Dynamic Mechanical Thermal Analysis-An Effective Testing Tool for a Recyclability Study of Glass

Reinforced Plastics

J I M H. SONG

BASF Corporation Wyandotte, Michigan 481 92

Glass fiber reinforcement usually gives substantial improvement in some key physical properties of plastics materials, such as heat resistance and stiffness (modulus), but at the expense of impact and flow (processability) properties. Upon recycling, however, we observe the reverse phenomenon. The key consideration of the recyclability of glass reinforced plastics is usually based on how much the key properties of glass reinforced materials are changed during a given recycling period. The assessment of the key physical properties of materials-heat resistance, im- pact, and stiffness-before and after recycling involves time-consuming and expen- sive molding testing processes. This paper demonstrates how those three properties of glass reinforced plastics materials before and after recycling can be determined by a single dynamic mechanical thermal analysis (DMTA) test, thus greatly simpli- fying the key property assessment work in a recyclability study of glass reinforced plastics.

INTRODUCTION heat resistance property is defined as a temperature where the storage modulus falls abruptly. n a previous paper ( l ) , it was demonstrated how one I could effectively recycle glass reinforced flame retar- EXPERIMENTAL

dant impact polystyrene by using a two level factorial design experiment along with subsequently con- structed response surface diagrams. In that paper, six different physical properties, including flammability, were evaluated with the use of typical testing meth- ods, which usually involve a molding process and cer- tain mechanical property testing.

In this work, we used the same material as before but employed a different testing method, dynamic me- chanical thermal analysis (DMTA). This test provides the information of the change(s) in three key physical properties, heat resistance, impact, and stiffness be- fore and after recycling without going through the injection molding process and physical property test- ing.

DMTA is a widely-used, dynamic mechanical ther- mal measurement technique, in which the modulus and/or damping of a material under oscillatory load or displacement is measured as a function of tempera- ture, frequency, or time or a combination of thereof. DMTA used here employed "tension" type loading. The shear storage modulus is thus correlated to the tensile or flexural modulus, and the tan delta (ratio of loss modulus and storage modulus) is related to the me- chanical damping (impact) property of material. The

Two materials-a virgin material and a recycled (five times) material were used for DMTA testing. The virgin material is a commercial BASF glass reinforced flame retardant (V-0) impact polystyrene grade. The testing apparatus is a dynamic mechanical thermal analyzer (DMTA) manufactured by Polymer Laboratory (Model Mark 2). The compression molded specimens (typi- cally 8 X 7 X 0.229 mm) were used for the present experiment. Dynamic heating scans were performed at 2°C /min from - 150°C to a specific end point where the sample had substantial softening.

RESULTS AND DISCUSSION

The effects of recycling on the key material proper- ties are demonstrated in Fig. 1 (ten-modulus) and Ftg. 2 (tensile tan delta). Figure 1 indicates that the tensile modulus and the heat resistance temperature of vir- gin material were drastically decreased through the five-time-recycling process. This result, of course, was expected from the previous experimental work (1). From Fig. 2 we observe that tan delta, the damping property of virgin material, was substantially in- creased after being recycled five times, indicating a substantial increase in the impact property. A side- by-side comparison of key physical property change(s)

JOURNAL OF VINYL &ADDITIVE TECHNOLOGY, SEPTEMBER 1996, Vol. 2, No. 3 221

Jim H . Song

Vltgln Maierld (Qiass filled FR-HIPS)

(23.0 “C)

: 2.09 O P P

0 .4 \

figure 2, Tan (loss/lmpact) Deita

Rg. 1 . Ten. modulus and heat re- sistance.

Fig. 2. Tan (loss/irnpact) delta.

2

7.5

I

Recycled Material 110 “c

. . I I . . . 0 50 700 I

i t Recycled Mstetid

1 , + - , , y \- 0. I - -

c _ - _ _ _ _ _ _ - - - - - - - _ _ - _ n

from recycling tested by two different methods is shown in Table 1 . Although both test methods give the same trend of property change(s) as a result of recy- cling, there are some discrepancies between the data

obtained previously (“Old Data”) by a typical testing method (ASTM test with injection molded specimens) and the data obtained by DMTA. Such differences, however, could be understood in light of the differ-

Table 1. Key Property Comparison.

Tensile Modulus Impact Strength Vicat Temp.

DMTA Old Data DMTA Old Data DMTA Old Data ~ -

( G W W a ) (Izod, Jim) (tan delta) (“C) (“C)

Virgin sample 2.99 2.09 106.8 0.18 105 110

Changes from recycling -1 9% 4 9 % +42% + 122% 4 7 ° C -5°C

Recycled sample (5 times) 2.42 1.07 151.1 0.40 100.3 105 t+*t***********.*l*l*,**********l*t**********.***”~*********~*~*****~****,******~”************~****~***~*,.*~*~~~~~.*~

222 JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, SEPTEMBER lGQf5, Vol. 2, No. 3

Dynamic Mechanical Thermal Analysis-An Effective Testing Tool for a Recyclability Study of Glass Reinforced Plastics

ences in specimen type. In the previous experiment, we used injection molded specimens, which are usu- ally highly oriented in comparison with the compres- sion molded specimens, which were used for the cur- rent DMTA test.

It is noted that DMTA can also provide the data for long-term material performance, such as the creep property, by using the technique of time/ temperature superposition principle, which is often a critical pa- rameter for determining product service life.

CONCLUSIONS

Using a DMTA test, we have demonstrated that the key property changes in glass reinforced flame retar- dant impact polystyrene as a result of recycling can be simply and effectively assessed. The test results

(trends) were consistent with those obtained a typical measurement method, which includes an injection molding specimen and three different property tests: tensile modulus, Izod impact, and Vicat softening temperature.

ACKNOWLEDGMENTS

The author would like to thank Dr. Paolo Racanelli, Polystyrene R&D director, BASF Corporation, and Mr. Larry Suek, BASF technical service specialist, for their continued support and many invaluable suggestions on this paper.

REFERENCE

1. J. Songetal., SPEANTECTech. Papers, 40,2970 (1994).

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