Use of Almond Shells and Rice Husk as Fillers of Poly(Methyl Methacrylate)

12 Pages·2017·4.43 MB·English

materials
Article
Use of Almond Shells and Rice Husk as Fillers of
Poly(Methyl Methacrylate) (PMMA) Composites
AlessandraSabbatini1,SilviaLanari2,CarloSantulli3,*andClaudioPettinari1 ID
1 GeneralandInorganicChemistryUnit,SchoolofPharmacy,UniversitàdegliStudidiCamerino,
viaS.Agostino1,62032Camerino(MC),Italy;[email protected](A.S.);
[email protected](C.P.)
2 TeucoS.p.A.,viaVirgilioGuzzini2,62010Montelupone(MC),Italy;[email protected]
3 SchoolofArchitectureandDesign,UniversitàdegliStudidiCamerino,vialedellaRimembranza,
63100AscoliPiceno,Italy
* Correspondence:[email protected];Tel.:[phone]
Received:6June2017;Accepted:15July2017;Published:28July2017
Abstract: Inrecentyears,woodfibreshaveoftenbeenappliedasthereinforcementofthermoplastic
materials,suchaspolypropylene,whereastheiruseincombinationwiththermosettingresinhas
beenlesswidespread. ThisstudyconcernstheproductionofPMMA-basedcompositesbypartly
replacingaluminatrihydrate(ATH)withwoodwastefillers,namelyricehusksandalmondshells,
whichwouldotherwisebedisposedbyincineration. Theamountoffillerintroducedwaslimited
to10%asregardsricehusksand10or15%almondshells,sinceindicationsprovidedbyreactivity
testsandviscositymeasurementsdidnotsuggestthefeasibilityoftotalreplacementofATH.Asa
matteroffact,theintroductionofthesecontentsofwoodwastefillerinPMMA-basedcompositedid
notresultinanysignificantdeteriorationofitsmechanicalproperties(Charpyimpact,RockwellM
hardnessandflexuralperformance).Somereductionofthesepropertieswasonlyobservedinthecase
ofintroductionof15%almondshells. Afurtherissueconcernedtheyellowingoftheorganicfiller
underexposuretoUVlight. Ontheotherhand,averylimitedamountofwaterwasabsorbed,never
exceedingvaluesaround0.6%,despitethesignificantporosityrevealedbythefiller’smicroscopic
evaluation. Theseresultsareparticularlyinterestinginviewoftheapplicationenvisagedforthese
composites,i.e.,woodreplacementboards.
Keywords: PMMA;almondshells;ricehusk;mechanicalcharacterization;viscositymeasurements
1. Introduction
Inrecentyears,disposingofagro-wasteinwaysotherthanincinerationorlandfillinghasoften
beenconsidered. Inparticular, whenagro-wastearewood-likematerials, hencewithasignificant
lignincontent,theymaybeintroducedinamaterial(mostofteninpolymers)andmodify,hopefullyin
apositivesense,itsmechanicalandstructuralperformance.
Asregardsthematerialsthatareconsideredinthisstudy,ricehullshavebeenproposedasthe
fillerforcement-basedcomposites[1]. Ricehullscanbeconsideredasroughlyformedbyaround
40wt%cellulose,30wt%lignin,20wt%silicaand10wt%othercomponents[2]. Thecombined
presenceofligninandsilicaintheporousstructureofricehullsshowspotentialforexampleforthe
decontaminationofenvironmentalobjects[3],whileontheotherhandprovidingsignificantinterest
in terms of offering an increased hardness and tear strength to a polymer matrix [4]. It is worth
considering though that an increase of properties by the introduction of rice husk in materials is
generallyobtainedthroughtheextensiveuseofmodifications,suchasgrafting[5]orapplicationof
foamingagents[6]. Aworkonpoly(methylmethacrylate)withricehuskreportedtheapplicationofa
treatmentwithtriphenylphosphine[7].
Materials2017,10,872;doi:10.3390/ma10080872 www.mdpi.com/journal/materials
Materials2017,10,872 2of12
Incontrast,almondshellsarecomposedofa37wt%ofcellulose,32wt%hemicellulose,27wt%
ofligninand4wt%ofothercomponents[8]. Moststudiesareaimedthereforeattheirpyrolysis,in
somecasesdiscussingalsotheenzymaticdigestibilityoftheircellulosecontent[9]. However,attempts
inthesenseoftheirre-useasfillerinmaterialshavebeenlimitedsofar. Itispromisingthoughthat
theirintroductioninamountsupto30wt%inapolypropylenematrixwithouttreatmentimproved
the stiffness of the composite by over 50%, demonstrating also a sufficient compatibility with the
matrixandincreasingthetemperaturesfortheonsetofthermaldecomposition[10]. Anotherstudy
concerned their introduction in a biodegradable polymer, such as polylactic acid (PLA), in which
caseitwasinterestinglysuggestedthatthermaldecompositionbehaviourofalmondshelldoesnot
substantiallydependonthealmondvariety,whichmeansthatinherentvariabilityoftheagro-waste
fillerdoesnotresultinsignificantlyaffectinginjectability[11].
This study is aimed at evaluating the introduction of the above fillers, namely rice husk and
almond shells, to compare their effectiveness in partly replacing alumina trihydrate (ATH) in
poly(methyl methacrylate) matrix (PMMA). This is a common practice when PMMA is used as
areplacementmaterialforwood, whichmayforexampleimproveitsfatigueperformance[12]or
compensateforitsratherpoordeformabilityandprocessability[13]. Thishasaparticularsignificance,
since ATH derives from the industrial treatment of bauxite (a mineral obtained by mining) with
sodium hydroxide at 270 ◦C [14], and also because the introduction of fillers, such as rice husk or
almondshells,doesresultinsomeweightreduction(ATHdensityisaround2.4,againstaround0.6for
almondshells[15]andaround0.55forricehusk[16]). Theobjectivewouldalsobesomecostreduction,
consideringthatATH,whenorderedonlargescale,hasamarketpriceintheorderof1000Eurosper
ton,whilealmondshellsorricehuskwouldcomefromthefoodprocessingsystematbasicallynocost.
Themainquestionandhencetheobjectiveofthisworkistoelucidatewhetherthisadditiondoesnot
compromiseprocessingandmechanicalperformance,sotoallowtheapplicationofthePMMA-based
materialasawoodreplacementboard.
2. Experimental
2.1. PreliminaryWork: ReactivityTests
Theexothermicpolymerizationwasrecordedbyathermocoupledatalogger,PicoLogD-08,on
thereferencematerial(Duralight® PMMA)andonthematerialwithaddedfillers,groundalmond
shellswithgranulometries0–180µm,180–400µmand0–400µmandricehuskwithgranulometry
0–400µm,inamountsfrom5to20%. Thethermocoupleispositionedinthecentreofthepotwhich
containstheslurry. Dataloggingisstartedwhenthethermocoupleisimmersedintheslurryand
the time is counted starting from the addition of the last catalyst. The acquisitions are performed
every5sandtheregistrationisstoppedwhenthepolymerizationtemperaturebecomeslowerthan
75◦C.Theoptimalformulationsarethosehavingtheexothermicpeakinthetimerange1200(±200)
s, characteristicofDuralight® with62wt%filler, arangewhichishighlightedbyverticallinesin
Figure1.
Materials2017,10,872 3of12
Materials 2017, 10, 872 3 of 12

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Materials2017,10,872 4of12
Table1.Viscositymeasurements(atatemperatureof21±2◦C)fordifferentfillersandamounts.
RiceHusk Viscosity(cPs) Temperature %Torque %Torque
Spindle
0–400µm 2RPM 4RPM 10RPM (◦C) min max
5% LV3 8578 8458 8182 20.6 14.3 68.2
10% LV4 14397 13197 12297 19.0 4.8 20.5 F1
15% LV4 30293 26994 22255 20.1 10.1 37.1
20% LV4 48889 37342 29813 21.5 16.3 49.7
AlmondShell Viscosity(cPs) Temperature %Torque %Torque
Spindle
0–180µm 2RPM 4RPM 10RPM (◦C) min max
5% LV4 15597 14097 12237 20.5 5.2 20.4
10% LV4 29394 24745 20576 19.7 9.8 34.3 F2
15% LV4 58487 46640 35272 21.2 19.5 58.8
20% LV4 107377 84731 n.d. 21.4 35.8 56.5
AlmondShell Viscosity(cPs) Temperature %Torque %Torque
Spindle
0–400µm 2RPM 4RPM 10RPM (◦C) min max
5% LV3 10138 9298 8146 21.5 16.9 67.9
10% LV3 14217 12927 11313 22.3 23.7 94.3 F3
15% LV4 25195 21145 17156 22.1 8.4 28.6
20% LV4 32093 27864 23694 21.3 10.7 39.5
AlmondShell Viscosity(cPs) Temperature %Torque %Torque
Spindle
180–400µm 2RPM 4RPM 10RPM (◦C) min max
5% LV3 9778 9088 8182 20.4 16.3 68.2
10% LV3 9538 8728 8254 20.3 15.9 68.8
15% LV3 12777 10888 9586 20.8 21.3 79.9 F4
20% LV4 12597 10798 9478 22.1 4.2 15.8
Table2.Compositionofthefourmaterialformulationsproduced.
Component F1(%) F2(%) F3(%) F4(%)
Acrylicresin 36.35 36.35 36.35 36.35
Pre-treatedATH(20µmgrade) 52 52 47 52
Ricehusk0–400µm 10
Almondshell(0–180µm) 10 5
Almondshell(180–400µm) 15 5
Peroxide 0.45 0.45 0.45 0.45
Accelerator 0.2 0.2 0.2 0.2
Activator 1 1 1 1
2.4. MechanicalTests
ThreepointflexuraltestsaccordingtoUNIENISO178standardwereperformedusingaGaldabini
Quasar 10 dynamometer (Galdabini, Cardano al Campo (VA), Italy). After an automatic pre-load
of 2 N, the load was applied in displacement control mode and employing a cross-head speed of
2 mm/min on specimens with dimensions 180 mm length, 15 ± 0.5 mm width and 9.5 ± 0.5 mm
thickness. Thespanlengthusedwas160mm.
Hardnessmeasurement(RockwelltypeM)wasperformedusinganOMAG206RTDdurometer
(CasavolaMacchineUtensiliS.p.A.,CiniselloBalsamo(MI),Italy)accordingtoUNIENISO2039-2
standard. Afterapre-loadof98.07N±2%,aloadof980.70N±2%wasappliedonspecimenswith
minimumthicknessof6mm.
Materials2017,10,872 5of12
Charpy impact tests were performed according to UNI EN ISO 179-1 standard, using an
“ImpactPlast”Galdabini(Galdabini, CardanoalCampo(VA),Italy)pendulumwithenergyof1J,
paralleltothethickness,onunnotchedspecimenswithminimumlengthof80±2mm,minimum
widthof10.0±0.2mmandminimumthicknessof4.0±0.2mm. Thespanlengthwas62mm.
2.5. UVResistance
UVresistanceatdryconditionswasexaminedbyexposureofthesamplesurfacetonineOSRAM
Ultra-Vitalux 300 Wlamps (OSRAM SpA, Milano, Italy). The changein colour to beattributed to
UV weathering was evaluated using an X-Rite Ci62 colorimeter (X-Rite, Grand Rapids, MI, USA)
after 250 and 500 h of exposure. In particular, the CIE/Lab L*a*b colour space tristimulus values
and related quantities allows eliminating subjectivity in colour perceptions and colour difference
judgments[18]. IntheL*a*b*diagram,asphericalcoloursolid,L*indicateslightness,anda*andb*are
thechromaticitycoordinates. Here,a*andb*indicatecolourdirections(+a*isthereddirection,−a*is
thegreendirectionwhile+b*istheyellowdirectionandthe−b*isthebluedirection). Bycomparing
measurementsoftargetcolourswithsamplespecimens,itispossibletoexpressthenatureofacolour
differencebetweentwomeasuredspecimens.
2.6. ResistancetoWater
Teststoevaluatetheresistancetoboilingwater(immersionfor2h)andtosteam(exposurefor
1.5h)wereperformedbyusinganSBFALCthermostaticbath(FALCINSTRUMENTSSRL,Treviglio
(BG),Italy)at100◦C,measuringonceagaincolourvariationwithanX-RiteCi62colorimeter(X-Rite,
GrandRapids,MI,USA).
WaterabsorptionmeasurementswerecarriedoutaccordingtoUNIENISO62standardandthe
samplemasswasmeasuredusinganOrmaEB200Sanalyticbalance(OrmaSrl,Milano,Italy).
2.7. ScanningElectronMicroscopy
Scanningelectronmicroscopy(SEM)fortheobservationofsectionedsampleswascarriedout
usingaCambridgeStereoscanS260microscope(CAMBRIDGESCIENTIFICPRODUCTS,Watertown,
MA,USA).Toallowtheirobservation,thesamplesweregoldcoated.
3. Results
TheMMApolymerizationisafreeradicalreaction,characterizedbyanexothermicpeakduring
theprocess. Theamountoffillerintroducedintheformulationinfluencestheexothermicpeakbothin
timeandtemperature.Thestudyofthepolymerizationcurveisnecessarytoestablishtherightamount
oforganicfillerthatcanbeintroducedintheformulationtoreplaceATH,avoidingmodificationsin
theexothermiccurvecomparedtothatofDuralight®. Infact,alowertemperaturepeakand/oradelay
resultinanincompletereactioninthematerialand,asaconsequence,thepresenceofahigherporosity
andthereforepossiblyhigherabsorptionofliquidsandlowerphysicalandmechanicalproperties,
whichiswellknownonPMMA[19,20]. Fromthetemperaturevs. timecurvesreportedinFigure1the
followingevidencescanbeoutlined:
(1) Keepingconstantthecatalystsamount,thecomparisonofthericehuskexothermicpeakswith
thestandardDuralight®,makesvisiblethatthereactivitypeakobtainedwith5and10%ofrice
huskislocatedinthereactivityrangeofDuralight®. Inordertosubstitutethehighestamountof
ATHwiththeorganicfiller,thereferenceformulationcontainsa10%ofricehusk.
(2) Acomparisonofthealmondshell(0–180µm)dispersionexothermicpeakswiththestandard
Duralight®, makes visible that the reactivity peak is not reached in the reactivity range of
Duralight®. Concerningthetemperature,thecompliantformulationsarethosecontaining5and
10%ofalmondshell(0–180µm)replacingATHfiller. Hence,thereferenceformulationcontains
10%ofalmondshells(0–180µm).
Materials2017,10,872 6of12
Materials 2017, 10, 872 6 of 12
(3) Acomparisonofthealmondshell(180–400µm)dispersionexothermicpeakswiththestandard
Duralight®,makesvisiblethatallthereactivitypeaksarecompliantintimeandtemperature.
The reference formulation will contain 15% of almond shells, instead of the 20%, which itself
Thereferenceformulationwillcontain15%ofalmondshells,insteadofthe20%,whichitself
complies to Duralight® standard, because the dispersion with 20% of almond shell has a highly
compliestoDuralight® standard,becausethedispersionwith20%ofalmondshellhasahighly
variable viscosity and therefore is likely to have not very consistent properties. This fact can
variable viscosity and therefore is likely to have not very consistent properties. This fact can
bring to formation of defects during the sheets production (i.e., air bubbles) leading to invalid
bringtoformationofdefectsduringthesheetsproduction(i.e.,airbubbles)leadingtoinvalid
mechanical characterization.
mechanicalcharacterization.
(4) A comparison of the almond shell (0–400 μm) dispersion exothermic peaks with the standard
(4) Acomparisonofthealmondshell(0–400µm)dispersionexothermicpeakswiththestandard
Duralight®, makes visible that the reactivity peaks obtained with 5, 10 and 15% of almond shells
Duralight®,makesvisiblethatthereactivitypeaksobtainedwith5,10and15%ofalmondshells
(0–400 μm) are compliant in time and temperature. The reference formulation will contain 10%
(0–400µm)arecompliantintimeandtemperature. Thereferenceformulationwillcontain10%
of almond shells, instead of the 15 or 20%, which themselves comply to Duralight® standard,
ofalmondshells,insteadofthe15or20%,whichthemselvescomplytoDuralight® standard,
because the dispersions have high viscosity.
becausethedispersionshavehighviscosity.
The viscosity measurements of all formulations are reported in Table 1 and show generally a
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Materials2017,10,872 7of12
Materials 2017, 10, 872 7 of 12
Materials 2017, 10, 872 7 of 12
Materials 2017, 10, 872 7 of 12

FFiigguurree 33.. FFlleexxuurraall mmoodduulluuss rreessuullttss..
Figure 3. Flexural modulus results.
Figure 3. Flexural modulus results.

Figure 4. Charpy impact results.
FFFiiiggguuurrreee 444... CCChhhaaarrrpppyyy iiimmmpppaaacccttt rrreeesssuuullltttsss...

Figure 5. Rockwell hardness results.
Figure 5. Rockwell hardness results.
FFiigguurree 55.. RRoocckkwweellll hhaarrddnneessss rreessuullttss..
Samples exposed to UV light show a yellowing of the organic filler, in particular in the case of
Samples exposed to UV light show a yellowing of the organic filler, in particular in the case of
rice hSuamskp, lhese necxep ofoser dF t1o fUorVm luiglahtti osnh,o ww hae yree lalo wpoinsigti voef tΔheb odragtaan iisc foibllseerr, vine dp, aarsti cfurolamr iTna tbhlee c3a.s eT hoef
rice Shaumskp,l ehseenxcpeo fsoerd Fto1 UfoVrmliguhlattsihonow, wahyeerlelo aw ipnogsiotfivthe eΔobr gdaantiac fiisll eorb,sinerpvaerdti,c ausla frrionmth Teacbalsee 3o.f rTihcee
hryyiueecleslllk ooh,wwuhiiesnnkngg,c epphrferooonrccceeeFss 1ssf ofiiosrs r nnFmaa1utt uufloarratraimllo ffnuoo,lrraw wwtihoooenoor,edd w ammhpaaeottrseeeirrt iiiaaav llessp ∆oeexsxbipptdioovasseteea ddΔi stbtoo o dbUUasVVtear bvbieeesccd aoa,uubasssseeef r roovoffem tdthh,T eeaa oosb xxlfeiirddo3aam.ttiTio ohTnnea rrbyeeleaaelcc lto3tii.woo nTnin h oogeff
ytheell ocwelilnuglo psero. cTehsse isp hnoattoulryasl ifso rr ewacotoiodn m inatveorlivaless etxhpeo sperdim toa rUyV h byedcraouxsyel ogfr tohuep o xoind atthioe nC r6e aacntido nt hoef
pthroec ecseslliuslonsaetu. rTahlefo rpwhootoodlymsisa tereriaacltsioenxp ionsveodlvtoesU tVheb epcraiumsearoyf thhyedorxoixdyalt igonroruepa ctoinon thofe thCe6 cealnludl otshee.
tsheec ocnedllaurlyo shey. dTrhoex ypl hgortooulypssi so nre athctei oCn2 inavnodl vCe3s othf et hper icmelalruyl ohsey dmrooxleycl uglerso.u Tph oesne trheea cCti6o nasn dca uthsee
Tsehceopnhdoatroyl yhsyisdrreoaxcytli ognrionuvposl voens tthhee pCri2m aanrdy hCy3d roofx tyhleg rcoeullpuloonset hmeoCl6ecaunldest. hTehseesceo nrdeaacrtyiohnysd croaxuysel
sdeacroknednainryg haynddr oyxeylllo gwrionugp sp hoenn othme eCno2n a n[2d3 ]C. 3I no ft hthe ec acesell uolof sael mmoonledc uslhees.l lsT, hFes2e, Fre3a catniodn sF 4c,a uthsee
gdraorukpensionng thaendC 2yaenlldowCi3nogf pthheenceolmluelonsoenm [o2l3e]c. uIlne s.thTeh ecsaesere aocf tiaolnmsocnadu seshdeallrsk, eFn2in, gFa3n danyde llFo4w, itnhge
dyealrlkoewniinngg eafnfedc t yise llleosws icnogn spishteennot,m pernoobnab l[y2 3d].u eIn t ot hthee claoswe eor fc oanlmteonnt do f scheelllulsl,o sFe2 a, nFd3 toan tdh eF d4a, rtkheer
pyheellnoowminegn oenffe[2ct3 ]i.s Ilnestsh ecocnassiestoefnat,l mproonbdabshlye ldlsu,eF 2to, Fth3ea nlodwFe4r, cthonetyeenltl oowf icneglluelfofescet aisndle stos ctohne sdisatreknetr,
yineiltlioawl cinolgo uefrf eocft t hise lseasms cpolness.i stent, probably due to the lower content of cellulose and to the darker
pinroitbiaalb clyoldouuer otof tthhee sloawmeprlecso.n tentofcelluloseandtothedarkerinitialcolourofthesamples.
i nitial colour of the samples.
Materials2017,10,872 8of12
Table3.ColourchangeduetoUVweathering.
Materials 2017, 10, 872 8 of 12
Exposure F1 F2 F3 F4
Table 3. Colour change due to UV weathering.
∆L 0.86 −0.47 0.54 0.51
Exposure ∆a F−10.16 F02.14 −F03.61 −0F.348
250h L∆ b 0.816. 24 −−0.04.72 8 00..5724 −00..4551
∆E 1.52 0.56 1.08 0.78
a −0.16 0.14 −0.61 −0.38
250 h
b∆ L 1.214. 70 −−0.02.82 5 01..7642 1−.801.45
E∆ a 1.−520 .20 0.05.64 6 −11.0.183 −00..7768
500h L∆ b 1.710. 21 −00.2.253 −10.6.440 −01..7811
∆E 2.10 0.57 2.03 2.08
a −0.20 0.46 −1.13 −0.76
500 h
b 1.21 0.23 −0.40 −0.71
On the other hand, samplestEes ted in2.1b0o iling w0.5a7t er (2 h2).0a3n d in c2o.n08ta ct with steam (1.5 h)
showaseriouschangeincolourrelativetothestandardsamples,whichareinherentlytranslucent:
On the other hand, samples tested in boiling water (2 h) and in contact with steam (1.5 h) show
aglobalrepresentationofthecolourofsamplesinthedifferentconditionsisreportedinFigure6a–d.
a serious change in colour relative to the standard samples, which are inherently translucent: a
In particular, a whitening process is more likely to be observed. The likely explanation of this
global representation of the colour of samples in the different conditions is reported in Figure 6a–d.
phenomenonisthatmicro-fissuresareformedbetweenthepolymericmatrixandtheinorganicand
In particular, a whitening process is more likely to be observed. The likely explanation of this
organpihcefinlolemrse:nothni sisp thhaetn momicreon-ofinssuhraess baeree nfofrrmeqeud ebnettlwyeoebns tehrev pedolyinmtehriec imntaetrraixc tainodn tbheet winoeergnaPniMc aMndA and
ATHoforgraenxica mfilplelres:i nthairsc phhiteencotmureanlopna hnaesls b[e2e4n] .frIenqtuheentplyre osbensetrcvaesde ,ind ethsep iitnetetrhaectcioonm bpeotwsiteeens uPrMfaMceAb eing
slightalnydr oAuTgHh ,fonro efixlalmerplloes isnh aarschbieteecntudrealt epcatnedelsi n[2a4n].y Ins athmep pleressuenntd cearseth, deeasgpeitien gthceo cnodmitpioosnitsei nsuvrefsatcieg ated.
Furthbeerimngo srleig,hthtley aromuoguh,n ntoo ffiwlleor oldossfi lhleasr bineterno ddeutceectdedd oine sanreys sualmtipnletsh uenadbesro trhpet iaogneinogf jcuosntdaitimonins imal
investigated. Furthermore, the amount of wood filler introduced does result in the absorption of just
amountofwater(Figure7).
a minimal amount of water (Figure 7).
(a)
(b)
(c)
Figure6.Cont.
Materials2017,10,872 9of12
Materials 2017, 10, 872 9 of 12
Materials 2017, 10, 872 9 of 12
(d)
(d)
Figure 6. (a) Colour change due to ageing in formulation F1; (b) Colour change due to ageing in
FFiigguurree 66.. ((aa)) CCoolloouurr cchhaannggee dduuee ttoo aaggeeiinngg iinn ffoorrmmuullaattiioonn FF11;; ((bb)) CCoolloouurr cchhaannggee dduuee ttoo aaggeeiinngg iinn
formulation F2; (c) Colour change due to ageing in formulation F3; (d) Colour change due to ageing
ffoorrmmuiunll aafottirioomnnu FlFa22t;i;o ((cnc) )FC C4o. ololouurrc chhaannggeed duueet otoa gaegienigngin info fromrmulualtaiotinonF 3F;3(;d ()dC) oClooulorucrh cahnagnegdeu deutoe atog eaignegining
fionr fmorumlautiloantioFn4 .F4.

Figure 7. Absorbed water after immersion at ambient temperature.

SEM observations were conducted in order to study the interaction existence between the
FFiigguurree 77.. AAbbssoorrbbeedd wwaatteerr aafftteerr iimmmmeerrssiioonn aatt aammbbiieenntt tteemmppeerraattuurree..
polymeric matrix and the organic filler. In the case of rice husk, it is possible to observe that the filler
has a tubular structure and it is disposed linearly (Figure 8a) or in bundles (Figure 8b). The rice husk
SEM observations were conducted in order to study the interaction existence between the
SfiElleMr iso vbesreyr vwaetlilo wnsrapwpeerde inco tnhed upocltyemdeirnic omradterirx teovesnt uifd, yin tshoemein ctaesreasc, tai odnetaecxhimsteenntc ies dbeettewcteeedn the
polymeric matrix and the organic filler. In the case of rice husk, it is possible to observe that the filler
polym(Feigruicrem 8ac)t.r Tixhiasn cdant hbee eoxrpglaaniniecdfi blyle trh.eI nfactth seomcaes ewoeafkr iicneterhauctsiko,nsit aiss hpyodsrsoigbelne btoonodbs seexrivste, bthuat t the
has a tubular structure and it is disposed linearly (Figure 8a) or in bundles (Figure 8b). The rice husk
fillerthhaersea ist unbout laa rresatcrtuiocntu breetawnedeni tthise dmisaptroixs eadndli ntheea rfliylle(rF wighuirceh 8caa)n ocrreinateb ua nsdtrloensg( Fcihgeumrieca8lb b).onTdh.e rice
hfiullsekrH fiisol lwvereerivsye vrw,e trehylelw rwee irlsal pwnopr eaedpvp idiened ntchinee tophf oeflipylloemrly epmraicret rimcicleamst rcailxter aeixrvlyee vnpe uinfl,li ifinn,gi n soosumot meo fec tachsaees sem,s a,ata rdidxee,t taiancc hchmomneternnatts tii ssw dditeehtt eecctteedd
(Figuwreh a8tc i)n. dTichaitse dca bny bae p erxevpiloauins esdtu dbyy othn ep ofalycpt rsoopmylee nwe/eraicke ihnutsekr accotmiopnoss iatess h [y25d]r: othgiesn c obuolndd asls eox biset , but
(Figure8c).Thiscanbeexplainedbythefactsomeweakinteractionsashydrogenbondsexist,butthere
therea titsr inbuotte ad troe athceti olonw bere tawmeoeunn tt hofe f imlleart rinixtr oadnudc etdh ein f iolulerr c awseh.i Achs ac acnon csreeqauteen ace ,s tthroen cgo mchpoesmitiec haal sb ond.
isnotareactionbetweenthematrixandthefillerwhichcancreateastrongchemicalbond. However,
Howae vheert,e trhogeeren eiosu ns om eovripdheonlcoeg yo fw fihlilcehr pisa rrteicslpeosn cslibealer lyfo rp uthllein gd eocrueta soefd t hme emchaatnriicxa,l inp rcoopnetrrtiaesst, with
thereisnoevidenceoffillerparticlesclearlypullingoutofthematrix,incontrastwithwhatindicated
whatc oinmdpiacraetded to b tyh ea D purreavliigohut®s vsatuludeys. oCno npvoelryseplryo, piny tlheen eca/rsiec oe fh aulmsko ncdo mshpelolss,i tite iss [p2o5s]s: ibthlei st oc oobusledr vael so be
byapreviousstudyonpolypropylene/ricehuskcomposites[25]: thiscouldalsobeattributedtothe
that the filler has a honeycomb (Figure 9a) and tubular structure (Figure 9b). The almond shells are
attributed to the lower amount of filler introduced in our case. As a consequence, the composite has
loweramountoffillerintroducedinourcase. Asaconsequence,thecompositehasaheterogeneous
well covered by the polymeric matrix, but a neat separation is observed at the interface between the
ma ohrpemtheaortlorogigxe ynawenodhu itsch hem isfoirlrleepsrph oo(Fnliosggiubyrle e wf9ochr).i tchAhe s disfeo crrr eerasicpseeo dnhsmuisbeklc,e h iatfsno irdc aettlahpcehr omdpeeenrcttr ieefarsos,mecdo m thmpea ermcehadatrntioxic tahclre eaDptreuosr paael irgthiets®,
compared to the Duralight® values. Conversely, in the case of almond shells, it is possible to observe
valuehse.tCeroongveneresoeulsy ,stirnutchtuercea, swehoicfha limn tounrnd dshecerlelsa,seits itshpe omsescibhlaentiocaol bresseirsvtaentchea, atnthde infi tlhleirs chaasse aa hcloenareeyrc omb
that the filler has a honeycomb (Figure 9a) and tubular structure (Figure 9b). The almond shells are
(Figupruel9l-ao)uta nisd otbusbeurvlaabrlset rthuacntu irte w(Fasig tuhree c9abse). fTorh ericaelm hounskd. sShomelels oacrceuwrreenllcec oovf epruedll-obuyt thhaes pboeleynm eric
mwaetllr iecxxo,pvbleauritneeadd nb ebyay tt htsheee pp afoarlacyttm iothenartii cst moheba stterhriexvr,em bdouapttl aats hntiece ainut tsseeerdpf aaicsre antbiooett nwa i esc eoonmbtspheaertvimbeidlaiz tareitdx t haoenn dei,n ttsheuercfhfia cllaees r bm(eFtawilgeeuicer ne 9thc)e.
matraixn haynddri dteh ep ofliyllperro p(yFliegnuer e( M9Ac)P. PA), sw fhoirc hr iacse ah umsakt,t eirt so fd efatactc hpmroevnidt efdr obmet tethr ep rmopaetrritxie sc rfeoar tes a
As for rice husk, its detachment from the matrix creates a heterogeneous structure, which in turn
heterwogooedn-epolausst isct rcuomctpuorsei,t ews h[2ic6h]. iOnn t uthren odthecerr ehaasneds, tahpep mliceactihoann oicf aglr roeusnidst aalnmceo,n adn sdh eilnls t hasi sb cioa-swe aas tcel earer
decreasesthemechanicalresistance,andinthiscaseaclearerpull-outisobservablethanitwasthecase
pull-roeusot uirsc eo bins ethrverambloes etthtianng (iet. gw., ausr etah-efo rcmasaeld feohry dreic) ep ohluymske.r Spoamneels ofocrc uwroreond cree polaf cpemuleln-ot uptr ohvaesd been
forricehusk. Someoccurrenceofpull-outhasbeenexplainedbythefactthatthethermoplasticusedis
effective [27]: yet the matrix is not recyclable in that case, while both PMMA and MAPP would be. In
explained by the fact that the thermoplastic used is not a compatibilized one, such as maleic
notacompatibilizedone,suchasmaleicanhydridepolypropylene(MAPP),whichasamatteroffact
general terms, the introduction of fillers, as rice husk and almond shells, would be regarded as
anhydride polypropylene (MAPP), which as a matter of fact provided better properties for
providedbetterpropertiesforwood-plasticcomposites[26]. Ontheotherhand,applicationofground
possible and a viable option in production of PMMA polymer panels, although some caution would
wood-plastic composites [26]. On the other hand, application of ground almond shells as bio-waste
almobned nsehedelelds ians tberiom-sw oafs itnecrreeassoinugrc teheinir tahmeorumnotss eatbtoinvge 1(0e%.g,. ,inu rtheaat- ftohrism waoldueldh pyodses)ibplyo lcyommeprropmainsee lsfor
resource in thermosetting (e.g., urea-formaldehyde) polymer panels for wood replacement proved
woodmraetpelraiacle pmroednutcptrioonv.e deffective[27]:yetthematrixisnotrecyclableinthatcase,whilebothPMMA
effective [27]: yet the matrix is not recyclable in that case, while both PMMA and MAPP would be. In
andMAPPwouldbe. Ingeneralterms, theintroductionoffillers, asricehuskandalmondshells,
general terms, the introduction of fillers, as rice husk and almond shells, would be regarded as
woul dberegardedaspossibleandaviableoptioninproductionofPMMApolymerpanels,although
possible and a viable option in production of PMMA polymer panels, although some caution would
somecautionwouldbeneededintermsofincreasingtheiramountsabove10%,inthatthiswould
be needed in terms of increasing their amounts above 10%, in that this would possibly compromise
possiblycompromisematerialproduction.
material production.
Materials2017,10,872 10of12
Materials 2017, 10, 872 10 of 12
Materials 2017, 10, 872 10 of 12

(a) (b) (c)
(a) (b) (c)
Figure 8. (a–c) SEM micrographs showing the interaction of rice husk within the poly(methyl methacrylate)
Figure 8. (a–c) SEM micrographs showing the interaction of rice husk within the poly(methyl
mFiagturriex -8 a. l(ua–mc)i nSaE Mtri hmyicdrroagtrea (pPhMs sMhoAw-AinTgH th)e m inatterriaxc. tion of rice husk within the poly(methyl methacrylate)
methacrylate)matrix-aluminatrihydrate(PMMA-ATH)matrix.
matrix- alumina trihydrate (PMMA-ATH) matrix.

(a) (b) (c)
(a) (b) (c)
Figure 9. (a–c) SEM micrographs showing the interaction of almond ground shells within the
FPFiMigguuMrreAe -99A.. T((Haa–– mcc)) aStSrEEixMM. mmiiccrrooggrraapphhss sshhoowwiinngg tthhee iinntteerraaccttiioonn ooff aallmmoonndd ggrroouunndd sshheellllss wwiitthhiinn tthhee
PMMA-ATH matrix.
PMMA-ATHmatrix.
4. Conclusions
4. Conclusions
4. CoTnhcleu rseipolnascement of ATH filler in PMMA-based composite materials by organic bio-waste filler,
in paTrthiceu rleapr laricceem heunstk o fo rA aTlHm ofinllde rs ihne PllsM, Mis Ap-obsassibelde cuopm tpoo asinte a mmaotuenrita losf b1y5 %or gina nwice bigioh-tw. Hasotew feivlleerr,,
ThereplacementofATHfillerinPMMA-basedcompositematerialsbyorganicbio-wastefiller,in
rinea pcharintigc uelfafer crtiicvee hreussukl tos rw aolmulodn dde psheenldls f, riosm p othssei bmleo rupph otolo agny aanmdo tuhnet doifs t1r5ib%u tiino nw oefi gthhet .f iHlleorw ietsveelrf,,
particularricehuskoralmondshells,ispossibleuptoanamountof15%inweight. However,reaching
orebavcihoiunsgly e fwfeicthti vmeo rrees ucrltitsi cwaoliutyld t hdee pheignhde frr iotms a tmheo umnot.r p hology and the distribution of the filler itself,
effectiveresultswoulddependfromthemorphologyandthedistributionofthefilleritself,obviously
obvioAufstelyr awniathly msinorge t chrei triecasulilttys ,t hite c hanig bhee rc oitns calmudoeudn tth. a t:
withmorecriticalitythehigheritsamount.
AAlflt ethr ea naaglryicsuinltgu trhael wreassutlet sf,i lilte cra anll boew cso tnhcel updoelydm thearitz: ation of the composite materials.
Afteranalysingtheresults,itcanbeconcludedthat:
TAhlle t hlaeb aogrraitcourlytu srhale ewt ahstaes figlloeord a lmlowecsh tahneic paol lpymroepreizrtaiteiso nc oomf tphaer ecodm top oDsiuter amliagthetr®i aslsta. ndard, in
Alltheagriculturalwastefillerallowsthepolymerizationofthecompositematerials.
partiTcTuhhleea rll aanbbooo rrraaettaoolr ryyp usslhhl-eeoeeuttt h hiasas so gbgosooeorddv emmde efccrhhoaamnni ictcahalel ppmrroaoptpreierxrt tiiaeenssd cc ootmhmep pdaarerecedrde tatosoe D Diunur rafalleliigxguhhrtt®a®l ,s stitamannpddaaacrrtdd a,, niindn
hpaarrdtincueslas rp nroop reeratile sp uisl lf-aoru ftr oism o bbesienrgv ecdri tfircoaml. the matrix and the decrease in flexural, impact and
particular no real pull-out is observed from the matrix and the decrease in flexural, impact and
hardTneesssts p irno bpoeirltiinegs iws afaterr f raonmd ibne icnogn tcarcitti cwailt.h steam reveal some incompatibility of the acrylic resin
hardnesspropertiesisfarfrombeingcritical.
with Tthees tfsi lilne rbso, wilihnigc hw laetaedr sa tnod s ionm ceo ncrtiatcict awl iwthh istteenaimng r eevffeeaclt .s Tomhee U inVc oemxppoastuibriel isthyo owf sth ae yaeclrlyolwici nregs oinf
Testsinboilingwaterandincontactwithsteamrevealsomeincompatibilityoftheacrylicresin
twhiet ho rtghaen fiicll erersc,y wclhedic hfi llleeards,s n taom soemlye i nc rtihtiec acla wseh oitfe rnicine gh eufsfke ctth. aTth ies UduVe etxop tohseu nrae tsuhroawl psh ao ytoe-loloxwidiantgio onf
withthefillers,whichleadstosomecriticalwhiteningeffect. TheUVexposureshowsayellowingof
othf ec eolrlugalonsiec. recycled fillers, namely in the case of rice husk that is due to the natural photo-oxidation
theorganicrecycledfillers,namelyinthecaseofricehuskthatisduetothenaturalphoto-oxidation
of celAlusl oas fei.n al consideration, this strategy can be considered viable on PMMA composites, though
ofcellulose.
with Asosm a ef iinsaslu ceos ninsi dteerrmatsio onf, fthililse rs tdriasttergibyu ctaionn b aen cdo nasmidoeurnetd tvoi abbel ein otrno PdMucMedA a cnodm aplsoos iitnes t, etrhmous gohf
Asafinalconsideration,thisstrategycanbeconsideredviableonPMMAcomposites,though
bweihtha vsioomure oisvseure sti mine t. eNrmostw oift hfisltlaenr ddiinsgtr itbhuatti,o nit aisn ds uagmgoesutnetd toth baet tinhter oudsue coedf caonmd paalstiob iilniz eterrsm ms aoyf
with some issues in terms of filler distribution and amount to be introduced and also in terms of
ibmehparvovioeu trh iosv peirc ttuimree, .p Nosostiwbliyt hlesatadnindgin tgo tshuactc,e sits fiusl sruefgogremstuelda titohna to ft hthe eu csoem opf ocsoitme pwaittihb ielvizeenr sl amrgaeyr
behaviourovertime.Notwithstandingthat,itissuggestedthattheuseofcompatibilizersmayimprove
aimmporuonvtes tohfi bs ipoi-cwtuarsete, pfiollsesrisb layn lde athdeinregf otor es uwcictehs ssofuml er effuorrtmheurl aetnivonir oonf mtheen ctoalm bpeonseiftiet sw. ith even larger
thispicture,possiblyleadingtosuccessfulreformulationofthecompositewithevenlargeramountsof
amounts of bio-waste fillers and therefore with some further environmental benefits.
bio-wastefillersandthereforewithsomefurtherenvironmentalbenefits.
Author Contributions All the authors conceived and designed the experiments; S.L. and A.S. performed the
AeAxuupttehhrooimrr CeCnootnnst;tr raiiblblu utthtiieoo nansus:t hAAollrll stt hhanee aaaluuytzthheoodrr stsh cceoo dnnaccteeaiiv vaeenddd a acnnoddn tddrieebssuiiggtenndee ddto tt hwheer ieetxixnppgee rrtihimme eepnnattpss;e; rSS ..L L.. aanndd AA..SS.. ppeerrffoorrmmeedd tthhee
eexxppeerriimmeennttss;; aallll tthhee aauutthhoorrss aannaallyyzzeedd tthhee ddaattaa aanndd ccoonnttrriibbuutteedd ttoo wwrriittiinnggt thheep paappeerr.
Conflicts of Interest: The authors declare no conflict of interest.
C Coonnflfliiccttsso offI Inntteerreesstt:: TThhee aauutthhoorrss ddeeccllaarreen nooc coonnflfilcictto offi nintteerreesst.t.