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Article Tensile Strength and Moisture Absorption of Sugar Palm- 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 , Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; [email protected] (S.N.S.S.); [email protected] (S.M.S.); [email protected] (T.T.D.-A.); [email protected] (M.A.A.H.); [email protected] (B.S.) 2 Laboratory of Biocomposite Technology, Institute of Tropical 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: [email protected]

 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 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 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 with n- 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 1 1 low-speed tensile test for PVB is 0.008 s− –0.317 s− , while the value of the strain rate in the high-speed 1 1 tensile test is 8.7 s− –1360 s− . 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 in . 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 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 , laminated glass is used in . 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 Figure1. 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 Polymers 2020, 12, x 1923 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 cost,Sugarhave renewability, somepalm advantagesfibers havenon-toxicity, oversome traditional advantages abrasiveness, reinforcement over density, traditional and fiber biodegradabilityreinforcement materials in termsfiber [3]. materials of cost, renewability, in terms of cost,non-toxicity, renewability, abrasiveness, non-toxicity, density, abrasiveness, and biodegradability density, and [3 ].biodegradability [3].

Figure 1. Sugar palm fiber. Figure 1. SugarSugar palm palm fiber fiber.. 2.1.2. PVB Films 2.1.2. PVB PVB Films Films The PVB film was cut into a square shape with dimensions of 150 mm × 150 mm by using The PVBPVB filmfilm was was cut cut into into a squarea square shape shape with with dimensions dimensions of 150 of mm 150 mm150 mm× 150 by mm using by scissors. using scissors. The polymer interlayer of PVB is tough and ductile, used for× applications that require adhesionscissors.The polymer Theto many interlayerpolymer surfaces, interlayer of PVB strong is of tough bonding, PVB and is flexibtough ductile,ility, and used and ductile,for toughness. applications used forFigure applications that 2 requireshows thethat adhesion image require of to adhesionthemany PVB surfaces, films. to many strong surfaces, bonding, strong flexibility, bonding, and flexib toughness.ility, and Figure toughness.2 shows Figure the image 2 shows of the the PVB image films. of the PVB films.

Figure 2. PVBPVB films. films. Figure 2. PVB films. 2.2. Fabrication Fabrication 2.2. Fabrication Various compositions with different different weight percentages of sugar palm fiber fiber and PVB were producedVarious byby hotcompositionshot compressioncompression with molding molding different to to form weightform laminated laminated percentages composites. composites. of sugar Firstly, Firstly, palm certain fibercertain layers and layers PVB of cut ofwere PVB cut PVBproducedfilm werefilm were placedby hot placed oncompression the on mold, the mold, and molding the and sugar theto form palmsugar laminated fibers palm were fibers composites. placed were inplaced the Firstly, middle, in the certain thenmiddle, other layers then layers ofother cut of layersPVB filmfilm of PVB werewere film placedplaced were onon placed top the ofmold,SPF. on top Theand of samplesthe SPF. sugar The were pa sampleslm then fibers hot were were pressed then placed withhot pressedin a loadthe middle, of with 40 tons. a thenload The otherofhot 40 tons.layerscompression The of PVBhot machine compressionfilm were was placed setmachine to on a 165 top was◦ Cof settemperatureSPF. to Thea 165 samples °C where temperature were the pre-heat then where hot time pressed the was pre-heat 5with min, a thetime load heating was of 40 5 min,tons.time wastheThe heating 10hot min, compression time and thewas cooling 10machine min, time and was wasthe set cooling 5 to min. a 165 Thus,time °C wastemperature the total5 min. time Thus, where taken the the in total hot pre-heat time compression taken time inwas washot 5 20 min. The laminated composite samples with dimensions of 150 mm long 150 mm wide 5 mm compressionmin, the heating was time 20 min. was The 10 min, laminated and the composite cooling time samples was 5with min. dimensions Thus, the× total of 150 time mm taken long× in × 150hot mmcompressionthick wide were × fabricated,5 wasmm 20thick min. and were The the fabricated, laminated samples were andcomposite the then samples ready samples forwere testing.with then dimensions ready The image for oftesting. of150 sample mm The long image laminate × 150 of samplemmcomposites wide laminate × for5 mm short composites thick cut were SPF for isfabricated, presented short cut and inSPF Figure theis presented samples3. werein Figure then 3.ready for testing. The image of sampleThe laminate three different composites compositions for short cutof the SPF samples is presented with indifferent Figure weight3. percentages of PVB and SPF wereThe three 80% differentPVB–20% compositions SPF, 70% PVB-30% of the samplesSPF, and with 60% different PVB–40% weight SPF. Thesepercentages sample of were PVB thenand differentiatedSPF were 80% by PVB–20% the size ofSPF, SPF, 70% either PVB-30% long cut SPF, (SPF-L) and 60% or short PVB–40% cut (SPF-S). SPF. 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.

2.3. CharacterizatThe three diionfferent and Analysis compositions of the samples with different weight percentages of PVB and SPF were 80% PVB–20% SPF, 70% PVB–30% SPF, and 60% PVB–40% SPF. These sample were then di2.3.1.fferentiated Tensile Test by the size of SPF, either long cut (SPF-L) or short cut (SPF-S).

2.3. CharacterizationThe speed of the and Instron Analysis 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 2.3.1.tensile Tensile strength Test is 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 was2.3.2. cut Moisture into a dog-boneAbsorption structure Test with an overall length of 120 mm for the tensile test. The tensile strength is the maximal force per unit area acting on a plane transverse to the applied load and is a fundamentalThe moisture measure absorption of the internal text was cohesive performed forces at within 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.and dried Moisture in an Absorption oven to remove Test all moisture inside the sample. The samples were then placed in a containerThe moisture filled with absorption distilled wate textr was for performeddifferent time at roomintervals, temperature. which were The 5 days, samples 10 days, were 15 cut days, into square20 days, shapes and 25 of days. 30 mm The moisture30 mm from absorption the composite was determined sheets. All by samples the mathematical were washed formula thoroughly given × andin Equation 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,𝑤 𝑤 which∘ were 5 days, 10 days, 15 days, 𝑀𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝑢𝑝𝑡𝑎𝑘𝑒% 100 (1) 20 days, and 25 days. The moisture absorption was determined𝑤∘ by the mathematical formula given in Equation (1) [19]: where w f w0 Moisture uptake (%) = − 100 (1) w 1. wf = mass of the sample at Day 25 (g) 0 ×

2.where 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).

3.3.1. Results Tensile andProperties Discussion

3.1.3.1.1. Tensile 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 proportionFigure 4of presents PVB, the the higher modulus the ofstiffness elasticity of valuesthe sample. for the Moreover, composites. the With different the modulus cuts of beingthe sugar the measurepalm fiber of thealso sti hadffness a ofmarginal the samples, influence the trend on th ine the modulus graph shows of the that samples. the higher This the is proportionbecause the of PVB, the higher of the the fiber sti ffbecomesness of theworse sample. with Moreover,the increase the in di thefferent fiber cuts length. of the Therefore, sugar palm the fibermodulus also hadof the a marginalshort fiber influence is greater on than the the modulus long fiber. of the samples. This is because the dispersion of the 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 PolymersPolymers 20202020,, 1212,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 88

1.201.20 1.001.00 0.840.84 0.800.80 0.730.73 0.800.80 0.700.70 0.660.66 0.540.54 0.600.60 0.400.40 0.200.20 0.000.00 Average modulus (MPa) Average modulus Average modulus (MPa) Average modulus PVBPVB PVBPVB PVBPVB PVBPVB PVBPVB PVBPVB 80-S80-S 80-L80-L 70-S70-S 70-L70-L 60-S60-S 60-L60-L SampleSample compositioncomposition

FigureFigure 4. 4. AverageAverage modulus modulus ofof elasticityelasticity ofof thethe compositecomposite samples.samples. S, S, short short cut; cut; L,L, longlong cut.cut.

3.1.2.3.1.2. Tensile Tensile StressStress TheThe tensiletensile stressstress valuevalue showshow thethe strengthstrength capacitycapacity ofof thethethe samplessamplessamples ininin tensiletensiletensile loading.loading.loading. Figure Figure 5 55 showsshows thatthat thethe the highesthighest highest tensiletensile tensile stressstress stress waswas was recordedrecorded recorded forfor for PVBPVB PVB 70-S70-S 70-S followedfollowed followed byby PVBPVB by PVB 70-L,70-L, 70-L, PVBPVB PVB60-L,60-L, 60-L, PVBPVB 80-S,PVB80-S, 80-S,PVBPVB PVB80-L,80-L, 80-L, andand PVB andPVB PVB 60-S.60-S. 60-S. TheThe Thesuperiorsuperior superior tensiletensile tensile stressstress stress exhibitedexhibited exhibited byby thethe by thePVBPVB PVB 70-S70-S 70-S samplesample sample cancan can bebe explainedbeexplained explained byby by(1)(1) (1) thethe the higherhigher higher concentrationconcentration concentration ofof of SPFSPF SPF coco contentntentntent (the(the (the breakingbreaking breaking strengstreng strengththth ofof of fibersfibers fibers is is muchmuch greatergreater thanthanthan that thatthat of of theof thethe matrix), matrix),matrix), (2) the (2)(2) smaller thethe smallesmalle size ofrr SPFsizesize in ofof PVB, SPFSPF which inin PVB,PVB, limits whichwhich the stress limitslimits concentration thethe stressstress concentrationaroundconcentration the fiber aroundaround during thethe tensile fiberfiber loadingduringduring tensiletensile relative loadinloadin to thegg counterpart relativerelative toto thethe sample counterpartcounterpart with long samplesample SPF, and withwith (3) longlong the possibleSPF,SPF, andand attainment (3)(3) thethe possiblepossible of optimal attainmentattainment wetting ofof optimal foroptimal SPF on wettingwetting PVB in forfor this SPFSPF sample. onon PVBPVB inin thisthis sample.sample.

2.502.50

2.002.00 1.49 1.591.59 1.551.55 1.531.53 1.49 1.38 1.501.50 1.38 1.101.10 1.001.00

0.500.50 Average tensile stress Average tensile Average tensile stress Average tensile at maximum load (MPa) at maximum at maximum load (MPa) at maximum 0.000.00 PVBPVB 80-S80-S PVB PVB 80-L80-L PVB PVB 70-S70-S PVB PVB 70-L70-L PVB PVB 60-S60-S PVB PVB 60-L60-L SampleSample compositioncomposition

FigureFigure 5. 5. AverageAverage tensile tensile stress stress at at maximum maximum loadload ofof thethe compositecomposite samples.samplessamples..

InIn general, general, the the decrement decrement in in the the tensile tensile stress stress va valuevaluelue of of the the different didifferentfferent composites composites occurred occurred beyond beyond 30wt%3030wt% wt% SPFSPF SPF loading.loading. loading. ThisThis This trendtrend trend cancan can bebe attributedattributed be attributed toto thethe to influenceinfluence the influence ofof matrixmatrix of matrix discontinuitydiscontinuity discontinuity withwith risingrising with fillerrisingfiller contentcontent filler content inin thethe matrix,matrix, in the matrix,whichwhich resultedresulted which resulted inin poorpoor stressstress in poor transfertransfer stress fromfrom transfer thethe matrix frommatrix the toto the matrixthe fillerfiller to [20].[20]. the SimilarfillerSimilar [20 ].findingsfindings Similar findingswerewere reportedreported were reported elsewhereelsewhere elsewhere forfor thth forermoplasticermoplastic starch/silkstarch/silk starch/silk fiberfiber fiber compositescomposites composites [21],[21], [21], seaweed/polypropyleneseaweedseaweed//polypropylenecomposites compositescomposites [20 [20],[20],], pineapple pineapplepineapple leaf leafleaf fiber fiber/polyfiber/poly/polypropylenepropylenepropylene composites compositescomposites [22], and[22],[22], sugar andand palmsugarsugar fiberpalmpalm/ phenolic fiber/phenolicfiber/phenolic composites compositescomposites [23]. [23].[23]. Meanwhile, MeanMeanwhile,while, the thethe anomalous anomalousanomalous trend trendtrend exhibited exhibitedexhibited by byby the thethe PVB PVBPVB 6060 compositescomposites where where PVB PVB 60-S 60-S exhibited exhibited lesser lesser tens tensiletensileile stress stress than than the the PVBPVB 60-L60-L counterpartcounterpart can can bebe attributedattributed to to the the clustering clustering of of the the short-sized short-sized fibers fibersfibers due due to to the the high high surfacesurface area area ofof thethe particlesparticles andand thethe highhigh volumevolume fraction fraction of of SPFSPF inin PVB,PVB, thusthus promotingprpromotingomoting fiber-fiberfiber-fiberfiber-fiber interactionsinteractions andand thethe subsequentsubsequent defectivedefective strengtheningstrengtheningstrengthening of ofof the thethe composite. composite.composite. Moreover, MoreoverMoreover a,, similaraa similarsimilar finding findingfinding was waswas reported reportedreported by Facca byby FaccaFacca et al. etet [24 al.al.]. [24].[24].

3.1.3.3.1.3. TensileTensile StrainStrain

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 Figure 66 showsshows thatthat thethe greatergreater thethe proportionproportion ofof PVB,PVB, thethe higherhigher thethe tensiletensile strain. Based onon FigureFigure6 ,6, the the di differentfferent types types of of cut cu (longt (long and and short) short) influenced influenced the the tensile tensile strain strain of the of thesample sample where where the percentagesthe percentages of tensile of tensile strain stra forin PVB for 80-S,PVB PVB80-S, 70-S, PVB and 70-S, PVB and 60-S PVB were 60-S all were greater all greaterthan the than percentages the percentages of the tensile of the strain tensile of strain PVB 80-L, of PVB PVB 80-L, 70-L, PVB and 70-L, PVB 60-L.and PVB This 60-L. shows This that shows short thatcutSPF short has cut greater SPF has tensile greater strain tensile than strain the longthan cutthe SPF.long Thecut SPF. isotropic The isotropic behavior behavior is one of is the one reasons of the reasonsfor this. for this.

500

400 356.91 347.32 337.87 300.66 299.79 320.34 300

200

100 at maximum load (%) at maximum Average tensile strain Average tensile 0 PVB 80-SPVB 80-LPVB 70-SPVB 70-LPVB 60-SPVB 60-L Sample composition

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

3.2. Moisture Moisture Absorption For the development of reliable biocomposite mate materials,rials, low moisture absorption is an essential factor toto be be considered considered in thein the selection selection of natural of natu fibersral asfibers the reinforcingas the reinforcing material sincematerial high since absorption high willabsorption adversely will a ffadverselyect the dimensional affect the dimensional stability of thestability composite, of the especiallycomposite, in especially terms of mechanicalin terms of performance,mechanical performance, porosity formation, porosity and formation, water retention and water capacity retention [25,26 capacity]. Figure [25,26].7 shows Figure that PVB 7 shows 60-L thathas thePVB highest 60-L has water the highest uptake (andwater corresponding uptake (and corresponding percent increment) percent compared increment) to PVB compared 70-L and to PVB 70-L80-L, and which PVB are 80-L, 0.068 which g (2.32%), are 0.068 0.031 g g(2.32%), (1.04%), 0.031 and g 0.019 (1.04%), g (0.63%), and 0.019 respectively, g (0.63%), after respectively, 25 days (water after 25uptake days was(water calculated uptake was by subtractingcalculated by the subtracting weight of the weight sample of after the 25sample days after from 25 the days dry from weight). the Thisdry weight). phenomenon This phenomenon can be attributed can tobe the attributed addition to of the diff erentaddition amounts of different of PVB amounts and SPF. PVBof PVB has and the propertiesSPF. PVB has of good the properties water resistance, of good whereas water resistan SPF hasce, poor whereas water SPF resistance. has poor Hence, waterwith resistance. the increasing Hence, proportionwith the increasing of PVB, the proportion sample exhibited of PVB, a the lower sample amount exhibited of water a uptake, lower whereas,amount of as thewater proportion uptake, whereas,of SPF increased, as the proportion the samples of showed SPF increased, greater waterthe samples uptake dueshowed to the greater properties water of uptake SPF. Longer due to fibers the propertiestend to increase of SPF. the Longer percentage fibers of tend water to increase absorption. the percentage The rate of waterof water absorption absorption. is greatly The rate aff ofected water by absorptionthe specimen’s is greatly density affected and void by the volumes. specimen’s The density incorporation and void of volumes. long fibers The into incorporation the mix decreased of long workabilityfibers into the and mix increased decreased the workability void space. and Consequently, increased the the void longer space. the Consequently, fiber, the higher the is longer the water the fiber,absorption. the higher Hence, is the the water introduction absorption. of compatibilizers, Hence, the introduction coupling agents,of compatibilizers, or chemical treatmentcoupling agents, can go ora long chemical way toward treatment improving can go the a moisturelong way resistance toward ofimproving these composites the moisture [27]. resistance of these composites [27].

5.00 4.08 4.00

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

Polymers 2020, 12, x FOR PEER REVIEW 6 of 8

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 Figure 6, the different types of cut (long and short) influenced the tensile strain of the sample where the percentages of tensile strain for PVB 80-S, PVB 70-S, and PVB 60-S were all greater than the percentages of the tensile strain of PVB 80-L, PVB 70-L, and PVB 60-L. This shows that short cut SPF has greater tensile strain than the long cut SPF. The isotropic behavior is one of the reasons for this.

500

400 356.91 347.32 337.87 300.66 299.79 320.34 300

200

100 at maximum load (%) at maximum Average tensile strain Average tensile 0 PVB 80-SPVB 80-LPVB 70-SPVB 70-LPVB 60-SPVB 60-L Sample composition

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

3.2. Moisture Absorption For the development of reliable biocomposite materials, low moisture absorption is an essential factor to be considered in the selection of natural fibers as the reinforcing material since high absorption will adversely affect the dimensional stability of the composite, especially in terms of mechanical performance, porosity formation, and water retention capacity [25,26]. Figure 7 shows that PVB 60-L has the highest water uptake (and corresponding percent increment) compared to PVB 70-L and PVB 80-L, which are 0.068 g (2.32%), 0.031 g (1.04%), and 0.019 g (0.63%), respectively, after 25 days (water uptake was calculated by subtracting the weight of the sample after 25 days from the dry weight). This phenomenon can be attributed to the addition of different amounts of PVB and SPF. PVB has the properties of good water resistance, whereas SPF has poor water resistance. Hence, with the increasing proportion of PVB, the sample exhibited a lower amount of water uptake, whereas, as the proportion of SPF increased, the samples showed greater water uptake due to the 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, Polymersor chemical2020, 12 treatment, 1923 can go a long way toward improving the moisture resistance of these7 of 8 composites [27].

5.00 4.08 4.00

3.00 2.44 2.32 2.00 1.04 1.00 0.71 0.63 Water uptake (%) Water uptake 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.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 ICAM2E Conference, Langkawi, Malaysia. The study was part of the research project GP-IPS/9438714. Conflicts of Interest: The authors declare no conflict of interest.

References

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