bridge deck. Figure 3 shows that the rheology index increased steadily with the increased of
NCO/OH ratio. It was due to the increased of foaming reaction of CPUG which resulted an increase ofrheology index of the samples. CPUG produced using NCO/OH ratio of 2.6:1 had the highest ability
to flow and expand as it exhibit the highest rheology index which was 2.43cm/g compared to the otherINTERNATIONAL CONFERENCE ON NANOMATERIALS: SCIENCE,
ENGINEERING AND TECHNOLOGY (ICoNSET) 2019
CPUG samples. The rheology index obtained in this research concurs well with the value obtained inprevious findings which stated that the best range of rheology index for PU grouting material was
between 0.4cm/g to 5cm/g [13]. As NCO/OH ratio increases, the rate of foaming reaction will increase
thus resulted an increase of the expandability of the foam which led to increase of rheology index [9].

Rheology index (cm/g)

3
2.5
2
1.5
1
0.5
0

NCO/OH ratio

2.0:1

2.2:1

2.4:1

2.6:1

Figure 3. Rheology index of CPUG samples.
3.4. Flexural Properties
Figure 4 and Table 2 show that the flexural strength of CPUG samples increased with the increased of
NCO/OH ratio. CPUG with NCO/OH ratio of 2:1, 2.2:1 and 2.4:1 had flexural strength of 3.76Mpa,
5.78Mpa and 8.81Mpa respectively. CPUG with NCO/OH ratio of 2.6:1 had the highest flexuralstrength which was about 11.01Mpa.

Flexural strength, MPa

14
12
10
8
6
4
2
0
2.0:1

2.2:1

2.4:1

2.6:1

NCO/OH ratio

Figure 4. Flexural strength of CPUG samples.
Figure 5 and Table 2 show that the flexural modulus of CPUG samples also increased steadily with theincreased of NCO/OH ratio. CPUG with NCO/OH ratio of 2.6:1 had the highest flexural modulus
which was about 1069.50 MPa compared to the other CPUG samples. The increment of both flexuralstrength and flexural modulus of CPUG can be relate to the increased of crosslinking in CPUG which
resulting an increased of CPUG’s density while the density of PU grout increased proportional to theincreased of NCO/OH ratio [9]. Both flexural strength and flexural modulus obtained in this researchwere tantamount to previous findings which stated that the flexural strength and flexural modulus ofrigid PU foam increased proportionally to the increased of density of rigid PU foam [14].

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Flexural Modulus, MPa

1200
1000
800
600
400

200
NCO/OH ratio

0
2.0:1

2.2:1

2.4:1

2.6:1

Figure 5. Flexural modulus of CPUG samples.

Compression strength, MPa

3.5. Compression strength
Figure 6 shows that the compression strength of CPUG samples increased with the increased of
NCO/OH ratio. However, compression strength value for 2.4:1 and 2.6:1 composition remain constantat 2 Mpa indicating that CPUG samples had achieve its optimum compression strength. Apart from
that, the compression strength of CPUG can be relate to the apparent density. The apparent density of
CPUG samples increased with the increased of NCO/OH ratio as the hard segment content in CPUG
increased which resulting an increase of crosslinking density and rigidity of CPUG. This make CPUG
samples become harder to be compressed thus resulting a higher compression strength result [9].
Besides, the apparent density also increased as there was an increase of compaction arrangement ofcellular structure which resulted an increased in compressive strength [15-16]. The compressive
strength of CPUG was parallel to the previous studies which stated that the compressive strength
obtained for PU grout having densities around 100-300kg/m3 was in range between 1-5Mpa [12].
2.1
2
1.9
1.8
1.7
1.6
1.5

NCO/OH ratio

2.0:1

2.2:1

2.4:1

2.6:1

Figure 6. Compression strength of CPUG samples.
3.6. Morphological properties
Based on figure 7, CPUG samples consist of spherical and polyhedral shape of closed cell foam. The
diameter of a single cell foam in four different CPUG samples decreased with the increased of
NCO/OH ratio. The cell foam was produced from the exothermic reaction between polyol andisocyanate which then trigerred the phase separation. The reaction caused the evaporation of blowing
agent into gaseos phase and followed by difussion of small air bubbles into the nuclei which thenentrapped and resulting small size of cell foam formed in the CPUG matrix [11]. As NCO/OH ratio
increased, the exothermic reaction rate increased, thus increased the amount of diffusion of air bubbles
into the nuclei which resulting a decreased in cell foam size.

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a)

b)

c)

d)

Figure 7. SEM micrograph of CPUG samples. (a) CPUG 1. (b) CPUG 2. (c) CPUG 3. (d) CPUG 4.
Apart from that,the decreased in cell foam size also caused by the decreased of cell wall’s elasticity
which caused by the allophanate crosslinking. These make the growth and coalescence of bubbles in
CPUG become difficult and resulted a small size of cell foam. Smaller size of cell foam caused anincreased of surface contact area between cell foam which resulting a more stable CPUG system [12].
Therefore, CPUG 4 had the most stable system compared to the other samples as it exhibit the smallest
size of cell foam. The overall cell foam diameter of CPUG samples obtained was in range between
339µm to 230µm. These findings was slightly different with previous research which stated that for
PU grout that had densities in range between 100-500kg/m3, the cell foam diameter was in range
between 0-150µm [12]. The difference is possible due to different equivalent weight of castor oil andisocyanate used in this research compared to previous research.
4. Conclusions
In conclusion, the rise time of CPUG decreased while tack free time increased with the increasing
NCO/OH ratio. This was due to the increased of allophanate crosslinking in CPUG samples. Apparent
density of CPUG increased with the increased of NCO/OH ratio. This was due to the increased of hard
segment in CPUG which enhancing the crosslinking in CPUG samples. The rheology index of CPUG
increased with the increased of NCO/OH ratio as there was an increase of foaming reaction whichmake the CPUG samples expanding greatly. CPUG having NCO/OH ratio of 2.6:1 give the highest

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flexural strength, flexural modulus and compression strength. The increased of NCO/OH ratio caused
the acceleration of foaming reaction rate of CPUG which resulting a decreased in size of cell foam.
Acknowledgments
The authors acknowledge Universiti Teknologi MARA for BESTARI Grant Scheme 600IRMI/PERDANA 5/3 BESTARI (055/2018), International Polyurethane Technology Foundation andthe university for the research facilities.
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