Interfacial and Mechanical Properties ofg-Fe2O3/Segmented Polyurethane/Poly(vinyl chloride)Composites

SUDARYANTO, TAKASHI NISHINO, MASAKI UENO, SEIJI ASAOKA, KATSUHIKO NAKAMAE

Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University, Rokko, Nada,Kobe 657-8501, Japan

Received 27 October 2000; accepted 22 March 2001Published online 3 October 2001; DOI 10.1002/app.2158

ABSTRACT: Segmented polyurethane (SPU)/poly(vinyl chloride) (PVC) blends were par-ticulated with g-Fe2O3. Interfacial properties of the composite were studied through theadsorption behaviors of SPU and PVC and their blends on g-Fe2O3 particles surface.Mechanical properties of the composite were measured with dynamic mechanicalanalysis and tensile test measurements. PVC with functional groups (FPVC), becauseof strong interactions, showed preferential adsorption on g-Fe2O3 compared with SPUand PVC. Moreover, the g-Fe2O3 particles were covered by FPVC in the g-Fe2O3/SPU/FPVC composite. The adsorption layer of FPVC protected SPU from catalytic degrada-tion by g-Fe2O3, resulting in increasing hydrolytic stability for SPU. © 2001 John Wiley& Sons, Inc. J Appl Polym Sci 82: 3030–3035, 2001

Key words: segmented polyurethanes; poly(vinyl chloride) (PVC); polymer blends;interfacial properties; composites

INTRODUCTION

Recently, high-performance materials have beenrequired in many important fields, but variousdemands in the fields could not always be fulfilledwith materials consisting of only one kind of sub-stance. Thus, materials with two or more kinds ofsubstances, that is, composite materials, havebeen designed for complying with each demand.Nowadays, high-performance composite materi-als are available with a whole range of properties,and they are used in various applications, fromaerospace to electronics to sports equipment. Be-cause composites are manufactured by the com-bination of two or more kinds of substances, thecharacterization of interfacial properties is quite

important, and controlling these properties is oneof the most important aspects in designing com-posites.

We investigated the interfacial interaction be-tween a variety of polymers and inorganic parti-cles and found that polymers with a properamount of polar groups are available as bindersfor magnetic tapes, inks, paints, and so forth.1,2 Inprevious articles, we investigated the miscibilitiesof segmented polyurethane (SPU) and poly(vinylchloride) (PVC).3 There, the chemical structure ofSPU and the functional groups of PVC were foundto affect the miscibilities and mechanical proper-ties of the blends. The SPU/PVC blend system isthe most common binder for magnetic recordingtape, in which g-Fe2O3 particles are particulated.However, the interfacial hydrolysis of SPU cata-lyzed by g-Fe2O3 led to the degradation of theproperties of the composites, limiting the durabil-ity of the SPU binder.4

Correspondence to: T. Nishino (tnishino@kobe-u.ac.jp).Journal of Applied Polymer Science, Vol. 82, 3030–3035 (2001)© 2001 John Wiley & Sons, Inc.

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In this study, the interfacial and mechanicalproperties of composites made of SPU/PVC andg-Fe2O3 were investigated, and a polymer blendsystem with reduced degradation is proposed.

EXPERIMENTAL

Materials

Polyurethane with a hard-segment content of 30wt % was prepared with a conventional prepoly-mer preparation method as described in previousreports.4,5 PVC from Wako Pure Chemical Indus-tries, Ltd. (Osaka, Japan), with a number-aver-age molecular weight (Mn) of 75,000, or function-alized PVC (FPVC) from Nippon Zeon Co., Ltd.(Kawasaki, Japan), with an Mn value of 38,000,was blended with SPU.

Figure 1 shows the blend processing and chem-ical structure of each component. SPU and PVCor FPVC (50/50 w/w) were codissolved in N,N9-dimethylformamide (DMF), a good solvent for

each polymer, a with total polymer concentrationof 10 wt %. The solution was sufficiently stirredand kept for 24 h at room temperature. The sam-ple was prepared by the casting of the solutionunder vacuum at 60°C for at least 48 h. Theg-Fe2O3-particulated films were also prepared bythe addition of g-Fe2O3 into the solution, whichwas then mixed with a ball mill for 48 h and castunder vacuum at 60°C for at least 48 h. g-Fe2O3(Pfizer Laboratories, Cambridge, MA) with a sur-face area of 19.3 m2/g was used as the filler, andits content was fixed at 50 wt %.

Interfacial Properties

The adsorption behavior of the polymers ong-Fe2O3 was studied as follows. DMF solutions ofthe polymers were prepared in desired concentra-tions. A glass tube (25-cm3 capacity) containing1.0 g of g-Fe2O3 and 10 cm3 of the polymer solu-tion was shaken for 24 h. Then, it was allowed tostand for another 48 h at 30°C for equilibration ofthe adsorption of the polymer onto the g-Fe2O3

Figure 1 Preparation method of the g-Fe2O3-filled composite based on SPU/PVCblends.

PROPERTIES OF g-FE2O3/SPU/PVC COMPOSITES 3031

surface. The polymer concentration after adsorp-tion was determined through the measurement ofthe supernatant with gravimetry. The adsorbanceof the polymer on g-Fe2O3 was determined viacalculation of the concentration change of the so-lutions before and after adsorption. The adsor-bance was plotted with the equilibrium concen-tration of the solution after adsorption. The com-petitive adsorbance of each component in theblend system was determined through the mea-surement of the nitrogen content of the solutionsbefore and after adsorption by elemental analysis(Sumigraph NCH-2, Sumika Chemical AnalysisService, Osaka, Japan).

The interfacial tension of the water/polymersolution in nitrobenzene was measured with a duNouy ring method.6 Nitrobenzene was used be-cause it was a good solvent for each polymer andhad a high interfacial tension at the water inter-face (27.6 mN/m). We carried out the measure-ments by pulling up the du Nouy ring from thenitrobenzene phase (bottom) to the water phase(upper).

Mechanical Properties

A dynamic mechanical analyzer (ITK Co., DVA-200, Osaka, Japan) was used for characterizingthe dynamic mechanical properties of the particu-lated composites. Rectangular samples (5 mm3 10 mm 3 0.3 mm) were measured at 10 Hz in astretching mode over a temperature range of2100 to 120°C at a heating rate of 6°C/min.

A tensile tester (Shimadzu, Autograph AGS-1kND, Kyoto, Japan) was also used for determin-

ing the mechanical properties of the composites.Samples, after being immersed in boiling waterfor 72 and 168 h, were also examined. Each sam-ple was strained at 2 mm/min at room tempera-ture with an initial length of 15 mm.

RESULTS AND DISCUSSION

Interfacial Properties

Figure 2 shows the adsorption isotherms of PVCand FPVC on g-Fe2O3 from DMF solutions. Theadsorbance of FPVC increased with the equilib-rium concentration of the polymer and saturatedat about 1.9 mg/m2. This isotherm obeyed theLangmuir type. However, no adsorption ong-Fe2O3 was observed for PVC. We previouslyreported that the existence of a proper amount ofpolar groups in a polymer backbone brings higheradsorbance of the polymer to a metal oxide sur-face. In particular, a polymer containing strongacid, such as sulfonate groups or phosphategroups, adsorbs on g-Fe2O3.7,8 Therefore, theseresults clearly show that the functional groups,especially sulfonate groups, in FPVC play an im-portant role in the adsorption behavior of PVC ong-Fe2O3.

Figure 3 shows the adsorption isotherms ofFPVC and SPU from an SPU/FPVC blend (50/50w/w) solution on g-Fe2O3. Arrows indicate thesaturated adsorbance of SPU and FPVC fromeach individual solution. SPU showed almost no

Figure 2 Adsorption isotherms of (E) PVC and (F)FPVC on g-Fe2O3 from a DMF solution at 30°C.

Figure 3 Adsorption isotherms of (F) FPVC and (h)SPU from an SPU/FPVC blend solution on g-Fe2O3.Arrows indicate the saturated absorbance of FPVC andSPU from each separated solution.

3032 SUDARYANTO ET AL.

adsorption on g-Fe2O3. However, the adsorbanceof FPVC in the blend system increased with theequilibrium concentration of the polymer and sat-urated at about 1.7 mg/m2. This isotherm wasalmost equal to that in Figure 2. This indicatesthat the interaction of FPVC with g-Fe2O3 isstronger than that of SPU, and the existence ofSPU in the blend system does not disturb theadsorption behavior of FPVC on the surface ofg-Fe2O3.

The surface of g-Fe2O3 particles possesseschemically or physically adsorbed water. Thus,the surface of g-Fe2O3 particles can be expressedwith the water phase qualitatively; that is, theadsorption behavior of polymers at the liquid/solid interface could be interpreted on the basis ofthe interfacial tension at the water/polymer solu-tion interface and the contact angle of water onthe polymer film.8

Figure 4 shows the relationship between thepolymer concentration in a solution and the inter-facial tension in a water/nitrobenzene solution ofSPU, PVC, and FPVC. The interfacial tension forPVC was independent of the concentration,whereas that of SPU slightly decreased and thatof FPVC abruptly decreased with increasing poly-mer concentration. It is well known that the poly-mer with a stronger interaction with metal oxidegives a lower interfacial tension for the water/polymer solution than a polymer with a weakerinteraction with metal oxide. Accordingly, thedecrement of the interfacial properties should bedue to an orientation of the polymer at the inter-

face, and FPVC acts as a surfactant.9 These re-sults corresponded to the result in Figures 2 and3, in which PVC and SPU did not adsorb butFPVC strongly adsorbed on the g-Fe2O3 surface.

Figure 5 shows the relationship between theconcentration of FPVC and the interfacial tensionbetween water and FPVC and SPU/FPVC blendsolutions. The interfacial tensions for both theFPVC and SPU/FPVC blend systems decreasedwith increasing FPVC concentration. This indi-cates that the adsorption behavior of FPVC wasnot hindered by the existence of SPU in the SPU/FPVC blend system. These results evidentlyshowed that FPVC preferentially adsorbed ong-Fe2O3 particles, as shown in Figure 3, in whichthe functional groups play a great role.

Mechanical Properties

Figure 6 shows the temperature dependence ofmechanical tan d for the SPU/FPVC blend andg-Fe2O3/SPU/FPVC composite. Both samples hada single tan d peak regardless of the existence ofg-Fe2O3; this showed the high miscibility of thisblend.10 The peak top temperature of tan d in-creased with the incorporation of g-Fe2O3. Theintensity of the tan d peak of the g-Fe2O3/SPU/FPVC composite was lower than that of the SPU/FPVC blend. This is undoubtedly due to the exis-tence of g-Fe2O3 as fillers.11–15 Previously, wereported that the interaction between poly(methylmethacrylate) and g-Fe2O3 as fillers led the shift-ing of the tan d peak to a higher temperature.11 A

Figure 5 Relationship between the concentration ofFPVC and the interfacial tension in a water/nitroben-zene solution of (F) FPVC and (h) an SPU/FPVC blend.

Figure 4 Relationship between the polymer concen-tration and the interfacial tension in a water/nitroben-zene solution of (h) SPU, (E) PVC, and (F) FPVC.

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similar result was also reported by Yim et al.12 fora silica-filled polymer composite. The effect of theinterfacial interaction on the tan d peak intensitywas also discussed in detail by several research-ers, who observed that the lower the tan d peakintensity was, the stronger the interaction wasbetween the polymer and the metallic particle asa filler.13,14 In a more recent study, Cuillery etal.15 reported the influence of the metal/polymerinteraction on the tan d peak of a laminated ma-terial. There is no doubt that the incorporatedfiller interfered with the molecular motion of thematrix at the interface, resulting in the incrementof the peak top temperature and the decrement ofthe peak intensity of tan d. Thus, the degree of thedecrement in the intensity of the tan d peak canbe a criterion of the interfacial interaction. Thevalue of rtand, the intensity ratio of the tan d peakof a sample with a filler to that without a filler,was determined as follows:

rtand5tan d peak intensity with g-Fe2O3/tan d

peak intensity without g-Fe2O3

Table I shows the rtand values of composites withdifferent components. The g-Fe2O3 content ofeach composite was 50 wt %. The rtand value forg-Fe2O3/SPU is higher than unity. It is thoughtthat the filler might disturb the formation of thehard domain of SPU; this results in the increasein the molecular motion. Small interfacial inter-action between the polymer and filler could also

be a reason for the increasing tan d peak reportedby Tario et al.13 The rtand value of the g-Fe2O3/SPU/FPVC composite was smaller than that ofthe g-Fe2O3/SPU/PVC composite. This suggests astronger interaction between FPVC and g-Fe2O3than between PVC and g-Fe2O3.

Figure 7 shows the relative elongation at breakand relative tensile strength of g-Fe2O3/SPU,g-Fe2O3/SPU/PVC, and g-Fe2O3/SPU/FPVC com-posites after immersion in boiling water for 72and 168 h. The elongation at break and tensilestrength before immersion were taken to be100%. The elongation at break of g-Fe2O3/SPUgreatly decreased after immersion. However, forcomposites based on the blend systems, especiallythe SPU/FPVC blend, the decrease in the elonga-tion could be reduced. It is obvious, therefore, thatPVC and FPVC increased the hydrolytic stabilityof SPU. A similar tendency was also observed for

Figure 6 Temperature dependence of the mechanicaltan d value for an SPU/FPVC blend and a g-Fe2O3/SPU/FPVC composite.

Table I rtand Values of g-Fe2O3/SPU, g-Fe2O3/SPU/PVC, and g-Fe2O3/SPU/FPVC Composites

Composite rtand

g-Fe2O3/SPU 1.2g-Fe2O3/SPU/PVC 0.8g-Fe2O3/SPU/FPVC 0.4

Figure 7 Histograms of the relative elongation atbreak (front, gray) and the relative tensile strength(back, black) of g-Fe2O3/SPU, g-Fe2O3/SPU/PVC, andg-Fe2O3/SPU/FPVC composites (left to right) after im-mersion in boiling water. The values before the immer-sion were taken to be 100%.

3034 SUDARYANTO ET AL.

the tensile strength. The tensile strength of theg-Fe2O3/SPU composite decreased after immer-sion in boiling water. This might have beencaused by degradation through the interfacial hy-drolysis of SPU catalyzed by g-Fe2O3. However,the tensile strength of the composite based onSPU/FPVC increased after immersion. Thismight have been caused by the progression of theepoxy moiety during immersion in boiling water.

Figure 8 shows a schematic representation ofthe g-Fe2O3/SPU/FPVC composite. The results ofthis study show that the g-Fe2O3 particle could becovered by the FPVC component. Thus, the cata-lytic hydrolysis effect of g-Fe2O3 particles on thedegradation of SPU can be reduced by FPVC pref-erentially adsorbed on g-Fe2O3.

CONCLUSIONS

The interfacial and mechanical properties of ag-Fe2O3 particulated composite based on theSPU/PVC blend system were investigated. The

interaction of FPVC with g-Fe2O3 was strongerthan the interactions of SPU and PVC withg-Fe2O3. That is the reason FPVC showed prefer-ential adsorption on g-Fe2O3 particles. Moreover,SPU in the SPU/FPVC blend system did not in-terfere with the adsorption behavior of FPVC. Onthe basis of these results, we concluded that theg-Fe2O3 particles were covered by FPVC in theSPU/FPVC blend system. The FPVC layer pro-tected SPU from catalytic degradation byg-Fe2O3;this resulted in increased hydrolytic stability ofthe SPU matrix.

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Figure 8 Schematic representation of the g-Fe2O3/SPU/FPVC composite.

PROPERTIES OF g-FE2O3/SPU/PVC COMPOSITES 3035