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PVC 基多 元增韧 复合材料 制备 性能 研究

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PVC基多元增韧复合材料的制备与性能研究,PVC,基多,元增韧,复合材料,制备,性能,研究

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Investigation of the Addition of Nano-CaCO3at DryMixing or Onset of Fusion on the Dispersion, Torque,and Mechanical Properties of Compounded PVCS.H. Sajjadi Jazi, M. Nasr Esfahany, R. BagheriDepartment of Chemical Engineering, Isfahan University of Technology, Isfahan 8415683111, IranA Brabender torque rheometer equipped with an internalmixer was used to study the influence of compoundingmethod on the properties of (rigid PVC)/(treated anduntreated nano-CaCO3) nanocomposites. Two differentmethods were studied for the addition of surface treatedand untreated nano-CaCO3during the melt mixing ofrigid PVC. Direct dry mixing of rigid PVC and nano-CaCO3, and addition of nano-CaCO3at the onset of PVCfusion were investigated. Dispersion of treated anduntreated nano-CaCO3was studied by X-ray diffractionand scanning electron microscopy. Results showed thatusing direct dry mixing improved the dispersion of nano-CaCO3in the PVC matrix by lowering the fusion time.The mechanical properties of the nanocomposite sam-ples such as impact strength, tensile strength, and elon-gation at break were improved by using this method.The addition of treated nano-CaCO3at the onset offusion caused a simultaneous decrease in torque. Also,rigid PVC nanocomposites prepared with treated nano-CaCO3showed better mechanical properties than thoseof nanocomposites prepared with the untreated nano-CaCO3.J. VINYL ADDIT. TECHNOL., 18:153160, 2012.2012Society of Plastics EngineersINTRODUCTIONIn recent years, organicinorganic composites, particu-larlynanocomposites,havereceivedgreatattentionbecause these materials often exhibit unexpected proper-ties 1. Various nanoscale fillers, including montmorillon-ite, silica, calcium carbonate, and aluminium oxide, havebeen reported to improve the mechanical and thermalproperties of polymers, such as toughness, stiffness, andheat resistance 2, 3. The effects of fillers on the me-chanical and other properties of the composites dependstrongly on particle shape and size (aspect ratio), aggrega-tion size, the fraction of filler, surface characteristics,degree of dispersion, and interactions between the fillerparticles and the polymer matrix 25.Nanoscale calcium carbonate (nano-CaCO3) is one ofthe most common spherical nanoscale fillers being usedto prepare nanocomposites 6. The CaCO3 has attractedmore attention because it eliminates HCl gas that is foundduring the thermal degradation of PVC 7. Owing totheir high surface energy and surface area, nanoparticleshave a strong tendency to agglomerate, thereby makingthe homogeneous dispersion of nanoparticles in a polymermatrix the most important problem in nanocompositepreparation 8, 9. In situ polymerization of vinyl chloride(VC) in the presence of CaCO3nanoparticles lead to thebreakdown of the agglomerates of these particles 9.Untreated nano-CaCO3particles were reported to agglom-erate in the polymer matrix due to their large specific areaand high polar surface energy 10. It was also reportedthat surface treated CaCO3prevented agglomeration, thusimproving the dispersion of nano-CaCO3particles in thepolymer matrix.The effect of nano-CaCO3on the mechanical proper-ties of PVC has been studied by several authors 3, 4, 1013. It was reported that the impact strength and youngsmodulus were noticeably improved by the addition of 525phr (parts by weight per hundred parts of resin) nano-CaCO3, but the yield strength and elongation at break werereduced. The optimum content of nano-CaCO3particles forthe best impact strength was reported to be about 15 phrfor PVC/nano-CaCO3composites 10, 12.The effect of montmorillonite addition sequence duringPVC compounding on the performance of PVC/(layeredsilicate) nanocomposites was studied 14. Four differentcompoundingadditionsequenceswereexamined:(i)direct dry mixing of PVC and nanoclay, (ii) addition ofnanoclay at compaction, (iii) addition of nanoclay at onsetof fusion, and (iv) addition of nanoclay at equilibrium tor-que were studied and it was concluded that the incorpora-tion of nanoclay (montmorillonite (MMT) and organic-modified montmorillonite (OMMT) at the onset of fusionresulted in a much better dispersion and overall perform-ance of the composites. This finding motivated us to studythe addition sequence for nano-CaCO3compounds. Thus,in the present study, we seek to ascertain the effects ofCorrespondence to: M. Nasr Esfahany; e-mail: mnasrcc.iut.ac.irDOI 10.1002/vnl.20317Published online in Wiley Online Library ().? 2012 Society of Plastics EngineersJOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012the direct dry mixing of nano-CaCO3particles with PVCand the addition of nano-CaCO3into the PVC at the onsetof fusion, on the dispersion and mechanical properties ofthe composites.EXPERIMENTALMaterialsThe study used commercial-grade raw materials. Sus-pension-grade PVC with a K value of 6567 was obtainedfrom CGCP, Thailand. Other additives were suppliedfrom Baerlocher (Germany). The PVC formulation isshown in Table 1. The mean particle size of the treatednano-CaCO3is 76 nm (surface is modified by a fattyacid), and the mean particle size of the untreated nano-CaCO3is 70 nm; both are offered by Solvay AdvancedFunctional Minerals (the product names are WINNOFILand SOCAL, respectively).Preparation of Samples1. For direct dry blending of nano-CaCO3 with PVC beforemelting, PVC powder and processing additives have beenhand-mixed for 5 min. Then, nano-CaCO3was added, andhand-mixing was continued for about 5 more minutes.The mixture was then melted by using a Brabender Plas-tograph EC apparatus equipped with an electrically heatedmixing head (W 50 EHT mixer) and having a 50 cc vol-ume capacity and two noninterchangeable rotors. Theprocessing temperature, rotor speed, and blending timewere set to 1708C, 60 rpm, and 5 min, respectively.2. For blending at the onset of fusion, PVC and additiveswere introduced into the mixer under the previous condi-tions. When the compounds reached the onset of fusion,according to curve of torque versus time, nano-CaCO3particles were added.Each sample weighted 60 g and occupied 80% of themixer capacity. The compounds of the composites wereobtained in the form of lumps at a high temperature.These lumps were immediately compression-molded at1808C under 230 bars for 5 min in order to obtain tensileand impact specimens.CharacterizationTensile strength testing was carried out by using aHounsfield tensile testing machine according to ISO 527.Dumb-bell-shaped test specimens were tested at a strainrate of 10 mm/min. Notched Izod impact specimendimensions were 4 3 10 3 80 mm3, and the impactenergy was 2.5 j. Each property was measured at least sixtimes, and average was reported.The impact fractured surfaces were examined with anSEM(scanningelectronmicroscopy)X60(Tokyo,Japan)at an accelerating voltage of 20 Kv. The frac-tured specimen surfaces were coated with a thin layer ofgold. The coating was carried out by pacing the specimenin a high-vacuum evaporator and vaporizing the metalheld in a heated tungsten basket.X-ray diffraction (XRD) showed the agglomeration ofnano-CaCO3particles in the PVC matrix. The XRD anal-ysis was performed on X pertMPD PAN analytical(Philips) diffractometer by using CuKa (k 0.154) radia-tion at a generated voltage of 40 Kv and a current of 30mA at room temperature. The diffractions were scannedfrom 10 to 708 in the 2h range in 0.058 steps with a con-tinuous scan.RESULTS AND DISCUSSIONBehavior of PVC FusionUnderstanding PVC morphology is very important inthe study of the behavior of PVC fusion. The PVC is notsoluble in its monomer, thus when the PVC grows duringpolymerization process, it is precipitated from its mono-mer. Precipitated polymers form microdomains or submi-croparticles ?1030 nm in diameter 2, 15. The PVC hasless than 10% by weight of crystalline structure owing toits partially syndiotactic nature. The crystalline domainsact as slightly crosslinking points 16. Depending on thesize and perfection of the crystalline domains in PVC, itsmelting range varies between 115 and 2458C 17. How-ever, in the polymerization process, the microdomains areagglomerated to form primary particles 12 lm in size.The effect of these primary particles on flow behavior ofPVC is important 16. Many primary particles form agrain which is irregular in shape and about 100150 lmin size 2. To obtain good mechanical properties, grainboundaries must be eliminated, and microparticles mustbe compacted together. During further interdiffusion ofthe PVC chains, the boundaries between the submicropar-ticles disappear, and a three-dimensional network of poly-mer chains forms 14.The change in the applied torque with time during theprocessing of PVC in an internal mixer at 1708C is shownin Fig. 1. This process involves an initial mechano-chemi-cal stage, which causes damage to the polymer chains.Oxygen ingress is formally excluded by means of a hy-draulic ram; the only oxygen present is that initiallytrapped in the polymer particles. Figure 1 also relates theformation of entanglements in the polymer to the appliedtorque in the mixer. Two distinct stages in the growth ofTABLE 1.PVC formulationIngredientContent (phr)aPVC with K value 6567 (CGPC, Thailand)100Organic tin stabilizer (BS OM 1000)4Processing aid (Degalan 10-FD)2Calcium stearate1.6PE wax (BL PA-L)0.16Treated and untreated nano-CaCO3(Winnofil and Socal)15aParts by weight per hundred parts of resin.154JOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012DOI 10.1002/vnlboth these parameters can be observed. Both reach a highlevel in the first stage, and both show a higher level ofincrease in the second stage. In the PVC, both unsaturationand peroxides are produced during the first minute of proc-essing, and a tin stabilizer acts by retarding the formationof peroxides and the further formation of unsaturation.The mechanisms of PVC fusion have been studied indetail by several authors 15, 1719. The loading of thePVC compound into the hot rheometer mixing chamberbrings about a considerable increase of the torque (PointA, Fig. 1). At this point, the PVC grains are not packed,and they have their initial shape and size. After a shorttime (1015 s), owing to the rise of the sample tempera-ture above the glass transition temperature, the PVCgrains packed together, thereby showing a weak peak intorque. The PVC grains have not been destroyed yet.While the temperature of the sample is increased, thegrains soften and deform, and the torque continuouslydecreases until a minimum (Point B) is reached, at whichthe PVC grains are further compacted together. At thecompaction point (Point B), most of the PVC grains aretorn apart, and some of them are broken into primary par-ticles 19.Low interaction between the primary particlesis specified by the low torque 18. On the other hand,according to several studies, minimum point of torquecurve signifies the beginning of the gelation (fusion) pro-cess, and its numerical value allows us to determine thefusion percolation threshold as well as the work needed toperform the gelation of the PVC. So, minimum torqueachieves the free material flow that fills the chamber 20,and the torque starts to increase as melting entanglementand fusion begins. Subsequently, with increasing tempera-ture, interaction between the primary particles becomesstronger, thus causing increased entanglement of the PVCchainsandtherefore,theviscosityofthesampleincreases, thereby resulting in increase in torque 21. Atthe maximum torque, when interaction between the pri-mary particles reaches a maximum 17, torque shows amaximum as well. Point X shows the compaction and theonset of fusion. At this point, the material reaches a void-FIG. 1.Typical fusion curve of PVC.FIG. 2.XRD patterns of (rigid PVC)/(15 phr nano-CaCO3) with the different methods of preparation: (a)direct dry mixing of treated nano-CaCO3, (b) direct dry mixing of untreated nano-CaCO3, (c) addition oftreated nano-CaCO3at the onset of fusion, and (d) addition of untreated nano-CaCO3at the onset of fusion.DOI 10.1002/vnlJOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012155free state and starts to melt at the interface between thecompacted material and the hot metal surface. At thispoint also, the melt temperature is remarkably increased,and therefore the melt viscosity is decreased, and torquestarts decreasing. The time between the loading Point (A)and the fusion Point (X) is defined as the fusion time.Similarly,thetemperature,torque,andenergywithrespect to Point X are referred to as fusion temperature,fusiontorque,andfusionenergy,respectively22.Finally, at equilibrium torque (Point E), the particulatestructure of PVC begins to disappear entirely 14.Dispersion of Nano-CaCO3in the PVC MatrixFigure 2a2d shows the XRD patterns of (rigid PVC)/(15 phr treated and untreated nano-CaCO3) for both directdry mixing (Method 1) and addition of nano-CaCO3atthe onset of fusion (Method 2). A distinct peak appears at2h 298 for samples prepared by both methods, but thepeak heights are different. Figure 2a and 2d shows theshortest and highest peaks, respectively. When the peakheight becomes shorter, it can be inferred that the exfoli-ated structure is mixed with the intercalated structure 2,23. Since all samples have the same filler content, thedifferences between the peak heights are related to theagglomeration of nano-CaCO3particles. A higher peakshows that more agglomerates are present. It was shownthat the peak height at 2h 298 increased with increasingfiller content (15 wt%) 3.Figure 2b and 2c does not show a considerable differ-ence concerning their peak heights; thus agglomerates inthese two composites are approximately the same. TheseFIG. 3.SEM micrographs of the impact fracture surface of rigid PVC and (rigid PVC)/(15 phr nano-CaCO3), nanocomposites: (a) PVC without filler, (b) direct dry mixing of treated nano-CaCO3, (c) direct drymixing of untreated nano-CaCO3, (d) addition of treated nano-CaCO3at onset of fusion, and (e) addition ofuntreated nano-CaCO3at onset of fusion.156JOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012DOI 10.1002/vnlresults also show that dry blending of nano-CaCO3withthe PVC matrix results in better dispersion than the addi-tion of nano-CaCO3at the onset of fusion.In order to quantify the relative degrees of dispersionof treated and untreated nano-CaCO3particles within thePVC matrix and the effect of direct dry mixing of nano-CaCO3with the PVC matrix versus addition of nano-CaCO3at the onset of fusion, impact fracture surfaceswere observed in SEM micrographs (Fig. 3b3e). Figure3b and 3c is related to direct dry mixing of treated anduntreated nano-CaCO3with the PVC matrix. As can beseen, agglomerates of nano-CaCO3in Fig. 3b are fewerand smaller than those appear in Fig. 3c. As a result ofthe surface treatment of nano-CaCO3, good compatibilitywas achieved, and good compatibility also improved thedispersion and reduced the agglomerates of nano-CaCO3particles in the PVC matrix. Also, Fig. 3d and 3e demon-strates the addition of treated and untreated nano-CaCO3at the onset of fusion. The untreated nano-CaCO3par-ticles show poor dispersion in the PVC matrix, with sizesreaching up to 2 lm and with many cavities present,which lead to a reduction in interfacial contact areabetween the particles and matrix. Repeatedly, as shown inthesefigures,theadditionoftreatednano-CaCO3improved the dispersion of nano-CaCO3. Further, compar-ison of Fig. 3b and 3d shows that the addition of nano-CaCO3at onset of fusion was insufficient to disperseagglomerates of nano-CaCO3. Comparison of direct drymixing with addition of nano-CaCO3at the onset offusion shows that the improvement of dispersion of thenanoparticles is due to the increasing residence time ofnanoparticles in the internal mixer. Also, PVC and nano-CaCO3have longer mixing times, which can lengthen thenanoparticles under high stress fields. Consequently, thiseffect causes the agglomerates of nano-CaCO3to breakdown. These results are also in accordance with those ofX-ray analysis.Effect of the Method of Addition of Calcium CarbonateNanoparticles on the TorqueThe Brabender Plastograph was used in these tests, andthe torque was in proportion with mass of the sample.Figure 4 shows torque-time curves for direct dry mixingand addition at onset of fusion of treated and untreatednano-CaCO3. Figure 4a and 4b demonstrates the changesin torque and temperature versus time for treated anduntreatednano-CaCO3, directly dry-mixedwithrigidPVC. Both curves are similar. Figure 4b and 4c showsthe curves of torque and temperature-time related totreated and untreated nano-CaCO3addition at onset offusion. In this figure, the torque-time curves are com-pletely different. Addition of treated nano-CaCO3at theonset of fusion leads to strong decrease in torque, whileFIG. 4.Curves of torque and temperature-time for compounding of rigid PVC with nano-CaCO3: (a) directdry mixing of treated nano-CaCO3, (b) direct dry mixing of untreated nano-CaCO3, (c) addition of treatednano-CaCO3at onset of fusion, and (d) addition of untreated nano-CaCO3at onset of fusion. Color figurecan be viewed in the online issue, which is available at .DOI 10.1002/vnlJOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012157the addition of untreated nano-CaCO3at the onset offusion results in a slight increase in torque. This out isdue to the addition of untreated nano-CaCO3to moltenPVC. As the mass of sample in the chamber of internalmixer is increased, the torque is increased. So, after thehomogeneous dispersion of nano-CaCO3in molten PVCagain the torque is decreased. Moreover, by adding thetreated nano-CaCO3at the onset of fusion of PVC, themass of sample in the chamber of internal mixer isincreased, but because the fatty acid on the surface of thenano-CaCO3acts as a lubricant, it can reduce the torque.So, these two phenomena are compete with each other,and in a moment the torque is significantly reduced.Therefore, the treated nano-CaCO3can reduce friction,and torque is lowered. Also, in the case of the addition oftreated nano-CaCO3at the onset of fusion, the tempera-ture is slightly reduced for a short time. This reductionoccurs for two reasons: first, addition of treated nano-CaCO3decreases friction, and second, incorporation ofnano-CaCO3with environment temperature slightly low-ers the temperature of the molten mixture.Fusion MeasurementsThe results for time to fusion from the Brabender plas-tograph are shown in Table 2. These results show that thenano-CaCO3fillers reduced the time of fusion and thatthe treated nano-CaCO3resulted in the lowest time offusion. When the time of fusion is reduced, the melt stateis reached more quickly, so the nano-CaCO3particleshave remained under high shear stress for a longer time,thus resulting in better dispersion of nanoparticles. Fer-nando and Thomas 24 showed that as the size of nano-CaCO3was reduced, the time of fusion decreased. How-ever, during fusion process, the grains of PVC aredestroyed and converted into primary particle flow units,and at the time of fusion, some of these particles becomesubmicron particles in the nanoscale range. Matuana 14concluded that the incorporation of MMT and OMMT atthe onset of fusion would result in a much better disper-sion of nanoparticles in the matrix because of the reducedsize of the PVC particles, thus leading to better perform-ance. But, in the present study conflicting results for thecalcium carbonate nanoparticles were obtained. Sincefusion state is reached more rapidly for the direct drymixing method, and the total process time is constant, alonger time of mixing of nanoparticles with molten poly-mer is available, and better dispersion is expected.Dispersionofagglomerate depends on the forcesapplied to it and the forces holding it together. Dispersionoccurs most easily when the droplet viscosity is optimizedto 110 times lower than that of the continuous phase.When the droplet viscosity is very low, the material doesnot break up into droplets, but rather extends to a thinnerand thinner thread. In many cases, this is an adequateresult for dispersion. However, when the droplet viscosityis too high, the droplet cannot be broken down in shear,even at the highest stresses accessible. Under this condi-tion, the droplet is rotated and remains virtually sphericalin the shear field. Dispersion occurs much more readilywith elongational work than with shear work. This elon-gational work is also recognized as kneading. Dispersionby elongation is visualized in Fig. 5 15, 17.Results for temperature at 1 s are shown in Table 2. Atthis time, PVC without filler started fusion, but compo-sites of treated and untreated nano-CaCO3were com-pletely fused and had lower viscosity. This phenomenonhelped to improve the dispersion of nanoparticles. So,direct mixing of PVC and nano-CaCO3was more effec-tive in the dispersion of nanoparticles than the addition ofnano-CaCO3later at the onset of fusion.Mechanical Properties of (Rigid PVC)/(Nano-CaCO3)CompositesFigures 68 show the influence of the method of add-ing treated and untreated nano-CaCO3on the impactstrength, elongation at break, and tensile strength of rigidPVC composites, respectively. Figure 6 indicates thatdirect dry mixing of treated nano-CaCO3into the PVCmatrix improved the impact strength more than the directdry mixing of untreated nano-CaCO3into the matrix. Thisimprovement is attributed to the better compatibilitybetween treated nano-CaCO3and PVC matrix. It is alsoobserved that the impact strength resulting from directdry mixing of nano-CaCO3is higher than that from theaddition of nano-CaCO3at the onset of fusion. Theincreasing of impact strength through this addition methodresults from the longer residence time after fusion fordirect addition of nano-CaCO3. In this method of addi-tion, PVC and nano-CaCO3had a longer mixing time,which led to the reduction and breakdown of the agglom-TABLE 2.Temperature at 71 s and time to fusion of blends fromBrabender plastographMaterialsTime tofusion (s)Temperatureat 71 s vs. PVCwithout filler 8CPVC without filler91 6 10184Direct dry mixing of PVC and15 phr of treated nano-CaCO329 6 1196Direct dry mixing of PVC and15 phr of untreated nano-CaCO334 6 1198FIG. 5.Elongation of agglomerates or droplets is effective in disper-sion 15.158JOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012DOI 10.1002/vnlerates of nano-CaCO3particles. This process improvedthe dispersion, and under high stress, primary particleflow units and nanoparticles interdiffused together. On theother hand, Fig. 3 shows a micrograph of the impact frac-ture surface in which the addition of nanoparticle fillersalters the fracture behavior. While Fig. 3a shows a rela-tively smooth brittle fracture surface for PVC withoutfiller, Fig. 3b3e shows that nano-CaCO3particles areobviously on the fracture surface of the composites andappear, in many cases, to be clearly separated from thematrix. The creation of voids around the nano-CaCO3particles is the result of their stress-concentration effect.The scale and number of voids varied with additionmethod of nano-CaCO3particles.Figure 7 shows the influence of the addition methodon elongation at break. The elongation at break of compo-sites preparing through addition of nano-CaCO3at onsetof fusion is lower than that for direct dry mixing. PurePVC has the highest elongation at break. It should benoted that direct dry mixing of nano-CaCO3into the PVCmatrix gave higher elongation at break than the additionof nano-CaCO3at onset of fusion, while the addition ofuntreated nano-CaCO3gave lower elongation at breakthan that obtained for the same addition method of treatednano-CaCO3. Figure 8 shows the results for tensilestrength. Tensile strength is decreased by the addition ofnano-CaCO3for both addition methods. Addition of nano-CaCO3at the onset of fusion decreased tensile strengthmore than direct dry mixing of nano-CaCO3with PVCmatrix. Ishiaku et al. studied the effect of mixing time onmechanical properties of PVC and epoxidized natural rub-ber blends. They concluded that increased mixing timeimproved the homogeneity and dispersion of the blendsand enhanced their mechanical properties 25. It is recog-nized that the tensile strength of composites is influencedby the filler fraction and the interaction between particlesand matrix. With the addition of the nano-CaCO3par-ticles, the cross-sectional area of polymer matrix able tobear loads is reduced, and only small amount of stresscan be transferred from the matrix to the filler particles ifa large aggregation of nanoparticles is present in the ma-trix. Since the PVC/nano-CaCO3composites prepared byaddition of nano-CaCO3at onset of fusion had manyagglomerations, both number and size, these compositeshad lower tensile strength than those composites made bydirect dry mixing of nano-CaCO3into the PVC matrix.On the other hand, the interfacial adhesion plays a criticalrole in improving the tensile strength of the composites.The stronger the interfacial adhesion the composite has,the larger the stress that can be transferred to inorganicparticles from the matrix, a situation which leads tohigher tensile strength. Treatment of nano-CaCO3par-ticles with fatty acid enhanced the interfacial adhesion ofthe corresponding composite, and thus it led to tensilestrength higher than that obtained with untreated nano-CaCO3. The composites filled with the untreated nano-CaCO3particles had moderately poor interfacial adhesionand had lower tensile strength.FIG. 7.Effects of addition of treated and untreated nano-CaCO3onelongation at break of rigid PVC composites: (1) PVC, (2) direct drymixing of treated nano-CaCO3, (3) direct dry mixing of untreated nano-CaCO3, (4) addition of treated nano-CaCO3at the onset of fusion, and(5) addition of untreated nano-CaCO3at the onset of fusion.FIG. 8.Effects of addition of treated and untreated nano-CaCO3ontensile strength of PVC composites: (1) PVC, (2) direct dry mixing oftreated nano-CaCO3, (3) direct dry mixing of untreated nano-CaCO3, (4)addition of treated nano-CaCO3at the onset of fusion, and (5) additionof untreated nano-CaCO3at the onset of fusion.FIG. 6.Effects of addition of treated and untreated nano-CaCO3onnotched Izod impact strength of rigid PVC composites: (1) PVC, (2)direct dry mixing of treated nano-CaCO3, (3) direct dry mixing ofuntreated nano-CaCO3, (4) addition of treated nano-CaCO3at the onsetof fusion, and (5) addition of untreated nano-CaCO3at the onset offusion.DOI 10.1002/vnlJOURNAL OF VINYL & ADDITIVE TECHNOLOGY 2012159Generally, although Matuana reported that the silicatelayer spacing was slightly larger when nanoclays wereadded at the onset of fusion rather than at other additionpoints, irrespective of the nanoclay modification, and thatthe greatest improvement in mechanical properties wasachieved when the nanoclay was introduced into PVC atthe onset of fusion 14, the above results show that theaddition of nano-CaCO3into the PVC matrix at the onsetof fusion caused the mechanical properties to deteriorate.This phenomenon is due to low mixing time of PVC andnano-CaCO3particles in this method of mixing.CONCLUSIONS(Rigid PVC)/(treated and untreated nano-CaCO3) com-posites were prepared via a melt blending method. Twodifferent compounding addition methods were examinedduring the melt b