research article rheological behavior of renewable...

Research ArticleRheological Behavior of Renewable Polyethylene (HDPE)Composites and Sponge Gourd (Luffa cylindrica) Residue

Viviane Alves Escoacutecio1 Elen Beatriz Acordi Vasques Pacheco1

Ana Lucia Nazareth da Silva1 Andreacute de Paula Cavalcante2 and Leila Leacutea Yuan Visconte1

1 Instituto de Macromoleculas Universidade Federal do Rio de Janeiro (UFRJ) Avenida Horacio Macedo2030 Centro de Tecnologia Predio do Bloco J 21941-598 Rio de Janeiro RJ Brazil2Instituto de Quımica Universidade do Estado do Rio de Janeiro (UERJ) Rua Sao Francisco Xavier 524 MaracanaPavilhao Haroldo Lisboa da Cunha Sala 310 3∘ Andar 20550-900 Rio de Janeiro RJ Brazil

Correspondence should be addressed to Viviane Alves Escocio vivi75imaufrjbr

Received 26 February 2015 Accepted 27 April 2015

Academic Editor Saiful Islam

Copyright copy 2015 Viviane Alves Escocio et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Thepresent study reports the results of rheological behavior of renewable composites based on amatrix of high density polyethylene(HDPE) made from ethanol distilled from sugarcane and lignocellulose filler from waste generated in the processing of spongegourds for bathing use The composites were prepared with 10 20 30 and 40wt of filler in a twin-screw extruder The materialswere analyzed in a parallel plate rheometer and a melt-flow indexer The composite morphology was determined by scanningelectron microscopy The composite viscosity increased with filler content suggesting possible formation of filler agglomeratesThis result was confirmed by Cole-Cole diagrams

1 Introduction

Knowledge of the rheological properties of melted polymersis important because it permits selecting the best materialfor a determined application and processing technique [1]Molar mass size distribution of macromolecules number ofstructural conformations and the possible entanglement ofpolymer chains are factors responsible for the large differ-ences in flow between various polymers during processingThe flow properties of viscoelastic fluids also depend ontemperature deformation rate and processing time [2]

Besides these aspects during processing by either extru-sion or injection molding polymers are subjected to varioustypes of deformation due to the complex geometry of thedevices used Rheological testing provides information on thedeformations and strains of polymers and their compositesunder flow conditions to enable understanding and predict-ing their final morphology and thus their properties [3]

There are only a few reports in the literature on therheological behavior of HDPE composites of fossil origin(called conventional HDPE here) combined with cellulose

To the best of our knowledge there are no published stud-ies of composites made of totally renewable polyethyleneGonzalez-Sanchez et al [4] studied the rheological behaviorof composites made of HDPE or polypropylene (PP) with10 25 40 and 48 by weight of cellulose fiber before andafter five reprocessing cycles The fiber used was eucalyptuspulp The effects of shear rate fiber content and type ofmatrix were analyzed in the virgin and reprocessed com-posites The rheological data obtained by capillary rheom-etry scanning electron microscopy and thermogravimetryshowed a decline in viscosity of the HDPE reprocessed atlow shear rates This decrease was more pronounced in thecomposites containing higher fiber concentrations due to thethermal degradation of the fibers at low shear rates (lowerthan 100 sminus1) The authors also observed a greater loss ofpseudoplasticity of the PP composites than those made withHDPE In another study ofHDPE composites Li andWolcott[5] also assessed the rheological properties with a capillaryrheometer and used different cellulose filler from maple andpine logs with different diameters The authors observed

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015 Article ID 714352 7 pageshttpdxdoiorg1011552015714352

2 International Journal of Polymer Science

thewall slip velocity and its dependence on thewood contenttype of filler and shear stress According to literature [67] the wall slip effects are generally observed in the flowof highly viscous two-phase materials in rheometers pipesor any channel with smooth walls Near the smooth solidboundary the local microstructure is depleted because thesuspended particles could not penetrate the solid walls Liand Wolcott [5] also analyzed the extensional flow findingthat the extensional viscosity is more dependent on the woodcontent than on the species Mohanty and Nayak [8] studiedthe viscoelastic behavior of composites of HDPE and sisalfiber also using capillary rheometry They observed thatthe composites viscosity increased with the incorporationof fiber a finding also reported by other researchers andthat treatment of the polyethylene with maleic anhydridecaused an increase in the viscosity due to the better adhe-sion of the polymer matrix to the fiber which was con-firmed by scanning electron microscopy Besides this otherdynamic properties (storage modulus 1198661015840 loss modulus 11986610158401015840and tan delta 120575) also increased with cellulosic reinforce-ment

The objective of this study was to investigate the rhe-ological behavior in a parallel plate rheometer of a totallyrenewable composite made of polyethylene derived fromethanol with different concentrations of added filler fromsponge gourd processing residue (10 20 30 and 40wt)

2 Experimental

21 Raw Materials The high density polyethylene (HDPE)SHC 7260 (Braskem Brazil) was obtained from sugarcaneethanol Its density is 0959 gcm3 and the melt-flow indexis 72 g10min (190∘C 216 g) The sponge gourd residue(cellulosic filler) was provided by the company BushingsBonfim state of Minas Gerais Brazil This filler has densityof 13 gcm3 particle size of lt015mm and moisture contentof 107 by weight

22 Composite Preparation The HDPE composites with 1020 30 and 40wt of sponge gourd residue were processedin a Tecktril model DCT-2 corotating interpenetrating twin-screw extruder The cellulosic filler was conditioned beforeprocessing in an oven with air circulation for 24 hours at atemperature of 60∘C Before addition of the material in theextruder the polymer and the milled filler were manuallypremixed The extrusion conditions were as follows rotatingspeed of 300 rpm feeder rotation of 15 rpm temperature inprocessing zone 1 90∘C zones 2 to 5 140∘C zones 6 to 9160∘C and head 180∘C The obtained pellets were heated at60∘C to remove moisture

23 Composite Characterization

231 Melt-Flow Index (MFI) Before performing this test thesamples in the form of pellets were dried in an oven with aircirculation for 24 hours at 60∘C The melt-flow index (MFI)(ASTM D1238) [9] was measured in a Dynisco KayenessPolymer Test Systems model LMI 4003 melt indexer

232 Melt Rheology The oscillatory flow measurementsnamely the complex viscosity 120578lowast the storage modulus1198661015840 and the loss modulus 11986610158401015840 of the pure HDPE and its

composites were determined in a TA Instruments rheometermodel AR 2000 A strain sweep test was initially conductedto determine the linear viscoelastic region of the materialsDynamic frequency sweep test (strain 03 frequency 01to 600 rads and temperature at 170∘C)was subsequently per-formed to determine the dynamic properties of thematerialsusing a parallel-plate geometry with 25mm of diameter anda gap set at 05mm

Stress relaxation experiments are the fundamental way inwhich relaxation modulus 119866(119905) can be definedThe relaxingstress data are used to determine 119866(119905) directly

119866 (119905) =120591 (119905)

1205740

(1)

The stress relaxation tests were conducted at a constantstrain of 03 and at a temperature of 170∘C

233 Surface Morphology and Dispersion Characteristic Themorphology of the samples was examined by SEM using aJeol model JSM-6510LV microscope Gold sputtering of thespecimens fractured in the impact test was carried out usinga Denton Desk V vacuum sputter system The samples werefractured at room temperature

3 Results and Discussion

31 Melt-Flow Index (MFI) The melt-flow index (MFI) isa physical parameter that is widely used to evaluate theability of a polymer to flow when melted The MFI value(Figure 1) declined as the sponge gourd residue concentrationincreased due to the increased viscosity of the HDPEfillersystem compared to the pureHDPEWith the addition of 10by weight of cellulose the MFI decreased by 19 while for afiller content of 20wt the decline was 43 andwith additionof 40wt the decrease was 83 in relation to the pure HDPE

By the rule of mixtures criterion [10] the addition of10wt of cellulose filler should cause a decrease of 10in the MFI but this did not occur Instead the result ofthe property for this composition was 68 g10min (20lower than for the pure polymer) Similar MFI behavior wasobserved byMohanty and Nayak [11] for conventional HDPEcomposites obtained from petroleum and bamboo fiberCellulosic fillers are incompatible with the polymer matrixand have a tendency to form aggregates during processing[12] which might further impede the flow of the polymermatrix

32 Melt-State Rheology Viscosity is one of the most com-monly used parameters to investigate the behavior of polymermaterials during processing since the majority of transfor-mation processes occur in shear flowsThemeasure of storagemodulus (1198661015840) and loss modulus (11986610158401015840) which are relatedrespectively to the energy stored and dissipated during acycle is also widely used to study the processing of polymermaterials The storage modulus depends on the rigidity of

International Journal of Polymer Science 3

84

68

48

30

14

0

2

4

6

8

10

1000 9010 8020 7030 6040HDPEfiller (wtwt)

MFI

(g10

min

)

Figure 1 Melt-flow index of composites of renewable HDPE andsponge gourd filler

10

100

1000

10000

100000

001 01 1 10 100Strain ()

HDPE minus G998400

HDPE minus G998400998400

HDPE + 10 filler minus G998400








G998400

andG998400998400

(Pa)

Figure 2 Strain sweep results for neat renewable HDPE and itscomposites containing different wt of sponge gourd filler

the macromolecules and their entanglement while the lossmodulus depends on the bonds which control conforma-tional changes in chain segments and the displacement ofone chain in relation to another [2] In turn the rheologyof composites is influenced by the interactions that occurbetween the polymer matrix and the filler along with thestructure size and shape of the particles and the quality oftheir dispersion throughout the melted matrix [13ndash15]

Strain sweep tests were conducted at 170∘C in nitrogenatmosphere with a constant frequency of 1Hz and in thestrain range of 001 to 100 As it can be seen in Figure 2the response of all samples does not depend on the strain(both1198661015840 and11986610158401015840 exhibit a constant plateau) and the behavioris well within the linear viscoelastic region However theplateau region shortens with higher cellulosic filler contentsin HDPE matrix 30 and 40wt It can also be seen that 11986610158401015840is dominating over 1198661015840 for all composites analyzed indicatingthat the overall behavior is dominated by viscous segmentalfrictions The composite with 10wt of filler exhibits quitesimilar trend as neat HDPE As filler content increasesthe gap between 11986610158401015840 and 1198661015840 values decreases showing thatviscous behavior becomes less pronounced with higher filler

1

10

100

1000

10000

100000

1000000

01 1 10 100 1000Frequency (rads)

2

HDPE minus G998400










G998400 G998400998400

(Pa)

Figure 3 Variation of the storage modulus 1198661015840 and loss modulus11986610158401015840 as a function of frequency for neat renewable HDPE and its

composites containing different wt of sponge gourd filler

loading in HDPE matrix and a tendency to a gradual switchfrom viscoelastic liquid-like to solid-like behavior occursFrom the above experiments the strain was then set at 03to ensure that the response of all materials would be withinthe linear viscoelastic region

Small amplitude oscillatory shear measurements wereperformed at 170∘C and 03 strainThe dynamic moduli1198661015840and 11986610158401015840 are showed in Figure 3 for HDPE and HDPEfillercomposites The obtained behavior in frequency sweep is inaccordancewith the results of strain sweep In factHDPE andHDPE composites exhibit11986610158401015840 gt 1198661015840 in awide frequency rangeindicating that the materials present a pronounced viscousbehavior however as filler content increases the gap between11986610158401015840 and 1198661015840 tends to decrease and a characteristic solid-like

behavior tends to occurAccording to Jiang et al [16] a homopolymer with nar-

row molecular weight distribution presents a characteristicterminal behavior of 1198661015840 prop 1205962 In the present study theneat HDPE did not deviate significantly from the standardterminal behavior 1198661015840 prop 120596118 As filler was added in HDPEmatrix a deviation from 1198661015840 prop 120596096 for 10 wt filler to1198661015840

prop 120596069 for 40wt filler was observed This behavior

indicates a solid-like viscoelastic behavior as filler content isincreased In other words the addition of sponge gourd fillerin the HDPE matrix prevents a complete relaxation due tophysical jamming

The frequency at which 1198661015840 and 11986610158401015840 moduli curves crosseach other reflects the transition from viscous to elasticresponse of the viscoelastic melts [17]

Table 1 shows the crossover point (1198661015840 = 11986610158401015840) and thefrequency values 120596

119888 where these cross points occurred

The results show that a decrease of up to 20wt of fillerin the HDPE matrix in the cross point and in the crossover


Table 1 Modulus and frequency values in the cross point119866101584011986610158401015840 forthe compositions analyzed

Sample codes Cross point1198661015840

= 11986610158401015840 (Pa) 120596

119888

(rads)

HDPE 101700 398HDPE + 10 filler 89590 398HDPE + 20 filler 76340 158HDPE + 30 filler 108400 158HDPE + 40 filler 148900 100

1

10

100

1000

10000

100000


HDPEHDPE + 10 fillerHDPE + 20 filler

HDPE + 30 fillerHDPE + 40 filler

Com

plex

visc

osity

120578lowast

(Pamiddot

s)

Figure 4 Variation of the complex shear viscosity as a function offrequency for neat renewable HDPE and its composites containingdifferent wt of sponge gourd filler

frequency values was observed It indicates that materialswith more elastic behavior tend to be produced but at thesame time the composites present a shear thinning behavioras frequency increases As filler content was further addedto HDPE matrix (30 and 40wt) an increasing cross pointvalue was observed while crossover frequency values stilldecreased This behavior can be related to a characteristic ofsolid-like behaviormore pronounced in these high load com-posites as compared with the other compositions Probablyit occurred due to the tendency to form aggregates duringprocessing when higher filler contents are present whichmight further hinder the HDPE matrix flow as mentionedbefore

The variation of the complex viscosity as a function offrequency (Figure 4) is another way to show these latestresults

Figure 4 shows that neat HDPE and 10wt filler compo-sition present similar flow behavior in the whole frequencyrange analyzed Only at low frequency values the compositepresents a slightly higher viscosity values in relation to neatHDPE When 20wt of filler was added higher viscosityvalues were obtained but a frequency-thinning characteristiccan also be observed reaching similar flow behavior in

Time (s)



100E + 06

100E + 05

100E + 04

100E + 03100E minus 03 100E minus 02 100E minus 01

Rela

x m

odul

usG

(Pa)

Figure 5 Variation of relaxation modulus with time for neatrenewable HDPE and its composites containing different wt ofsponge gourd filler The experiments were performed at a constantstrain of 03 in nitrogen atmosphere

0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000 2500 3000 3500 4000 4500



Imag

inar

y vi

scos

ity120578

998400998400(P

amiddots)

Dynamic viscosity 120578998400 (Pamiddots)

Figure 6 Cole-Cole representation of the viscoelastic properties ofneat HDPE and HDPEfiller composites

relation to the neat HDPE and 10wt filler composition athigher frequencies Probably it occurred due to the fact thatup to 20wt of filler aggregates can disentangle allowingpolymer chain to flow However at higher filler contentsdisentanglement processes become more difficult in thefrequency range analyzed and thus higher viscosity valueswere observed

The variation of the relaxation modulus with time isreported in Figure 5 The results show that 119866(119905) (119866(119905) =120590(119905)120574

0) of HDPE presents a behavior similar to a polymer

with high molecular weight and narrow distribution thatis a plateau zone appears in which the modulus is nearly


(a) (b)

Filler

(c)

Debonding

(d)

Pull-out

(e)

Pull-out

(f)

Figure 7 SEM micrographs of fracture surfaces for the following samples sponge gourd residue with particle size lt015mm (a) renewableHDPE (b) and renewable HDPEcellulosic filler composites (c) 9010wtwt (d) 8020wtwt (e) 7030wtwt and (f) 6040wtwt

constant At longer times flow occurs and the 119866(119905) curvemoves towards a ldquoterminal zonerdquo where the modulus relaxesat sufficiently long times For HDPEfiller composite with10wt filler a similar behavior is observed in relation toneat HDPE for long times As filler was added in HDPEmatrix 119866(119905) extends to long time and the magnitude of 119866(119905)value increases with the filler concentration This behavioris another indication for the formation of filler aggregates(such as ldquotemporary networkrdquo)when higher filler contents areadded hindering the occurrence of relaxation processes Ateven longer periods of time the ldquonetworkrdquo disentangles anda decrease of 119866(119905) values is once again observed

Linear viscoelastic characteristics derived from the resultsof rheological measurements are also shown in a differentrepresentation in Figure 6 using the so-called Cole-Cole

plots for HDPE and HDPEfiller composites In this repre-sentation the 12057810158401015840 parameter (where 12057810158401015840 = 1198661015840120596) the so-calledimaginary viscosity is plotted against dynamic viscosity 1205781015840(where 1205781015840 = 11986610158401015840120596) The plot should be a perfect arc if higherorder structures are absent and the relaxation behavior ofthe melt can be described by a single relaxation time [17]According to Abranyi et al [18] studies on heterogeneoussystems in melts containing network the elastic componentof viscosity (12057810158401015840) increases and the structure has a largerrelation time

Data shown in Figure 6 indicate that the addition of fillerleads to an increase of the elastic behavior of the compositesand larger relaxation times can be observed as increasing fillerloads are added in HDPE matrix indicating the presence offiller aggregates


33 Morphology Analysis Figure 7 shows scanning electronmicroscope (SEM) images of the filler alone with particlesize smaller than 015mm pure HDPE and compositesFigure 7(a) shows the irregularities of the sponge gourdfiller which is characteristic of natural fibers Figure 7(b)shows the fracture surface of the pure HDPE with slightroughness after being submitted to impact resistance testconducted at room temperature a factor that can explain thisroughness Somedisplacement of fibers can be seen in Figures7(c) and 7(d) which increases on rising filler content dueto the low adhesion of the polymerfiller interface FinallyFigures 7(e) and 7(f) show the pull-out of the fillers and alsothe greater surface roughness of the composite with 40wtfiller Filler agglomeration can be observed corroborating therheological results

4 Conclusion

The rheological behavior of the composites comprisingrenewable HDPE and cellulosic filler showed that the vis-cosity of the system increases with higher filler contentThis result suggests that the filler acts as a barrier to chainflow According to Cole-Cole diagram this system formsagglomerates due to the incompatibility of the matrix andfiller The melt-flow index results show values lower thanexpected also corroborating the possible formation of filleragglomerates in the composite Strain and frequency sweepanalysis showed that with the increase filler content thegap between 11986610158401015840 and 1198661015840 values decreases showing thatviscous behavior becomes less pronounced with higher fillerloading in HDPE matrix and a tendency to a gradual switchfrom viscoelastic liquid-like to solid-like behavior occursThe SEM micrographs allowed observing roughness at thefracture surface and fracture mechanisms in the compositessuch as pull-out displacement of filler and formation ofagglomerates a consequence of the low adhesion betweenthe polymer matrix and cellulosic filler These results arein accordance with rheological behavior observed It cantherefore be concluded that it is possible to obtain compositesmade from totally renewable polymer with good rheologicalproperties enabling reduction of negative environmentalimpacts

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank Fundacao de Amparo aPesquisa do Estado do Rio de Janeiro (FAPERJ) Coor-denacao de Aperfeicoamento de Pessoal de Nıvel Superior(CAPES) Banco Nacional de Desenvolvimento (BNDES)Financiadora de Estudos e Projetos (FINEP) ConselhoNacional de Desenvolvimento Cientıfico e Tecnologico(CNPq) and Center for Excellence in Recycling and Sus-tainable Development (in Portuguese Nucleo de Excelencia

em Reciclagem e Desenvolvimento SustentavelmdashNERDES) forfinancial support and BRASKEM for supplying the renew-able HDPE

References

[1] A S Sarvestani ldquoModeling the solid-like behavior of entangledpolymer nanocomposites at low frequency regimesrdquo EuropeanPolymer Journal vol 44 no 2 pp 263ndash269 2008

[2] S A Cruz M Farah M Zanin and R E Bretas ldquoAvaliacaodas propriedades reologicas de blendas de PEAD virgemPEADrecicladordquo Polımeros vol 18 no 2 pp 144ndash151 2008

[3] R E S Bretas andMA DrsquoAvilReologia de polımeros FundidosEdufscar Sao Carlos Brazil 2nd edition 2005

[4] C Gonzalez-Sanchez C Fonseca-Valero A Ochoa-MendozaA Garriga-Meco and E Rodrıguez-Hurtado ldquoRheologicalbehavior of original and recycled cellulose-polyolefin compos-ite materialsrdquo Composites Part A Applied Science and Manufac-turing vol 42 no 9 pp 1075ndash1083 2011

[5] T Q Li and M P Wolcott ldquoRheology of HDPE-wood compos-ites I Steady state shear and extensional flowrdquo Composites PartA Applied Science andManufacturing vol 35 no 3 pp 303ndash3112004

[6] Y Cohen and A B Metzner ldquoApparent slip flow of polymersolutionsrdquo Journal of Rheology vol 29 no 1 pp 67ndash102 1985

[7] R Komuro K Kobayashi T Taniguchi M Sugimoto and KKoyama ldquoWall slip and melt-fracture of polystyrene melts incapillary flowrdquo Polymer vol 51 no 10 pp 2221ndash2228 2010

[8] S Mohanty and S K Nayak ldquoRheological characterization ofHDPEsisal fiber compositesrdquo Polymer Engineering and Sciencevol 47 no 10 pp 1634ndash1642 2007

[9] ASTM D1238-10 Standard Test Method for Melt Flow Rates ofThermoplastics by Extrusion Plastometer Plastics 0801 ASTM-Annual Book of ASTM Standards Philadelphia Pa USA 2007

[10] J R Callister and DWilliam Ciencia e engenharia de materiaisuma introducao LTC Rio de Janeiro Brazil 7th edition 2002

[11] S Mohanty and S K Nayak ldquoShort bamboo fiber-reinforcedHDPE composites influence of fiber content and modificationon strength of the compositerdquo Journal of Reinforced Plastics andComposites vol 29 no 14 pp 2199ndash2210 2010

[12] Z N Azwa B F Yousif A C Manalo and W Karunasena ldquoAreview on the degradability of polymeric composites based onnatural fibresrdquoMaterials and Design vol 47 pp 424ndash442 2013

[13] SNandi S Bose SMitra andAKGhosh ldquoDynamic rheologyand morphology of HDPE-fumed silica composites effect ofinterface modificationrdquo Polymer Engineering and Science vol53 no 3 pp 644ndash650 2013

[14] P V Joseph Z Oommen K Joseph and S Thomas ldquoMelt rhe-ological behaviour of short sisal fibre reinforced polypropylenecompositesrdquo Journal of Thermoplastic Composite Materials vol15 no 2 pp 89ndash114 2002

[15] S Mohanty S K Verma and S K Nayak ldquoRheologicalcharacterization of PPjute composite meltsrdquo Journal of AppliedPolymer Science vol 99 no 4 pp 1476ndash1484 2006

[16] L Jiang J Zhang and M P Wolcott ldquoComparison ofpolylactidenano-sized calcium carbonate and polylactidemontmorillonite composites reinforcing effects and toughen-ing mechanismsrdquo Polymer vol 48 no 26 pp 7632ndash7644 2007

[17] T F Cipriano A L N Silva A H M F T Silva A M FSousa G M Silva and C R Nascimento ldquoRheological and


morphological properties of composites based on polylactideand talcrdquo Journal of Materials Science and Engineering B vol11 pp 695ndash699 2013

[18] A Abranyi L Szazdi B Pukanszky and G J VancsoldquoFormation and detection of clay network structure inpoly(propylene)layered silicate nanocompositesrdquoMacromolec-ular Rapid Communications vol 27 no 2 pp 132ndash135 2006

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Nano

materials


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thewall slip velocity and its dependence on thewood contenttype of filler and shear stress According to literature [67] the wall slip effects are generally observed in the flowof highly viscous two-phase materials in rheometers pipesor any channel with smooth walls Near the smooth solidboundary the local microstructure is depleted because thesuspended particles could not penetrate the solid walls Liand Wolcott [5] also analyzed the extensional flow findingthat the extensional viscosity is more dependent on the woodcontent than on the species Mohanty and Nayak [8] studiedthe viscoelastic behavior of composites of HDPE and sisalfiber also using capillary rheometry They observed thatthe composites viscosity increased with the incorporationof fiber a finding also reported by other researchers andthat treatment of the polyethylene with maleic anhydridecaused an increase in the viscosity due to the better adhe-sion of the polymer matrix to the fiber which was con-firmed by scanning electron microscopy Besides this otherdynamic properties (storage modulus 1198661015840 loss modulus 11986610158401015840and tan delta 120575) also increased with cellulosic reinforce-ment

The objective of this study was to investigate the rhe-ological behavior in a parallel plate rheometer of a totallyrenewable composite made of polyethylene derived fromethanol with different concentrations of added filler fromsponge gourd processing residue (10 20 30 and 40wt)

2 Experimental

21 Raw Materials The high density polyethylene (HDPE)SHC 7260 (Braskem Brazil) was obtained from sugarcaneethanol Its density is 0959 gcm3 and the melt-flow indexis 72 g10min (190∘C 216 g) The sponge gourd residue(cellulosic filler) was provided by the company BushingsBonfim state of Minas Gerais Brazil This filler has densityof 13 gcm3 particle size of lt015mm and moisture contentof 107 by weight

22 Composite Preparation The HDPE composites with 1020 30 and 40wt of sponge gourd residue were processedin a Tecktril model DCT-2 corotating interpenetrating twin-screw extruder The cellulosic filler was conditioned beforeprocessing in an oven with air circulation for 24 hours at atemperature of 60∘C Before addition of the material in theextruder the polymer and the milled filler were manuallypremixed The extrusion conditions were as follows rotatingspeed of 300 rpm feeder rotation of 15 rpm temperature inprocessing zone 1 90∘C zones 2 to 5 140∘C zones 6 to 9160∘C and head 180∘C The obtained pellets were heated at60∘C to remove moisture

23 Composite Characterization

231 Melt-Flow Index (MFI) Before performing this test thesamples in the form of pellets were dried in an oven with aircirculation for 24 hours at 60∘C The melt-flow index (MFI)(ASTM D1238) [9] was measured in a Dynisco KayenessPolymer Test Systems model LMI 4003 melt indexer

232 Melt Rheology The oscillatory flow measurementsnamely the complex viscosity 120578lowast the storage modulus1198661015840 and the loss modulus 11986610158401015840 of the pure HDPE and its

composites were determined in a TA Instruments rheometermodel AR 2000 A strain sweep test was initially conductedto determine the linear viscoelastic region of the materialsDynamic frequency sweep test (strain 03 frequency 01to 600 rads and temperature at 170∘C)was subsequently per-formed to determine the dynamic properties of thematerialsusing a parallel-plate geometry with 25mm of diameter anda gap set at 05mm

Stress relaxation experiments are the fundamental way inwhich relaxation modulus 119866(119905) can be definedThe relaxingstress data are used to determine 119866(119905) directly

119866 (119905) =120591 (119905)

1205740

(1)

The stress relaxation tests were conducted at a constantstrain of 03 and at a temperature of 170∘C

233 Surface Morphology and Dispersion Characteristic Themorphology of the samples was examined by SEM using aJeol model JSM-6510LV microscope Gold sputtering of thespecimens fractured in the impact test was carried out usinga Denton Desk V vacuum sputter system The samples werefractured at room temperature

3 Results and Discussion

31 Melt-Flow Index (MFI) The melt-flow index (MFI) isa physical parameter that is widely used to evaluate theability of a polymer to flow when melted The MFI value(Figure 1) declined as the sponge gourd residue concentrationincreased due to the increased viscosity of the HDPEfillersystem compared to the pureHDPEWith the addition of 10by weight of cellulose the MFI decreased by 19 while for afiller content of 20wt the decline was 43 andwith additionof 40wt the decrease was 83 in relation to the pure HDPE

By the rule of mixtures criterion [10] the addition of10wt of cellulose filler should cause a decrease of 10in the MFI but this did not occur Instead the result ofthe property for this composition was 68 g10min (20lower than for the pure polymer) Similar MFI behavior wasobserved byMohanty and Nayak [11] for conventional HDPEcomposites obtained from petroleum and bamboo fiberCellulosic fillers are incompatible with the polymer matrixand have a tendency to form aggregates during processing[12] which might further impede the flow of the polymermatrix

32 Melt-State Rheology Viscosity is one of the most com-monly used parameters to investigate the behavior of polymermaterials during processing since the majority of transfor-mation processes occur in shear flowsThemeasure of storagemodulus (1198661015840) and loss modulus (11986610158401015840) which are relatedrespectively to the energy stored and dissipated during acycle is also widely used to study the processing of polymermaterials The storage modulus depends on the rigidity of


84

68

48

30

14

0

2

4

6

8

10

1000 9010 8020 7030 6040HDPEfiller (wtwt)

MFI

(g10

min

)


10

100

1000

10000

100000

001 01 1 10 100Strain ()

HDPE minus G998400










G998400

andG998400998400

(Pa)




1

10

100

1000

10000

100000

1000000


2

HDPE minus G998400










G998400 G998400998400

(Pa)
















= 11986610158401015840 (Pa) 120596

119888

(rads)


1

10

100

1000

10000

100000




Com

plex

visc

osity

120578lowast

(Pamiddot

s)





Time (s)



100E + 06

100E + 05

100E + 04


Rela

x m

odul

usG

(Pa)


0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000 2500 3000 3500 4000 4500



Imag

inar

y vi

scos

ity120578

998400998400(P

amiddots)








(a) (b)

Filler

(c)

Debonding

(d)

Pull-out

(e)

Pull-out

(f)








4 Conclusion




Acknowledgments



References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




84

68

48

30

14

0

2

4

6

8

10

1000 9010 8020 7030 6040HDPEfiller (wtwt)

MFI

(g10

min

)


10

100

1000

10000

100000

001 01 1 10 100Strain ()

HDPE minus G998400










G998400

andG998400998400

(Pa)




1

10

100

1000

10000

100000

1000000


2

HDPE minus G998400










G998400 G998400998400

(Pa)
















= 11986610158401015840 (Pa) 120596

119888

(rads)


1

10

100

1000

10000

100000




Com

plex

visc

osity

120578lowast

(Pamiddot

s)





Time (s)



100E + 06

100E + 05

100E + 04


Rela

x m

odul

usG

(Pa)


0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000 2500 3000 3500 4000 4500



Imag

inar

y vi

scos

ity120578

998400998400(P

amiddots)








(a) (b)

Filler

(c)

Debonding

(d)

Pull-out

(e)

Pull-out

(f)








4 Conclusion




Acknowledgments



References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






= 11986610158401015840 (Pa) 120596

119888

(rads)


1

10

100

1000

10000

100000




Com

plex

visc

osity

120578lowast

(Pamiddot

s)





Time (s)



100E + 06

100E + 05

100E + 04


Rela

x m

odul

usG

(Pa)


0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000 2500 3000 3500 4000 4500



Imag

inar

y vi

scos

ity120578

998400998400(P

amiddots)








(a) (b)

Filler

(c)

Debonding

(d)

Pull-out

(e)

Pull-out

(f)








4 Conclusion




Acknowledgments



References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

Filler

(c)

Debonding

(d)

Pull-out

(e)

Pull-out

(f)








4 Conclusion




Acknowledgments



References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





4 Conclusion




Acknowledgments



References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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