The document discusses the influence of fiber loading, surface treatment, and other factors on the impact strength of coir polyester composites. It finds that treating coir fibers with an alkali solution improves adhesion between the fiber and polyester matrix. Composite samples were tested according to ASTM standards while varying fiber content, treatment time, and solution concentration. Response surface methodology was used to develop a regression model relating these fabrication parameters to impact strength. The optimal parameters to maximize impact strength were found to be 28% fiber loading, treatment in a 5% solution for 45 hours, achieving an impact strength of 42.15 kJ/m2.

1. Influence of Fiber Loading and Surface treatment on the Impact Strength of
Coir Polyester Composites
S.Karthikeyan1
, S.Jayabal2
andS.Kalyana Sundaram3
1
PG Scholar, Department of Mechanical Engineering, A.C.College of Engineering
and Technology, Karaikudi – 630 004,
2
Assistant Professor, Department of Mechanical Engineering, A.C.College of
Engineering and Technology, Karaikudi – 630 004,
3
Research Scholar, Department of Mechanical Engineering, A.C.College of
Engineering and Technology, Karaikudi – 630 004,
Abstract
The mechanical properties of natural fiber composites depend on many parameters such as
fiber loading, modulus, fiber content, fiber length, and orientation, in addition to the fiber-
matrix interfacial bond strength. In this work, coir fiber with varying fiber content was
selected as reinforcements to prepare polymer based matrices and the problem of reduced
fiber-matrix interfacial bond strength has been diluted by chemical treatment of coir fibers
with alkali solution. The effect of fiber loading, solution concentration and soaking time on
the impact strength of the composites were analyzed using statistical techniques. Response
Surface Methodology (RSM) approach was used to model and optimize the impact properties
of coir-polyester composites.
Keywords: Coir fiber, Polymer composites, Impact strength, Response surface methodology.
1. Introduction
India, endowed with an abundant availability of natural fibers such as jute, coir, sisal,
pineapple, ramie, bamboo, banana etc., has focused towards the development of natural fiber
composites primarily to explore value-added application avenues [1-3]. Such natural fiber
composites are well suited as wood substitutes in the housing & construction sector. Coir
based composites have been developed as substitutes for plywood & medium density fiber
boards. Panel & flush doors have also been developed out of these composite boards
especially for low-cost housing needs. Other product development activities include usage of
sisal fiber based composites as panel & roofing sheets. However poor mechanical properties
of natural fiber composites caused due to poor interfacial bonding between fiber and matrix
restrict their use in engineering application [4-7]. Many researches have been carried out in
the past to improve the bindability between fibers and matrix through alkali treatment [8-10].
This work in aimed at identifying the suitable treatment parameters and fiber loading
condition for better impact properties of coir fiber reinforced polyester composites.
2. Experimental procedure
2.1 Materials
In the present study, the commercially available coir fiber was procured in dry
condition and was treated with sodium hydroxide solution to remove the lignin content. The
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2. matrix material used in this investigation was commercially available unsaturated polyester
resin. The hand lay-up process was followed for fabricating composites as per design matrix.
2.2 Fabrication and testing of Composites
The raw coir fibers were soaked in a solution of sodium hydroxide of varying
concentration and soaking time. The fibers were then washed to neutral pH and dried at room
temperature, 23 ± 2°C, and for 2–3 days. The coir composites were prepared as per 3 Level
full factorial designs (Table.1) with the fabrication parameters namely; fiber content (10%,
25% and 40%), soaking time (24hrs, 48hrs and 72hrs) and solution concentration (2%,4%
and 6%). After fabrication, the test specimens were subjected to Impact test as per ASTM
D256 standard.
Table 1.Design factorial levels
Parameters Low Intermediate High
Fiber loading,% 10 25 40
Solution concentration,% 2 4 6
Soaking time, Hrs 24 48 72
2.3 Modeling and Optimization using RSM
The tensile and impact properties obtained from experimental investigation were used
to develop the regression model between fabrication parameters and mechanical properties.
Response surface methodology is the technique used in this investigation to build empirical
model between the output response (impact strength) and independent variables (fiber
content, soaking time and solution concentration). The mathematical model developed was
justified based on 3D response surface plot and coefficient of correlation resulted from
statistical software (Design Expert V 8).The model thus developed was optimized to
maximize the tensile and impact properties of sisal fiber reinforced polyester composites.
3. Results and Discussion
3.1 Effect of fiber loading and surface treatment on impact properties of composites
The chemical treatment using sodium hydroxide solution has removed the excess
lignin content present over the fiber surface. The presence of a rougher fiber surface has
promoted a mechanical interlock between the fibers and the resin matrix. The impact strength
was found to be better with the composite fabricated with 25% of fiber loading, the increase
or decrease in fiber loading beyond this level resulted with poor impact properties.
The effect of fiber loading and surface treatment on impact properties of composites
is shown in the Figure.1.The fibers soaked in 4% solution concentration for 48 hrs resulted in
better impact strength. The increase in solution concentration beyond this level resulted in
excess leaching of fibers which in turn diminished the mechanical properties of the fiber.
Hence it can be stated that fiber treated with 4% solution concentration for 48 hrs can
improve the adhesion between fiber surface and polyester matrix and fiber loading of 25%
may yield better impact properties to the composites.
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3. Figure.1 Effect of fiber loading and surface treatment on impact properties of composites
3.2 Regression Model
The regression model for impact strength of treated coir fiber reinforced polyester
composites was developed using Response surface Methodology (RSM). The 3D response
plot for the impact strength obtained from statistical tool is shown in the Figure .2 (a). The
plot indicated the interaction effect of fiber loading vs solution concentration, solution
concentration vs soaking time and soaking time vs fiber loading on the impact strength of the
composites. The coefficient of correlation (R2
) obtained for impact strength of the composite
was 0.82. The higher value of R2
(close to 1) indicated the significance of model developed
using Response surface methodology. The impact strength of the composites exhibited a
quadratic behavior as shown below
is = -29.34923+3.89578f1+2.88051f2-0.20522f3-0.22086f1f2+0.00001f1f3-0.031375f2f3-0.049832
f1
2+0.58489 f2
2+0.069222f3
2
(1)
Figure.2 Contour and 3D surface plot for the impact strength model
3.3 Optimization using RSM
Based on the mathematical equations formed by Response Surface methodology
technique, the fiber parameters were optimized and the optimal parameters to maximize
impact strength were obtained using Response Surface methodology (RSM). The maximum
value of impact strength of 41.18 kJ/m² was predicted at the fiber loading of 28 % and with
the fibers treated in 5% concentration solution for 45 hrs. The experiment value was found to
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4. be very closer to the predicted (Table 2.) which witnessed the effective prediction of PSO
technique.
Table.2 Confirmation Test on impact strength of the composites
Sl.No
Mechanical
properties
Fiber
Loading
(%)
Solution
Concentration
(%)
Soaking
Time
(Hrs)
Experimental /
Prediction
Values
(kJ/sq.m)
% Error
1
Impact
strength
28 6 5 42.15 /41.18 2.3
4. Conclusion
The mechanical strength of treated coir fiber reinforced polyester composites was
evaluated in this investigation as per ASTM D256, standard. The fabrication parameters
namely fiber content, soaking time and solution concentration were found to play prominent
role in the impact strength of the composites. The mathematical equation for predicting
impact strength over the wide range of conditions was formulated and optimized using RSM
technique. The prediction model was found to be significant and the optimum value was
found to be very closer to the experimental value. This specific investigation has paid way
for the possible development of engineering application based coir reinforced polyester
composite applications.
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