morphology evolution and location of ethylene–propylene copolymer in annealed...

Morphology Evolution and Location of Ethylene–PropyleneCopolymer in Annealed Polyethylene/PolypropyleneBlends

LIN LI, LIUSHENG CHEN,* PETER BRUIN,† MITCHELL A. WINNIK

Department of Chemistry and Erindale College, University of Toronto, 80 St. George Street, Toronto, Ontario,Canada M5S 1A1

Received 1 July 1996; revised 10 October 1996; accepted 17 October 1996

ABSTRACT: Binary blends of linear low density polyethylene (PE) and polypropylene(PP), and ternary blends of PE, PP, and EP copolymer (EPR) were prepared in a finelymixed state. In all blends the ratio of PP to PE was 85/15. In some of the blends, thePE component was labeled with a fluorescent dye; in other blends, the EPR componentwas labeled. These blends were investigated by laser scanning confocal fluorescencemicroscopy [LCFM] as a function of annealing time as well as EPR compatibilizercontent. In this way we were able to follow the evolution of sample morphology andthe location of the EPR in the blends. The presence of EPR in the blends retards thegrowth of droplets of the dispersed PE phase. When EPR was added in amounts up to5 wt %, it tended to cover the PE droplets in patches rather than form a true core-shellstructure. In the LCFM images, the EPR/PP interface appeared sharper than the EPR/PE interface. q 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 979–991, 1997Keywords: confocal fluorescence microscopy; polymer blends; polymer interfaces; com-patibilizers

INTRODUCTION ity of the two polymers under their processing con-ditions, and leads to strong segregation of the two(crystalline) polymers at lower temperatures.For past several decades, there has been signifi-

cant interest in blends of polyethylene (PE) with This immiscibility leads to unacceptable mechani-cal properties for PE/PP blends. The poor elonga-polypropylene (PP),1–21 in part because both poly-

mers are in such wide use in the plastics industry, tional properties and poor impact strength inthese blends are related to poor stress transfer atand in part because of the inevitability of such

mixtures in recovered postconsumer plastics in- the interface.2,10,16

In general, the mechanical properties of poly-tended for recycling. Although PE and PP havethe same chain backbone, the difference in their mer blends are governed by composition, morphol-

ogy and interface structure.22 For a given composi-side groups, {H and {CH3, limits the miscibil-tion, the morphology is determined by the blend-ing history and the interfacial properties, which

* Permanent address: Institute of Chemistry, Chinese reflect the immiscibility of two polymers underAcademy of Sciences, Beijing 100080, China the mixing conditions. The interfacial tension g12 ,† Permanent address: Taniaburg 33, 8926 LW Leeuwarden,

the viscosity ratio hd /hm , where hd and hm are vis-The NetherlandsCorrespondence to: M. A. Winnik cosities of the dispersed (minor) and the matrixContract grant sponsor: Ontario Centre for Materials Re- (major) components, and the shear flow all con-search

tribute to the creation of the phase struc-Contract grant sponsor: NSERC Canadaq 1997 John Wiley & Sons, Inc. CCC 0887-6266/97/060979-13 ture.23–25 At any given temperature, g12 is the key

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9607003/ 8Q24$$7003 02-25-97 14:39:50 polpa W: Poly Physics

980 LI ET AL.

Table I. Polyolefin Blends Prepared in This Work amounts to form separate domains or a continu-ous phase of its own.

EPR wt %: 0 2 5 10 The terms PE and PP refer to a variety of poly-Blend mers. PE refers to linear high density polyethyl-

f-PE/EPR/PP / / / / ene (HDPE), to linear copolymers of ethylenePE/f-EPR/PP — / / / with small amounts of other olefins (LLDPE),

and to traditional low density polyethyleneThe prefix ‘‘f’’ before PE or EPR means that the polymeris fluorescently labeled (f Å EF2). A total of seven blends were (LDPE) characterized by long chain branches. Inprepared. the broader context, it also refers to copolymers

containing small amounts of polar groups, includ-ing copolymers with acrylic acid or with vinyl ace-tate, and to PE derivatives in which the PE isfactor determining the interface structure as de-

scribed by the thickness of the interface. The ratio maleated or otherwise modified to introduce asmall level of polar functionality. PP has a similarhd /hm has a significant effect on the morphology

for a system under a shear flow. For the blends broad meaning, with the additional feature of tac-ticity variation. One would anticipate that EPRwith hd /hm õ 1, the minor component is more eas-

ily dispersed by shear in the matrix phase, while might have different miscibilities with these dif-ferent polymers, and that modification of the EPRa lower viscosity of the major component will tend

to promote coalescence of the dispersed phase.23– structure would have its own important effect.In this context, it is useful to have a technique27 The addition to a polymer blend of a compatibi-

lizer, which is intimate with both polymers, may that can monitor the miscibility of component likea compatibilizer, present in small amounts, in adramatically change the interface structure by re-

ducing the interfacial tension.26–30 Compatibiliz- polyolefin blend system. This is normally difficultto observe. One approach took advantage of theers can be block copolymers, graft copolymers, or

even ‘‘random’’ copolymers. When added to poly- enhanced solubility of EPR in organic solventscompared to PE and PP.20,21 Thin sections of themer blends, compatibilizers stabilize the dis-

persed phase and retard or prevent the coarsening blend were exposed to xylene, which selectivelydissolved the EPR, effectively etching the sample.of phase morphology.

Ethylene–propylene rubbers (EPR), including These sections were examined by scanning elec-tron microscopy (SEM), and the voids in the sam-random and block copolymers of ethylene–propyl-

ene and ethylene–propylene–diene copolymers, ple were taken to indicate the locus of the EPR.From the presence of the ring-like structures theyhave been used to modify the performance of poly-

olefin blends.16–21 The addition of EPR to a PE/ observed, Stehling et al. inferred that the EPRcoated the PE droplets in a PP matrix.21a WhilePP blend contributes to an improvement in the

tensile and impact strength of the blend.16–21 This this technique provides the resolution of SEM, itleaves open the question of how the etching pro-improvement in tensile and impact strength has

been explained in terms of the compatibilizing ef- cess perturbs the sample morphology.Another method for observing small PE do-fect of the EPR on the PE/PP blends.16–21 If EPR

were similarly immiscible with PE and PP, and if mains in a crystalline PP matrix was reportedrecently by Stachursky et al.21b These authorsthe spreading coefficient were appropriate,20 then

in a system in a thermodynamically stable state, took samples containing 20% PE in a PP matrixand heated them to just above the melting tem-it would localize in the interface of the blend and

cover the dispersed phase like a shell. Experimen- perature of the PE (1207C). In the optical micro-scope at this temperature, the PE appears as liq-tally, it has been found that the EPR is somewhat

more miscible with PE than PP, and there is some uid droplets with sharp boundaries inside thespherulites of PP.indication that an interpenetrating structure of

EPR in PE may exist in certain PE/PP blends An alternative approach is based upon laserscanning confocal fluorescence microscopyprepared by extrusion.20,21 Because of the immis-

cibility of PE and EPR, however, upon annealing (LCFM).31 In this technique, the minor compo-nent is covalently labeled with a fluorescent dyethe EPR appears to separate from the PE phase

and form an interphase between the PE and PP such as fluorecein, blended with the other compo-nents, and subjected to a certain thermal history.phases.20 At high concentrations of EPR in PE/

PP blends, the EPR may not only become localized One then can observe the sample directly by fluo-rescence microscopy. This technique has the dis-at the interface, but may be present in sufficient


ETHYLENE–PROPYLENE COPOLYMER 981

Figure 1. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend. ThePE was labeled with a fluorescein. The scale bars are 10 mm. (a) As compression moldedat 1207C for 5 min from a finely mixed powder made by solvent precipitation. (b–e)Compression-molded films prepared at 1207C for 5 min and annealed at 1757C for 10,31, 100, and 310 min, respectively. In these and all subsequent images, the phaseslabeled with the fluorescent dye appears white. The black regions refer to domainswithout dye.

advantage that resolution is limited to that of op- preparation, and also, in situ depth profiling ispossible. Confocal optics allows only light fromtical microscopy, and by the possibility that polar

groups on the dye can interact with polar groups the focal plane to reach the detector. Thus, bychanging the focus, one can optically section theon one of the components. On the other hand, one

can examine systems without special sample sample. With appropriate software, three-dimen-


982 LI ET AL.

Figure 2. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 2 wt % EPR. The PE was labeled with a fluorescein. The scale bars are 10 mm.(a) As compression molded at 1207C for 5 min from a finely mixed powder made bysolvent precipitation. (b–e) Compression-molded films made at 1207C for 5 min andannealed at 1757C for 10, 31, 100, and 310 min, respectively.

sional image reconstruction of the morphology be- these blends, the EPR phase was easily visible inthe LCFM instrument. Our most important obser-comes possible. Because of this power, LCFM is

beginning to see significant use in the study of vations were that the EPR was localized at theinterface between PP and LLDPE, but when thepolymer blends.32–35

We have recently reported a preliminary inves- LLDPE contained polar groups introducedthrough maleation, the EPR dissolved in the PEtigation of 5 wt % EPR, labeled with fluorescein,

in a blend of 81 wt % PP and 14 wt % PE.34 In phase.34 We have now repeated these experiments



Figure 3. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 5 wt % EPR. The PE was labeled with a fluorescein. The scale bars are 10 mm.(a–d) Compression-molded films prepared at 1327C for 5 min and then annealed at1757C for 10, 31, 100, and 310 min, respectively.

and describe them in detail. We show how sam- ated ethylene–propylene copolymer and its un-maleated precursor, with a ratio of ethylene :ples can be prepared so that the domains sizes

are too small to be resolved by LCFM. As these propylene Å 60 : 40, were supplied by Texaco.Before maleation, the EPR had Mw Å 80,000 andsamples are annealed, the domain sizes grow. We

follow the influence of the EPR on the evolution Mn Å 40,000. By infra red (IR) spectroscopy, wefound that the maleated PE has 0.68 mol %; andof the domains and the location of the EPR in the

system. the maleated EPR has 0.47 mol % maleic anhy-dride groups. Through reaction with adventitiouswater, a large portion of the anhydrides in thepolymers used to make blends were in the formEXPERIMENTALof carboxylic acid groups.

Polymers

Linear low-density polyethylene (LLDPE) sup- Labeled Polymersplied by Du Pont Canada for this work contains Synthesis of the Fluorescein Derivativeca. 6 mol % butene and has a density of 0.930 (Mw

Å 35,900, Mn Å 12,200). The maleated polyethyl- The fluorescent dye used to label polyolefins inthis work was the ethyl ester of 6 *-aminofluores-ene (Dupont) was prepared from this sample. The

difference in molecular weight and polydispersity cein (EF2), which was synthesized from 6 *-fluo-resceinamine (F2, Aldrich) through the followingin the two samples is not significant. Polypropyl-

ene (PP) used was a commercial polymer (East- procedure: concentrated H2SO4 (10.6 mL, 0.2 mol)was added to a solution of F2 (3.5 g, 0.01 mol) inman) with Mw Å 164,000 and Mn Å 46,900. Male-


984 LI ET AL.

dissolution was completed, a solution of EF2 (0.64g, 0.017 mol) in a mixture of (60 mL of dioxane/ 10 mL of THF) was added to the system. Thereaction proceeded for 5 h. Then, the temperaturewas raised to 1607C with concomitant distillationof the low boiling solvents. The solution in theremaining o-dichlorobenzene was stirred at 1607Cunder N2 for an additional 15 h and then precipi-tated by pouring it into a large amount of acetone(2 L) at room temperature. The labeled polymer,obtained by filtration, was purified by washing itwith acetone until no fluorescence emission wasdetected in the filtrate. Further purification wascarried out by dissolving the polymer in toluene(1.5 wt %) at 607C and precipitating it by pouring

Figure 4. Depth profile (from the surface to a depth the solution into acetone. This last procedure wasof 8 mm in steps of 1.0 mm) from the compression-molded repeated twice. For the purification of EF2-la-film of 15 : 85 LLDPE/PP blend with 5% EPR, annealed beled PE, xylenes was used as a solvent, and theat 1757C for 310 min. The PE is labeled with a fluores-

dissolution temperature was 1107C.cein. The scale bar is 10 mm. The image labeled ‘‘i’’represents the top confocal plane of the sample, andthat labeled ‘‘ix’’ is 8 mm below the surface. Blending

All polyolefin blends were prepared through thefollowing procedure: A mixture (3 g) of solid PE,absolute ethanol (250 mL) with 5 g of molecularPP, and EPR in the desired ratio was added tosieves 3A for removing H2O, and the solution wasxylenes (BDH, 300 mL), and the system wasstirred under reflux for 6 h. After filtering, ethanolheated to 1157C with stirring under N2 for dissolu-was removed on a rotary evaporator at 507C, leav-tion of polymers. A completely clear solution wasing a red viscous liquid. H2O (100 mL) was added,obtained after 30 min at 1157C. It was then pouredand the solution was neutralized with 4% NaOH.into 1500 mL of acetone with fast stirring. TheA red solid was collected by filtration. The solidprecipitate, a fine powder, was obtained by filtra-was washed with H2O, dried in at 607C in a vac-tion or by centrifugation, and dried at 607C in auum oven for 6 h, and dissolved at 707C in a mix-vacuum oven for about 6 h. Before drying, ca. 0.5ture of ethanol/toluene (1 : 2 v/v), filtered whilewt % antioxidant (Ciba–Geigy, Irganox B-225)hot and then kept at room temperature for over-was dissolved in acetone and added to each sam-night for crystallization. The red crystals obtainedple at this stage in order to prevent possible oxida-were washed with a mixture of ethanol/toluenetion during annealing. For all blends described(1 : 4 v/v) and dried for 6 h at 607C in vacuumhere, the ratio of PE : PP was fixed at 15 : 85 w/oven. Yield: 76%. 1H-NMR and IR spectroscopyw, and the EPR content in the blends varied fromconfirm the presence of the ethyl ester and the0 to 10 wt %. The compositions of the blends areundisturbed structure of the fluoresceinamine. Ingiven in Table I.ethanol, the fluorescence of EF2 has a maximum

at 515 nm (lex Å 498 nm).

Molding and AnnealingLabeling the Polyolefin

Transparent films (thickness ca. 300 mm) wereprepared by compression molding for about 5 minAll the labeling reactions of maleated polyolefins

with EF2 were carried out under the same condi- in a Carver laboratory press at 120 to 1507C, de-pending on the content of EPR, followed immedi-tions, with variation only in the ratio of dye to

polymer related to the different levels of malea- ately by rapid cooling with iced water in order tominimize the crystallization of PE or PP. Mor-tion in the different polymers. A typical labeling

reaction procedure is as follows. Maleated EPR phology measurements show that films preparedin this way have a finely mixed structure.(10 g) was dissolved in o-dichlorobenzene (400

mL) with stirring at 807C under a N2 atmosphere. The films were annealed at 1757C for varioustimes (up to 310 min). The annealing was per-(Maleated PE was dissolved at 1107C.) After the



Figure 5. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 10 wt % EPR. The PE is labeled with a fluorescein. The scale bars are 10 mm.(a) As compression molded at 1507C for 5 min from a finely mixed powder preparedby solvent precipitation. (b–e) Compression-molded films made at 1507C for 5 min andannealed at 1757C for 10, 31, 100, and 310 min, respectively.

formed by inserting the compression-molded film ing, were used directly for morphology measure-ments by LCFM.as quickly as possible into a 1757C-preheated

mold with a thermocouple inside for monitoringMorphology Measurementstemperature. This procedure allowed the film to

reach the annealing temperature (175 { 17C) Laser confocal fluorescence microscopy (LCFM)was used to determine morphology in the blends.within 5 min. All films, with and without anneal-


986 LI ET AL.

Figure 6. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 2 wt % EPR. The EPR was labeled with a fluorescein. The scale bars are 10mm. (a–d) Compression-molded films made at 1207C for 5 min and then annealed at1757C for 10, 31, 100, and 310 min, respectively.

Samples were excited in the laser scanning confo- cipitation from a common good solvent, followedcal microscope (Bio-Rad MRC 600) with the 488 by compression molding under mild conditionsnm line of an Ar ion laser. Emission was detected (120–1507C for 5 min), which provided little op-at wavelengths greater than 515 nm. Before the portunity for domain growth.36 An example ismeasurements, the surface of each film was wiped given in Figure 1(a) in which no discrete domainswith ethanol (a nonsolvent) to remove impurities. can be resolved. Separate PE-rich and PP-richThe images were taken from the film surface or, phases may be present, but they are too small tothrough 1 mm steps, to a depth of 8 mm into the be resolved by optical microscopy. This morphol-film. The ‘‘surface’’ here is defined operationally ogy serves as the starting point for our observa-as the top confocal plane of the sample. tions of coarsening in the blend. Films were subse-

quently annealed at 1757C for various times topromote phase separation and coarsening. The

RESULTS AND DISCUSSION annealing times (10, 31, 100, and 310 min) werespaced logarithmically because polymer proper-

Starting Morphology and Coarsening ties often evolve according to a powerlaw be-of PE/PP Blends havior.

Coarsening at 1757C of the 15 : 85 PE/PP blendIn order to study effects of EP copolymers on theis shown in Figures 1(b) to 1(e). The bright ob-coarsening processes in PE/PP blends, it is neces-jects in the image are due to labeled PE dispersedsary to start the observation of coarsening from anin the unlabeled PP phase. In the initial state,initially finely mixed state of the polymer blends.

Well-mixed samples were prepared by rapid pre- Figure 1(a), the domain sizes are too fine to be



Figure 7. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 5 wt % f-EPR. The scale bars are 10 mm. (a–d) Compression-molded filmsprepared at 1327C for 5 min and then annealed at 1757C for 10, 31, 100, and 310 min,respectively.

resolved (i.e.,õ0.5 mm). After annealing at 1757C the disappearance of smallest domains cannot beobserved directly. There are many PE domainsfor only 10 min, however, coarsening led to the

bright sphere-like PE domains seen in Figure with sizes less than 1 mm, some of which are likelybeyond the resolution of the microscope.1(b). The scale bar in each image of Figure 1 is

10 mm, and the area sampled in each image is 107 Further coarsening can be observed at longerannealing times [Fig. 1(d) and (e)] . The forma-1 81 mm. To facilitate comparison among samples,

most images for these experiments were taken at tion of these large PE-rich domains, and their un-usual shapes, may be the result of flow in thethe same scale. The PE domains in Figure 1(b)

are about 0.5 to 1 mm. The contrast between the sample caused by thermal gradients or other fac-tors accompanying sample annealing. It is not un-bright domains and the background is not very

sharp in this image, indicating that phase separa- usual to find flow contributing to morphology evo-lution in samples annealed for long periods of timetion is far from complete. As the annealing time

is increased, PP is gradually excluded from the at temperatures above both Tg and the meltingpoint of both components.32bPE domains, and brighter and bigger PE-rich do-

mains are formed [c.f., Figure 1(c) , 1757C for 31min]. This process may involve coalescence of

Effects of EPR on Coarsening of PE/PP Blendssmaller PE domains and/or diffusion of PE mole-cules from smaller to larger domains (Ostwald If the EPR copolymer behaves like a surfactant

reducing the interfacial tension and stabilizingripening).37–39 Quantifying the contribution ofeach process here is difficult. The larger domains the system, two major effects should be detectable

in a PE/EPR/PP blend: a slowing down of theof the PE phase formed are not spherical, and


988 LI ET AL.

Figure 8. Confocal fluorescence micrographs from a 15 : 85 LLDPE/PP blend con-taining 10 wt % f-EPR. Scale bars Å 10 mm. (a–d) Compression-molded films preparedat 1507C for 5 min and then annealed at 1757C for 10, 31, 100, and 310 min, respectively.

coarsening rate and the formation of a finer dis- ratio, and examine the effects of the copolymer onthe morphology of the system.persed phase. In this study, we vary the amount

of EPR added to PE/PP blends at a fixed PE/PP Figure 2 shows the coarsening development ofa PE/PP blend containing 2 wt % EPR, startingfrom an initially well mixed state [Fig. 2(a): com-pression molded at 1207C]. One curious result isthat at short annealing times (10 and 30 min),the bright domains, indicating the location of thelabeled PE component, seem to be larger in theblend with 2 wt % EPR than in the pure PE/PPblend. There are various possible reasons for thisbehavior, including partial miscibility of the EPRwith the PE phase and the influence of the EPRon the mobility of the components in the system.In other samples, we observe that phase separa-tion of PE from mixtures of the three componentsis retarded as the amount of EPR in the blend isincreased.

EPR effects can be seen more clearly at longerannealing times [Fig. 2(c) and (d)] . The sizes ofbright domains do not increase significantly fromFigure 9. An enlarged image from the same sample

as in Figure 7(d). The scale bar is 10 mm. 31 min to 100 min annealing, but the contrast



Phase coarsening of the f-PE/PP blend with 5wt % EPR is shown in Figure 3(a) to (d). Herethe sizes of bright domains increase more slowlywith time than in the PE/PP blends without EPRor with only 2 wt % EPR, so that EPR contributessignificantly to reducing the growth rate of thedispersed phase. Even at the longest annealingtime (310 min), the size of the dispersed phasecontinues to grow. Here we note that most brightdomains are close to spherical in shape, as ex-pected for minimization of surface energy. Thecontinued growth of the PE domains indicatesthat the system has not yet reached a thermody-namically stable state, even though the EPR pro-vides stabilization to the system by reducing theinterfacial energy. The proper interpretation ofthese phenomena require further experiments todetermine the location of the EPR in the blend.This topic will be examined in the next section.

All the images shown above were taken fromthe surface layers of the polymer films. Laser con-focal fluorescence microscopy provides us with thepossibility of imaging at different depths withinthe film. An example is given in Figure 4. Thisfigure displays a series of images taken at 1 mmdepth increments into the film. The image in thelower right (Fig. 4ix) depicts the morphology 8mm beneath the surface for a f-PE/EPR/PP blendcontaining 5 wt % EPR, annealed at 1757C for310 min. Throughout the film at these depths,the distribution of the dispersed phase seems theFigure 10. Depth profiles (from the surface to a depth

of 8 mm in steps of 1.0 mm) from the compression-molded same, and no significant surface effect is observed.films of 15 : 85 LLDPE/PP blends containing 5 wt % f- The f-PE/PP blend with 10 wt % EPR exhibitsEPR (a) and 10 wt % f-EPR (b), annealed at 1757C for a coarsening behavior similar to that of the f-PE/310 min. The scale bars are 10 mm. The images labeled PP blend with 5 wt % EPR. At short annealing‘‘i’’ represent the top confocal plane of the sample, and times, as shown in Figure 5(a) (1507C for 5 min),those labeled ‘‘ix’’ are 8 mm below the surface. 5(b) (1757C for 10 min), and 5(c) (1757C for

31 min). At longer times (100 and 310 min), thehigh content of EPR does not contribute to a fur-becomes much sharper. This indicates that the

PE becomes more concentrated in these bright do- ther reduction of sizes of PE phase. The sizes seemto be slightly larger than those of the f-PE/PPmains, and that phase separation is more com-

plete than at earlier stages. A comparison of Fig- blend with 5 wt % EPR, annealed at 1757C for thesame times. With the information so far pre-ure 2(d) with Figure 1(d) demonstrates that the

addition of small amounts of EPR to a PE/PP sented, no unique explanation for this behavior isat hand. As we see in the following section, whereblend has reduced significantly the sizes of the

PE domains and has also narrowed the size distri- we describe experiments in which the EPR compo-nent is labeled, at these high concentrations ofbution. For the longest time of annealing (310

min), the sizes of bright domains have increased EPR, the surface of the PE droplets is nearly satu-rated, and the excess EPR forms large domainsfurther and some of them now tend to become

spherical. Note that although there are still a of its own.number of small domains with sizes less than 1

Location of EPR in PE/PP Blendsmm they do not make a significant contribution tofurther coarsening because of their small volume In general terms, there are three possibilities for

the location of EPR polymers in PE/PP blends. Iffraction.


990 LI ET AL.

the EPR is completely immiscible with both the In these micrographs, image ‘‘i’’ at the upper leftdepicts the top confocal plane, and image ‘‘ix’’ isPE and PP, it should form its own phase. The EPR

could be miscible with one of the components, in 8 mm beneath the surface. We see that similarstructures exist at all depths. In Figure 10(a),which case it would dissolve in that domain. Alter-

natively, if the EPR is partially miscible with both optical sectioning through the sample reveals thatobjects with a bright surface are in fact dark in-PE and PP, it is likely that at equilibrium the

EPR will become localized at the PP/PE interface. side, from which we conclude that the EPR coatsthe PE droplets. There is also a suggestion fromIn this case, EPR could serve as a bridge between

the components. To distinguish these possibilit- the weak glow from inside the domains that somef-EPR may be partially mixed with the PE-richies, one could determine the location of the EPR

by labeling it with a fluorescent dye. For example, phase. It also appears that the interface betweenEPR and PP is much sharper than that betweenif the EPR were fluorescently labeled, and if it

engulfed completely the minor component, one EPR and PE.At a high content of EPR (10 wt %) in the sam-should be able to observe core-shell structures in

the system by LCFM. ple, some large bright domains form in the blendthat do not have core-shell–like structures. WhenMost blends are prepared by processing, and

are not in a thermodynamically stable state. Un- we examine them by depth profiling, we see thatthey are uniformly fluorescent, indicating that theder these circumstances, the EPR may initially be

mixed with either PE or PP, or with both, because entire domain contains high concentrations of la-beled polymer, i.e., f-EPR. We interpret this as-of its partial miscibility with both polymers. In a

PE–PP blend, the location of an EP copolymer pect of the images in Figure 10(b) to indicate thatat these concentrations, significant amounts ofwill depend upon its composition (E/P ratio) , mo-

lecular weight, and structure (block or random). EPR have separated to form their own individualphase domains.An EPR sample with more E than P may be ex-

pected to have a higher miscibility with PE thanPP. Our EPR sample contains E/P in the ratio60/40, and there is some indication of local blocky CONCLUSIONSregions within the polymer. We anticipated forthese samples, that upon annealing, the EPR Binary blends of polyethylene (PE) and polypro-

pylene (PP), and ternary blends of PE, PP, andwould gradually separate from PE-rich phase togo to the PE/PP interface. EP copolymer (EPR) were prepared in a finely

mixed state. In some of the blends, the PE compo-Figures 6, 7, and 8 show the images of PE/PPblends containing 2 wt %, 5 wt %, and 10 wt % of nent was labeled with a fluorescent dye; in other

blends, the EPR component was labeled. Thesef-EPR, which were annealed at 1757C for varioustimes. We observe structures in which the EPR blends were investigated by laser scanning confo-

cal fluorescence microscopy (LCFM) as a functionengulfs droplets of the PE phase. As the EPR con-tent is increased, these core-shell–like structures of annealing time as well as EPR compatibilizer

content. In this way we were able to follow thecan be observed at earlier times (the annealingtime for the first appearance of this type of struc- evolution of sample morphology and the location

of the EPR in the blends.ture is 10 min for blends containing 10 wt % EPR,31 min for 5 wt % EPR, and 100 min for 2 wt % Coarsening in the 15 : 85 PE : PP blend was

fast at an annealing temperature of 1757C butEPR). An enlarged image (PE/f-EPR/PP, 5 wt %f-EPR, 1757C for 310 min) is presented in Figure significantly slowed down by adding small

amounts of EPR (2 to 5 wt % in the blend, 60/409 for a better view of the phase structure. Onesees that the labeled EPR is located at the surface E/P). Under these circumstances, the EPR copol-

ymer is localized at the interface between the PEof (dark) droplets of unlabeled PE. Rather thana uniform core-shell structure, one has patches or droplets and the PP matrix to form structures

that have core-shell–like characteristics. The im-small droplets of EPR at the surface of the PEphase. ages of samples with labeled EPR show that the

EPR coating of the PE droplets is patchy ratherTo confirm this conclusion, images at variousdepths (from the surface in steps of 1 mm) were than uniform, and suggest that small amounts of

the EPR remain in the PE phase. Adding addi-obtained as shown in Figures 10(a) (PE/f-EPR/PP, 5 wt % f-EPR, 1757C for 310 min) and 10(b) tional amounts of EPR (10 wt %) does not contrib-

ute to further reduction of domain sizes for the(PE/f-EPR/PP, 10% f-EPR, 1757C for 310 min).



19. L. D’Orazio, R. Greco, C. Mancarella, E. Martus-dispersed phase. Under these circumstances, sep-celli, G. Ragosta, and C. Silvestre, Polym. Eng. Sci.,arate domains of EPR in the polymer blend can be22, 536 (1982).identified by in situ depth profile measurements.

20. W.-J. Ho and R. Salovey, Polym. Eng. Sci., 21, 839Recent experiments40 with a labeled EPR sam-(1981). These authors state that the solubility pa-ple with an E/P ratio of 80/20 suggest that hererameter and surface tension of EPDM are interme-

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morphology evolution and location of ethylene–propylene copolymer in annealed...

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