thermal behavior of isotactic poly(propylene)/maleated poly(propylene) blends

Full Paper

Thermal Behavior of Isotactic Poly(propylene)/Maleated Poly(propylene) Blends

Catalin Vılcu, Cristian Grigoras, Cornelia Vasile*

This paper analyzes the thermal and thermo-oxidative degradation behavior, phase separ-ation, melting, and crystallization of blends consisting of isotactic poly(propylene) (IPP) andpoly(propylene) grafted with maleic anhydride (PP-g-MA). It has been established that,depending on the blend composition and crystallization/preparation procedure, the blendsof IPP and PP-g-MA can either co-crystallize orevidence phase separation. This conclusion hasbeen attained by comparing the DSC results ofcrystallization under dynamic and isothermalconditions with X-ray diffraction results. On thebasis of the obtained results, the optimummixingratios have been established as 95–85 wt.-% IPP/5–15 wt.-% PP-g-MA. Thermo-oxidative behaviorhas been studied by thermogravimetry anddifferential thermal analysis.

Introduction

In the last decade, special attention has been paid to

crystalline/crystalline polymer blends, such as high-

density polyethylene/linear low-density polyethylene or

other different types of polyethylenes,[1–3] linear low-

density polyethylene/modified poly(propylene) blends,[4]

poly(propylene) with different tacticities,[5–8] and vinyli-

dene fluoride/hexafluoaroacetone copolymer/vinylidene

fluoride tetrafluoroethylene copolymer blends,[9] as they

may provide a versatile and low-cost solution for better

control of the properties and quality of the end products.

Maleic anhydride (MA)-grafted poly(propylene) (PP-g-

MA) was proven to be an effective functional molecule

C. Grigoras, C. Vasile‘P. Poni’ Institute of Macromolecular Cemistry, 41 A Grigore GhicaVoda Aleey, 700487, Iasi-RomaniaFax: þ40 232 211299; E-mail: [email protected]. Vılcu‘Gh. Asachi’ Technical University, Textile and Leather Faculty, 67 DMangeron Street, 700050, Iasi-Romania

Macromol. Mater. Eng. 2007, 292, 445–457

� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

for the reactive compatibilization of PP with polyamide,

in both binary[10–12,20] and complex blends,[13,14] or as

a compatibilizer in synthetic polymer/natural fiber

composites.[15–19] Studies on the miscibility of isotactic

poly(propylene) (IPP) with PP-g-MA[15–17] have established

that, depending on their molecular weight and the MA

content in PP-g-MA, such polymers can either co-crystallize

or phase-separate. In the case of high molecular weight

and low MA content, the pair tends to co-crystallize,

otherwise, phase separation occurs, which would influ-

ence the mechanical properties of IPP/PP-g-MA-based

materials.[21] Co-crystallization of these blends depends

on the crystallization conditions. Phase morphology is

determined by the crystallization kinetics, and not by

thermodynamic reasons.[22,23] The above mentioned stu-

dies mainly followed the use of the IPP/PP-g-MA system in

composite materials, as the low amount of MA assures the

polymers’ good adhesion to glass fibers, thus increasing

compatibility, dimensional stability, and resistance to

cracking propagation.[18] For a possible utilization of these

blends in fiber production, the present paper discusses the

thermal and thermo-oxidative degradation behavior,

DOI: 10.1002/mame.200600425 445

C. Vılcu, C. Grigoras, C. Vasile

Table 1. Properties of IPP.

Property Method Unit Value

Melt flow rate (230 -C/2.16 kg) ASTM D1238 g � (10 min)S1 9.5–14.0

Density at 23 -C ASTM D1505 g � cmS3 0.905–0.917

Tensile strength MSI 2-2000 MN �mS2 >25

Elongation at break MSI 2-000 % >500

Izod impact strength ASTM D256 J �mS1 >15

Vicat temperature ASTM D1525 -C >150

446

phase separation, melting and crystallization of IPP/

PP-g-MA blends, in correlation with the fibers’ properties.

Experimental Part

Materials

IPP Midilena III-J 1700 was provided by the Petrochemical Works

MIDIA, Romania, while PP-g-MA was kindly supplied by EXXON

Chemicals. The main characteristics of these polymers are given

in Table 1 and 2, respectively. Both polymers had only basic

stabilization.

Blend Preparation

The blends were obtained as both granules and fibers by succes-

sive mixing and extrusion operations on a pilot installation

(extruder Sandoz A. G. Basel, Switzerland type S 025.1) with the

following parameters: screw diameter 25 mm, screw length 20 D

mm, four heating zones, 2� 1 100 W, temperature profile in

extrusion operation 168, 180, 165, 155–145 8C, rotation speed

16–160 rpm.

Analytic Methods

The following methods have been used: X-ray diffraction, DSC,

thermogravimetry/derivative thermogravimetry (TG/DTG), and

optical microscopy in polarized light.

Table 2. Properties of PP-g-MA.

Property Method

Melt flow rate (190 -C/1.2 kg) ASTM D 123

Density ASTM D 792

MA content FTIR (Exxon

Melting temperature DSC

Vicat temperature ISO 306

HDT ISO 75 (B)

Volatility DIN 53723

Color DIN 55981



The X-ray diffractograms were recorded on a DRON-2.0 type

diffractometer provided with a cobalt anode tube and Co Ka

radiation. Calibration was done prior to the experiments. The data

were processed with a Kaleidagraf programme. Determination of

the crystallite size and of microdeformation was made by the

method proposed by Averbach, presented in Taylor’s book,[24]

while the crystallinity degree was evaluated comparatively with

two reference samples, one with a crystallinity exceeding 98%, the

other one was totally amorphous.[25] Prior to these evaluations,

the diffractograms were normalized and corrections were applied.

The melting and crystallization behavior of the IPP/PP-g-MA

blends was investigated by DSC on a Mettler DSC 12 E instrument.

The samples, sealed in standard Al pans, were scanned at a rate of

10 8C �min�1 in dynamic nitrogen atmosphere with a flow rate of

30 cm3 �min�1. The sample mass was �10 mg. Before the

experiments, the temperature scale was calibrated with indium.

Indium has a melting temperature of 156.6 8C and a heat of fusion

of 28.45 J � g�1. The samples were subjected to two consecutive

heating/cooling scans, from room temperature to 200 8C, at a

cooling rate of 5 8C �min�1. The melting and crystallization peak

temperatures (Tm and Tc, respectively), and heats of fusion and

crystallization (DHm and DHc, respectively) were determined. The

surfaces under the DSC curve were determined by weighing, using

calibrated paper, while the crystallinity index was evaluated from

the ratio of the experimental value of the melting heat and from

the melting heat of an IPP sample with 100% crystallinity of

DHm¼250 J � g�1.[26]

Microscopic examination of the crystallization behavior was

carried out on an IOR MC1 microscope provided with a heating/

cooling device The experiments were performed under both

Unit Value

8 g � (10 min)S1 22

g � cmS3 0.9

) % 0.4

-C 138

-C 121

-C 63

ppm <2 000

yellow index <30

DOI: 10.1002/mame.200600425


Figure 1. X-Ray diffractograms of IPP (a) and different IPP/PP-g-MA blends (b–d) as indicated on the figure.

dynamic and isothermal conditions. The heating/cooling rates

were 5 8C �min�1. Examination in polarized light, at various

magnifications (300� and 600�), was also performed.

The thermogravimetric (TG), derivative thermogravimetric

(DTG), and differential thermal analysis (DTA) curves were

recorded on a Paulik-Paulik-Erdey-type Derivatograph, MOM,

Budapest, under the following operating conditions: heating rate

(b) of 12 8C �min�1, temperature range 25–600 8C, film sample

mass 50 mg in platinum crucibles, self-generated atmosphere.

Two curves were recorded for each sample. The actual (b) values

were evaluated from the temperature-time curve, and the

calculated (b) values were further employed in the estimation

of the kinetic parameters. Three or four repeated readings

(temperature and weight loss) were performed on the same TG

curve, each of them having at least 15 points.

Kinetic analysis of the TG data was carried out on a single curve

using both integral Coats-Redfern[27] (CR) and Reich-Levi[28] and

differential Swaminathan-Modhavan[29] (SM) methods. The sub-

script of the overall kinetic parameters: activation energy (E),

pre-exponential factor (A), and reaction order (n), indicates the

evaluation method.



For the last method, the general expression of the conversion

function was considered:

bda=dT ¼ Ae�E=RTfamð1 � aÞn½� lnð1 � aÞ�pg (1)

where a¼wt/w1 is the degree of conversion [ratio of the weight

loss at time t (wt) and at the end of the process (w1)], T is the

temperature in K, A is the pre-exponential coefficient, E is the acti-

vation energy, R is the gas constant, f(a)¼ {am (1�a)n [–ln(1� a)]p}

is the differential form of the conversion function, n is the reaction

order, while m and p are other exponents of the differential con-

version function. Exponents m, n, and p may take different values

with respect to the reaction mechanism or physical processes that

occur during heating. From a mathematical point of view, both

positive and negative values of A, E, or of the exponents can

accurately describe the TG or DTG curves, although not every value

has a kinetic significance. The positive values of the kinetic para-

meters A and E should be used as a selection criterion for ‘the most

probable kinetic parameters’. As additional criteria used in our

studies, mention should be made of: the good reproducibility of the

kinetic parameters obtained from different TG data readings, the

www.mme-journal.de 447


Table 3. Crystallographic data for IPP and crystalline IPP/PP-g-MA blends.

Sample 2ua) db) I ec) Dd) CIX-rayse)

A a.u. nm

IPP 17.109 5.934 143 0.035 29.69 0.787

20.099 5.064 130

22.262 4.587 35

30.009 3.429 15

33.146 3.115 13

95 IPP/5 PP-g-MA 16.475 6.158 157 0.062 20.0 0.697

19.491 5.242 166

21.686 4.706 52

26.468 3.874 41

29.687 3.488 6

32.573 3.168 20

90 IPP/10 PP-g-MA 16.958 5.986 159 0.031 19.90 0.733

20.066 5.077 141

22.191 4.601 56

30.022 3.428 24

33.439 3.089 14

85 IPP/15 PP-g-MA 16.795 6.171 140 0.028 38.05 0.776

19.829 5.256 141

21.971 4.743 51

29.926 3.487 19

33.185 3.151 7

80 IPP/20 PP-g-MA 16.348 6.171 139 0.028 27.08 0.771

19.367 5.256 140

21.509 4.743 57

29.498 3.487 19

32.757 3.151 14

a)Bragg angle; b)Interplanar distance; c)Degree of crystallite distortion of crystalline network; d)Average crystallite size; e)Crystallinity

index from X-ray diffraction measurements.

448

maximum values of the correlation coefficient or the minimum

values of the average square errors for each experimental point of

the DTG or TG curves, with respect to the calculated ones, using the

obtained kinetic parameters, etc. The global kinetic parameter

values, used for comparative purposes, have been evaluated under

the same conditions for all studied samples.

Results and Discussion

X-Ray Diffraction Results

As generally known, IPP has three crystallographic forms,

namely: monoclinic (a), hexagonal (b) and triclinic (g), with

different densities. The monoclinic a-form is the most



frequently occurring one, while the g-form is found in

degraded samples with low molecular weight or crystal-

lized at high pressure. Both diffractogram patterns (see

Figure 1) and the results of indexing show that the

monoclinic a-form is maintained up to a content of

20 wt.-% PP-g-MA in IPP.

Crystallographic data (see Table 3) show that all peaks

are shifted towards smaller Bragg angles, the one at

the 2u¼ 338, which remains constant, is the exception. In

the diffractogram of the 95 wt.-% IPP/5 wt.-% PP-g-MA

blend, a new small peak appears at a 2u¼ 26.58. At the

same time, the interplanar distance increases with

increasing PP-g-MA content. Consequently, one may

assume that the two components co-crystallize, while

DOI: 10.1002/mame.200600425


Figure 2. DSC curves for melting (a) and crystallization (b) of iPP, PP-g-MA, and their blends for the first run. The IPP/PP-g-MA ratio isindicated on the figure.

Figure 3. DSC curves for melting of IPP, PP-g-MA, and their blendsfor the second run. The IPP/PP-g-MA ratio is indicated on the figure.

the interplanar distance slightly increases to accommo-

date the functional MA groups. Distorsion of the crystal-

line network is also high for the 95 wt.-% IPP/5 wt.-%

PP-g-MA blend, while, for other blends, the e values (degree

of crystallite distorsion of the crystalline network) are

close to that of IPP. The crystallite sizes are smaller in the

95 wt.-% IPP/5 wt.-% PP-g-MA and 90 wt.-% IPP/10 wt.-%

PP-g-MA blends, while for the other blends they are close to

the size of crystallites in IPP. For the 95–90 wt.-%

IPP/5–10 wt.-% PP-g-MA composition (Table 3), the

crystallinity degree decreases up to a content of 15 wt.-%

PP- g-MA, and then reaches a value close to that of IPP again.

The blends with a PP-g-MA content that exceeds 20 wt.-%

PP-g-MA crystallize very slowly (see the microscopic results

below).

Dynamic Conditions: DSC Results

A very detailed DSC study on the IPP/PP-g-MA blends was

performed by Cho et al.,[4,22] who found a strong

dependence of the melting/crystallization behavior on

the thermal history of the sample. For example, the IPP and

PP-g-MA crystallites prepared at a lower cooling rate

(�1 8C �min�1) melt separately, which indicates the exis-

tence of phase separation in the blends, while the

specimens prepared at a relatively high cooling rate


� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mme-journal.de 449


Figure 4. Variation of the melting (a) and crystallization (b)temperatures in the first and second run with PP-g-MA content.evaluated by the additivity rule.

Figure 5. Variation of the melting and crystallization heat with PP-g

Figure 6. Variation of the crystallinity index with a indicelui dePP-g-MA content.

450Macromol. Mater. Eng. 2007, 292, 445–457


co-crystallize. Both multiple fusion endotherms or single

melting peaks may be observed by DSC, depending on the

cooling conditions. Multiple peaks or shoulders observed

before melting, and asymmetric melting endotherms can

also appear, because of the recrystallization or reorganiza-

tion of crystals initially formed during non-isothermal

crystallization.

In our case, the preparation of IPP/PP-g-MA blends for

fiber production led to relatively homogeneous materials,

in which both components co-crystallized or a clear phase

separation did not take place, as such all DSC curves exhibit

a single melting/crystallization peak (see Figure 2a and 2b,

respectively).

The peaks that correspond to the components differ in

both characteristic temperatures and area under the peaks.

The melting temperature of IPP is 167 8C, while that of

PP-g-MA is 154 8C. The crystallization temperatures are

-MA content.

DOI: 10.1002/mame.200600425


Figure 7. DSC curves of isothermal crystallization at 136 8C of IPP,PP-g-MA, and their blends.

Figure 8. Crystallization heat under dynamic and isothermalconditions versus PP-g-MA content.

115 and 102 8C for IPP and PP-g-MA, respectively. The

characteristic temperatures of the melting and crystal-

lization process of the blends vary with blend composition

(Figure 3).

In the second run, the situation is totally different as the

samples have been crystallized under different conditions,

namely at 5 8C �min�1. Both the peak shape and charac-

teristic temperatures are particular for each blend.

One may suppose that different morphologies are form-

ed, without clear phase separation. The endothermal melt-

ing of IPP is recorded as an asymmetric peak, PP-g-MA

exhibits two melting peaks, at 153 and 144 8C, while

melting of the blends also occurs through multiple melting

processes. The 50 wt.-% PP/50 wt.-% PP-g-MA exhibits two

melting peaks, while other blends exhibit a peak with a

shoulder. Although a multiple melting process (a peak

with shoulder), which corresponds to blends melting, is

also present, it is only the shoulder temperature (of 166–

167 8C), which corresponds to that of IPP, that remains

almost unchanged in the blends. On the contrary, the peak

Table 4. DSC data for isothermal crystallization of IPP, PP-g-MA,and IPP/PP-g-MA blends.

Sample tCmaxa) tCb) DHc

c) CIDSC,cryst.d)

min min J � gS1

IPP 7.8 19.4 141.8 0.57

95 IP/5 PP-g-MA 14.5 35.0 125.5 0.50

90 IPP/10 PP-g-MA 14.0 35.7 103.5 0.42

85 IPP/15 PP-g-MA 13.5 38.0 101.8 0.41

80 IPP/20 PP-g-MA 12.1 40.2 100.4 0.401

50 IPP/50 PP-g-MA 21.2 50.0 91.9 0.37

PP-g-MA 13.9 �60.0 10.5 0.042

a)Time needed to reach the maximum rate of crystallization;b)Time of crystallization at 136 -C; c)Heat of crystallization; d)Crys-

tallinity index obtained from the crystallization DSC peak.



found at lower temperatures (161–157 8C), and only for

blends melting, does not coincide, again, with those of

PP-g-MA (Figure 3). As a function of blend’s composition,

this peak is shifted towards higher temperatures, which

means that, under the cooling conditions applied, new

types of crystallites, different from those in PP-g-MA,

which are much more resistant and melt at higher tem-

peratures, are being formed.

Melting and crystallization temperatures remain approxi-

mately constant up to a PP-g-MA content of 20 wt.-%. In

addition, positive deviation from the additivity rule appears

(Figure 4) while, at higher PP-g-MA contents, the values

decrease.

Melting and crystallization heats also show deviation

from the additivity rule (Figure 5). These deviations are

positive for melting heat and negative for crystallization

heat. The melting heats obtained in the first run are higher

than those of the second run. Consequently, it may be

assumed that, during mixing, higher degrees of crystal-

linity were obtained than during crystallization at a

controlled cooling rate. Variation of the crystallinity index

determined by DSC (Figure 6) agrees well with that found

by X-ray diffraction (see Table 3).

All values determined by DSC decrease with increasing

the PP-g-MA content because, as expected, the degree

of crystallizability of this copolymer is low. In a new

crystallization process, important changes have been

recorded, therefore, an isothermal study of crystallization

is especially important.

Crystallization under IsothermalConditions: DSC Results

After several experiments and upon comparison of the DSC

results with those of optical microscopy, the temperature



Figure 9. Evolution of the isothermal crystallization process of PP-g-MA at 136 8C followed by optical microscopy in polarized light.

452

of 136 8C was selected for an isothermal study of the

crystallization process. The DSC curves of the crystal-

lization process developed at this temperature are shown

in Figure 7.

The shape and position of the curves with respect to the

crystallization time clearly show that PP-g-MA retards the

crystallization process. With increasing PP-g-MA content

in the blends, the crystallization peaks are shifted towards

longer crystallization times and thus become broader. The

crystallization characteristics evidenced by these curves

are listed in Table 4.

The data in Table 4 show that by incorporation of only

5 wt.-% PP-g-MA in IPP the crystallization time is doubled,

while, by further increasing the amount of PP-g-MA, the

increase of the crystallization time is important only for

50 wt.-% PP-g-MA. For the other blends, only a small

increase is observed. In this last case, crystallization is very



difficult, with the DSC curve of this blend being similar to

that of PP-g-MA. The crystallization heat moderately

decreases up to a PP-g-MA content of 50 wt.-%, and then

a decrease is pronounced (Figure 8).

Variation of the crystallization heat with the PP-g-MA

content, obtained under isothermal conditions, is similar

to that found under dynamic conditions.

Results of Optical Microscopy in Polarized Light

As known, IPP, PP-g-MA, and their blends crystallize to

form spherulites whose dimensions increase with crystal-

lization time. Maltese crosses become clearly visible after

25–35 min crystallization time in the case of PP-g-MA

while, for IPP and its blends, this time is 5–10 min shorter,

according to DSC results. At longer crystallization times,

the spherulites coalesce to form agglomerates (Figure 9).

DOI: 10.1002/mame.200600425


Figure 10. Optical microscopy images (polarized light) of the melt crystallization of IPP, PP-g-MA, and their blends at 136 8C after 10 min.

Figure 11. Evolution of the isothermal crystallization process of IPP at 141 8C followed by optical microscopy in polarized light.


� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mme-journal.de 453


Figure 12. Evolution of the isothermal crystallization process of 95 IPP/5 PP-g-MA at 136 8C followed by optical microscopy in polarized light.

454

By comparing the optical images of different blends at

the same crystallization time (see Figure 10) the differ-

ences in the crystallization behavior are easily evidenced.

As a function of the sample’s composition, crystallites of

various sizes are formed, and their concentration decreases

with the increase of the PP-g-MA amount in the blends.

The IPP spherulites are numerous and large, and their

dimensions decrease for the 95 wt.-% IPP/5 wt.-% PP-g-MA

blend. For the other blends, different dimensions and

shapes are found. Depending on blend composition, they

appear at different crystallization times, which are shorter

Figure 13. Crystallite size versus crystallization time for IPP,PP-g- MA, and 95 IPP/5 PP-g-MA blend.



than that in the case of PP-g-MA. The same observations

were made at other crystallization temperatures, such as

140 and 145 8C, a case in which the crystallization time

was longer. The differences of the crystallization pathway

of the 95 wt.-% IPP/5 wt.-% PP-g-MA blend, which seems to

have a particular behavior with respect to IPP, are evident

Figure 14. Derivative thermogravimetric curves of IPP, PP-g-MA,and their blends.

DOI: 10.1002/mame.200600425


Figure 15. DTA curves of IPP, PP-g-MA, and their blends.

Table 6. DTA results: Characteristic temperatures of the thermo-oxidative decomposition range from DTA curves.

Sample Ti Td1 Td2 Tf

-C -C -C -C

IPP 300 370 381 421

95 IPP/5 PP-g-MA 301 361 386

90 IPP/10 PP-g-MA 306 365 405

85 IPP/15 PP-g-MA 310 361 385

80 IPP/20 PP-g-MA 300 356 402

50 IPP/50 PP-g-MA 279 369 396

PP-g-MA 312 377 341 428

if comparing Figure 10 and 11 and the curves plotted in

Figure 12.

It is very clear that the crystallites present in the blend

(Figure 12) are smaller than those of IPP (Figure 11), and are

uniformly distributed, mainly in the first 20 min of

crystallization. The smallest crystallites appear from

PP-g-MA at longer crystallization times (Figure 9). By

comparing the slope of the crystallite size versus the time

curves, it appears that the rate of crystallization decreases

as the PP-g-MA content increases (Figure 13).

Table 5. Characteristic temperatures and mass loss from TGA curves

Sample Tia) Td1a) Td2a)

-C -C -C

IPP 172 367

95 IPP/5 PP-g-MA 179 323 361

90 IPP/10 PP-g-MA 172 315 349

85 IPP/15 PP-g-MA 172 333.5 354

80 IPP/20 PP-g-MA 163 358

50 IPP/50 PP-g-MA 158 377

PP-g-MA 168 337.5 351

a)Ti, Td1, Td2, and Tdf are onset, maximum rate of mass loss, and e

respectively; b)Mass loss corresponding to main decomposition step.



To achieve structural compatibility, the polymeric

components of a blend should ideally co-crystallize into

a single phase and the resulting blend should behave like a

homogeneous material. The results from the obtained data

show that the 95–85 wt.-% IPP/5–15% PP-g-MA composi-

tion represents a window of compatibility for these blends,

in which the functional maleic groups can be accommo-

dated in the crystalline lattice of IPP, to result in relatively

homogeneous blends with interesting properties.

The presence of multiple melting peaks in the DSC

thermograms can be primarily explained by the presence

of polymer fractions that possess different structural

characteristics. Equally, the melting and recrystallization

processes developed during heating may also contribute to

the occurrence of multiple peaks in the DSC thermograms.

However, the miscibility of the IPP/PP-g-MA blends in

the solid state depends on the method of cooling from the

melt. Plotting of peak crystallization temperature as a

.

Tdfa) Dwb) Dwtotal

-C % %

at Td1 at Td2

408 – 95.9

402 58.0 87.9 91.2

385 46.8 75.3 92.1

386 67.3 87.9 93.6

387 – 94.5

406 – 97.6

382 70.7 80.3 91.8

nd of process temperatures of thermo-oxidative decomposition,



Table 7. Overall kinetic parameters for the main process of decomposition of IPP, PP-g-MA, and their blends.

Sample ECR nCR ESM ln ASM nSM ELR,a¼ 0

kJ �molS1 kJ �molS1 kJ �molS1

IPP 71.2 0.7 72.5 12.7 0.8 86

95 IPP/5 PP-g-MA 88.4 1.4 66.5 12.3 1.1 87

90 IPP/10 PP-g-MA 82.4 1.2 62.1 12.3 1.0 68

85 IPP/15 PP-g-MA 78.3 1.1 68.3 12.6 0.9 83

80 IPP/20 PP-g-MA 60.1 0.6 54.2 8.9 0.6 75

50 IPP/50 PP-g-MA 65.3 0.9 52.3 8.6 0.7 –

PP-g-MA 60.2 0.8 50.0 8.2 0.8 –

456

function of composition indicates the difficulties of co-

crystallization for high PP-g-MA contents, which suggests

that, during the crystallization of blends with a prevalent

content of maleated PP, the PP-g-MA component is ex-

cluded during crystallization, and phase separation occurs.

The results agree with those reported in other papers.[4]

Thermo-Oxidative Behavior

The thermo-oxidative behavior is specific to each type of

studied sample, as evidenced by both TG/DTG and DTA

curves (Figure 14 and 15), and also by TG and DTA data

(Table 5 and 6).

Over the 172–408 8C temperature range, IPP almost

totally decomposes, the mass loss being of 95.88 wt.-%.

Upon PP-g-MA incorporation, this main decomposition

Figure 16. Variation of the activation energy evaluated by Reich-Levi method (ERL) versus conversion degree for IPP, PP-g-MA, andtheir blends.



step becomes much more complicated. The DTG peak is

split in two, and a new step of decomposition, which

corresponds to that of PP-g-MA decomposition, takes

place at temperatures below 323–333 8C. The peak at

higher temperatures is assigned to IPP, while it is shifted

towards lower temperatures (361–349 8C) for the blends

that contain 5–15 wt.-% PP-g- MA and 100 wt.-% PP-g-MA.

A peculiar behavior is exhibited by the blends with a

higher PP-g-MA content (from 20 to 50 wt.-%), which also

evidence a simple decomposition processes, as indicated

by single DTG peaks with temperatures of the maximum

decomposition rate of 358 and 377 8C, respectively. This

should be a result of a more pronounced interaction

between the components in these blends, formed during

melt crystallization. The other two characteristic tempera-

tures, namely onset temperature (Ti) and the one corres-

ponding to the end of the decomposition process (Tdf), take

values between those of the components, with the

exception of the blend containing 5 wt.-% PP-g-MA, which

starts to decompose at a temperature higher than 179.5 8Cversus 172 8C for IPP.

In DTA curves, the decomposition processes are endo-

thermic (Figure 15). Two steps, whose characteristic

temperatures are different from those of the components

(Table 6) are recorded, and agree with those found in the

DTG curves.

All samples are characterized by multiple peaks or peaks

with inflexions. With respect to those of the components,

the endothermic effect is smaller for all blends, except the

50 wt.-% IPP/50 wt.-% PP-g-MA blend, in which the compo-

nents decompose independently. Again, the endotherms

of the decomposition processes of the 95–90 wt.-% IPP/

5–10 wt.-% PP-g-MA blends are more reduced than those

of the other blends, which indicates a better thermo-

oxidative stability.

Variation of the overall kinetic parameters [evaluated

by Coats-Redfern (ECR) and Swaminathan-Modhavan (ESM)

(not shown) methods] of the main process of decomposi-

DOI: 10.1002/mame.200600425


tion (Table 7 and Figure 16), evidence, once more, that their

values decrease with increasing PP-g-MA content.

The overall activation energies of decomposition of the

95–85 wt.-% IPP/5–15 wt.-% PP-g-MA blends are higher

than those of IPP and of the other blends (see Table 7), as

they are more thermally stable. This is also evidenced by

the Reich-Levi (ELR vs a) plot of activation energy variation

with conversion degree, mainly for the beginning of

decomposition (a!0). The curve of 95 wt.-% IPP/5 wt.-%

PP-g-MA lies alone above all the other curves of both

parent components and of the other blends.

Conclusion

The thermal behavior of IPP/PP-g-MA blends with crystal-

lizable components has been studied by DSC, DTA, TG, and

optical microscopy in polarized light. The main character-

istics of the melting, crystallization, and thermo-oxidative

decomposition have been determined. Depending on the

blend composition and crystallization/preparation pro-

cedure, the blends of IPP and PP-g-MA can either co-

crystallize or evidence phase separation. This conclusion

was attained by coupling the DSC results of crystallization,

under dynamic and isothermal conditions, with X-ray

diffraction results. On the basis of the obtained results, the

optimum mixing ratios, as tested in the textile field, have

been established as 95–85 wt.-% IPP/5–15 wt.-% PP-g-MA.

Thus, fibers with superior physico-chemical and good

tinctorial properties could be produced. Such results will be

presented in a subsequent paper.

Received: November 8, 2006; Revised: January 31, 2007; Accepted:February 1, 2007; DOI: 10.1002/mame.200600425

Keywords: crystallization; maleic anhydride; melting; poly(pro-pylene) (PP); thermo-oxidation

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thermal behavior of isotactic poly(propylene)/maleated poly(propylene) blends

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