Tensile Strength and Moisture Absorption of Sugar Palm-Polyvinyl Butyral Laminated Composites - MDPI

polymers
Article
Tensile Strength and Moisture Absorption of Sugar
Palm-Polyvinyl Butyral Laminated Composites
Shamsudin N. Syaqira S 1 , Z. Leman 1,2,3, *, S. M. Sapuan 1,2,3 , T. T. Dele-Afolabi 1 ,
M. A. Azmah Hanim 1,3 and Budati S. 1
 1 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra
 Malaysia, 43400 Serdang, Selangor, Malaysia; syaqirashamsudin@gmail.com (S.N.S.S.);
 sapuan@upm.edu.my (S.M.S.); deleafolabitemitope@gmail.com (T.T.D.-A.);
 azmah@upm.edu.my (M.A.A.H.); sindhubudati408@gmail.com (B.S.)
 2 Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP),
 Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
 3 Faculty of Engineering, Universiti Putra Malaysia, Advanced Engineering Materials and Composites
 Research Center, (AEMC), 43400 Serdang, Selangor, Malaysia
 * Correspondence: zleman@upm.edu.my
 



 Received: 28 May 2020; Accepted: 23 July 2020; Published: 26 August 2020 


 Abstract: Natural fiber reinforced composites have had a great impact on the development of
 eco-friendly industrial products for several engineering applications. Sugar palm fiber (SPF) is
 one of the newly found natural fibers with limited experimental investigation. In the present
 work, sugar palm fiber was employed as the natural fiber reinforcement. The composites were hot
 compressed with polyvinyl butyral (PVB) to form the structure of laminated composites and then were
 subjected to tensile testing and moisture absorption. The maximum modulus and tensile strength of
 0.84 MPa and 1.59 MPa were registered for samples PVB 80-S and PVB 70-S, respectively. Subsequently,
 the latter exhibited the highest tensile strain at a maximum load of 356.91%. The moisture absorption
 test revealed that the samples exhibited better water resistance as the proportion of PVB increased
 relative to the proportion of SPF due to the remarkable hydrophobic property of PVB in comparison
 with that of SPF.

 Keywords: laminate composites; polyvinyl butyral (PVB); sugar palm fiber (SPF); tensile strength;
 moisture absorption

1. Introduction
 Natural fiber reinforced polymer composites are composite materials composed of a polymer
matrix imbedded with natural fiber reinforcement. Recent investigations have showcased natural fiber
reinforced composites as viable alternatives to glass reinforced composites for the development of
both structural and functional components, especially in the automotive, aircraft, and architectural
industries. Natural fibers exhibit exceptional properties such as light weight, low density, low cost,
comparable tensile qualities, non-abrasiveness with respect to equipment, non-irritating with respect
to skin, renewability, reduced energy consumption, recyclable, and biodegradable [1]. However,
this composite system is marred by drawbacks such as sensitivity to water and moisture absorption,
its polar and hydrophilic nature, quality variations, and low thermal stability [2].
 Sugar palm tree can produce various kinds of products like palm sugar, fruits, and fibers [3].
Sugar palm tree is a species that can be found naturally in forests, and it was originally a member of the
Palmae family and belongs to the subfamily of Arecoideae and tribe Caryoteae [4–6]. Sugar palm is also
known to be a fast growing palm, which can achieve maturity within 10 years [7]. The geographical

Polymers 2020, 12, 1923; doi:10.3390/polym12091923 www.mdpi.com/journal/polymers

Polymers 2020, 12, 1923 2 of 8

distribution of sugar palm covers the Indo-Malay region and as wide as South Asia to South East
Asia [8]. Moreover, by using this fiber, the plant waste can be utilized. In addition, the sugar palm fiber
can easily be found, as it highly available at a very low cost. Bachtiar et al. investigated the tensile
properties of sugar palm fiber and reported values of a 3.69 GPa Young’s modulus, 190.29 MPa tensile
strength, 19.6% strain to failure, and density of 1.26 kg/m3 [9].
 Polyvinyl butyral (PVB) is a polyacetal structure produced by the process of the condensation
of polyvinyl alcohol with n-butyraldehyde in the presence of an acid catalyst [10]. Previous research
had shown PVB to be a random terpolymer that contains butyral and hydroxyl side groups with a
small amount of acetate units under 13 C NMR spectroscopy [11]. The final structure can be a random
terpolymer of 76% vinyl butyral, 22% vinyl alcohol, and 2% vinyl acetate [12]. PVB has excellent
ductility and adhesive properties with respect to the glass plane. The value of the strain rate in the
low-speed tensile test for PVB is 0.008 s−1 –0.317 s−1 , while the value of the strain rate in the high-speed
tensile test is 8.7 s−1 –1360 s−1 . PVB also behaves as a hyperelastic material influenced by the loading
rate, while the response of PVB is characterized by a time-dependent non-linear elastic behavior under
dynamic loading. The ductility of PVB reduces as the strain rate increases. Thus, it has been proposed
that PVB has outstanding mechanical properties and excellent optical clarity [13]. The stress-strain
curves of PVB under high strain rates are elastoplastic, whereas, at low strain rates, it possesses a
non-linear viscoelastic property [14].
 PVB is mainly used as safety glass in laminated glass. With growing safety awareness and customer
demand for safety features, laminated glass has become popular. Laminated glass is the formation of
a sandwich-like structure of two or more layers of glass and a plastic interlayer. The purpose of the
interlayer is to retain the fragments after a fracture has occurred, thus helping to reduce the risk of
personal injury due to glass shards. It is often comprised of two glass plies bonded with an interlayer of
plasticized PVB [15]. For example, in the automotive industry, laminated glass is used in windshields.
In the aerospace industry, it is used in airplane windows, while for architectural purposes, it is used as
glass panels for buildings. By using laminated glass, the safety, security, fire resistance, and sound
attenuation properties can be enhanced [16]. Moreover, laminated glass can also resist high impacts
such as bullets and blast loads, as well as being applicable for safety and security purposes such as
protection against hurricanes and cyclones. These safety features will help to reduce personal injury
and property damage during severe weather events [17]. In conclusion, laminated glass is a type of
safety glass that holds together when shattered, since the interlayer (PVB) keeps the layers of glass
bonded even when they are broken, and its high strength prevents the glass from breaking into large,
sharp pieces. Virtually all laminated glass products produce the characteristics of the “spider web”
cracking pattern when the impact is not enough to completely pierce the glass [18].
 In this work, sugar palm fiber was employed as a reinforcement material in PVB polymer matrix
to develop SPF-PVB laminated composites with different compositions through the hot compression
method. The developed laminated composites were subjected to tensile properties and moisture
absorption tests. The influence of different sizes of SPF and the composite ratio on the tensile strength,
tensile modulus, tensile strain at maximum load, and moisture absorption were investigated.

2. Materials and Methods

2.1. Materials

2.1.1. Sugar Palm Fiber
 An image of the sugar palm fiber used in the current study is presented in Figure 1. The fiber used
was sugar palm (Arenga Pinnata) fiber, which is in brown color, with the length of the sugar palm fiber
being about 1.19m, and the fiber diameter ranges from 94 µm to 370 µm. The fiber is stiff and durable.
The retting process was used to separate the stalk from the core part of the sugar fiber. The fibers were
dried for about 2 weeks at room temperature after cleaning off the dirt. Then, these fibers were cut
into two different sizes, i.e., short cut (0.1 cm–0.5 cm) and long cut (4.0 cm–5.0 cm). Sugar palm fibers

1923
Polymers 2020, 12, x FOR PEER REVIEW 3 of 8
Polymers 2020, 12, x FOR PEER REVIEW 3 of 8
Sugar palm fibers have some advantages over traditional reinforcement fiber materials in terms of
have renewability,
Sugar
cost, some
 palmadvantages
 fibers have over
 sometraditional
 advantages
 non-toxicity, reinforcement
 overdensity,
 abrasiveness, fiberbiodegradability
 traditional
 and materials in terms
 reinforcement fiber of cost, renewability,
 [3].materials in terms of
non-toxicity, abrasiveness, density, and biodegradability [3].
cost, renewability, non-toxicity, abrasiveness, density, and biodegradability [3].

 Figure 1. Sugar palm fiber.
 Figure
 Figure 1.
 1. Sugar
 Sugar palm
 palm fiber.
 fiber.
2.1.2. PVB Films
 PVB Films
2.1.2. PVB Films
 The PVB film was cut into a square shape with dimensions of 150 mm × 150 mm by using
 The PVB
scissors. The film
 filmwas
 PVBpolymer wascut
 cutinto a square
 into
 interlayer shape
 aofsquare
 PVB withwith
 isshape
 tough dimensions of 150
 anddimensions
 ductile, used for×applications
 ofmm
 150 150 mm
 mm by mm
 × 150 using
 thatbyscissors.
 using
 require
The polymer
scissors. The
adhesion interlayer
 polymer
 to many of PVB
 interlayer
 surfaces, is tough and
 strongofbonding, ductile,
 PVB is flexibility, used
 tough andand for applications
 ductile, used for
 toughness. that require
 applications
 Figure 2 shows the adhesion
 thatimage
 requireto
 of
many
the PVBsurfaces,
adhesion strong
 to many
 films. bonding,
 surfaces, flexibility,
 strong bonding,and toughness.
 flexibility, Figure
 and 2 shows
 toughness. the image
 Figure of the
 2 shows thePVB
 imagefilms.
 of
the PVB films.

 Figure 2. PVB
 PVB films.
 films.
 Figure 2. PVB films.
2.2. Fabrication
2.2. Fabrication
2.2. Fabrication
 Various compositions with different
 different weight
 weight percentages
 percentages of of sugar
 sugar palm
 palm fiber
 fiber and
 and PVB
 PVB were
 were
 Various compositions with
produced
 Various
produced by hot compression
 by compositions
 hot compression molding
 with to
 different
 molding form laminated
 to weight composites.
 percentages
 form laminated Firstly, certain
 of sugarFirstly,
 composites. palm fiber layers
 certainand of cut
 PVB of
 layers PVB
 were
 cut
film were
produced
PVB placed
 by hot
 film were on theonmold,
 compression
 placed and theand
 molding
 the mold, sugar palm
 to form
 the fibers
 palmwere
 sugarlaminated placed
 werein
 composites.
 fibers theFirstly,
 placedmiddle, then
 in thecertain other
 middle,layerslayers
 then of of
 cut
 other
PVB
layersfilm
PVB film were placed
 werefilm
 of PVB placed on
 were top of
 onplaced SPF.
 the mold, The samples
 andofthe
 on top sugar
 SPF. were
 Thepalm then hot
 fibers
 samples pressed
 were
 were with
 placed
 then a load of
 in the middle,
 hot pressed 40 tons.
 with a then The hot
 load other
 of 40
compression ◦ C temperature where the pre-heat time was 5 min, the heating
layers
tons. The hotmachine
 of PVB film werewas
 compression set
 placed to on
 machinea 165
 topwas ofset
 SPF.to The
 a 165samples were thenwhere
 °C temperature hot pressed with atime
 the pre-heat loadwas
 of 405
time was
tons.
min, the 10
 hotmin,
 Theheating and the
 time wascooling
 compression 10 min,time
 machine andwaswas
 the 5 to
 min.
 setcooling Thus,
 a 165 the total
 °C was
 time temperaturetime
 5 min. taken
 where
 Thus, intotal
 thethe hot compression
 pre-heat
 time time in
 taken was
 washot5
20 min.
compressionThe
min, the heatinglaminated
 wastime composite
 wasThe
 20 min. 10 min, samples
 and the
 laminated with dimensions
 cooling time
 composite of 150
 was 5with
 samples mm long
 min.dimensions × 150
 Thus, the total
 of 150mm
 time
 mmwide
 taken ×
 longin5 mm
 hot
 × 150
thickwide
mm were×fabricated,
compression 5 was
 mm20 thickand
 min. werethefabricated,
 The samples were
 laminated thensamples
 composite
 and the ready
 samplesfor testing.
 with
 were The image
 dimensions
 then ready for of of
 150sample
 testing. mm laminate
 Thelong
 image× 150
 of
composites
mm wide × for
 5 short
 mm cut
 thick SPF
 were is presented
 fabricated, in
 and Figure
 the 3.
 samples
sample laminate composites for short cut SPF is presented in Figure 3. were then ready for testing. The image of
sample
 Thelaminate composites
 three different for short cut
 compositions SPFsamples
 of the is presented
 with in Figure weight
 different 3. percentages of PVB and
 The three
SPF were 80% different
 PVB–20%compositions of the samples
 SPF, 70% PVB-30% SPF, andwith
 60%different
 PVB–40% weight percentages
 SPF. These sampleofwere
 PVBthen
 and
SPF were 80% PVB–20% SPF, 70% PVB-30% SPF, and 60% PVB–40% SPF.
differentiated by the size of SPF, either long cut (SPF-L) or short cut (SPF-S). These sample were then
differentiated by the size of SPF, either long cut (SPF-L) or short cut (SPF-S).

Polymers 2020, 12, 1923 4 of 8
Polymers 2020, 12, x FOR PEER REVIEW 4 of 8

 Figure 3. Samples of laminate’s composites for short cut SPF.
 SPF.

 The three different
2.3. Characterization compositions of the samples with different weight percentages of PVB and
 and Analysis
SPF were 80% PVB–20% SPF, 70% PVB–30% SPF, and 60% PVB–40% SPF. These sample were then
2.3.1. Tensile Test
differentiated by the size of SPF, either long cut (SPF-L) or short cut (SPF-S).
 The speed of the
2.3. Characterization andInstron
 Analysis3366 machine was fixed to a constant speed of 50 mm/min, and the
sample was cut into a dog-bone structure with an overall length of 120 mm for the tensile test. The
tensileTensile
2.3.1. strength
 Testis the maximal force per unit area acting on a plane transverse to the applied load
and is a fundamental measure of the internal cohesive forces within a sample.
 The speed of the Instron 3366 machine was fixed to a constant speed of 50 mm/min, and the sample
was cut into a dog-bone structure with an overall length of 120 mm for the tensile test. The tensile
2.3.2. Moisture Absorption Test
strength is the maximal force per unit area acting on a plane transverse to the applied load and is a
 The moisture
fundamental absorption
 measure text was
 of the internal performed
 cohesive forcesatwithin
 room atemperature.
 sample. The samples were cut into
square shapes of 30mm × 30mm from the composite sheets. All samples were washed thoroughly
2.3.2. Moisture
and dried in anAbsorption Test all moisture inside the sample. The samples were then placed in a
 oven to remove
container filled with
 The moisture distilled water
 absorption for performed
 text was different time intervals,
 at room which were
 temperature. 5 days,
 The 10 days,
 samples were 15
 cutdays,
 into
20 days, and 25 days. The moisture absorption was determined by the mathematical
square shapes of 30 mm × 30 mm from the composite sheets. All samples were washed thoroughly formula given
in Equation
and dried in(1)
 an[19]:
 oven to remove all moisture inside the sample. The samples were then placed in a
container filled with distilled water for different ∘
 time
 % intervals, which
 100were 5 days, 10 days, 15 days,
 (1)
20 days, and 25 days. The moisture absorption was determined ∘ by the mathematical formula given in
Equation (1) [19]:
where w f − w0
 Moisture uptake (%) = × 100 (1)
1. wf = mass of the sample at Day 25 (g) w0
where
2. and wo = mass of the sample at Day 1 (g)

1. wf = mass of the sample at Day 25 (g);
3. Results and Discussion
2. and w0 = mass of the sample at Day 1 (g).
3.1.Results
3. Tensileand
 Properties
 Discussion

3.1.1.Tensile
3.1. Modulus
 Properties
 Figure 4 presents the modulus of elasticity values for the composites. With the modulus being
3.1.1. Modulus
the measure of the stiffness of the samples, the trend in the graph shows that the higher the
 Figure 4ofpresents
proportion PVB, the thehigher
 modulus
 the of elasticity
 stiffness values
 of the for theMoreover,
 sample. composites.theWith the modulus
 different being
 cuts of the the
 sugar
measure of the stiffness of the samples, the trend in the graph shows that the higher
palm fiber also had a marginal influence on the modulus of the samples. This is because the the proportion of
PVB, the higher
dispersion of thethe stiffness
 fiber of the
 becomes sample.
 worse with Moreover,
 the increasetheindifferent
 the fibercuts of the
 length. sugar palm
 Therefore, the fiber also
 modulus
had a marginal
of the short fiberinfluence
 is greateron the the
 than modulus of the samples. This is because the dispersion of the fiber
 long fiber.
becomes worse with the increase in the fiber length. Therefore, the modulus of the short fiber is greater
than the long fiber.

Polymers 2020, 12, 1923 5 of 8
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 12, xx FOR
 FOR PEER
 PEER REVIEW
 REVIEW 55 of
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 1.20
 1.20

 Average modulus (MPa)
 1.00
 1.00 0.84
 0.84 0.80
 0.80
 0.80
 0.80 0.73
 0.73 0.70
 0.70 0.66
 0.66
 0.54
 0.54
 0.60
 0.60
 0.40
 0.40
 0.20
 0.20
 0.00
 0.00
 PVB
 PVB PVB
 PVB PVB
 PVB PVB
 PVB PVB
 PVB PVB
 PVB
 80-S
 80-S 80-L
 80-L 70-S
 70-S 70-L
 70-L 60-S
 60-S 60-L
 60-L
 Sample composition
 Sample composition

 Figure 4.
 Figure 4. Average
 Average modulus
 Average modulus of
 of elasticity
 elasticity of
 of the
 the composite
 composite samples.
 samples. S,
 S, short
 short cut;
 cut; L,
 L, long
 long cut.
 cut.

3.1.2. Tensile
 Tensile Stress
3.1.2. Tensile
3.1.2. Stress
 Stress
 The tensile
 The tensile stress
 tensile stress value
 stress value show
 value show the
 show the strength
 the strength capacity
 strength capacity of
 capacity of the
 of the samples
 the samples in
 samples in tensile
 in tensile loading.
 tensile Figure 5
 loading. Figure
 loading. 55
shows that the
 the highest
 highest tensile
 tensile stress
 stress was
 was recorded
 recorded forfor
 PVB PVB70-S70-S followed
 followed by
shows that the highest tensile stress was recorded for PVB 70-S followed by PVB 70-L, PVB 60-L, PVB by
 PVB PVB
 70-L, 70-L,
 PVB PVB
 60-L, 60-L,
 PVB
PVB
80-S,80-S,
80-S, PVB PVB
 PVB 80-L,80-L,
 80-L, and and
 PVBPVB
 and PVB 60-S.60-S.
 60-S. The The
 The superior
 superior
 superior tensile
 tensile
 tensile stress
 stress
 stress exhibited
 exhibited
 exhibited by the
 by the
 by the PVB
 PVB PVB
 70-S
 70-S 70-S sample
 sample
 sample cancan
 can be
 be
be explained
explained
explained by by
 by (1)(1)
 (1) thethe
 the higher
 higher
 higher concentration
 concentration
 concentration ofofSPF
 of SPFcontent
 SPF content(the
 content (thebreaking
 (the breakingstrength
 breaking strengthof
 strength of fibers
 of is much
 fibers is much
 much
greater
greater than
greater thanthat
 than thatof of
 that the matrix),
 of the
 the (2) the
 matrix),
 matrix), (2)smaller
 (2) size of SPF
 the smaller
 the smaller sizeinof
 size ofPVB,
 SPFwhich
 SPF limitswhich
 in PVB,
 in PVB, the stress
 which concentration
 limits
 limits the stress
 the stress
around the fiber
concentration around
concentration during
 around the tensile
 the fiber loading
 fiber during relative
 during tensile to
 tensile loadingthe counterpart
 loading relative
 relative to sample
 to the with
 the counterpart longsampleand
 counterpart sample SPF, with
 with (3)long
 the
 long
possible
SPF, andattainment
SPF, and (3) the
 (3) of optimal
 the possible
 possible wetting
 attainment
 attainment of for SPF on
 of optimal
 optimal PVB in
 wetting
 wetting this
 for
 for SPF
 SPF sample.
 on PVB
 on PVB in
 in this
 this sample.
 sample.

 2.50
 2.50
 at maximum load (MPa)
 Average tensile stress

 2.00
 2.00
 1.59
 1.59 1.55
 1.55 1.53
 1.53
 1.49
 1.49
 1.50 1.38
 1.38
 1.50
 1.10
 1.10
 1.00
 1.00

 0.50
 0.50

 0.00
 0.00
 PVB 80-S
 PVB 80-S PVB
 PVB 80-L
 80-L PVB
 PVB 70-S
 70-S PVB
 PVB 70-L
 70-L PVB
 PVB 60-S
 60-S PVB
 PVB 60-L
 60-L
 Sample composition
 Sample composition

 Figure 5.
 Figure 5. Average
 Average tensile
 tensile stress
 stress at
 at maximum
 maximum load
 load of
 of the
 the composite
 composite samples.
 samples.

 In general,
 In general, the the decrement
 decrement in in the
 the tensile
 tensile stress
 stress value
 value of of the
 the different
 different composites
 composites occurred
 occurred beyond
 beyond
30 wt%SPF
30wt%
30wt% SPFloading.
 SPF loading.This
 loading. This
 This trendtrend
 trend cancan
 can be attributed
 be attributed
 be attributed toinfluence
 to the
 to the the influence
 influence of matrix
 of matrix
 of matrix discontinuity
 discontinuity
 discontinuity with
 with rising
 with rising
rising
filler filler
 content content
 in the in the
 matrix, matrix,
 which which
 resulted resulted
 in poor in poor
 stress stress
 transfer transfer
 from the
filler content in the matrix, which resulted in poor stress transfer from the matrix to the filler [20].from
 matrix theto matrix
 the to
 filler the
 [20].
filler
Similar
Similar[20].findings
 Similar findings
 findings were were reported
 were reported
 reported elsewhere
 elsewhere
 elsewhere for thermoplastic
 for thermoplastic
 for thermoplastic starch/silk
 starch/silk
 starch/silk fibercomposites
 fiber
 fiber composites [21],
 composites [21],
seaweed/polypropylene
seaweed/polypropylenecomposites
seaweed/polypropylene composites
 composites [20], pineapple
 [20],
 [20], pineapple
 pineapple leafleaf
 fiber/polypropylene
 leaf fiber/polypropylene
 fiber/polypropylene composites
 composites
 composites[22], and
 [22],sugar
 [22], and
 and
palm fiber/phenolic
sugar palm
sugar palm fiber/phenolic composites
 fiber/phenolic composites [23].
 composites [23]. Meanwhile,
 [23]. Meanwhile, the
 Meanwhile, the anomalous
 the anomalous trend
 anomalous trend exhibited
 trend exhibited
 exhibited byby the
 by the PVB
 PVB 60
 the PVB 60
composites where
composites where PVB PVB 60-S
 60-S exhibited
 exhibited lesser
 lesser tensile
 tensile stress
 stress than the PVB
 than the PVB 60-L
 60-L counterpart
 counterpart can can be be
attributed to
attributed to the
 the clustering
 clustering ofof the
 the short-sized
 short-sized fibers
 fibers due
 due to to the high surface
 the high area of
 surface area of the
 the particles
 particles andand
the high
the high volume
 volume fraction of SPF
 fraction of SPF inin PVB,
 PVB, thus
 thus promoting
 promoting fiber-fiber
 fiber-fiber interactions
 interactions andand the
 the subsequent
 subsequent
defective strengthening
defective strengtheningofof
 strengthening ofthe
 thecomposite.
 the composite.Moreover,
 composite. Moreover,
 Moreover, a similar
 aa similar
 similarfinding
 finding
 findingwaswasreported
 was by Facca
 reported
 reported et al.et
 by Facca
 by Facca et[24].
 al.
 al.
[24].
[24].

3.1.3. Tensile
3.1.3. Tensile Strain
 Strain

Polymers 2020, 12, 1923 6 of 8

Polymers 2020, 12, x FOR PEER REVIEW 6 of 8
3.1.3. Tensile Strain
 Tensile strain is the measurement of the relative length of the deformation of the samples due to
the tensile force applied. Figure 6 shows that the greater the proportion of PVB, the higher the tensile
strain. Based on on Figure
 Figure6,6,the
 thedifferent
 differenttypes
 typesofofcut
 cut (long
 (long and
 and short)
 short) influenced
 influenced thethe tensile
 tensile strain
 strain of
 of the
the sample
sample wherewhere the percentages
 the percentages of tensile
 of tensile strainstrain
 for PVB for80-S,
 PVB PVB
 80-S,70-S,
 PVBand70-S,
 PVBand60-S
 PVB 60-Sallwere
 were all
 greater
greater
than thethan the percentages
 percentages of thestrain
 of the tensile tensile
 of strain of PVB
 PVB 80-L, PVB80-L,
 70-L,PVB
 and70-L, and PVB
 PVB 60-L. This60-L.
 showsThis
 thatshows
 short
that short
cut SPF cutgreater
 has SPF has greater
 tensile tensile
 strain strain
 than than cut
 the long the SPF.
 long The
 cut SPF. The isotropic
 isotropic behaviorbehavior
 is one ofisthe
 one of the
 reasons
reasons
for this. for this.

 500
 at maximum load (%)
 Average tensile strain

 400 356.91 347.32 337.87
 300.66 299.79 320.34
 300

 200

 100

 0
 PVB 80-SPVB 80-LPVB 70-SPVB 70-LPVB 60-SPVB 60-L
 Sample composition

 Figure 6. Average
 Average tensile strain at maximum load of the composite samples.

3.2. Moisture
3.2. Moisture Absorption
 Absorption
 For the
 For the development
 development of of reliable
 reliable biocomposite materials, low
 biocomposite materials, low moisture
 moisture absorption
 absorption is is an
 an essential
 essential
factor to
factor tobebeconsidered
 considered in the selection
 in the of natural
 selection fibers as
 of natural the reinforcing
 fibers material since
 as the reinforcing materialhigh since
 absorption
 high
will adversely affect the dimensional stability of the composite, especially
absorption will adversely affect the dimensional stability of the composite, especially in terms of in terms of mechanical
performance, porosity formation,
mechanical performance, porosityand water retention
 formation, and water capacity [25,26].
 retention Figure[25,26].
 capacity 7 shows that PVB
 Figure 60-L
 7 shows
has the highest water uptake (and corresponding percent increment) compared
that PVB 60-L has the highest water uptake (and corresponding percent increment) compared to PVB to PVB 70-L and PVB
80-L,and
70-L which
 PVB are80-L,
 0.068which
 g (2.32%), 0.031g g(2.32%),
 are 0.068 (1.04%),0.031
 and g0.019 g (0.63%),
 (1.04%), and 0.019respectively,
 g (0.63%), after 25 days (water
 respectively, after
uptake was calculated by subtracting the weight of the sample after 25 days
25 days (water uptake was calculated by subtracting the weight of the sample after 25 days from the from the dry weight).
This phenomenon
dry weight). can be attributed
 This phenomenon cantobethe addition to
 attributed of the
 different amounts
 addition of PVB amounts
 of different and SPF. PVB hasand
 of PVB the
properties of good water resistance, whereas SPF has poor water resistance.
SPF. PVB has the properties of good water resistance, whereas SPF has poor water resistance. Hence,Hence, with the increasing
proportion of PVB, the
with the increasing sample exhibited
 proportion of PVB,a thelower amount
 sample of waterauptake,
 exhibited lower whereas,
 amount of as the
 waterproportion
 uptake,
of SPF increased, the samples showed greater water uptake due to the
whereas, as the proportion of SPF increased, the samples showed greater water uptake due to properties of SPF. Longer fibers
 the
tend to increase the percentage of water absorption. The rate of water absorption
properties of SPF. Longer fibers tend to increase the percentage of water absorption. The rate of water is greatly affected by
the specimen’s density and void volumes. The incorporation of long fibers
absorption is greatly affected by the specimen’s density and void volumes. The incorporation of long into the mix decreased
workability
fibers into theandmixincreased
 decreased theworkability
 void space.and Consequently,
 increased the thevoid
 longer
 space.theConsequently,
 fiber, the higher theislonger
 the water
 the
absorption. Hence, the introduction of compatibilizers, coupling agents, or chemical
fiber, the higher is the water absorption. Hence, the introduction of compatibilizers, coupling agents, treatment can go
a long way toward improving the moisture resistance of these composites
or chemical treatment can go a long way toward improving the moisture resistance of these [27].
composites [27].

 5.00
 4.08
 Water uptake (%)

 4.00
 3.00 2.44 2.32
 2.00
 1.04
 1.00 0.71 0.63

 0.00
 PVB 80-S PVB 80-L PVB 70-S PVB 70-L PVB 60-S PVB 60-L
 Sample composition

 Figure 7. Percentage of water uptake of the composites after 25 days.

properties of SPF. Longer fibers tend to increase the percentage of water absorption. The rate of water
absorption is greatly affected by the specimen’s density and void volumes. The incorporation of long
fibers into the mix decreased workability and increased the void space. Consequently, the longer the
fiber, the higher is the water absorption. Hence, the introduction of compatibilizers, coupling agents,
or chemical
Polymers 2020, 12,treatment
 1923 can go a long way toward improving the moisture resistance of these 7 of 8
composites [27].

 5.00
 4.08

 Water uptake (%)
 4.00
 3.00 2.44 2.32
 2.00
 1.04
 1.00 0.71 0.63

 0.00
 PVB 80-S PVB 80-L PVB 70-S PVB 70-L PVB 60-S PVB 60-L
 Sample composition

 Figure 7.
 Figure 7. Percentage
 Percentage of
 of water
 water uptake
 uptake of the composites
 of the composites after
 after 25
 25 days.
 days.

4. Conclusions
 In this work, the laminated composite sample with 80% of PVB and 20% of SPF showed the highest
stiffness value. However, increasing the proportion of PVB too much results in high tensile strain.
Furthermore, the comparison of two different cut sizes (long and short) was carried out, and their effect
on the tensile test and moisture absorption were examined. For the tensile test, the modulus of the
sample increased with a rising proportion of PVB due to the high bonding power and elasticity of PVB.
Other than that, the short cut SPF exhibited a stronger modulus compared to the long cut SPF. For the
moisture absorption test, the samples exhibited good resistance toward water with the increasing
proportion of PVB due to its properties of good water resistance from, while SPF demonstrated poor
water resistance. On the other hand, the long cut SPF showed better water resistance than the short
cut SPF. From these results, the optimum composition for the best overall performance was PVB 80-S
(20% SPF–80% PVB-short cut fiber), which is suitable for windshields and glass panels in buildings.
Further surface treatment can be done to improve the water resisting ability.

Author Contributions: Conceptualization, Z.L.; methodology, S.N.S.S.; Software, S.N.S.S.; validation, Z.L. and
S.M.S.; formal analysis, S.N.S.S. and Z.L.; investigation, S.N.S.S.; Resources, Z.L.; data curation, S.N.S.S.; writing,
original draft preparation, S.N.S.S.; writing, review and editing, T.T.D.-A., M.A.A.H. and B.S.; visualization,
Z.L. and S.M.S.; supervision, Z.L. and S.M.S.; project administration, Z.L. and S.M.S.; funding acquisition, Z.L.
All authors have read and agree to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments: The authors would like to thank the Department of Mechanical and Manufacturing
Engineering, Universiti Putra, Malaysia, for the opportunity given to conduct this study and to present some
of the findings at the ICAM2 E Conference, Langkawi, Malaysia. The study was part of the research project
GP-IPS/9438714.
Conflicts of Interest: The authors declare no conflict of interest.

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