Effects Of Nanoclay On Cellular Morphology And Water .
Iran. J. Chem. Chem. Eng.Research ArticleVol. 36, No. 4, 2017Effects of Nanoclay on Cellular Morphologyand Water Absorption Capacity ofPoly(vinyl alcohol) FoamJahanmardi, Reza* ; Eslami, Behnam; Tamaddon, HamedDepartment of Polymer Engineering, Science and Research Branch, Islamic Azad University, Tehran, I.R. IRANABSTRACT: The present work was aimed to examine the effects of incorporation of each oftwo different types of nanoclay, i.e. Cloisite Na and Cloisite 30B, into PVA foam on cellularmorphology and water absorption capacity. Foam samples containing 0.0-10.0 wt% of eachof the two types of nanoclay alone were prepared using mechanical foaming. Accordingly,PVA/organoclay/water suspensions were prepared first. Then other agents, i.e. catalyst, surfactantand crosslinking agent were added, respectively, to each of the prepared suspensions renderingprimary froths, which were converted to final foam samples at room temperature during a periodof 24 h. State of clay dispersion in the polymer matrix and cellular morphology of the prepared foamsamples were examined using X-Ray Diffraction (XRD) technique and Field Emission ScanningElectron Microscopy (FESEM), respectively. Also, dry foam density and water absorptionof the foam samples were measured gravimetrically. XRD patterns revealed the existence of intercalatedand exfoliated structures in the PVA/Cloisite 30B and the PVA/Cloisite Na foam samples,respectively. FESEM images demonstrated open-cell morphology for all the samples but the extentof cell wall rupture was more significant in the case of PVA/nanoclay foam samples. In addition,water absorption capacity of the PVA foam was shown to be decreased by the incorporationof either of the two types of nanoclay, which was explained in terms of the lower total pore volumein the PVA/nanoclay foam samples than in the neat PVA foam sample. Finally, the obtained resultswere explained in terms of the effects of the nanoparticles on the elevation of the rate of the drainagein the crosslinking PVA solution before the stabilization of the cellular structure.KEYWORDS: Nanocomposite; Foam; Cellular morphology; Poly(vinyl alcohol).INTRODUCTIONPolymeric foams are a class of materials whichcontain gas bubbles surrounded by polymeric matrix.Plastic foams are known for their excellent heat andsound insulations, high strength-to-weight ratio, highenergy or mass absorption, and materials saving [1-3].So, polymer foams have diverse application in a vastarea, such as, packaging, thermal insulation, acousticattenuation, membranes for separation, absorbents andso forth [4-6]. Foams of high porosity with interconnectedpores have also been used as tissue engineering scaffolds* To whom correspondence should be addressed. E-mail: r.jahanmardi@srbiau.ac.ir1021-9986/2017/4/59-679/ /5.9059
Iran. J. Chem. Chem. Eng.Jahanmardi R. et al.for cell attachment and growth [7]. Polymer foamscan be defined as either closed cell or open cell foams.In closed cell foams, the foam cells are isolated from eachother and cavities are surrounded by complete cell walls.In open cell foams, there is not certain wall between cellsand the structure is conjunct. Generally, closed cell foamshave lower permeability, leading to better insulationproperties. Open cell foams, on the other hand, providebetter absorptive capability.Poly(vinyl alcohol) (PVA) foams are rigid open-cellfoams that exhibit good mechanical propertiesat relatively low densities (0.02-0.2 g/cm3) [8, 9]. Theirunique properties, i. e., abrasion resistance, resiliency,high water absorption capacity and chemical stability,make them excellent choice for various applications,such as, washcloths, mops and surgical pads. These propertiesmake PVA foamed composites a good candidate forsurgical implants and dressings [10,11]. The wet foamsmake excellent dressings for burns, since they protectthe wound while keeping the area irrigated and allowing airto pass into the wound. However, the open-cell structureand hydrophilic nature of PVA foam restricts its usein both construction and packaging. Furthermore, the foamshave the capacity to accept large quantities of filler(800-1200%wt) without big change in their original properties.Besides, nanocomposites are a new class of materialsproviding superior properties compared to their microcomposite counterparts. Nanocomposites usually refer tocomposites in which at least one phase (the filler phase)possesses ultrafine dimensions (on the order of a fewnanometers). An addition of a small amount ofnanoparticles can significantly improve a variety ofproperties without sacrificing the lightweight of polymermatrices [12-14]. The combination of functionalnanofillers and foaming technology has a high potentialto generate a new class of materials that are light, strong,and multifunctional [15]. Hence, in recent years, polymernanocomposite foams have received increasing attentionin both the scientific and industrial community [16, 17].Nanocomposite foams have a high position and vast areaof applications, such as aerospace, automotive, packagingand home appliances.Low density is one of the most attractive properties ofpolymer foams as a light weight substitute for structuralor functional materials. However, the polymer foams’mechanical properties are almost always compromised60Vol. 36, No. 4, 2017after density reduction [18]. A combination of lightweight and high strength has always been the majorresearch objective in the research area of polymer foams.The physical and mechanical properties of polymer foamsnot only depend on the intrinsic properties of thepolymer, but also on the microstructure of the foam, suchas cell density, cell size and cell size distribution.The present study was carried out in order to examinethe capability of nanoclay in enhancement of waterabsorption capacity of PVA foams. Hence, we triedto prepare PVA/nanoclay nanocomposite foams, for the firsttime. Then, effects of incorporation of two different typesof nanoclay, i.e., Cloisite Na and Cloisite 30B, into PVAfoams on cellular morphology and water absorptioncapacity of the foams were investigated.EXPEIMENTAL SECTIONMaterialsIn this study, poly(vinyl alcohol) with averagemolecular weight of 72 kDa and hydrolysis degree of 99%was purchased from Merck Chemical Co. Two types ofmontmorillonite clay including sodium containing naturalmontmorillonite (with trade name of Cloisite Na ) andorganically modified nanonoclay (with trade name ofCloisite 30B) from Southern Clay Products Inc. wereused. Cloisite Na had Cation Exchange Capacity (CEC)of 92.6 meq per 100 g of clay and amount of clay surfacemodification in Cloisite 30B was equal to 90 meq per100 g clay. Formaldehyde in the form of 37% aqueoussolution from Sigma-Aldrich Chemical Co., polysorbate20 from Sino-Japan Chemical Co. and sulfuric acid(98% aqueous solution) and sodium hydroxide from MerckChemical Co. were used as received.Synthesis of poly(vinyl alcohol) nanocomposite foamsNanocomposite foams containing 0.0-10.0 wt% ofeach of the two types of nanoclay alone were preparedaccording to the following procedure: Firstly, fineorganoclay/water suspensions were prepared throughstirring for 2.5 h at 6000 rpm followed by sonication for15 minutes. Each of the prepared suspensions was thencombined with a certain amount of PVA/water solutionand stirred to render a homogeneous suspension in whichthe final concentration of the polymer was 10% by weight.Each of the aqueous PVA/clay suspensions wasthen sonicated for an extra 15 minutes. Certain amounts
Iran. J. Chem. Chem. Eng.Effects of Nanoclay on Cellular Morphology .Vol. 36, No. 4, 2017Scheme 1: Crosslinking and acetalization reactions of poly(vinyl alcohol) with formaldehyde [19].of sulfuric acid solution (65%) were then mixed with eachsuspension so that the final concentration of the acid became14% by weight. Then each prepared suspension was pouredinto a plastic vessel equipped with a rotary beater andwas mixed with certain amount of polysorbate 20 (i. e., 50%by weight of the polymer in the suspension) and the beaterwas increased to its highest speed (1000 rpm) untilan equilibrium maximum froth volume was reached.The aqueous solution of formaldehyde was then addedto the froth and let to be mixed for two minutes more.The amount of formaldehyde used was 51% by weight ofthe polymer which was 50% more than its stoichiometricratio to the polymer in the crosslinking reaction of thepolymer according to Scheme 1 [19]. The froth was thenpoured into a plastic mold and kept at room temperature fora period of 24 hours after which the cured foam was washedwith NaOH solution in order to neutralize the residual acidand formaldehyde. The procedure is illustrated schematicallyin Scheme 2. Also, sample designation and formulation ofthe prepared foam samples are given in Table 1.Measurements and characterizationsThe interlayer spacing of the organoclays wasmeasured by X-Ray Diffraction (XRD) technique usinga X’ Pert MPD model Philips instrument equipped with Curadiation source at 40 kV, 30 mA, λ 0.1542 nm, 2θranging between 2 and 10 and imaging speed of 0.01 s-1.The peak position in the spectrum (2θ) and the Braggequation as it is shown in equation (1) were used tocalculate distances between clay layers:n 2dsin (1)where, n is an integer, λ is the wavelength of X-raybeam (0.1542 nm), and d is the interplanar spacing ofthe organoclay crystals.The morphology of the prepared poly(vinyl alcohol)foams was observed by field emission scanning electronmicroscopy (FESEM) using a Leo 440i unit. Specimensfor FESEM were freeze-fractured in liquid nitrogen andthe fracture surface was sputter-coated with gold in argonplasma for 3 min. Images were obtained using 15kVaccelerating voltage.Water absorption capacity of the prepared foams wasmeasured according to ASTM C272. Firstly, five 75 75 12 mm3cubic specimens were cut from each foam sample.Then the specimens were dried in an oven, allowed to coolin a desiccator and then were weighed on an analyticalbalance to the nearest 0.01 g. The specimens thenwere immersed in deionized water to a depth of 50 mm andwere removed from the water after 24 hours. The specimenswere weighed immediately after that all surface water was wipedoff with a dry cloth. Water absorption capacity was definedas the maximum amount of water absorbed by dry foamand was expressed as wt% of the dry foam.In order to determine dry foam density, preparedfoams were dried and cut into small cubes using a chainsaw. Dimensions and weight of each cube were preciselymeasured and the cube density was simply calculatedby dividing the cube weight to its own volume. The drydensity of each foam sample was expressed asthe average of at least five cubic specimens.RESULTS AND DISCUSSIONState of clay dispersion in the prepared nanocompositesfoamsXRD technique has been extensively used fordetermination of the gallery height (d-spacing distance)in clay stacked particles [20]. XRD patterns of neat Cloisite30B and PVA/C5 foam sample containing 5 wt% of61
Iran. J. Chem. Chem. Eng.Jahanmardi R. et al.Vol. 36, No. 4, 2017Table 1: Formulation of the prepared PVA foam samples.Sample designationCliosite 30B (wt %)Cloisite Na -MMT (wt %)PVA0.0 (neat poly(vinyl alcohol) PVA/N1-1.0PVA/N2-2.0PVA/N5-5.0PVA/N10-10.0Scheme 2: A schematic representation for the procedure of the preparation of the nanocomposites foam samples.62
Effects of Nanoclay on Cellular Morphology .16000160001400014000Intensity (arbitrary unit)Intensity (arbitrary unit)Iran. J. Chem. Chem. Eng.12000100008000600040002000Vol. 36, No. 4, 201712000100008000600040002000000246810122 theta (degree)0246810122 theta (degree)Fig. 1: XRD patterns of (a) neat Cloisite 30B nanoclay and,(b) PVA/C5 foam sample.Fig. 2: XRD patterns of (a) neat Cloisite Na nanoclay and,(b) PVA/N5 foam sample.Cloisite 30B are shown in Fig. 1. As it is seen inthe figure, Cloisite 30B powder shows a diffraction peakat a 2θ angle of 4.86 which is corresponding to a d-spacingof 1.82 nm according to the Bragg equation. On the otherhand, the diffraction peak of the nanoclay in the PVA/C5foam sample has been weakened significantly andthe peak position has been shifted to 2θ angle of 4.46 .This indicates the formation of intercalated structures ofCloisite 30B in which the d-spacing of the clay plateletshas been increased to 1.98 nm. Also, XRD patterns ofneat Cloisite Na and PVA/N5 foam sample containing5 wt% of Cloisite Na are shown in Fig. 2. It is seen thatCloisite Na exhibits a diffraction peak at a 2θ angle of7.71 , which corresponds to a d-spacing of 1.15 nm.It should be mentioned that the calculated d-spacing of bothCloisite 30B and Cloisite Na are in close agreementwith the d-spacing values of 1.85 nm and 1.17 nm,respectively, provided by the supplier. Moreover,no diffraction peak is seen for Cloisite Na in the XRDpattern of the PVA/N5 foam sample that could beattributed to the exfoliation of the stacked structure of thenanoclay. It could be concluded that as Cloisite Na nanoclay has higher surface polarity, compared toCloisite 30B, interactions between the polar polymerchains and surfaces of the nanoclay particles in thePVA/Cloisite Na nanocomposite foam sample arestronger than those in the PVA/Cloisite 30Bnanocomposite foam sample [21]. So, the morecompatibility between the polymer and the nanoparticlesin the PVA/Cloisite Na nanocomposite foam leadsto a better state of dispersion in this nanocomposite incomparison to that in the PVA/Cloisite 30Bnanocomposite foam.Water absorption capacity and dry bulk density ofthe prepared foamsOne of the most important features of PVA foams istheir high water absorption capacity. So, water absorptioncapacity of the prepared foams was measured in this workand the obtained data is presented in Fig. 3. As it is seenin Fig. 3, the incorporation of each of the two types ofnanoclay into PVA foam results in a significant decreasein water absorption capacity of the prepared PVA foamsand the amount of the diminution is proportional to theconcentration of the nanoclay in the foam sample.As water is absorbed to the hydrophilic surface of cell wallsof PVA foam, it could be expected that water absorptioncapacity of PVA foam depends on its overall surfaceof cell walls. In addition, the overall surface of cell wallsin a PVA foam is dependent on its total pore volume which,in turn, is inversely proportional to its dry bulk density.Accordingly, dry bulk density of all the prepared PVAfoam samples was measured in order to examinethe above elucidation. The obtained data is illustrated in Fig. 4.As it is seen in in Fig. 4, dry bulk density is increasedby the incorporation of each type of nanoclay alone andthe amount of the enhancement of the density is proportionalto the concentration of the nanoclay in the foam sample.Therefore, this observation justifies the aboveexplanation. Accordingly, it could be concluded that the63
Iran. J. Chem. Chem. Eng.Jahanmardi R. et al.0.12Sample 091.600PVA/C1Dry foam density (g/cc)0.11.800PVAWater absorption capacity (%)2.0000.110.05Vol. 36, No. 4, 2017Sample designationFig. 3: Water absorption capacity of the prepared PVA foamsamples.Fig. 4: Dry bulk density of the prepared PVA foamsamples.incorporation of nanoclay into the PVA foam samplesdecreases their expansion ratio and their total porevolume, which, in turn, results in the enhancement of theirdry bulk density. Moreover, the data presented in Figs. 3and 4 suggest that each PVA foam sample containingCloisite Na has slightly higher water absorptioncapacity and relatively lower dry foam density incomparison with the PVA foam sample containingthe same concentration of Cloisite 30B. This observationis in agreement with the above explanation. However,finding a reason for the different expansion ratiosobtained by the incorporation of the same amount of eachof the two different types of nanoclay alone requiresevaluation of the cellular morphology of the preparedfoam samples which will be presented in the followingsection.for all the three samples, which is a general phenomenonfor poly(vinyl alcohol) foams [8, 9]. This is due to the factthat all liquid foams (froths) are thermodynamicallyunstable because of their higher surface free energyin comparison with their initial segregated gas and liquidforms. Thus, all liquid foams have a tendency to reducetheir free energy via collapse of foamed structure, whichin turn, takes place gradually through drainage and thinningand rupture of cell walls. Another driving forcefor thinning of cell walls and drainage is gravitational forces.The phenomenon could be detected in practice whena mold is filled with a crosslinking PVA froth. After a timea liquid layer appears at the bottom of the mold, whichcontains water, unreacted PVA, formaldehyde, acid andsurfactant. The liquid layer rises until the foam hascrosslinked and its cellular structure has been stabilized.On the other hand, crosslinking reaction of PVA foamprevents drainage and hence, rupture of cell walls throughincreasing elasticity, strength and insolubility of cell walls.Therefore, one can expect that the final morphology ofPVA foam is controlled by the competition between twofactors: first, the rate of drainage which depends onthe surface tension and the viscosity of PVA solution,and second, the rate of crosslinking which is dependent onthe concentration of PVA resin, acid catalyst andformaldehyde. In the case of the formulations usedin our work which is similar to the formulation used forthe production of most commercial PVA foams,the competition led to the observed open-cell structure.Cellular morphology of the prepared foam samplesIn order to find a reason for the observed effects of theincorporation of each of the nanoclays on expansion ratioof the prepared PVA foam samples, cellular morphology ofthe foams was studied by using FESEM. FESEM imagesof neat PVA foam sample and the PVA/C1 samplecontaining 1% by weight of Cloisite 30B and the PVA/N1sample containing 1% by weight of Cloisite Na ,respectively, are illustrated in Fig. 5, with three differentmagnification factors. In images a-1, b-1 and c-1of Fig. 5,which have the lowest magnification factor amongthe other images of the figure, open-cell morphology is seen64
Iran. J. Chem. Chem. Eng.Effects of Nanoclay on Cellular Morphology .Vol. 36, No. 4, 2017Fig. 5: FESEM images of (a-1 to a-3) PVA, (b-1 to b-3) PVA/C1 and (c-1 to c-3) PVA/ N1 foam samples withthree different magnifications. Magnification factors are specified at the bottom of the images.In addition, through comparison of the images a-2,b-2 and c-2 of Fig. 5, it could be deduced that the localcollapse of the cellular structure is more pronouncedin the nanocomposite foam samples. Moreover, bycomparing images a-3, b-3 and c-3 of Fig. 5, which havehigher magnification factor and hence, could show moredetails about the cell walls, one can infer that the ruptureof cell walls has occurred more severely in the PVA/C1and the PVA/N1 samples than in the PVA sample.This phenomenon could be ascribed to the followingtwo reasons: First, increase of density of the foaming solutionby the incorporation of nanoclay which in turn, enhancesthe rate of the drainage before the stabilization ofthe foam structure, and second, that the nanoclay plateletsmay act as shields which obstruct the formationof crosslinks between adjacent poly(vinyl alcohol) chainsaccording to Scheme 3, and hence, delay the stabilizationof the cellular structure. A similar role for nanoclayplatelets in polyurethane foams was mentioned byLee et al. [15]. However, it should be noted here thatthe proposed mechanism is elementary and additionalanalytical experiments is required to prove it. As a whole,one can conclude that the
Effects of Nanoclay on Cellular Morphology and Water Absorption Capacity of Poly(vinyl alcohol) Foam Jahanmardi, Reza* ; Eslami, Behnam; Tamaddon, Hamed Department of Polymer Engineering, Science and Research Branch, Islamic Azad University, Tehran, I.R. IRAN ABSTRACT: The present work was aimed to examine the effects of incorporation of each of two different types of nanoclay, i.e. Cloisite .
methods and to investigate the effects of nanoclay reinforcement on the wear and microhardness of GICs. The incorporation of small amounts of nanoclay as reinforcing fillers in dental materials has shown a remarkable impact on mechanical properties [11]. The nanoclay (montmorillonite) used in this work is a member of the smectite clay family (2:1 layered silicates or phyllosilicates), and has .
EFFECTS OF DIFFERENT NANOCLAY LOADINGS ON THE PHYSICAL AND MECHANICAL PROPERTIES OF MELIA COMPOSITA PARTICLE BOARD This study investigated the effects of adding a filler of nano-sized particles of Cloisite Na (nanoclay) to urea-for-maldehyde resin on the physical and mechanical properties of particle boards made with this resin. Cloisite Na was introduced at rates of 2%, 4% and 6% of the dry .
The effects of nanoclay on surface morphology, degradation rate, thermal characteris-tics, mechanical properties, in vitro biomineralization, and cellular interactions were evaluated. We hypothesize that the nanoclay-enriched electrospun structure can support the osteogenic differentiation of hMSCs, along with the pro- duction of mineralized matrix. The features would enable the use of .
The effects of nanoclay and glass fiber on the microstructural, mechanical, thermal, and water absorption properties of the recycled WPCs were investigated. X-ray diffraction showed that the nanoclay intercalates in the WPCs. Additionally, scanning electron micrographs revealed that the glass fiber is adequately dispersed. According to the analysis of mechanical properties, the simultaneous .
Comfortex Cellular, Prelude Shades and Cellular Blinds Price List and Reference Guide Effective April 1, 2018 This price list and reference guide contains product pricing, product specifications and technical information for the complete line of Comfortex Cellular, Prelude Shades and Odysee Cellular Blinds. Cellular and Prelude Shades Overview
CLAY NANOPARTICLES EFFECTS ON PERFORMANCE AND MORPHOLOGY OF POLY(VINYLIDENE FLUORIDE) MEMBRANES A . (PVDF-Nanoclay and PVDF-PVP-Nanoclay) membranes is presented. All membranes were synthesized by the phase inversion process, using 18% PVDF, n-methylpyrrolidone as solvent and water as the non-solvent. Demineralized water cross-flow permeation tests were conducted to evaluate the membranes .
Nanoclay and Water Uptake Effects on Mechanical Properties of Unsaturated Polyester Necar Merah and Omer Mohamed Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Correspondence should be addressed to Necar Merah; nesar@kfupm.edu.sa Received 15 September 2018; Accepted 18 November 2018; Published 3 January 2019 Academic Editor: Jim .
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