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European Polymer Journal 44 (2008) 755–768

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POLYMERJOURNAL

Polymer toughening using residue of recycled windshields:PVB film as impact modifier

Ticiane Sanches Valera, Nicole Raymonde Demarquette *

University of Sao Paulo, Materials and Metallurgical Engineering Department, Av. Prof. Mello Moraes, 2463, 05508-900 Sao Paulo, Brazil

Received 24 August 2007; received in revised form 12 December 2007; accepted 13 December 2007Available online 8 January 2008

Abstract

In this work, poly(vinyl butyral) (PVB) film originated from the mechanical separation of windshields was tested as animpact modifier of Polyamide-6 (PA-6). The changes undergone by PVB film during the recycling process and the blendmanufacturing were evaluated by thermal analyses, infrared spectroscopy and loss on ignition. Blends of PA-6/originalPVB film and PA-6/recovered PVB film were obtained in concentrations ranging from 90/10 to 60/40. The mechanicalproperties of the blends were investigated and explained in light of the blends morphologies, which in turns were correlatedto the changes undergone by the PVB film during the recycling process. The original film presented a plasticizer content of33 wt.%, which decreased to as low as 20 wt.% after the recycling and blend preparation processes. The PA-6/PVB filmblends presented lower values of tensile strength and Young’s modulus than Polyamide-6, but all blends presented a dra-matic increase in their toughness, with a special feature for the 40 wt.% blend, which resulted in a super toughened material(impact strength exceeding 500 J/m). Similar results were obtained with recovered PVB film and super tough blends werealso obtained. The use of recovered PVB resulted in a smaller improvement of the impact strength due to the loss of plas-ticizer undergone during the recycling process. The morphological observations showed that if the interparticle distance issmaller than around 0.2 lm (critical value), the notched Izod impact strength values increase considerably and the fracturesurface of blends exhibit characteristics of tough failure.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Recycled windshield; Recovered PVB film; Toughening agent; Polyamide-6

1. Introduction

Windshields or laminated safety glasses consist ofa ‘‘sandwich” of a film of poly(vinyl butyral), PVB,between two sheets of glass. PVB is a random amor-phous copolymer of vinyl butyral, vinyl alcohol,

0014-3057/$ - see front matter � 2007 Elsevier Ltd. All rights reserved

doi:10.1016/j.eurpolymj.2007.12.012

* Corresponding author. Tel.: +55 11 3091 5693; fax: +55 113091 5243.

E-mail address: [email protected] (N.R. Demarquette).

and vinyl acetate whose properties can be tailoredby the percentage of each monomer within the chain[1]: the hydrophobic vinyl butyral units provideelasticity, toughness and compatibility with variousplasticizers and the hydrophilic vinyl alcohol unitsconfer high adhesion to inorganic materials suchas glass. In order to be used in laminated safetyglasses PVB is normally blended to around30 wt.% of a plasticizer such as alkyl phthalates [2]or dibutyl sebacates [3]. Due to its structure and

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756 T.S. Valera, N.R. Demarquette / European Polymer Journal 44 (2008) 755–768

presence of plasticizer, PVB film possesses similarproperties to rubber [4]. In spite of the high priceof PVB film (about US$15/m2) and the large quan-tity of windshields that are annually discarded inlandfields (100 thousand tons per year of which7% consist of PVB film, in the USA alone [5]) verylittle work has been conducted on finding alterna-tives to disposal of laminated glass residues to land-fields. Cha et al. [4,6,7] showed that it was possibleto use uncontaminated scrapped PVB film collectedfrom windshield production as an impact modifierof Polyamide-6 (Nylon-6). Polyamides are pseudo-ductile polymers often blended to rubbers [8] toenhance their low notched impact strength [9]. ThePVB film used by Cha et al. [4,6,7] was very similarto virgin PVB film as it corresponded to the indus-trial residues that could not be used in the wind-shields. However, during the production ofwindshields and the recycling process, the propertiesof PVB film may change: the plasticizer may beeliminated and the PVB may suffer degradation[2,3,10]. It is therefore of interest to study thechanges undergone by PVB film during the manu-facturing of the windshields and recycling processand the possibility of using the PVB film residueas impact modifier.

Polymer toughening has drawn a lot of attentionfrom academics and plastic industry [4,6,7,9,11–37]as impact strength is one of the most importantmechanical properties of plastics. It is well knownthat pseudo-ductile matrixes, such as Polyamidestoughened with rubber material, present higher duc-tility, crack resistance and mainly greater impactstrength, when compared to the one of the purematrix [23]. Various theories have been proposedto explain toughening mechanism, including stressrelief by cavitation of rubber particles, matrix craz-ing and shear yielding. More details can be found indifferent monographs on the subject [8,9,22,23,25–28].

Wu [22,26] proposed that interparticle distance(between the nodules of the dispersed phase) is themost important parameter that controls the brit-tle-to-tough transition of rubber/polymer blends.If the interparticle distance, given by Eq. (1) is smal-ler than a critical value (called critical interparticledistance) the blend will be tough, otherwise, theblend will be brittle:

s ¼ dp

6/

� �13

� 1

" #ð1Þ

where s is the interparticle distance between the sur-faces of two nearest neighboring particles, d is theparticle diameter and / is the rubber volumefraction.

The critical interparticle distance is independentof rubber volume fraction and particle size and ischaracteristic of a given matrix. This parameteralone can explain the effects of rubber volume frac-tion, particle size, polydispersity, coalescence ofrubbery phase and morphology on toughness [22].Since Wu proposed the interparticle distance model,many authors worked on the subject [27–34,36,37]and it was found that the critical interparticle dis-tance can be affected by different parameters, suchas temperature and speed of impact tests, notchradius of samples for impact test, interfacial tensionbetween blend components and other properties ofthe rubbery and matrix phases [29,30,32,33,36,37].

In the present work, PVB film originated from themechanical separation of windshields, either fromindustrial fabrication waste or from post-consump-tion products was tested as an impact modifier forPolyamide-6 (PA-6). The changes undergone by thePVB film during windshield manufacture and recy-cling process were evaluated. Blends of PA-6/origi-nal PVB film/ and PA-6/recovered PVB film wereobtained. Their mechanical properties were com-pared and explained in light of blend morphologyand of the changes undergone by the PVB film duringthe blend manufacturing and the recycling process.

2. Experimental

2.1. Materials

The properties of the polymers used in this workare listed in Table 1. Three types of PVB were usedin this work: original PVB film corresponding tothe material used in the production of windshields(Solutia, Saflex RB41), recovered PVB film origi-nated from the grinding of windshields rejected inthe production line or post-consumption, and purePVB without plasticizer to quantify the loss of plas-ticizer from the PVB film during the recycling pro-cess. Two types of recovered PVB film were used:one was originated from an industrial recycling com-pany (R2) and the other (R1) was ground using amodified blade grinder, in our laboratories. Theground material, originated from both the industrialand lab-scale process, was sieved (ASTM #10, sieveopening 2 mm) and the passing material was blendedto Polyamide-6 by extrusion. The PVB plasticizer

Table 1Characteristics of the studied materials

Materials Property Values

PVB film Melt flow index (g/10 min) 2.88 (235 �C, 2.16 kg)Refractive index 1.478 (23 �C)Density (g/cm3) 1.066 (23 �C)Tensile strength (MPa) 22.2Elongation (%) 190Tensile modulus (MPa) 6.4

Plasticizer Molecular formula C22H42O6

Molecular weight 402.6Density (g/cm3) 0.95Flash point (�C) 207

PA-6 Melt flow index (g/10 min) 27.5 (235 �C, 2.16 kg)Density (g/cm3) 1.14 (23 �C)Tensile strength (MPa) 57.4Elongation (%) 259Tensile modulus (MPa) 2471

T.S. Valera, N.R. Demarquette / European Polymer Journal 44 (2008) 755–768 757

present in commercial PVB film used in this workwas triethylene glycol di-2-ethylhexanoate.

y = 0.275x + 0.839

R2 = 0.990

4

6

8

10

12

14

Car

bony

l ban

d ar

ea (

at 1

730

cm-1

)

2.2. Blending and sample preparation

Two types of blends were prepared in this work:

1. PA-6/original PVB film with concentrations ofPVB film ranging from 0 to 40 wt.%.

2. PA-6/recovered PVB film (obtained from thegrinding process) with concentrations of PVBfilm of 20 and 40 wt.%. – those two concentra-tions were chosen as a function of the resultsobtained when studying the PA-6/original PVBfilm blends.

The blends were prepared using a Laboratorytwin-screw extruder (Haake Rheomex PTW16) withfour heating zones with temperatures ranging from230 to 250 �C, and then injected to form samples forimpact and tensile tests using a Demag ErgotechInjection molding machine with a diameter of25 mm and L/D of 20. The processing temperaturesalong the injection barrel ranged from 220 to 250 �C.

The blends with virgin PVB film and recoveredPVB film using an industrial grinder were extrudedonce and twice in order to study the reprocessing(recycling) of the blends.

0

2

0 10 20 30 40 50

Plasticizer content (wt%)

Fig. 1. Calibration curve used to determine the plasticizercontent.

2.3. Characterization

2.3.1. Infrared spectroscopy

A Nicolet 560 IR – Magna infrared spectrometerwas used to access the possible degradation of PVB

film and quantify the amount of plasticizer withinthe PVB films before and after recycling process.In order to quantify the amount of plasticizer withinthe different PVB film samples, a calibration curvewas obtained using 6 blends of pure PVB with 0–40 wt.% plasticizer. The samples were dissolved inchloroform, in a concentration of 10 mg/mL. Thesolutions were placed in a cell with KBr window,and subsequently analyzed. The absorbance of thecarbonyl band at 1730 cm�1 was used to quantifythe plasticizer content and a calibration curve withcarbonyl band area versus weight fraction of plasti-cizer was obtained. This curve was used to deter-mine the plasticizer content in samples of originalPVB film, recovered PVB film, and the films submit-ted to one and two extrusions, and injected. Fig. 1shows the calibration curve obtained. It can be seenthat the absorbance of –OH group (area of –OHgroup peak) increases linearly with the concentra-tion of plasticizer present in the blends of PVBand plasticizer, following Beer–Lambert’s law.However, there was a non-zero intercept becausethe PVB copolymer presents vinyl acetate units inits structure.

2.3.2. Differential scanning calorimetry (DSC) and

thermogravimetrical analysis (TGA)

The blends were analyzed using a DSC Q10 (TAInstruments). Approximately 5 mg of material wasused for each experiment. The sample was heatedat a heating rate of 10 �C/min, then cooled at a rateof 10 �C/min to �40 �C and finally reheated at arate of 10 �C/min to 250 �C. The experimental


procedures were based on ASTM3417 andASTM3418. Thermogravimetric analyses werecarried out in a DTA/TG STA409 (Netzch) todetermine the loss mass from PVB films and blends,from ambient temperature to 300 �C, in flowing syn-thetic air, at 20 �C/min heating rates.

All the samples were dried under vacuum at atemperature of 60 �C for at least 48 h prior to ther-mal analyses.

2.3.3. LOI – loss on ignition

The fragments of ground PVB film were burnedin a laboratory electric oven at 600 �C for 3 h todetermine the residual amount of glass. The valuesreported represent the average of three tests.

2.3.4. Mechanical properties

They were measured using an EMIC DL-2000universal testing machine. The Young‘s moduluswas determined using testing velocity of 1 mm/minand the others tensile properties were obtainedusing a testing velocity of 50 mm/min. NotchedIzod impact strength was measured using a CEASTimpact testing machine. The radius of notch used inthe specimens was of 0.25 ± 0.05 mm and angle of45 ± 1� (ASTM D256, specimen type 3). The resultsof mechanical properties reported in this workcorrespond to the average of at least 15measurements.

2.3.5. Morphology

The morphology of all the blends was character-ized by scanning electron microscopy. To obtain agood contrast between the phases, the PVB filmwas dissolved with ethanol. Quantitative analysisof the morphology was performed using Carl ZeissVision KS-300 software. The impact strength speci-mens after testing were used for qualitative analysesof the fracture surface. In the case of the quantita-tive morphological analyses, Saltikov’s correction[38] was used.

2.3.6. Rheological characterization

The shear viscosity of the polymers as a functionof shear rate was evaluated using a capillary rheom-eter Instron 4467 at a temperature of 250 �C. Thedie used had a diameter of 0.76 mm and L/D of34. Rabinowitsh correction was applied to theexperimental results. All the samples were driedunder vacuum at a temperature of 60 �C for 48 hprior to rheological measurements.

3. Results and discussion

3.1. Mechanical separation process

The windshields were recycled and two types ofwastes were obtained, scrapped PVB film and par-ticulate glass. The PVB films were ground. Themean values of the LOI tests for ground PVB filmswere: 99.2 wt.% and 99.3 wt.% for R1 (recoveredfilms obtained in laboratorial scale) and R2 (recov-ered films obtained using industrial grinder), respec-tively, showing that the fragments of films arealmost glass-free.

3.2. Changes undergone by the PVB film during the

blend manufacturing and the recycling process

Fig. 2 presents the infrared spectra of originaland recovered PVB films, and of films that havebeen submitted to extrusion and injection moldingprocesses. Fig. 2a–d shows four different film spec-tra regions: the band at 3489 cm�1, correspondingto –OH group (Fig. 2a), together with the band rel-ative to C–H stretching at 2970 cm�1 (Fig. 2b), theband at 1140 cm�1 relative to C–C(@O)–O stretch-ing of vinyl acetate units (Fig. 2c), and the band at1730 cm�1 of C@O group (Fig. 2d). It can be seenfrom Fig. 2a–c, that the featured regions the spec-tra of the original and recovered PVB films are sim-ilar, showing no changes in absorbance, indicatingthat the PVB chain did not undergo any modifica-tions in the vinyl alcohol and vinyl acetate struc-tures and therefore did not suffer thermaldegradation. According to El-Din et al. [2] the ini-tial point of thermal degradation of PVB is thevinyl acetate unit, the weakest unit of the PVBstructure, which gets detached from the main chain.In subsequent steps, the molecule suffers scissionand the ring of the vinyl butyral unit opens, leadingto the formation of chains with C@C double bonds.These changes involve a reduction in the absor-bance of –OH, C–H stretching and C@O bandsand disappearance of band corresponding to PVBvinyl acetate unit. None of these changes wereobserved in the spectra presented in Fig. 2a–c. Itcan be seen from Fig. 2d that the only band thatwas changed is the one related to ester units, pres-ent in the PVB and in the plasticizer. Once the PVBunit bands did not change, the variation in absor-bance of the C@O band was attributed only tothe plasticizer. The plasticizer is most likely exuding– or degrading – during the manufacturing of the

87

56

3

2

4000 3500 1300 1200 1100 1000 900

1

4

Inte

nsity

(a.

u.)

Wavenumber (cm-1)

Wavenumber (cm-1) Wavenumber (cm-1)

Wavenumber (cm-1)

87

56

321

4

Inte

nsity

(a.

u.)

8

7

65

43

12

Inte

nsity

(a.

u.)

200027002750280028502900295030003050310031503200 1500

8

7

5

6

3

2

1

4

Inte

nsity

(a.

u.)

a c

b d

Fig. 2. Infrared spectra of the PVB films. 1 = original PVB film; 2 = R2 recovered PVB film; 3 = R1 recovered PVB film; 4 = originalPVB film (1 extrusion step); 5 = original PVB film (2 extrusion steps); 6 = R1 recovered PVB film (1 extrusion step); 7 = R2 recoveredPVB film (2 extrusion steps); 8 = R2 recovered PVB film (1 extrusion step). (a) The band at 3489 cm�1, corresponding to –OH group; (b)together with the band relative to C–H stretching at 2970 cm�1; (c) the band at 1140 cm�1 relative to C–C(@O)–O stretching of vinylacetate units; and (d) the band at 1730 cm�1 of C@O group.

Table 2PVB film plasticizer content obtained using a calibration curve

Sample Weight fraction (%)

Original PVB film 33R1 recovered PVB film 27R2 recovered PVB film 26Original PVB film (1 extrusion step) 28Original PVB film (2 extrusion steps) 24R1 recovered PVB film (1 extrusion step) 21R2 recovered PVB film (1 extrusion step) 20R2 recovered PVB film (2 extrusion steps) 19


windshields, recycling process and/or blend prepa-ration. Table 2 presents the plasticizer contents ofthe PVB films evaluated using the calibration curvepresented in Fig. 1. It can be seen that the originalfilm presents a plasticizer content of 33 wt.%, cor-roborating values of the literature [1]. The plasti-cizer content decreases to as low as 26 wt.%during the recycling process (R1 and R2 films).When the films are extruded only once, the plasti-cizer content of the original and the recovered filmsare reduced in about 15% and 23%, respectively.The double extrusion leads to a decrease in plasti-cizer content of 27% for both original and recov-ered PVB film. These results are in goodagreement with the ones of Dhaliwal and Hay [3]who studied the degradation process of recovered

PVB films. The authors showed that from 200 to250 �C (maximum process temperature used in thiswork), the only changes of PVB films was loss ofplasticizer.

Table 3Glass transition temperature (Tg) of PVB copolymer and PVBfilms, and the melting temperatures of blends

Samples Glasstemperature(�C)

Melttemperature(�C)

PVB copolymer 71Original PVB film 4R1 recovered PVB film 11R2 recovered PVB film 13PA-6 222PA-6/original PVB film (90/10) –

single extrusion222

PA-6/original PVB film (80/20) –single extrusion

222


222


221

PA-6/original PVB film (80/20) –double extrusion

220

PA-6/R1 PVB film (80/20) –single extrusion

219


220

PA-6/R2 PVB film (80/20) –double extrusion

220

PA-6/original PVB film (60/40) –double extrusion

220


221


220

PA-6/R2 PVB film (60/40) –double extrusion

220

Table 4Thermogravimetric analyses of PA-6, PVB copolymer, PVBfilms, and blends

Samples Weightloss (%)

Original PVB film 4.1R1 recovered PVB film 2.8R2 recovered PVB film 2.1PA-6 0.7PA-6/original PVB film (90/10) – single extrusion 2.5PA-6/original PVB film (80/20) – single extrusion 3.3PA-6/original PVB film (70/30) – single extrusion 3.5PA-6/original PVB film (60/40) – single extrusion 3.8PA-6/original PVB film (80/20) – double extrusion 2.6PA-6/R1 PVB film (80/20) – single extrusion 2.0PA-6/R2 PVB film (80/20) – single extrusion 1.5PA-6/R2 PVB film (80/20) – double extrusion 1.2PA-6/original PVB film (60/40) – double extrusion 2.7PA-6/R1 PVB film (60/40) – single extrusion 2.2PA-6/R2 PVB film (60/40) – single extrusion 2.0PA-6/R2 PVB film (60/40) – double extrusion 1.6


Table 3 shows the glass transition temperature(Tg) of PVB copolymer and PVB films, and themelting temperatures of blends. It can be seen thatthe Tg of the pure copolymer is higher than the onesof the films, due to the presence of plasticizer in thefilms. The values found in this work corroborate theones obtained by Cascone et al. [21] and Dhaliwaland Hay [3]. It can also be seen from Table 3 thatthe melting temperature of the Polyamide-6 matrixis not affected, within experimental error, by theaddition of PVB film. These results indicate thatthe plasticizer did not migrate to PA-6 phase.

Table 4 presents a summary of thermogravimet-ric analyses of PA-6, PVB, and blends. In Table 4,it is shown the weight loss of the samples for tem-peratures ranging from 25 to 250 �C. The resultspresented in Table 4 show that the thermal degrada-tion of the matrix is only slightly affected by thepresence of PVB film, since the weight loss of theblends is always less than 4 wt.%. Hence, the PVB

film maintains the thermal properties of the matrix,one of requirements for an efficient toughness agent,besides the improvement in impact properties [8]. Itcan also be noticed in Table 4 that the blends withhigher PVB film content present the greatest weightlosses. These results are in good agreement with theones presented in Table 2 since the PVB film weightloss is attributed to loss of plasticizer, the loss isgreater for the blends containing higher plasticizerconcentrations in the films.

3.3. Rheological characterization

Fig. 3 presents the viscosity of pure phases as afunction of shear rate. The vertical lines in Fig. 3correspond to the applied shear rate during extru-sion and injection molding processes (around 1000and 10,000 s�1, respectively [39]). The curves inFig. 3 show that the original PVB films presentthe smallest viscosity values, and the viscosity ofthe recovered films are of the same order of magni-tude, within experimental error. The original filmspresent the largest reductions in viscosity, due tothe higher concentration of plasticizer in their com-positions. Table 5 presents the dispersed phase/matrix viscosity ratio for all studied binary systemsat a shear rate that corresponds to the injectionmolding shear rate. For comparison purposes, theplasticizer content of PVB films presented in Table2 is shown again. It can be seen that the viscosityratio increases with decreasing amount ofplasticizer.

1000 10000

10

100

PA-6 (single extrusion) PA-6 (double extrusion) R2 Recovered PVB film (single extrusion) R2 Recovered PVB film (double extrusion) R1 Recovered PVB film (single extrusion) Original PVB film (double extrusion) Original PVB film (single extrusion)

Vis

cosi

ty (

Pa.

s)

Shear rate (s-1)

Fig. 3. Viscosity of pure phases as a function of shear rate.

Table 5Dispersed phase/matrix viscosity ratio for all studied binary systems at a shear rate that corresponds to the injection molding shear rate(10,000 s�1)

Sample Viscosity ratio Weight fraction of plasticizer (%)

Original PVB film (single extrusion)/PA-6 (single extrusion) 0.36 28Original PVB film (double extrusion)/PA-6 (double extrusion) 0.56 24R1 recovered PVB film (single extrusion)/PA-6 (single extrusion) 0.51 21R2 recovered PVB film (single extrusion)/PA-6 (single extrusion) 0.53 20R2 recovered PVB film (double extrusion)/PA-6 (double extrusion) 0.58 19

For comparison purposes, the plasticizer content of PVB films presented in Table 4 is shown again.


3.4. Blend morphology

Fig. 4 presents typical morphologies of theblends studied here. Fig. 4a and b shows PA-6/ori-ginal PVB film (60/40) blend, submitted to, respec-tively, one and two extrusion steps, Fig. 4c and dshows PA-6/R2 recovered PVB film (60/40), afterone and two step extrusions, respectively. Table 6summarizes the quantitative experimental resultsof morphological observations. For comparisonpurposes, the notched Izod impact strength valuesobtained for the blends are also presented. It canbe seen that all blends studied present particle sizesgreater than 0.1 lm and below 1 lm, and exhibitlow polydispersity (dv/dn < 2), which are favorableconditions for a successful rubber toughening[8,23]. It can be also seen from Table 6 that dn

increases with increasing PVB film concentrationdue to dispersed phase coalescence. It can be alsoseen from Table 6 that dn of PA-6/original PVB film(1E) blend is larger than the one of PA-6/R1 recov-ered PVB film (1E) and PA-6/R2 recovered PVBfilm (1E) blends, and that dn of PA-6/original PVBfilm (1E) blend is larger than dn of PA-6/original

PVB film (2E) blend. These results can be explainedin light of viscosity ratio that increases during therecycling process or after the second extrusion.These results are in good agreement with the resultsof Wu [40] who suggested that the finest morphol-ogy is reached when the viscosity ratio is close toone.

3.5. Mechanical properties of the blends

3.5.1. Original PVB film/PA-6 blends

Figs. 5 and 6 present the tensile strength andYoung’s modulus of the blends as a function ofthe original PVB film content (wt.%), respectively.The results show that both the tensile strength andmodulus decreased when the PVB contentincreased. A reduction in those two mechanicalproperties is a common observation in rubbertoughened polymers because of the lower strengthand modulus of the dispersed phase [9,22–28].

Fig. 7 presents the notched Izod impact strengthof the blends using original PVB films. It can be seenfrom Fig. 7 that the notched Izod impact strengthincreases when the PVB film content increases,

Fig. 4. Typical morphologies of the blends. 1E = one extrusion step and 2E = two extrusion steps. (a) PA-6/original PVB film (60/40), 1E,after ethanol etching. (b) PA-6/original PVB film (60/40), 2E, after ethanol etching. (c) PA-6/recovered PVB film (60/40), 1E, after ethanoletching. (d) PA-6/recovered PVB film (60/40), 2E, after ethanol etching.

Table 6Quantitative results of the morphology of studied blends: dv = volume average diameter and dn = number average diameter

Sample dn dv Polydispersity (dv/dn) Notched Izod impact strength (kJ/m2)

PA-6/original PVB (90:10), 1E 0.53 1.04 1.9 166 ± 12PA-6/original PVB (80:20), 1E 0.68 1.06 1.6 233 ± 48PA-6/original PVB (70:30), 1E 0.86 1.40 1.6 326 ± 49PA-6/original PVB (60:40), 1E 1.05 1.79 1.7 1590 ± 39PA-6/original PVB (80:20), 2E 0.53 0.97 1.8 215 ± 23PA-6/original PVB (60:40), 2E 0.60 0.86 1.4 1279 ± 69PA-6/R1 recovered PVB – (80:20), 1E 0.44 0.71 1.6 202 ± 18PA-6/R2 recovered PVB – (80:20), 1E 0.48 0.91 1.9 202 ± 26PA-6/R2 recovered PVB – (80:20), 2E 0.57 1.02 1.8 196 ± 26PA-6/R1 recovered PVB – (60:40), 1E 0.61 0.99 1.6 1289 ± 46PA-6/R2 recovered PVB – (60:40), 1E 0.51 0.97 1.9 1239 ± 72PA-6/R2 recovered PVB – (60:40), 2E 0.59 0.92 1.6 1108 ± 40

1E = one extrusion step and 2E = two extrusion steps. For comparison purposes, the notched Izod impact strength values of the blendsare also presented here.


and that the PA-6/original PVB film blends can beconsidered tough (for PVB film concentrations upto 30%) and super tough (for PVB film concentra-tion of 40%) [8]. The results obtained in this workpartially corroborate the results reported by Cha

et al. [4], who used scrapped PVB films, very similarto original PVB film, as an impact modifier for Poly-amide-6. The greatest difference between the valuesreported by the authors and the results obtainedin this work is in the impact strength values of the

0

10

20

30

40

50

60

70

0 10 20 30 40

PVB Film content (wt.%)

Ten

sile

Str

engt

h (M

Pa)

Fig. 5. Tensile strength versus original PVB film content (wt.%).

500

700

900

1100

1300

1500

1700

1900

2100

2300

0 5 10 15 20 25 30 35 40 45

PVB Film Content (wt.%)

You

ng's

Mod

ulus

(M

Pa)

Original PVB film (1E)

Original PVB film (2E)

Fig. 6. Young’s modulus versus original PVB film content(wt.%). 1E = material extruded once, 2E = material extrudedtwice.

0

400

800

1200

1600

2000

Not

ched

Izo

d Im

pact

Str

engt

h (J

/m )

0 10 20 30 40

PVB Film content (wt.%)

Fig. 7. Notched Izod impact strength (J/m) as a function ofdispersed phase content (wt.%).

0

200

400

600

800

1000

1200

1400

1600

1800

0.01 0.1 1 10

Interparticle distance (μm) or Average particle diameter (μm)

Not

ched

Izo

d Im

pact

Str

engt

h (J

/m)

Interparticle distance

Average particle diameter

60/40 Blends

80/20 Blends

70/30 Blend

60/40 Blends

70/30 Blend

80/20 Blends

90/10 Blends

Fig. 8. Notched Izod impact strength versus interparticle dis-tance and average particle size.


higher PVB film content blends. In the case of the60/40 PA-6/PVB film blend, Cha et al. [4] obtainedan impact strength value of about 42 kJ/m2,whereas in this work, 157 kJ/m2 was obtained.These differences can be due to the type of PVB filmused, the processing conditions, and the test condi-tions [8,23] that are different in both studies.

The results presented in Table 6 indicate that thefinest morphology does not correspond to the bestimprovement in impact strength, since the sampleswith original PVB film present the greatest averageradius and the best impact strength indicating thatthere is no straight correlation between the dis-persed phase particle size and the impact strength.Fig. 8 shows the notched Izod impact strength forall blends versus the average particle diameter, dn,and the interparticle distance parameter proposed

by Wu [22,26]. The results for the recovered PVBfilm/PA-6 blends are also included in this graphalthough the effect of recycling will be discussedlater in the paper. When the Izod impact strengthis plotted as a function of the interparticle distance,a single curve can be fitted to the experimental data.This curve suggests that there is a particular singleinterparticle distance for which a sudden change inimpact strength is observed. The same conclusioncannot be drawn if the average particle size is con-sidered. It can be seen in Fig. 8 that the critical inter-particle distance is around 0.2 lm since that in thisregion there was a sudden change in the Izod impactstrength values corroborating the results of Borgg-reve et al. [27]. It can be noticed from Fig. 8 thatthe blends with PVB film contents higher than

Fig. 9. Micrograph of the notched Izod impact fracture of (a) PA-6, (b) PA-6/original PVB film (80/20) blend, (c) PA-6/original PVB film(60/40) blend, (d) a magnification of 60/40 blend micrograph, after etching.


20 wt.% present an interparticle distance greaterthan the critical. The interparticle distance of allblends seem to be dependent only on their PVB con-tent, regardless the kind of PVB film used (originalor recovered), or the number of extrusion steps (sin-gle or double).

Fig. 9 shows typical fracture surfaces of notchedIzod impact strength specimens of PA-6 and PA-6/PVB film (80/20 and 60/40) blends. The fracture

surfaces show the presence of two different regionsin the PA-6 and 80/20 blend specimens (Fig. 9aand b). The inside region of the circles presentedin Fig. 9a and b features a mirror zone, which iscommonly observed in samples for which fractureis preceded by craze formation. The outside circleregion, called hackle region [41], presents rough sur-faces, with divergent lines pointing towards thecrack propagation directions. The 60/40 blends pre-

60

42 43 42 41 41

62

24

44

36 36 37

0

10

20

30

40

50

60

70

PA-6 (1 and 2E) PVB O (1E) PVB O (2E) PVB R2 (1E) PVB R2 (2E) PVB R1 (1E)

Ten

sile

Str

engt

h (M

Pa)

PA-6/PVB film (80/20)


Fig. 10. Tensile strength versus recovered and original PVB film content. The specimens were extruded once or twice. 1E = materialextruded once, 2E = material extruded twice, R1 = recovered film using lab-scale grinder; R2 = recovered film using an industrial grinder;O = original film.

2093

1259

1695

1596 16

98

1600

2075

793

1100

1136

1139

1091

0

500

1000

1500

2000

2500

PA-6 (1 and 2E) PVB O (1E) PVB O (2E) PVB R2 (1E) PVBR2(2E) PVB R1 (1E)

You

ng’s

Mod

ulus

(M

Pa)



Fig. 11. Young’s modulus of the blends with recovered and virgin PVB film. 1E = material extruded once; 2E = material extruded twice;R1 = recovered film using lab-scale grinder; R2 = recovered film using an industrial grinder; O = original film.


sented in Fig. 9c show an extensive matrix yielding,characteristic deformation of tough failure. Thetough fracture proceeds entirely within the PA-6matrix, without exposing the PVB film particles (seeFig. 9d). Since the shear yielding of the matrix ismore effective to improve the impact strengththan crazing, it is expected that the 60/40 blends

present greater fracture energy than 80/20blends. These observations are in good agreementwith the interparticle distance parameter since the60/40 blends exhibit values of interparticle distancesmaller than the critical value (around 0.2 lm),whereas 80/20 blends presented values above thecritical.


3.5.2. Recovered PVB film/PA-6 blends

The PVB concentrations that resulted in bestcombination of impact strength and tensile proper-ties were found to be 20 and 40 wt.% of PVB film.Adding 40 wt.% PVB film to PA-6 resulted in anincrease of impact strength of about 1400% whencompared to the one for pure PA-6, although pre-senting the smallest tensile strength and modulus.Adding 20 wt.% PVB film to PA-6 resulted in areduction in the tensile strength values of at least50% smaller than the ones for the 40 wt.% PVB filmblend, but the improvement in impact strength wasnot as significant. Hence, the 80/20 and 60/40 com-positions were chosen for studying the substitutionof original PVB film from recovered PVB film.

Figs. 10–12 present a comparison of the tensilestrength, Young’s modulus and notched Izodimpact strength of the blends obtained with originalPVB and with recovered PVB (for both processesR1 and R2). All those mechanical properties weredetermined for samples extruded once (1E) andtwice (2E). The following observations can be donewhen analyzing those three figures.

(1) Both recycling processes (industrial R2 or labscale R1) result in blends with similar mechan-ical properties within experimental error.

95

233

215

104

1590

1279

0

200

400

600

800

1000

1200

1400

1600

PA-6 (1 and 2E) PVB O (1E) PVB O (2E)

Not

ched

Izo

d Im

pact

Str

engt

h (J

/m)

Fig. 12. Notched Izod impact strength of the blends with original andonce; 2E = material extruded twice; R1 = recovered film using lab-O = original film.

(2) The notched Izod impact strength values of theblends containing recovered films are higherthan the ones for pure PA-6. However, theblends containing recovered films show a lowerimpact strength value than the ones containingthe original PVB film, except in the case of the60/40 original PVB blend extruded twice.

(3) Independently of the type of PVB film used,super tough blends were obtained when40 wt.% of PVB film is added to PA-6.

(4) The tensile strength and Young’s modulus ofthe blends obtained using recovered PVB areof the same order of magnitude as the onesof the blends obtained using pure PVB filmsprocessed twice; the specimens with originalPVB film as toughening agent, submitted toonly one extrusion presented the smallest ten-sile strength and modulus.

(5) The tensile strength of the 80/20 blends sub-mitted to one or two extrusions are of thesame order of magnitude within experimentalerror. In the particular case of the 60/40 origi-nal PVB blend, a large increase of tensilestrength was observed when the blend wasprocessed twice (see Fig. 10). The tensilestrength increased in about 83% when theblend was reprocessed.

202

196

202

1239

1108

1289

PVB R2 (1E) PVB R2 (2E) PVB R1 (1E)



recovered PVB film as impact modifier. 1E = material extrudedscale grinder; R2 = recovered film using an industrial grinder;

50

250

450

650

850

1050

1250

1450

1650

0 5 10 15 20 25 30

Plasticizer content (wt.%)

Not

ched

Izo

d Im

pact

Str

engt

h(J/

m) PA-6/PVB film (80/20)


Fig. 13. Notched Izod impact strength of the blends as a functionof plasticizer content. 1E = material extruded once; 2E = mate-rial extruded twice; R1 = recovered film using lab-scale grinder;R2 = recovered film using an industrial grinder; O = originalfilm.


(6) When comparing the 80/20 and 60/40 blends itcan be seen, as expected, that the tensilestrength and Young’s modulus of the 80/20blends (for every kind of PVB film used) arelarger than the ones of 60/40 blends. An oppo-site trend is observed for the notched impactstrength.

Fig. 13 presents the notched Izod impact strengthof the blends studied in this work as a function ofplasticizer content. It can be seen that the notchedIzod impact strength decreases almost linearly withdecreasing concentrations of plasticizer, mainly inthe blends with high concentration of dispersedphase. Theses results indicate that the PVB filmplasticizer content is a factor that needs to be con-trolled of one wants to use recovered PVB film asan impact modifier.

4. Conclusions

In this paper, an alternative to use the PVB filmfrom recycled windshields as a toughening agent oran impact modifier for Polyamide-6 was presented.The results showed that the original PVB film pre-sents a plasticizer content of 33 wt.%, whichdecreased to as low as 20 wt.% after the recyclingand blend preparation processes. The PA-6/originaland recovered PVB film blends showed a reductionin their tensile strength and Young’s modulus val-ues, when compared to the ones for PA-6 matrix,but all blends presented a dramatic increase in theirtoughness, with a special feature for the 40 wt.%

blend, which resulted in a super toughened material.The use of recovered PVB film as impact modifier isconditioned to the quantification of the loss of plas-ticizer undergone during the windshield recyclingprocess and blend preparation since the amount ofplasticizer controls the viscosity ratio of the dis-persed and matrix phases, which in turns controlsthe morphology of the blends and their properties.The morphological observations showed that if theinterparticle distance is smaller than around0.2 lm (critical value), the notched Izod impactstrength values increase considerably. Conse-quently, the fracture surface of these blends exhib-ited characteristics of tough failure.

Acknowledgments

The authors would like to thank FAPESP,CAPES and CNPq for financial support. Saint-Gobain Sekurit, Celanese Chemical Europe andSolutia do Brasil for providing the materials usedin this study.

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