Journal of Reinforced Plastics and Composites

Journal of Reinforced Plastics and Compositeshttp://jrp.sagepub.com/'Greening' of unsaturated polyester resin based bulk molding compound with acrylated epoxidizedsoybean and linseed oils: effect of urethane hybridizationS. Grishchuk, R. Leanza, P. Kirchner and J. Karger-KocsisJournal of Reinforced Plastics and Composites 2011 30: 1455 originally published online 30 September 2011DOI: 10.1177/0731684411421541The online version of this article can be found at:http://jrp.sagepub.com/content/30/17/1455Published by:http://www.sagepublications.comAdditional services and information for Journal of Reinforced Plastics and Composites can be found at:Email Alerts: http://jrp.sagepub.com/cgi/alertsSubscriptions: http://jrp.sagepub.com/subscriptionsReprints: http://www.sagepub.com/journalsReprints.navPermissions: http://www.sagepub.com/journalsPermissions.navCitations: http://jrp.sagepub.com/content/30/17/1455.refs.html>> Version of Record - Dec 6, 2011Proof - Sep 30, 2011What is This?Downloaded from jrp.sagepub.com by guest on December 9, 2011

Grishchuk et al. 1457Differences in the unsaturations of the soybean andlinseed oils (different contents of unsaturated linoleic,linolenic, oleic and saturated palmitic, and stearic fattyacid derivatives in the structure of respective triglycerides)used result in different epoxidation degrees.In addition, different acrylation levels are realized inthe oils used in this study. Note that AESO andAELO were acrylated up to higher degrees comparedto EASO – cf. Table 1. As network modifier, a PMDI(isoPMDI 92150 of BASF Group, Elastogran GmbH,Lemfo¨rde, Germany) served in this study.Specimen preparationThe oils were incorporated in 5, 10, and 15 wt% (withrespect to the base resin) in the parent BMC by mixingin a laboratory Brabender Plastograph (Du¨sseldorf,Germany) kneader equipped with a 50 cm 3 mixingchamber. Kneading occurred at 100 rpm at ambienttemperature for 7 min. PMDI was introduced in theBMC, diluted by the vegetable oils used, also by kneadingin the Brabender chamber. Throughout this article,the following coding is used: BMC resin type (UP) indicatingurethane hybridization (UH) and PMDI amountin the latter case (UPUH1, 2 or 3) – plant oil abbreviation(according to Table 1) with its amount. ThreePMDI/UP (without styrene) weight ratios, namely0.6 : 1 (UPUH1), 0.65 : 1 (UPUH2), and 0.7 : 1(UPUH3) were used for the preparation of hybridBMCs. So, BMC UP–AELO-5% means a BMC containing5 wt% AELO (with respect to the base resincontaining both UP and styrene), whereas BMCUPUH3–AESO-5% a PMDI hybridized version containingthe highest amount of PMDI (PMDI/UPweight ratio ¼ 0.7 : 1) diluted with 5 wt% AESO withrespect to the base resin. Note that the UH conceptwas adapted only for BMCs with 5 wt% functionalizedplant oil. For sake of a better overlook, the above designationsare summarized in Table 2.Plaques (160 100 mm 2 )ofca 4 mm thickness wereproduced by hot pressing at T ¼ 170 C for 5 min using160 kN load. These conditions were selected based ondifferential scanning calorimetric tests performed onthe BMC. Specimens from the plaques were cut bysawing.TestingThe thermo-mechanical performance of the BMCswas studied by dynamic-mechanical thermal analysis(DMTA). DMTA traces (storage modulus, E 0 ; andthe mechanical loss factor, tan vs. temperature) weredetermined on rectangular specimens (60 8 4mm 3 ;length width thickness) by DMA Q800 of TAInstruments (New Castle, DE, USA) in flexural modeat 10 Hz frequency. Tests were performed under displacementcontrol (15 mm amplitude) using sinusoidaloscillation under dynamic conditions in the temperaturerange 100 C to +300 C at a heating rate of1 C/min.The static fracture toughness (K c ) and fractureenergy (G c ) were determined on the compact tensionTable 1. Basic characteristics of the functionalized plant oils usedOil Viscosity at 25 C (Pas) Acid value (mg (KOH)/g) Epoxy value (mg (KOH)/g) Density at 25 C (g/mL)EASO 29.1 8.1 8.5 1.04AESO 26.0 15.1 1.8 1.03AELO 29.7 17.3 1.2 1.04Table 2. Designations of the BMCs producedDesignationBMC UP-RefBMC UP–EASO(AESO, AELO)-5(10,15)%BMC UPUH1(2,3)-RefBMC UPUH1(2,3)–EASO 5%CompositionParent UP-based BMCBMC UP compounds with different plant oils, namely EASO,AESO, and AELO. The content of the latter with respectto the UP resin is given in wt% (5, 10, or 15)BMC UP compounds modified by PMDI. The PMDI/UPratios are 0.6:1, 0.65:1, and 0.7:1 (if it was already 1, then consideronly : in 0.7:1!) for the systems markedby 1, 2, and 3, respectivelyBMC UP compounds containing both PMDI and EASO.The PMDI/UP ratio varies for the systems denoted by 1, 2, and 3as indicated above, whereas the EASO content is constant (5 wt%)Downloaded from jrp.sagepub.com by guest on December 9, 2011

1458 Journal of Reinforced Plastics and Composites 30(17)(CT) specimens (dimensions: 35 35 3 (thickness)mm 3 ). The CT specimens were cut from the plaques,notched by sawing and the notch root sharpened byrazor blade tapping prior to testing on a Zwick 1445machine (Zwick, Ulm, Germany) at room temperature(RT) with velocity of 1 mm/min crosshead speed. K c andG c were computed in accordance with the ISO 13586-1standard. The fracture surface of the CT specimens wasinspected in a scanning electron microscope (SEM;JSM-5400 of Jeol, Tokyo, Japan). Prior to SEM, thefracture surfaces were sputtered with a platinum/palladiumalloy to create a conductive cover layer.The dynamic impact properties were characterized bythe Charpy impact strength, measured on unnotched specimensaccording to ISO 179/1. The specimens (80 10 4mm 3 –length width thickness, span length 62 mm)were subjected to high-speed (3 m/s) impact bending atRT on an instrumented pendulum of Ceast (Pianezza,Italy). The energy of the hammer used was 4 J.The resins were subjected to thermogravimetric analysis(TGA) in a DTG-60 device of Shimadzu (Columbia,MD, USA). The TGA experiments were conductedunder nitrogen atmosphere in the temperature range25 C to +900 C with a heating rate 10 C/min.Results and discussionDMTA behaviorFigures 2 and 3 show the E 0 vs. T and tan vs. T tracesfor the UP-based BMC at 5 wt% (with respect to thebase resin) functionalized plant oil type, and as afunction of EASO content, respectively. The DMTAresults covering the E 0 modulus at RT, T g (based onthe a-peak position in the tan vs. T trace), and intensityof the latter are tabulated in Table 3. One canrecognize that the incorporation of 5 wt% functionalizedplant oil in the co-reactive matrix markedlyreduced the stiffness (E 0 modulus) of the BMCs. Theoil type affected the stiffness in the glassy state, moreexactly the E 0 modulus below the temperature range50–60 C. The latter temperature is closely matchedwith that of the T g of the styrene cross-linked acrylatedepoxidized plant oils. 12 It is also found that the E 0modulus drop follows the ranking: Ref > EASO >AESO > AELO. This ranking, accompanied withsome increase in the T g values, is in line with the initialamount of co-reactive acrylic groups in the related oils(cf. Table 1). Moreover, one can get the impression thatchemical incorporation of functionalized oils in the networkstructure in higher amounts has a stronger impacton the stiffness of the resulting BMCs in the glassy statethan just physical plasticization. Incorporation of theplant oils affected both the broadening and intensity ofthe alpha-relaxation peak. Enhanced broadening andintensity suggest that a wider range of segmental unitstakes part in the alpha-relaxation process of a moreirregular networks compared to the reference one.This is linked with different amounts of partiallyreacted molecular fragments within the networksformed in the presence of oils of different functionalities.The shoulder in the temperature range of 60 Cislinked with the homo- and copolymerization reactions(with both styrene and UP) of the related plant oils.Figure 2. Storage modulus (E 0 ) and mechanical loss factor (tan ) as a function of temperature for BMCs modified in 5 wt% withdifferent functionalized plant oils. Note: Numbering follows the legends from the top to the bottom.Downloaded from jrp.sagepub.com by guest on December 9, 2011

Grishchuk et al. 1459Figure 3. Storage modulus (E 0 ) and mechanical loss factor (tan ) as a function of temperature for BMCs modified with varyingamount of EASO. Note: Numbering follows the legends from the top to the bottom.Table 3. Dynamic mechanical, fracture mechanical, and impact properties of modified UP-based BMCsDesignationT g ( C)E 0 (GPa) E 0 (GPa)25 C T g +50 C Shoulder T g1 T g2K c (MPam 1/2 ) G c (kJm 2 ) a K (kJ/m 2 )BMC UP-Ref 18.7 4.7 75 180 – 3.97 0.23 2.40 0.22 3.54 0.51BMC UP–AELO 5% 13.8 3.0 70 175 – 3.40 0.24 1.99 0.24 4.22 0.43BMC UP–AESO 5% 14.7 3.0 70 172 – 3.69 0.33 2.23 0.35 2.68 0.26BMC UP–EASO 5% 16.0 3.2 70 169 – 4.13 0.25 2.72 0.33 3.58 0.44BMC UP–EASO 10% 14.6 3.8 75 158 – 4.41 0.41 2.57 1.00 1.60 0.18BMC UP–EASO 15% 9.9 2.3 70 175 – 3.72 0.26 2.18 0.22 1.38 0.16BMC UPUH1–EASO 5% 12.9 2.1 73 209 235 3.77 0.59 2.57 0.46 3.86 0.57BMC UPUH2–EASO 5% 11.2 1.6 83 – 234 3.89 0.14 2.36 0.29 4.74 0.90BMC UPUH3–EASO 5% 12.1 1.1 73 215 242 4.11 0.43 2.29 0.18 4.97 0.50BMC UPUH2-Ref 11.1 1.9 90 – 237 3.51 0.13 1.74 0.18 5.34 0.49This is quite a complex reaction pathway as discussedrecently. 4,13 The beta-relaxation, caused by the motionsof the phenyl rings around the methylene links 14 peakedat a temperature of 90 C, increased slightly by the oilmodification. Above the temperature range 50–60 C,the stiffness of the BMCs was similar and independentof the plant oils used. The E 0 vs. T traces run, however,further well below that of the reference BMC. Theseobservations confirm that the oils acted as a reactiveplasticizer for the UP resin, lowering its cross-link density.On the other hand, strong reduction in the stiffnessof the modified BMCs in glassy state is probably causedby a change in the matrix/filler interactions. In theopinion of the authors, the matrix adhesion to GFand kaolin is negatively influenced by the incorporationof the functional plant oils used.Based on the DMTA spectra in Figure 3, one canestablish that with increasing dilution of the parent UPresin by EASO, the stiffness of the BMC graduallydecreases. This was accompanied with the broadeningof the alpha-relaxation peak and with its shiftingtoward lower temperatures. Further stiffness reductionwas observed by increasing the amount of EASO (atleast in the glassy state). Unexpectedly, BMC containing10 wt% EASO (with respect to the base resin)showed a higher E 0 compared to other EASO containinghybrids in the viscoelastic state. In combinationwith lower intensity of the main relaxation peakDownloaded from jrp.sagepub.com by guest on December 9, 2011

1460 Journal of Reinforced Plastics and Composites 30(17)compared to other systems, this fact suggests that amore regular network structure is realized in this case.By contrast, higher intensities of the T g peaks comparedto BMC UP-Ref are the characteristic forBMCs containing 5 and 15 wt% of EASO, indicatingthe development of less regular networks. A possiblereason behind this observation is the occurrence ofchemical reactions between the residual groups (epoxyand hydroxyl) of EASO and co-reacting groups (carboxyland hydroxyl) of UP resin, superimposed tothe free radical induced co-polymerization reactions.Recall that all these reactions strongly influence theformation of the final network. Despite strong plasticizationeffect, the system containing 15 wt% of EASOshowed the highest T g value compared to those of otherEASO containing BMCs. This underlines again howcomplex the chemical pathway and final network structuremay be, if multifunctional co-reactants, such asEASO, are used in UP-based BMC formulations.Interesting results were obtained by hybridization ofBMCs with PMDI (BMC UP–EASO 5% was selectedfor this purpose). Strong increase in T g was observedfor hybrids compared to both reference and EASOcontainingBMCs (Figure 4, Table 3). This indicatesthat PMDI is an effective ‘hybridizer’ for UP-basedBMC formulations. However, a drastic reduction ofthe stiffness was observed in this case. This is probablydue to strong dilution (lower filler content) and selectiveabsorption of reaction products on the filler surfacecaused by the incorporation of PMDI whose amountis comparable with that of the UP resin. It is surmisedthat the reaction of PMDI with the water content ofkaolin (>10%) is that key factor which negatively influencesthe final properties of related hybrids. The kaolin,covered by a soft interphase layer, is likely losing itsfiller activity. To prove this argument, it is, however,necessary to work with BMCs which do not containkaolin or other fillers with crystal water.For the example of UPUH2-based systems, it wasshown that 5 wt% EASO has only marginal effect onthe stiffness of hybrid BMC (cf. Figure 4). This wasaccompanied with some reduction of T g as well aswith a broadening of the alpha-relaxation peak andwith its shift toward lower temperatures. Some increaseof the intensity of T g peak and no significant influenceon the beta-relaxation were also detected in this case.Some differences were detected for the UPUH systemscontaining lower (BMC UPUH1–EASO 5%)and higher amount of PMDI (BMC UPUH3–EASO5%) compared to BMC UPUH2–EASO 5% (cf.Figure 5). The stiffness of the former systems is higherthan that for BMC UPUH2–EASO 5% practically inthe whole investigated temperature range. Moreover,the alpha-relaxation (with double-peak) exhibitedlower intensity for BMC UPUH1–EASO 5% andBMC UPUH3–EASO 5% systems compared to that ofBMC UPUH2– EASO 5% and BMC UPUH-Ref. Thisindicates that a more regular, but still heterogeneousnetwork structure was formed in BMC UPUH2–EASO 5% and BMC UPUH2-Ref. Probably, notonly dilution phenomena, but also the ratio between –NCO and other co-reacting groups influenced the finalFigure 4. Influence of hybridization with PMDI on the storage modulus (E 0 ) and mechanical loss factor (tan ) as a function oftemperature for BMC UP-Ref and BMC UP–EASO 5%. Note: Numbering follows the legends from the top to the bottom.Downloaded from jrp.sagepub.com by guest on December 9, 2011

Grishchuk et al. 1461viscoelastic properties of the BMC hybrids. At the sametime, the highest amount of PMDI yielded the highestT g value for BMC UPUH3–EASO 5% compared tothe other hybrids including the reference compound (cf.Table 3 and Figure 5).Static fracture mechanics and related failureThe fracture toughness (K c ) and energy data (G c ) aresummarized in Table 3. Based on the related data andconsidering their scatter range, the following trends canbe deduced:. At 5 wt% oil modification, EASO yielded someimprovement in both the K c and G c data in contrastto AESO and AELO.. There was practically no change in both the K c andG c data with increasing EASO content.. PMDI incorporation (UPUH2-Ref) reduced thefracture mechanical parameters compared to theunmodified UP (UP-Ref). With increasing PMDIamount at 5 wt% EASO content K c and G c slightlyincreased and decreased, respectively. This – in linewith the expectation – suggests that increasing crosslinkdensity enhanced the stiffness, however, at costof the toughness. It is worthy to note that the G cvalue of the UPUH–EASO hybrids was higher thatthat of UPUH2-Ref.As the K c and G c data of the BMC samples wereonly marginally affected by the oil modification, nochange was expected in respect to their failure modes.This was the case, in fact, as shown in Figure 6. Therelated SEM pictures give explanation for the scatterin the K c and G c data (cf. Table 3). Note that theorientation of the short GFs with respect to the notchingdirection (i.e., final crack plane) is crucial: the moreGF are aligned in the loading and thus transverse to thenotch direction, the higher the fracture mechanicalparameters are. 15The effect of PMDI is highlighted in Figure 7.Comparing the fracture surfaces of the referenceBMC without and with PMDI, one can notice thatPMDI reduced the matrix micro-cracking and contributedto a better GF/matrix adhesion. The latterstrongly affected the pull-out of GF. The overalleffect of this change was, however, quite small on thefracture mechanical parameters – at least under quasistaticloading conditions.Dynamic impact behavior and related failureThe unnotched Charpy impact strength values are alsolisted in Table 3 for the BMCs investigated. At 5 wt%oil content, AELO slightly improved and EASO didnot affect, while AESO slightly reduced the impactstrength. This means that characteristics of the functionalizedplant oils may affect the dynamic impactbehavior of BMCs. The related change can hardly betraced to some alteration in the failure mode, as demonstratedin Figure 8. Note that the basic characteristicsof the fractures surfaces are identical.Figure 5. Storage modulus (E 0 ) and mechanical loss factor (tan ) as a function of temperature for selected BMCs hybridized withdifferent amounts of PMDI. Note: Numbering follows the legends from the top to the bottom.Downloaded from jrp.sagepub.com by guest on December 9, 2011

1462 Journal of Reinforced Plastics and Composites 30(17)Figure 6. SEM pictures taken from the fracture surfaces of the CT-specimens cut of the unmodified (a) and with 15 wt% EASOmodified(b) BMCs.Figure 7. SEM pictures taken from the fracture surfaces of the CT specimens cut of the unmodified (a) and with PMDI-modified(PMDI/UP ratio ¼ 0.65/1) BMCs (b).With increasing EASO content, the Charpy impactstrength dropped to more than the half of the BMCreference value. On the other hand, the differencebetween the related data of BMC with 10 and 15 wt%oil contents was negligible. The observed change in theCharpy data suggests that the actual amount of fillerand reinforcement controls the Charpy impact responseof BMCs. Adding PMDI resulted in a prominentincrease in the unnotched Charpy impact strength ofthe reference BMC. The SEM pictures in Figure 9 evidencethat PMDI incorporation improved the matrix/GF adhesion. This is well reflected in reduced GFpull-out length and in the appearance of sheathedGF surface – compare SEM pictures at the samemagnification in Figures 8 and 9. Further, PMDI‘compacted’ the filled matrix which became less pronefor multiple matrix cracking. The latter is, however, anefficient energy absorbing mechanism. Apparently, thefiber-related events (fracture and pull-out) owing to theimproved GF/matrix adhesion compensated thismatrix-related change. The combined action of EASOand PMDI was comparable with that of the PMDIalone – cf. Table 3.It is worthy to note that the effect of PMDI underdynamic loading is far more pronounced than in thefracture mechanical tests under static loading. It isdue to the fact that the matrix- (brittle cracking inour case) and fiber-related failure (fracture, pull-out,Downloaded from jrp.sagepub.com by guest on December 9, 2011

Grishchuk et al. 1463Figure 8. SEM pictures taken from the fracture surfaces of Charpy specimens cut of the unmodified (a) and with 5 wt% EASOmodifiedBMC (b).Figure 9. SEM pictures taken from the fracture surfaces of Charpy specimens cut of the PMDI-modified BMC without (a and b) andwith 5 wt% EASO (c and d).Downloaded from jrp.sagepub.com by guest on December 9, 2011

1464 Journal of Reinforced Plastics and Composites 30(17)debonding) events, including their relative frequency,which control the fracture behavior, strongly dependon the loading conditions (static, dynamic). 16Thermogravimetric behaviorThe TGA curves of the BMCs investigated areshown in Figures 10 and 11. Find that their thermaldegradation occurred in two steps. The first step witha maximum degradation rate at 320 C and yielding aweight loss of ca 25 wt% represents the degradation ofthe UP matrix. This value is in line with the informationof the BMC producer (see above) and supportedalso by TGA results achieved on UP and BMCsystems. 17 Further, plant oil modification affectedonly this degradation step (cf. Figures 10 and 11).Figure 10. TGA curves of BMCs modified with different plant oils in 5 wt% amount. Note: Numbering follows the legends from thetop to the bottom.Figure 11. TGA curves of BMCs modified with different EASO amounts. Note: Numbering follows the legends from the top to thebottom.Downloaded from jrp.sagepub.com by guest on December 9, 2011

Grishchuk et al. 1465Figure 12. TGA curves of BMCs containing 5 wt% EASO in absence and presence of various amounts of PMDI (PMDI/UP (withoutstyrene) weight ratios of 0.6:1 – UPUH1, 0.65:1 – UPUH2, and 0.7:1 – UPUH3). Note: Numbering follows the legends from the top tothe bottom.With increasing EASO content, the weight loss of theBMCs increased accordingly. The second step showingan inflexion point at a temperature of 750 C reflects thedecompositions of carbonate minerals, used as fillers, in theBMC. Assuming that this filler is solely CaCO 3 , theamount of the latter in the BMC recipe can be estimatedfor 20 wt%. Based on this estimate, the kaolin contentmay be at 36 wt%. The residue at T ¼ 900 Cisintherange 53–55 wt%, which is well matched with the totalamount of GF and kaolin in the parent BMC formulation.Hybridization of BMCs with PMDI resulted inslightly improved thermal stability (Figure 12).However, onset of the degradation occurred somewhatearlier in the temperature scale. For the example ofBMC UPUH2 system, it was also shown that incorporationof 5 wt% EASO (with respect to the base UPresin solution) enhanced the first degradation step. Onthe other hand, thermal stability of the hybrid BMCs isnot influenced by increasing the amount of PMDI. Thefinal residue at 900 C of UPUH-type BMCs was onlyslightly reduced compared to that of UP BMC-Ref,despite obvious dilution of the formulations by PMDI.ConclusionThis article was dedicated to check the effects of dilutionof UP resin based BMCs with acrylated zepoxidizedsoybean and linseed oils. These functionalizedoils were added up to 15 wt% in the parent BMC.In addition, PMDI was used as further modifier.Modification with the plant oils was associated with astrong reduction of the stiffness (E-modulus) of theBMCs in the glassy state. An even larger drop in theE-modulus was noticed for the BMC after polyisocyanatemodification. The latter was traced to a reactionof –NCO with the crystal water of kaolin, present asmajor filler – apart from chalk and GF – in the BMCrecipe. On the other hand, the glass transition temperatureof the compounds was markedly enhanced via the‘urethane route’. The static fracture mechanical parametersdid not change prominently with the modification(plant oil type and amount and addition of polyisocyanate).The Charpy impact strength proved to be moresensitive to the above modifications than the static fracturemechanical parameters. This was explained bydifferences in the occurrence of the fiber- and matrixrelatedindividual failure events affected by the plantoils, and especially by the further addition of polyisocyanate.The thermal degradation behavior of themodified BMCs did not change profoundly as a functionof the modification performed. The results suggestthat the BMC recipe should be adjusted when the‘greening’ of BMC via matrix modification with functionalizedplant oils is the target. ‘Adjustment’ meansrecipe modifications to compensate the loss in theperformance of BMCs owing to the introduction offunctionalized plant oils. In this respect, the hybridizationwith PMDI seems to be quite promising, providedthe formulation does not contain hydrated fillers.FundingThis research was performed in the framework of a bilateralcooperation program between Germany (DAAD) andHungary (MO¨ B) which is gratefully acknowledged.Downloaded from jrp.sagepub.com by guest on December 9, 2011

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