Preparation of montmorillonite modified phenolic resin for shell process

Research & DevelopmentMay 2009Preparation of montmorillonitemodified phenolic resin for shellprocess*Xiong Jianmin 1, Li Yuancai 1, Wang Wenqing , Xia Chun(I. School of Material Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China; 2. Schoolof Material Science and Engineering, Nanchang Institute of Aeronuutical Technology, Nanchang 330063, P. R. China)Abstract: The development of montmirillonite modified phenolic resin under microwave iradiation heatingwas investigated. The effect of montmorillonite content and stirring time on the structure and morphology ofsynthetic resin was analyzed. The optimum processing procedure was found to be 45 min strring time with 5.4%montmorillonite adition. Further, the platelet spacing increases with stiring time til montmorillonite exfoliated tonanoscales platelet. When montmorillonite is exfoliated, layered structure at nanoscale can be uniformly distributedin the resin. The overall performance of montmoillonite modified phenolic resin is improved remarkably, such asflow ability, tensile strength and toughness property of resin coated sand. However, the gelation speed decreasedslightly by adding montmoillonite.Key words: shell process; phenolic resin; montmorillonite; comprehensive performance; tensile strengthCLC number: TG221Document code: AArticle ID: 1672-6421(2009)02-119-05manufacturing complicated castings of high precisionmontmorillonite in phenolic resin was investigated. Then thewith phenolic resin as binder, for it possess a number ofperformance of montmorillonite modified phenolic resin, suchunique properties such as good storage of cores and shells, as flow ability, was asssed and quantified in detail.high specific strength, good breakdown capability and highcasting surface quality . The development of casting1 Experimental proceduretowards large-scale and precision production put forwardhigher demands for the performance of phenolic resin for shellMain materials used for this research were: analytically -pureprocess 51. Modification of phenolic resin is an effective wayphenol, aqueous formaldehyde and oxalic acid; chemical-purefor improving the performance, but the current used modifierhexamine and montmoillonite (MMT) Nat and octadecyl amine.for phenolic resin, such as tung oil, cashew nut shell liquid,The reaction took place in a three-necked vessel. The desiredsalicylic acid and bisphenol-A, can only provide sole andamount of 98wt.% phenol, MMT Na*, octadecyl amine, andlimited improvement 16-91.oxalic acid were added into the reactor. The mixture wasRecently, montmorillonite modified phenolic resin (i.e.stirred for 45 min, 30 min, and 15 min, respectively, or notphenolic resin/montmorillonite nano-composites) attracts greatstirred at all under microwave irradiation. Then the desiredinterest of many researchers 10141. Such composite can offeramount of aqueous formaldehyde and 10wt. % oxalic acidhighly improved comprehensive properties in both stiffnesssolution were charged into the reactor and the reactor wasand toughness, which is difficult to attain from individualheated by microwave irradiation to reflux. After 15 min,components, especially when montmoillonite is in the aqueous formaldehyde and oxalic acid solution were addedexfoliated structure with its characteristic nanometer size andas supplement. The reaction was suspended after another 25high aspect ratio 151. This study mainly concerns the synthesismin reflux. After settling, the aqueous layer was siphonedprocess of montmorillonite modified phenolic resin underoff. Vacuum distillation (up to 185C) stripped the remainingmicrowave iradiation heating. The effect of stiring time andvolatiles off the novolac under microwave irradiation. Thenthe product was discharged and cooled. The synthesis period*Xiong Jianminof montmorillonite modified phenolic resin under microwaveMale, born in 1981, Ph. D. Research interests are the preparationirradiation was much less than that for conventional heatingand modification of phenolic resin and related composites.method, and theref(中国煤化工fficiency.E-mail: xiongianmin@gmail.com|YHCNMHGCorresponding author: Li YuancaiE-mail: leeycchina@yahoo.com.cn2 Performance testsReceived: 2008-12-02; Accepted: 2009-03-04The morphology of the polymer was examined using X'Pert119.CHINA FOUNDRYVol.6 No.2PRO X-ray diffractometer. The diffractometer employs aspacing can be increased and the incident angle of diffractioncopper X-ray source that has an emission wavelength of 1.54Apeak decreases accordingly when polymer intercalated into theat room temperature in the range of 20=0.59- 10°. All samples interlayer, or the monomers polymerization in the interlayer,were cured before examined by X-ray diffraction (the curingthen montmorillonite is called in intercalation structure.When the platelet spacing further increases or randomly tillScanning electron microscope (SEM) images were obtained the platelet escaped the infuence of Van der Waals force, theby a Quanta 200 with EDAX energy dispersive spectrometermontmorillonite dispersed in separate sheets entirely in resin,(EDS). Softening point, curing time and flow distance of thethen the diffraction peak disappears and montmorilloniteresins were determined according to ZBG39005-89.is now in its exfoliation structure. The performance ofAfter preheated to 160C, 1,000 g of standard sand wasmontmorillonite modified phenolic resin is optimum whencharged into a laboratory muller. The sand was allowed tomontmorillonite is in its structure of exfoliation and uniformlyequilibrate to 135C, then 20 g of novolac resins was added,disperses in resin at nanoscales 014the sand and resins were mulled till 110C- 105C, and HTMAIn order to obtain the optimum process, the effect ofsolution, accounting for 10%- 15% of resin was added. Thestirring time and montmorillonite content on the structure and1.5 g of calcium stearate was added thereto, mulling continuedmorphology of phenolic resin was analyzed respectively. Byuntil the mixture was crumbled, and the coated sands werevarying the stirring time while keeping the montmorillonitethen discharged. Finally, the tensile and bending tests were content constant, it was found that the platelet spacingperformed on the resin coated sands in accordance with JB/increased monotonically with the stiring time. Figure 2 showsT8834-2001.intercalation and exfoliation for the phenolic resin with 5.4%Fracture deformation was measured during bending test. The montmorillonite that was stirred prior to polymerization fordisplacement transducer was reclined on the sample and was15 min, 30 min, 45 min, or not stirred at all under microwaveinitially set to zero, then loaded the specimen until fractured,irradiation. X-ray diffraction analysis shows that the plateletfinal reading from the displacement transducer was defined asspacing is 1.3 nm for not stirred sample, the platelet spacingfracture deformation.increased to 1.6 nm for the samples with 15 min stirring, and1.75 nm when stiring for 30 min, and there is no peak in the3 Results and Discussionstate of stiring 45 min, which implies that the montmorilloniteis completely in its structure of exfoliation. When the stiring3.1 Preparation of montmorillonite modifiedtime is no longer than 30 min, montmorillonite is mainly inphenolic resinintercalated structure. Montmorillonite is mainly in exfoliatedMontmorillonite monocrystal layer consists of a 2:1 layeredstructure when stirring longer than 40 min.structure of a dioctahedral aluminum sheet sandwiched betweentwo silica tetrahedral sheets of about 1 nm thick, and thecrystallographic structure of montmorillonite is schematicallyshowed in Fig. 1. Montmorillonite crystal is stack of themonocrystal layers which are linked by Van der Waals force,and the distance of layers is called platelet spacing (as doo inFig. 1). The platelet spacing can be calculated by Bragg equation2dsin0 =λ (d is the platelet spacing, 0 is the half incident angleand λ is incident rays wavelength) 16. Montmorillonite' s plateletspacing is about 0.96 nm in aggregate structure 5. The plateletFig. 2 XRD profiles for montmoillonite (content 5.4%) inphenolic resin with different stirring timesFigure 3 shows the XRD profiles of montmorillonite inphenolic resin with different montmorillonite contents (afterstirred for 45 min). For 2.7% and 5.4% montmorillonitecontent, there. 中国煤化工XRD profiles, sothe montmorillEiletely which canalso be confirmMHcNMHG4).For8.1%and9% montmorillonite, the peak location is the same and theFig. 1 Schematic diagram of ideal crystal structure ofplatelet spacing is 1.6 nm, which indicates that the averagemontmorillonite120Research & DevelopmentMay 2009Fig.4 SEM images of montmorillonite modified phenolicFig. 3 XRD profiles for montmorillonite in phenolic resinresin (stirring for 45 min, montmorillonite is 5.4wt.%)with different montmolonite content (stirring for45 min)3.2 Performance of montmorillonite modifiedmontmorillonite platelet spacing does not depend on thephenolic resinmontmorillonite content once the content exceeds the limit.(1) Softening pointMontmorillonite can only be intercalated structure when theThe performances of montmorillonite modified phenolicmontmorillonite content is less than 5.4%. Therefore, the resin were tested, and the data is summarized in Table 1.optimum process under microwave iradiation is stiring for 45It was found that the overall performances were improvedmin and the montmorillonite is 5.4%.significantly except for a slight decrease in gelation speed.Table 1 Comprehensive performance of montmorillonite modified phenolic resin*MontmoilloniteSofteningFlowThermalCold tensileAverage molecularCuring timecontentpointabilitytensile strengthstrengthweightwt.%mmMPa85597:301.122.622.31951.853.825.8611562.134.208.129781.963.76* The molar ratio of formaldehyde to phenol is 0.82.Softening point is taken as critical assessment to differentiatethe license tag of the phenolic resin for shell process. Figure 5shows that softening point decreases with the increase ofmontmorillonite content. When the montmorillonite contentexceeds 5.4%, the decrease of softening point becomesfaster. The softening of polymer corresponds to the increasedmotion freedoms of the molecular chain, and the energy ofmolecular chain' s movement increase with lengthening ofmolecular chain. Therefore, the softening point is thecharacteristics of average molecular weight (M,) of resin, andthe decrease of softening point is attributed to the reductionof M. The M。of resin was measured and calculated by gelpermeation chromatography (GPC), as listed in Table 1, whichFig. 5 Effect of montmorillonite content on the softeningpoint of modified resinconfirms that the M。of resin decreases with the increase ofmontmorillonite content. The reduction of M can be attributedto the concentration of montmorillonite platelet, whichbecomes faster.restrains the motion of long molecular chain and decreases the(2) Flow abilityprobability of the growth of long molecular chain, thus the M.Flow ability中国煤化工Y parameterof resin decreases. When the montmorillonite content exceedsfor preparing I:MYHCNMHG;v ability of5.4%, montmorillonite has mainly intercalated structure andmontmorillonite; improvedaggregates, which makes the long molecular chain moving remarkably, especially when the montmorillonite content ismore difficult, therefore the decrease of softening point5.4%. Figure 6 shows that the flow ability of montmorillonite121.CHINA FOUNDRYVol.6 No.2modified phenolic resin increases with the increase ofmontmorillonite content. As the montmorillonite contentexceeds 5.4%, the flow ability begins to decrease. There aretwo reasons to cause this phenomenon. First, the decrease ofM。of resin leads to an improvement of fow ability. Secondly,the nanoscales platelet dispersed in resin increases the distanceof long molecular chains and damages the polarity connectionof molecular, therefore the Van der Waals force of molecularis decreased and the flow ability of modified resin is improved.When the montmorillonite content is more than 5.4%, theintercalated structure and aggregate absorbs long molecularchain, therefore the Van der Waals force of molecular chainincreases and, adversely the flow ability of resin decreases.Fig. 7 Effect of montmorillonite content on the strength ofresin coated sandfracture deformation were used to characterize the toughnesspropertyls. The high hot flexural strength and large fracturedeformation correspond to good toughness. The effect ofmontmorillonite content on the toughness properties of resincoated sand is shown in Fig. 8. It can be seen clearly thatthe thermal flexural strength and fracture deformation ofmontmorillonite modified phenolic resin coated sand wereimproved remarkably compared with those of resin withoutmodification. The maximum toughness was achieved whenmontmorillonite content is 5.4%.Fig. 6 Effect of montmorillonite content on the flow abilityof modified resin(3) Gelation speedGelation speed is defined as the time required from softeningto melting, flowing and until the gelation of phenolic resinthat blended with curing agent. It is used for measuring thecuring time of resin, fast gelation means short curing time.The gelation speed of montmorillonite modified phenolic resindecreases slightly with the increase of montmorillonite content.This is due to low molecular weight (which needs morereaction time for cure) and montmorillonite platelet structureFig. 8 Effect of montmorillonite content on toughness(which hinders the collision of resin and curing agent).properties of resin coated sands(4) Strength and toughness of resin coated sandThe tensile strength of coated sand prepared by modifiedThe reason for the increase of tensile strength and toughnessphenolic resin is showed in Fig. 7. It was found that bothproperty of coated sand prepared by modified phenolic resin ishot and cold tensile strength increased with increasing due to the exfoliation of montmorillonite in the resin. Althoughmontmorillonite content at first, and started to decreasethe montmorillonite cannot absorb strain well, it can increaseonce montmorillonite content is more than 5.4%. When thethe material's toughness by roughening. Examination of themontmoillonite content is less than 5.4%, montmorillonite fracture surfaces reveals a substantial increase in the areais completely in exfoliated structure and uniformly dispersesof fracture via roughening. The implication is that the highin resin, so the tensile strength increased with the increase strength of the smectite platelets prevents their fracture whenof montmorillonite content. When montmorillonite content the polymer fails. The bonding between the montmorilloniteis more than 5.4%, montmorillonite is mainly in intercalatedand the polymer is substantial enough to transmit stressstructure and aggregate, which lead to uneven distribution of through the interfacial area and spread the effective area ofmontmorillonite in resin and weak boundary layer. Thus, thedeformation,中国煤化工of the inorganicetensile strength of resin coated sand begins to decrease.phase and theYHCNM HGYy of the polymerThe phenolic resin after curing is brittle, and the coated sandin the interfacipagate around thecore often cracks during pouring. This is closely related to themontmorillonite in a tortuous path that requires more energy.toughness property. In this study, hot flexural strength andBecause the bonding is better in montmorillonite modified122Research & DevelopmentMay 2009phenolic resin, the crack must overcome a more significantthe 5th International Conference on Engineering and Digitalbarrier to move along the interface when comparing withEnterprise Technology, Guiyang, China, 2006: 419- -423.7] Mwaikambo L Y, Ansell M P. Cure characteristics of alkalitraditional composites.catalysed cashew nut shell liquid-formaldehyde resin. Journalof Materials Science, 2001, 36 (15): 3693- -3698.4 Conclusions8] Hong K C, Ravasi M, Keil N, Vigeant B, Ma Y S. Effect oforganic acids on the mechanical properties of phenolic resin(1) Montmorillonite modified phenolic resin can be easilycomposites. Journal of Applied Polymer Science, 2000, 76(5):prepared under microwave heating. X-ray diffractions of642- -647.montmorillonite in phenolic resin showed that the platelet9] Wu H D, Chu P P, Ma C M. Thermodynamic properties of the .novolac type phenolic resin blended with polyhydroxy ether ofspacing increases with stirring time till exfoliation ofbisphenol A. Polymer, 1998, 39(3);: 703-709.montmorillonite. Montmorillonite can only exist in intercalated[10] Choi M H, Chung I J. Mechanical and thermal properties ofstructure when the montmorillonite content is more than 5.4%.phenolic resin-layered silicate nanocomposites synthesizedTherefore the optimum process is stirring for 45 min and theby melt intercalation. Journal of Applied Polymer Science,montmorillonite addition is 5.4%.2003, 90(9): 2316- -2312.(2) The softening point and flow ability of modified phenolic1] Jiang W, Chen S H, Chen Y. Nanocomposites from phenolicresin and various organo-modified montmorillonites:resin are improved remarkably by montmorillonite, especiallyPreparation and thermal stability. 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