Effect of quenching process on mechanical properties of flax/polypropylene
composites
A K P Dhanakodi & V R Giri Deva
Department of Textile Technology, Anna University, Chennai 600 025, India Received 16 March 2017; revised received and accepted 22 June 2017
Flax/polypropylene needle - punched nonwovens (550 g /m2) have been produced and then used as a preform for the
production of composites. In this study, better infiltration of polypropylene melt into the flax fibres has been achieved by altering the crystal structure of polypropylene in the preform. A modified sequence of production of composites is also proposed. The proposed method yields composite with 25, 98 and, 91% improvement in tensile, flexural and short beam strength properties as compared to the conventional method of manufacturing.
Keywords: Composite, Crystal structure, Flax, Needle - punched nonwoven, Polypropylene, Quenching process
1 Introduction
Composites are used in wide range of applications, such as aerospace, automobiles, consumer & electronic packaging and for other domestic applications1-4. Among
them, thermoplastic based composites have gained significant ground because of shorter processing cycles, shelf life, storage, recyclability and sustainability. Thermoplastic composites are lighter in weight, which, in turn, increases the process performance 5. Compared
to thermoset resins, the cost and environmental advantages make it a suitable choice for wide range of applications6.
Most of the matrices used in the preparation of thermoplastic composites are in the form of solid or liquid. The resin may be in the form of powder, fibre, film and fabric7, 8. The fibrous form of the resin is
usually blended with the reinforcement either manually by hand mixing or by preparing nonwoven fabrics using technologies such as needle - punching, hydro- entangling, stitch bonding and adhesive bonding. The preform thus prepared is then hot pressed to form the composites9.
The performance of the composites depends on the strength which is influenced by various factors. Among them, the bonding between the melted thermoplastic resin and reinforcement plays a significant role. Better bonding of the thermoplastic resin with fibre can be achieved by better wetting of reinforcement with the melted thermoplastic resin10.
This in-turn depends on the process conditions deployed for hot compaction, as it influences the flow behaviour of the polymer melt. It has been observed in our various preliminary trials that most of the fracture in the composites occurred by delamination11. Previous
works to improve the interfacial strength is by adding silane coupling agent, benzoylation, peroxide treatment steam explosion process, plasma, corona treatment, dielectric barrier techniques, ultrasound, ultraviolet treatment and with enzymes12–15.
Limited literature is available on changing the crystal structure of the polypropylene during composite manufacturing. The altering of the crystal structure changes the amorphous content of the polypropylene fibre. This is likely to aid in better melting, leading to the better realization of improved mechanical properties.
Needle - punched nonwovens with flax and polypropylene (PP) fibre have been prepared for this study. During consolidation process, the sample was heated at varying temperature followed by sudden quenching to obtain the β form. The samples were further hot pressed at varying temperature to obtain the composites. The influence of the quenching process on the mechanical properties and failure behaviour was analysed.
2 Materials and Methods
2.1 Raw Materials
Polypropylene (PP) fibres and flax were procured from Zenith fibres, Vadodara, Gujarat, India and Aditya Birla Nuvo Ltd., West Bengal, India respectively. ———————
a Corresponding author.
2.2 Composite The prepa polypropylen Composites process as p layers of th dimensions of composite of 4 mm thi compression 190° and 20 maintained a pressed for 1 were prepare followed b maintained reheated for samples prep mechanical p Further, to on compo temperature The quenche for 5 min at cooled bath consolidated 140°C to 20 RH-140°C, RH -180°C a 2.3 Characteri 2.3.1 Tensile T The tensi USA tester procedure Fig. 1 — L Preparation ared nonwov ne in 30:70 r were prepare per the line d he cross - l 25×25cm2 w es. The mat w ickness betwe n moulded at 00°C. The pre at 7.8 MPa. T 10, 15 and 20 ed by first he by quenchin for 1 min. r 5, 7.5 an pared at 200° properties. o study the ef osite prope was fixed ed samples w t 200°C follo h for 1 min. d at varying 0°C .The prep RH -150°C, and RH -200° isation Test
ile test was c r according D638-10. T Line diagram of ven web is m ratio having 5 ed by compre diagram given laid nonwov were used for
was further pl een the two p
a varying tem essure for co The control sa 0 min. The qu eating for 5, g in water The sample nd 10 min. °C for 10 mi ffect of reheat erties, the d at 200°C were prepared owed by quen The sample temperature pared sample , RH -160°C °C. carried out o to ASTM The tensile composite prepa made of flax a 550 gsm weig ession mould n in Fig. 1. ven mat of the preparat laced in a spa platens and w mperature 18 onsolidation w amples were uenched samp 7.5 and 10 m r cooled b es were furt The compos in yielded bet ting temperatu consolidat for 10 m first by heat nching in wa es were furt e ranging fr es were coded C, RH -170 n Instron 33 standard t test specim aration process and ght. ing Six the tion acer was 80°, was hot ples min bath ther site tter ure tion min. ting ater ther rom d as °C, 69, test men dimen speed streng results Tensi 2.3.2 F The per A flexur and th averag five sp Flexu where specim 2.3.3 S The the c evalua a 3-po by the test w 2344/ averag from given Short The used specim machi 2.3.4 X Wi experi X'Pert operat mono intens crysta literat 2.3.5 D Dif perfor Calori nsions were was set at gth (MPa) wa s based on the le strength Flexural Test e flexural test ASTM D790-1 ral test specim he machine ge flexural str pecimen result ral strength e P is the m men; and t, th
Short Beam Stren
e short beam composite sa
ate the value oint bend test e interlaminar was carried ou /D2344M -13 ge short beam five specim below: t beam streng e data record to evaluate t men dimensi ine speed was
X- Ray Diffractio ide angle iments were t³ Powder d ting at 45 kV chromator a sity versus allinity of the ture reported1 Differential Scan fferential scan rmed on a Ne imeter by va 165×13×4 m 5 mm/min. as determine e formula giv t was carried o 10 standard u men dimension speed was s trength (MPa) ts based on th
maximum load he thickness o ngth (SBS) m strength tes amples at r of interlamin t, which gene r shear test. T ut on the spec 3 standards us m strength (M men results b gth
ded during th the flexural s ions were 2 s set at 1mm/m on (XRD) X- ray performed diffractomete V and 30 mA and a scinti 2θ peaks w e samples was 6. nning Calorimet nning calorim etzsch DSC 7 arying the co mm and the . The averag d from five ven below:
out on the spe using Instron 3 ns were 125× et at 2 mm/ ) was determ e formula give d; b, the wid f the specime sts were perf room tempe nar shear stre erally promot The short beam
imens as per sing Instron 3 MPa) was de based on the e 3- point be strength also. 24×8×4 mm min. diffraction on a PAN er with a C A, and equipp illation detec was plotted s calculated a try (DSC) metry experim 7 Differential oling rate. T machine ge tensile specimen
… (1) ecimens as 3369. The ×13×4 mm /min. The ined from en below: ... (2) dth of the en. formed on rature to ngth. It is tes failure m strength ASTM D 3369. The etermined e formula ... (3) end test is . The test and the (WAXS) analytical Cu anode ped with a ctor. The and the as per the ments were Scanning To analyse
the effect o sequence fol (i) Heating 10°C/m (ii) Cooling 50°C/m (iii) Heating 10°C/m (iv) Cooling 10°C/m 2.3.6 Fourier T FTIR an polypropylen Elmer Spe The resolutio at 4 cm-1 wavenumber 2.3.7 Thermog Thermal of polyp thermogravim USA). The measuremen atmosphere temperature 3 Results an Needle -polypropylen are hot pres thus prepar properties, s strength prop the failure in specimens is matrix. The improve the better infiltra Polypropy different cry smectic stru 75%. It ha quenching o amorphous extended in the mats are quench cool is further h quench cool f quenching llowed is give from -40°C min. g from 200° min. g from -40° min. g from 200 min. Transforms Infr nalysis of t ne samples ectrum RX1 on for the co (24 scans c r ranged from gravimetric Anal stability of co propylene metric analyz sample weig nts were c with tempe to 700°C at a nd Discussion - punched n ne have been sed to form red are teste such as tensi perties. It is o n majority of s due to poor major goal e mechanical ation of PP m ylene fibre i ystal structu cture17. The as been repo of PP at 5°C w content18. Th the present w exposed at v led to room t hot pressed. led mat will
on the melt en below: C to 200°C °C to -40°C °C to 200°C °C to -40°C rared Spectrosco the control was perform 1 (Massach ollection of sp collected) an m 4000 cm-1 to lysis (TGA) ontrol and qu was stu zer (TA Instru ght taken was carried out erature rangi a heating rate n nonwovens n prepared an composites. ed for vario ile, flexural a observed from f the thermopl r adhesion be of the pres strength of melt into the n
is known to ures, namely crystallinity o orted in the would yield he same con work and the f
arying tempe temperature. F The hypothe be amorphou ting profile, C at a rate C at a rate C at a rate C at a rate opy (FTIR) and quench med on Per husetts, USA pectra was fix nd the scann o 400 cm-1 uenched samp udied us uments, TGA s 5 mg and in nitrog ng from ro of 10°C/min. with flax a d then the we The composi ous mechani and short be m the study t lastic compos etween fibre a sent work is f composites onwovens. o exist in fo α, β, ϒ a of PP is arou literature t fibres with h ncept has be flax/PP fibres eratures and th Finally, the m esis is that us in nature a the of of of of hed rkin A). xed ned ples ing A 7, the gen om . and ebs ites ical eam that site and to by four and und that igh een s in hen mat the and on fur ease a 3.1 Ten The of the the re presse increa in ten tensile contro increa pressi The maxim for fu fixed Th 200°C The tempe compo higher Fig. 2 propert
rther hot pre and have bette
nsile test e tensile stren e materials to einforcing fib ed at 180 - 2 ase in temper nsile strength e strength of ol sample. Th ased with th ing; the modu strain (%) a mum tensile urther studies at 200°C for he nonwoven C for 5 min fo samples are erature from osite sample r tensile mo — (a) Tensile ties of composite essing the PP er adhesion w ngth is directl o transfer stre bres. The co 200°C. It can rature for hot is observed. A f 27 MPa is o he modulus o he increasing ulus obtained at 200°C is properties ar the temperat studying the n mat is ini followed by q further hot 140°C to 1 es on furthe odulus and s properties of co es P fibres will m with the flax fi
ly related to t ess from the ntrol sample n be seen tha t pressing, an At 200°C, a m obtained in th of the sampl g temperatur at 200°C is s found 5% re achieved a ture of consol effect of quen itially hot p quenching in t pressed at 180°C. The er hot pressi strength. Figu omposites and ( melt with ibres. the ability matrix to es are hot at with an n increase maximum he case of es is also re of hot 1.54 GPa. . As the at 200°C, lidation is nching. pressed at ice water. t varying quenched ing show ure 2 (a) (b) Flexural
shows the te and 20.83 % has been obs to the bette adhesion of P 3.2 Flexural te Flexural s resist deform composites displacemen take place Figure 2(b) of the sampl maximum fl at RH 180°C quench coo strength valu the control layers is o increased f suggest that and efficient and the fibr entanglemen nonwoven, t Figure 3 thermoplasti images that occurred in q 3.3 Short Beam The mech not only o ensile proper % increase in served for Q-er infiltration PP with flax f est strength of th mation under involves b nt. Both tensil simultaneous shows the fle les prepared a lexural modul C. It should a led samples, ues are found sample. No observed du flexural mod the fibre is fu t stress transf res. Moreove nt of fibre thereby impro shows the ic composites better encap quench cooled m Strength (SB hanical prope on fibre arra rties of comp tensile modu - 180°C samp of the PP m fibre. he composite r load. The both bendin le compressio sly during fl exural modul at varying tem lus and streng also be noted , the flexura d to be higher delaminatio uring flexura dulus and s fully envelope fer occurs betw
er, during ho s also inc oving the stren
SEM imag s. It can be psulation of d samples. S) erties of a co angement bu Fig. 3 posites. A 19 ulus and stren ples. This is d
melt and bet
is the ability bending of ng and sh on and shear lexural loadi lus and stren mperatures. T gth are obtain d that for all al modulus a r as compared n into separ al testing. T strength valu ed by the mat
ween the mat ot pressing, reases in ngth propertie ges of flax/ seen from flax fibres h mposite depe ut also on — SEM microg % gth due tter y to the hear ring ing. gth The ned the and d to rate The ues trix trix the the es. /PP the has end the adhes quite interla betwe the co seen f compo may b polyp and m seen f short sampl sampl 3.4 XR Fig taken graph of the tens
F ion between relevant for aminar shear een reinforcem omposite spec
from the grap osites is high be due to th
ropylene and matrix owing t from the SEM
beam streng les after qu les. RD Analysis gure 5 shows before and a sile fracture surfa
Fig. 4 — Short be
the fibre an nonwoven b strength is a ment and matr cimens are giv ph that SBS o
her than the he better infi d better inter to hot pressin M images pro gth increases enching as s the XRD pe after quenchin ace
eam strength pro
nd the matrix based compos a measure of rix. The SBS ven in Fig. 4. of the quench control samp ltration of th rlocking of t ng which can ovided as an i by 91% for compared to eaks of polyp ng. The chara operties of comp x. This is sites. The f bonding results of . It can be hed cooled ples. This he molten the fibres be clearly inset. The r reheated o control propylene acteristics posites
peaks appear (in 2θ) to correspondin (131) planes sample at 2 β-hexagonal hexagonal p appears in q be seen from The appeara modification The crystall is found 3 which has advantageou 3.5 DSC Analy DSC anal to study th behaviour o taken durin specimens a heating cycl fibre is ob melting occ The area u The same s DSC itself w is followed carried out involved in cooled samp shift of 7° observed. Th 155°C and Fig. 5 — X- r at 14.16, 17 that of α-m ng to the (11 s. No noticea 2θ = 16° wh phase and i phase (β) is d quenched poly m peaks appea ance of β-ph n that has o inity % of th 7% compare a crystallinit usly used whil
ysis lysis of the s he influence of polypropyl ng heating a as shown in e, the melting bserved at curs at 152° under the m sample is the with a scannin by the heatin to simulate the work. On ples, the melt
C compared he onset and 166°C. The ray diffraction s 7.06, 18.65, 2 monoclinic c 10), (040), (1 able peak oc hich is chara it can be con detected. β -h ypropylene s aring at 2θ = hase confirm occurred due he quenched ed to the c ty of 54%. le preparing t samples has b of quenchi lene. DSC th and cooling n Fig. 6. In g point of the 173°C. The °C and it e melting peak en quenching ng rate of 50 ng of the spe e the experi n the further ing peak occ d to first he end of the m area under t spectra of polypr 21.34 and 21.9 crystal struct 130), (111) a ccurs in cont acteristic of nfirmed that hexagonal fo samples and c 16° and 21.0 ms the structu e to quenchi cooled samp control samp This could the composite been carried ing on melt hermograms cycle of the case of e polypropyle onset of ends at 178 is 88.92 J g cooled in °C/min and t ecimens. This imental proc heating quen urs at 166°C eating cycle melting peaks the thermogr ropylene sample 91° ture and trol the no orm can 03°. ural ing. ples ples be es. out ing are the f a ene the °C. J/g. the this s is cess nch . A is are ram reduce amorp reflect well k at a The quenc exothe tempe tempe literat β-pha es F es to 62.15 phous content ted in a decr known that PP lower temp cooling pro ched sample ermic peak i erature with erature simila ture 20. This ase crystal. H Fig. 6 — DSC th 5 J/g. This t of the samp rease in melt P in the β-ph erature com file of the es is given is obtained b h a should ar to the re also confirm However, du hermogram of po s suggests le has increas ting temperat hase crystal fo mpared to α control and in Fig. 6 broadened at der at an esults obtaine ms the forma uring norma olypropylene sam that the sed and is ture. It is orm melts crystal19. d rapidly 6(b). The t a lower elevated ed in the ation of a l cooling mples
(10oC/min), obtained. R crystallizes defective cry in 13°C is during norm rapid coolin formation of 3.6 TGA Analy The therm quench cool case of qu degradation of the contro α and β cry control sam while that o occurs at 354 an increase During rehea into α crysta During reh occurs, and improved the 3.7 FTIR Anal To correl spectroscopy peaks at 84 stretching c CH3 rocking stretching an is due to s Fig. 7 — Th a narrower Rapid cooli at 102°C, ystals are form
observed in mal cooling (10 ng (50°C/min f a β-phase cry ysis mal degradat led PP fibres uenched cool temperature i ol sample. In ystals are pres mple of polyp of the quenc 4°C. Moreove in amorpho ating in TGA al, resulting in eating, therm d this is als ermal stability lysis late the XRD y studies are 41cm-1 and oupled with g. The peak a nd CH3 wagg symmetric C hermogravimetric r crystallizat ng polyprop which indi med by rapid n crystallisati 0°C/min) in c n). This also ystal. tion profiles s are given in led samples, is 40 – 50°C quench coole sent. The we propylene oc ched polypro er, during que ous content i A, the β crysta n increased th mal induced so one of t y. D and DSC r e carried ou 900 cm-1 ar C-H deform at 1167 cm-1
ging. The pea C-H bending analysis of polypr tion profile pylene sam icates that cooling. A sh ion temperat comparison w o confirms of pristine a n Fig. 7. In , the onset higher than t ed samples b eight loss of ccurs at 260 opylene samp enching, there in the polym als are conver
hermal stabili d crystallisat the reasons results, infrar t (Fig. 8). T re due to C mation, CH2 a is due to C-ak at 1377 cm and the pe ropylene samples is mple the hift ture with the and the of that oth the °C, ples e is mer. rted ity. tion for red The C-C and - C m-1 eak at 14 asymm with sampl peaks 1167 chang appea amorp 4 Con The flax/P therm presen alterin results reheat prope can b manuf Ackn The to th throug Comm (BSR) Refer 1 Da Te 2 Ua Sc s Fig 459 cm-1 ca metric, in pl the pristin le shows a s and a slight cm-1 . This c ges occurred arance of thes phous phase. nclusion e major prob PP needle moplastic com nt work, the ng the crystal s in increase ting, compo rties are achi be deployed facturing unit owledgemen e author wou e Anna Un gh the BSR mission [F-N ) dated 05 Oc rences as D, Pradhan ext Prog, 44 (20 awongsuwan P, ci,132 (2015) 1. g. 8 — Absorban an be attribu ane CH3 ben ne PP sam an increase shift occurs can be corre d in the cr se bands conf blem faced punched -mposite is above limit l structure of d β – crystal sites with i ieved. The pr very easily i ts and is scala nt
uld like to ack niversity for R Fellowshi o. 25-1/2014 ct 2015], India A K, Chattop 12) 1. , Yang Y & H nce spectrum of uted to ben nding. On co mples, the in the inte between 984 lated to the rystal struct firms the form
in the prepa - nonwoven delamination tation is addr f polypropyle l structure. O improved m roposed gree in various co able. knowledge th the funding ip, Universi 4-15(BSR)/7-2 a. padhyay R & S Hamada H, J A f polypropylene s ding and omparison quenched ensity of 4 cm-1 and structural ure. The mation of aration of n based n. In the ressed by ene which On further mechanical en method omposites eir thanks g support ty Grant 288/2009/ Singh S N, Appl Polym samples
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