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SISOM 2011 and Session of the Commission of Acoustics, Bucharest 25-26 May

DYNAMIC MECHANICAL THERMAL EFFECTS IN CASE OF

POLYPROPYLENE/GLASS FIBRE COMPOSITES

Horia PAVEN, Zina VULUGA, Raluca GABOR, Andy Cristian NICOLAE

National Institute of Research and Development for Chemistry and Petrochemistry - ICECHIM,

Bucharest, ROMANIA, email: htopaven@netscape.net

Establishing appropriate end-use applications of composite materials with polymer-like matrix

needs a careful consideration of both mechanical and thermal features. By using the dynamic

mechanical thermal analysis (DMTA) technique, the primary quantities including the storage and

loss moduli and the corresponding loss factor at given frequencies for a large temperature range

are obtained, the results pointing out the influence of mechanical relaxation processes upon the

dynamic stiffness as well as regarding the true damping capacity. Moreover, the use of different

evaluation criteria is highlighted for various amounts of reinforcing component.

Keywords: Dynamic mechanical thermal analysis, polypropylene, glass fibre, composites.

1. INTRODUCTION

Obtaining materials with defined capacity to respond to a large spectrum of possible excitations

represents an important actual task [1].

In case of polymer materials, including the composite ones - in which they are, as a rule, the major

component - the consideration of native viscoelastic peculiarities are to be performed both from experimental

and theoretical standpoints, resulting in balanced approaches [2].

When the dynamic conditions are taken into account, the framework of linear viscoelasticity offers

either the variant of a sinusoidal strain, or that of a sinusoidal stress, as inputs. Accordingly, it is well known

that in the former case the output, resulting in a stress is expressed by a modulus-like quantity providing in

fact information on the dynamic stiffness, while in the later one, the resulting strain result in a compliance-like quantity make available a proper description of dynamic deformation capacity[3, 4].

In case of strain-controlled conditions, a complete set of viscoelastic characteristics include the

primary ones (storage -, M , loss -, M , absolute modulus, *M , and loss factor, tan M) as well as the

corresponding secondary quantities (storage -, MJ , loss -, MJ , absolute compliance, *MJ ). On the other

hand, in case of stress-controlled conditions, the complete set of viscoelastic quantities contains as primary

characteristics the storage -, , loss -,J J , absolute compliance, *J , and loss factor, tan J), while the

corresponding secondary ones include the storage -, JM , loss -, JM , and absolute modulus, *JM [5, 6].

All these linear viscoelastic quantities are frequency-, , and temperature-, T, sensitive, and in case

of composites the overall properties are, in principle, dependent on components properties, morphology and

various physical and/or chemical interactions, the existing DMTA being a versatile tool of study [7].

mailto:j_onisoru@yahoo.commailto:j_onisoru@yahoo.commailto:j_onisoru@yahoo.com

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2. METHOD AND RESULTS

Aiming at to better understand the interactions underlying the macroscopic properties of

composite in terms of those of components, when the matrix is a semicrystalline polymer (e. g.,polypropylene) and the filler is a short glass fibre, needs some comments concerning both the

polymer related contribution as well as the polymer-fibre interaction.

The dynamic mechanical thermal (DMT) characterization of semicrystalline polymers in

case of strain-controlled, or stress-controlled conditions, respectively, when temperature-sweep and

isochronal circumstances are taken into account, point out the existence of well defined peaks on

the diagrams of loss modulus and loss factor in the former situation, or of loss compliance and loss

factor ones in the later one, plotted versus temperature.

Below the melting temperature, Tm, the so-called -, -, and -mechanical relaxations are

located, the resulting peaks at temperatures T > T > Tbeing associated with activation of

corresponding dissipation processes which remains restrained below the appropriate temperature.

Accordingly, the lower temperature -relaxation is attributed to the segmental motion, whileintermediate, - one, is connected with transition of the bulk amorphous phase from glassy to

rubbery state, and higher temperature, -relaxation, is connected with segment exchange arising

between crystalline and amorphous domains, as well as to glass transition in the rigid amorphous

phase - representing the part of the amorphous phase located in the close vicinity of crystalline

lamellae whose mobility is restricted firmly by surrounding crystallites.

In principle, when in the polymer matrix a second, stiffer component is introduced, the

result is a composite presenting an overall higher stiffness, the interpretation of different variation

trends due to the amount of filler being relatively simple only if the considered polymer is a

single phase one. However, there are many practical cases when both an amorphous and a

crystalline phase are present, the interest concerning such semicrystalline polymers appearing as the

result of required sets of end-use properties. Of course, this is the natural consequence of

interactions between the polymer phases, as well as those relative to each polymer phase and the

filler. The considered components are a as received polypropylene - which is a

commercial heterophase copolymer grade with standard properties including density ( = 980

kg/m3), melt flow rate (MFR = 80 g/10 min.) and heat distortion temperature (HDT = 93 C @ 0.45

N/mm2), the polymer presenting some special features regarding high impact strength and high

stiffness. and a common standard glass fibre filler.

The test specimens, obtained by injection moulding, have the nominal dimensions of

35104 mm3.

The experimental system is a Q800 - DMTA (TA Instruments), the considered working

conditions being defined by a dual cantilever clamping, such that a flexural deformation mode isinvolved. The multi-frequency alternative (f = 0.5; 1; 5; 10; 50 Hz), is concerned, at 3 C/min

temperature-sweep rate in the range from -100 to 150 C.

The raw data, from many available, are the storage modulus (SM), loss modulus (LM) and

loss factor (TD) resulting for each fixed frequency, as temperature-dependent quantities.

The essential targets are:

- to obtain the SM(T), LM(T), and TD(T) in isochronal circumstances;

- to present the effect of frequency on different SM(T), LM(T), and TD(T) dependences;

- to identify the characteristic temperatures corresponding to mechanical relaxation peaks;

- to detect the effects of LM and TD criteria on mechanical relaxations detection;

- to point out the SM(f) dependences at different temperatures.

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Dynamic Mechanical Thermal Effects in Case of Polypropylene/Glass Fiber Composites117

Figure 1. The storage modulus vs. temperature at different frequencies for given amounts

of glass fibres PP0 (wt. 0%), PP1 (wt. 30%), PP2 (wt. 40%).

Figure 2. The loss modulus vs. temperature at different frequencies for given amounts

of glass fibres PP0 (wt. 0%), PP1 (wt. 30%), PP2 (wt. 40%).

Figure 3. The loss factor vs. temperature at different frequencies for given amounts

of glass fibres PP0 (wt. 0%), PP1 (wt. 30%), PP2 (wt. 40%).

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PP0 -L Table 1. 1 Values of storage modulus at low temperatures

Frequency Temperature

Hz

o

C-100 -75 -50 -25 0

0.5 3382 3251 2925 2556 2091

1 3404 3272 2961 2584 2129

5 3456 3324 3053 2651 2222

10 3476 3344 3093 2679 2261

50 3533 3401 3186 2757 2358

PP0 -MH

Table 1.2 Values of storage modulus at medium/hightemperatures

Frequency Temperature

HzoC

25 50 75 100 125

0.5 1520 1087 632 408 252

1 1552 1119 664 431 268

5 1623 1182 730 484 304

10 1656 1205 756 506 320

50 1740 1256 809 556 359

PP1 L Table 2. 1 Values of storage modulus at low temperatures

Frequency Temperature

HzoC

-100 -75 -50 -25 0

0.5 5629 5543 5084 4540 4001

1 5661 5569 5132 4577 4056

5 5740 5643 5265 4677 4188

10 5771 5673 5319 4718 4246

50 5857 5757 5458 4837 4390

PP1 -MH

Table 2.2 Values of storage modulus at medium/hightemperatures

Frequency Temperature

HzoC

25 50 75 100 125

0.5 3224 2477 1697 1262 914

1 3269 2534 1760 1313 952

5 3384 2646 1892 1430 1041

10 3432 2690 1944 1479 1080

50 3562 2783 2049 1588 1172

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Dynamic Mechanical Thermal Effects in Case of Polypropylene/Glass Fiber Composites119

PP2 -L Table 3. 1 Values of storage modulus at low temperatures

Frequency Temperature

Hz

o

C-100 -75 -50 -25 0

0.5 7398 7277 6810 6163 5581

1 7430 7303 6856 6200 5632

5 7517 7378 6988 6312 5785

10 7500 7420 7041 6361 5840

50 7709 7579 7226 6505 6010

PP2 -MH

Table 3.2 Values of storage modulus at medium/hightemperatures

Frequency Temperature

HzoC

25 50 75 100 125

0.5 4642 3727 2680 1998 1476

1 4706 3793 2764 2070 1533

5 4858 3930 2935 2233 1664

10 4922 3980 3000 2301 1724

50 5110 4107 3130 2448 1860

The SM data (Figure 1) point out a typical decrease with temperature, the trends illustrating also

stiffer values for higher amounts of filler. The frequency has a natural increase effect (see Table 1 to3), the

SM(T) curves being shifted toward higher temperatures.

The LM data (Figure 2) show characteristic peaks corresponding to intrinsic mechanical losses for

different relaxations - elast (lower), beta (higher) - reflecting for the former an elastomer-like amorphous

contribution, and for the later one, a typical plastomer-like relaxation. Furthermore, the effect of isochronal

test is a positive shift if increasing frequencies are considered.The influence of filler amount is questionable

for a 30% content, increasing significantly at an amount of wt. 40%.

The TD data (Figure 3) indicate again distinct characteristic peaks - appearing at higher values of

temperatures in comparison with those above quoted. However, it appears this TD criterion is by far less

meaningful than the LM one, including a fewer justifiable superposition of loss factors for different amounts

and/or frequencies, even if may appear there are some apparent similarities.

Comparative effects of using LM and TD evaluation criteria are illustrated in Figures 4 and 5,

distinguishing temperature-frequency- filler amount correspondences.

The frequency dependence of dynamic stiffness at different temperatures (Figure 6) clarifies the

influence of different amounts of fillers providing meaningful information upon end-use level terms.

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T LM elast

-60

-50

-40

-30

-20

-10

0

0.5 1 5 10 50

f(Hz)

T(C)

PP O

PP 1

PP 2

T TD elast

-60

-50

-40

-30

-20

-10

0

0.5 1 5 10 50

f(Hz)

T(C)

PP O

PP 1

PP 2

Figure 4. The characteristic temperatures corresponding to (elast-like) relaxations.

T LM beta

0

5

10

15

20

0.5 1 5 10 50

f(Hz)

T(C)

PP O

PP 1

PP 2

T TD beta

0

5

10

15

20

25

0.5 1 5 10 50

f(Hz)

T(C)

PP O

PP 1

PP 2

Figure 5. The characteristic temperatures corresponding to (beta-like) relaxations.

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Dynamic Mechanical Thermal Effects in Case of Polypropylene/Glass Fiber Composites121

PP0

0

500

1000

1500

2000

2500

3000

3500

4000

0 10 20 30 40 50 60

f(Hz)

SM(MPa) -75 C

-25 C

25 C

75 C

PP1

0

1000

2000

3000

4000

5000

6000

7000

0 10 20 30 40 50 60

f(Hz)

SM(MPa) - 75 C

- 25 C

25 C

75 C

PP2

0

1000

2000

3000

4000

5000

6000

7000

8000

0 10 20 30 40 50 60

f(Hz)

SM(MPa) - 75 C

- 25 C

25 C

75 C

Figure 6 The frequency dependence of storage modulus at different temperatures in case of

polypropylene matrix and the corresponding 30 and 40% glass fibre amount.

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Horia PAVEN, Zina VULUGA, Raluca GABOR, Andy Cristian NICOLAE 122

revealed by the loss modulus or loss factor dependence on temperature, with a physical

meaning bonus for the former quantity. The locations of the corresponding peaks are shifted towards higher

temperatures with the amount of filler - at given frequency - or for an increase of the frequency - at fixed

level of filler load.

ymers, Elsevier, Amsterdam, 2009.

I. Underlying relations, Materiale plastice, 47, 4, 523-526, 2010.6. PAVEN, H., Explicit analytical relations for stress-controlled rheodynamical quantities in the caseof Zener - Arrhenius model.

Underlying relations, Materiale plastice, 48, 2, 2011 (in print).7. DMTA Q 800,Thermal Analysis, TA Instruments, 2007.

CONCLUSIONS

The comprehensive description of viscoelastic behavior needs the consideration of one or other of

the two complete sets of M- or J-like characteristic quantities.

The primary viscoelastic quantities are obtained by using a suitable experimental technique either in

isochronal, temperature-dependent or in isothermal, frequency-dependent- circumstances, after that being

calculated the corresponding secondary characteristics.

The effects of using the glass fibre as reinforcing filler in a polypropylene matrix result, on the hand,

in an significant increase of dynamic stiffness, which decrease with temperature The obtained values are

higher at elevated frequencies, and the storage modulus versus temperature curves are shifted towards higher

temperatures when the frequency increase.

On the other hand, the existence of characteristic peaks corresponding to intrinsic mechanical

relaxations may be

REFERENCES

1. LAKES, R. S., Viscoelastic Solids, Cambridge Univ. Press, Cambridge, 2009.2. van KREVELEN, D. W., te NIJENHUIS, K., Properties of Pol3. KARGIN, V. A., SLONIMSKY, G. A., Brief Essays on the Physics and Chemistry of Polymers, Himija, Moscow, (in Russian),1967.

4. KRAUSZ, A. S., EYRING, G., Deformation Kinetics, Wiley, New York, 1975.5. PAVEN, H., Explicit analytical relations for strain-controlled rheodynamical quantities in the caseof Zener - Arrhenius model.

I.