The study is aimed at the evaluation of the influence of nucleating agent (t-butyl)benzoic aluminum (NA) in changing clarity, crystallization temperature (Tp) and radiation resistant properties of polypropylene copolymer, PP (co) with 6% of ethylene. It has been shown that crystallization temperature of PP (co)+NA did not change when the content of the NA less than 2%, but the super cooling temperature is a little bit increased when the content of the NA was 2 or higher than 2%. Clarity of the blend comprising of PP (co)+NA decreases with the addition of 2% or more NA (t-butyl)benzoic aluminum. However, the increase of the supercooling temperature makes possible to improve radiation resistance of the material

Nhan, Dang Duc

Quy, Nguyen Hong

Quynh, Tran Min

Vietnam Academy of Science and Technology: Journals Online

652
Journal of Chemistry, Vol. 45 (5), P. 652 - 655, 2007 
A DSC/TGA STUDY OF THE HETEROGENEOUS NUCLEATION OF 
CRYSTALLIZATION IN POLYPROPYLENE COPOLYMER 
Received 27 December 2006 
Dang Duc Nhan, Tran Minh Quynh and Nguyen Hong Quy 
Institute for Nuclear Science and Technology 
 
summary 
The study is aimed at the evaluation of the influence of nucleating agent (t-butyl)benzoic 
aluminum (NA) in changing clarity, crystallization temperature (Tp) and radiation resistant 
properties of polypropylene copolymer, PP (co) with 6% of ethylene. It has been shown that 
crystallization temperature of PP (co)+NA did not change when the content of the NA less than 
2%, but the super cooling temperature is a little bit increased when the content of the NA was 2 
or higher than 2%. Clarity of the blend comprising of PP (co)+NA decreases with the addition of 
2% or more NA (t-butyl)benzoic aluminum. However, the increase of the supercooling 
temperature makes possible to improve radiation resistance of the material.    
 
I - INTRODUCTION 
Nucleating agents are added to 
polypropylene (PP) in order to obtain optimum 
physical properties. It has been reported that the 
addition of nucleating agent changes the 
polymer’s crystallization temperature, spherulite 
size, density, clarity, impact and tensile 
properties considerably [1]. In this paper we 
report crystallization of a random copolymer of 
PP with 6% ethylene with a nucleating agent 
(NA), (t-butyl)benzoic aluminum, with its 
content varying from 0.1% to 2%. The random 
copolymer of PP with 6% ethylene has been 
particularly selected in view of its reported 
improved radiation stability compared to pure 
polyethylene due to lower crystallinity of the 
former [2]. Various crystallization parameters 
were estimated from Differential Scanning 
Calorimetry (DSC). Thermo-Gravimetric 
Analysis (TGA) has been carried out to assess 
thermal stability conferred upon propylene 
copolymer by the addition of nucleating agent. 
II - EXPERIMENTAL 
1. Materials 
Polypropylene copolymer containing 6% 
ethylene was from Chisso Corporation, Japan. 
The NA used was (t-butyl)benzoic aluminum 
(Merck, Germany) and was used as such 
without further purification. 
2. Mixing of materials 
The mixing copolymer with nucleating 
agent was carried out using a “Haake” mixer 
(Germany) at 40 rpm and 140oC. The product 
was compressed into sheets by molding under a 
pressure of 150 kg/mm2 for 3 minutes at 170oC
using a space of 0.5 mm after preheating for 5 - 
7 minutes at the same temperature. The hot 
sheets were then immediately cooled between 
the plates of a cold press at room temperature. 
For comparison of clarity, thin films were 
prepared by heat pressing the aforementioned 
sheet between aluminum foil at 170 - 180oC and 
under a pressure of 150 kg/mm2.
653
3. Measurements 
For TGA/DSC studies, a Simultaneous 
Thermal Analyzer by Netzsch (Germany) was 
used. The measurements were carried out at a 
heating rate of 5oC min-1 for DSC studies. The 
cell was heated from room temperature to 
185oC, and held for 15 minutes in order to 
eliminate any crystallization memory. 
Thermograms were acquired during the heating 
cycle and during the cooling cycle under static 
conditions. As all the experiments were carried 
out under identical setting, the data generated 
could be used to directly compare crystallization 
parameters. To ensure reproducibility of results, 
the measurements were done on at least 3 
samples of each blend composition. 
The thermal gravimetric analysis and DTA 
of the copolymer and the blends were carried 
out by taking the sample in the cell of the 
Netzsch (Simultaneous Thermal Analyzer) STA 
509 with S:Pt thermocouple at a heating rate 
range 25 - 600oC and at a flow rate of 200 cm3
min-1.
III - RESULTS AND DISCUSSION 
1. DSC Thermograms of crystallization of 
propylene copolymer and blends 
As mentioned earlier, a factor of 
considerable importance is the influence exerted 
by varying amounts of the nucleating agent on 
the degree of supercooling of propylene 
copolymer denoted by a range of Tp-Tm. Tp is the 
peak temperature and occurs at the intercept of 
the tangents to the sides of the exothermic curve 
and it is a measure of the temperature when the 
bulk of the polymer has crystallized. Fig.1 
shows “closed loop” thermogram of the melting 
and crystallization of pure copolymer, the 
degree of supercooling exhibited is around 
36.5oC (table 1). 
Figure 1 shows two peaks belonging to pure 
copolymer and blend containing 2% NA. 
Prominent crystallization exotherm peaks were 
observed for the copolymer as well as blends 
with nucleating agent. A steady increase of 
about 6oC up to 2% of the nucleating agent was 
observed (table 1) resulting in the decrease in 
supercooling. In the mass production of medical 
supplies, it means that the molding cycle will be 
shorter and hence more economical. 
Table 1: Values of various crystallization parameters of PP (co) in PP (co)+ 
NA blends from DSC and Tm values 
Tm,
oC Sample Tp ,
oC Tonset,
oC Tc - Tp,
oC W, mm H, J g-1 
156.5 PP (co) 120.0 129.0 7.5 10 95.01 
156.4 PP(co)+0.1%NA 122.4 129.3 6.9 10 86.65 
155.1 PP(co)+0.25%NA 122.8 128.0 5.2 10 63.71 
154.7 PP(co)+0.5%NA 123.4 129.8 6.4 11 81.09 
150.6 PP(co)+1.0%NA 124.3 130.0 5.9 9 78.03 
150.0 PP(co)+2.0%NA 126.0 132.0 6.0 8 91.25 
Various crystallization parameters estimated 
from the DSC thermograms included (Table I)
Tonset, Tc-Tp, Si, H and W and the significance 
of these parameters are described here and 
illustrated for clarity in Fig. 2. 
1. Tonset is the temperature of onset of 
crystallization which is the temperature 
when the thermogram initially vertically 
deviates from the baseline on the high 
temperature side of exothermal. 
2. Another temperature described as the 
“constructed temperature” and referred to as 
Tc is obtained at the intercept of tangents to 
the baseline and high temperature side of 
the exothermic peak. 
3. The rate of nucleation is also indicated by 
the parameter Si. 
4. The quantity Tc-Tp indicates the overall rate
654
of crystallization. The smaller the value the 
greater the rate of crystallization.  
5. The width at half-height of the exothermic 
peak is denoted by W which is a measure 
of crystallite size distribution; the smaller 
the W, the narrower the distribution and 
vice versa. 
6. The quantity H is the measure of the heat 
of crystallization. The unit of the H is 
Joule but the specific heat of crystallization 
has a unit of Joule per gram (J g-1) and it 
was calculated by dividing the H (Fig. 2) 
by the weight of the sample taken for the 
DSC analysis [2].  
 
Temperature, oC
Figure 1: DSC exotherms of 
(A) Crystallization curve of PP(co); (A’) its melting 
curve; (B) Crystallization curve of PP (co) + 2.0% 
NA; (B’) its melting curve
Table 2: Thermogravimetric analysis (TGA) of PP copolymer, PP (co), and PP (co) 
+ NA, (t-butyl)benzoic aluminum, blends 
Losses (%) at temperature (oC) 
Nature of sample 
10% 20% 40% 60% 80% 
Pure PP (co) 290 320 350 - 400 
PP(co)+0.1%NA 280 320 350 370 410 
PP(co)+0.25%NA 280 320 350 370 410 
PP(co)+0.5%NA 290 340 370 390 410 
PP(co)+1.0%NA 320 350 400 415 430 
PP(co)+2.0%NA 300 350 400 410 430 
Temperature, oC
Figure 2: Schematic of the method of estimation 
of various crystallization parameters from the 
DSC crystallization exotherm peak (for the data 
shown in table 1) 
Tc-Tp value was found to decline generally 
from pure copolymer to blends containing 
higher amounts of nucleating agent that 
demonstrates an increase in the overall rate of 
nucleation. With increase in Tp, the 
corresponding increase in Tonset would be 
expected which is indeed the case as exhibited 
by higher values of Tonset. Si value was found to 
increase progressively with the increase in 
quantity of the additive. An increase in Si upon 
addition of nucleating agent was observed in 
polypropylene by Beck et al. [1]. 
W values were unchanged at lower content 
of the nucleating agent. However, a decline in 
value was observed in blends containing 1% or 
2% as well as a narrow distribution. This 
presumably could be due to a faster rate of 
crystallization culminating in similar size of 
spherulites and thus narrower distribution. 
The H values were found to be low for the 
blends, demonstrating a low trend for 0.1, 0.25, 
655
0.50 % of nucleating agent, but the sample 
containing 2% of NA registered an increase. 
Although a higher rate of crystallization is 
achieved, the NA appears to depress the heat of 
crystallization, presumably due to suppression 
of the activation energy barrier thus facilitating 
the formation of crystallites requiring less 
thermal input. 
Prominent melting endothermic peaks of PP 
copolymer and its blends with NA were 
observed. Tm is found to decrease steadily, and a 
lowering of 6oC in the blend containing 2% NA 
is observed (table 1). The decrease could be 
attributed to the depressing of melting point 
induced by impurities, as generally observed in 
the melting behaviour of organic compounds. 
TGA of copolymer and blends 
For the blend range containing 0.1% to 
0.5% of NA, the thermograms show no 
improvement in thermal degradation rate, as 
shown in table 2. In the blend range 1% and 2%, 
considerable increase in temperature for losses 
of weight at 10%, 20%, 40%, 60% and 80% of 
the polymer was observed, indicating imparting 
of thermal stability to the blends by the 
nucleating agent. 
Clarity of PP copolymer blends 
The visual examination of thin films of 
copolymer, and those belonging to blends with 
NA, showed progressive increase in haze (lack 
of clarity) with the increase in amount of NA 
from 0.1 to 2 weight percentage. Our results 
agree with the observations of Zarah et al [3] 
who have concluded that the addition of the NA 
(t-butyl) benzoic aluminum did not improve the 
transparency, but a higher value of Tp was 
observed. This study, however, was confined to 
only addition of 0.1% NA and recording of only 
one of the crystallization parameters, Tp.
IV - CONCLUSION 
Three desirable properties needed to be 
improved in polypropylene comprise clarity, an 
increase in crystallization temperature and 
radiation resistance. Somewhat moderate 
improvement in Tp (or degree of supercooling) 
has been observed on addition of NA. The 
clarity seems to be affected adversely on 
addition of higher amounts of NA. As regards 
radiation resistance, one may expect that with 
the decreasing amorphous fraction of PP in the 
copolymer, the radiation resistance will be also 
not favorably influenced due to morphology. 
The dependence of radical termination rates on 
percent crystallinity in gamma irradiated iso-
tactic polypropylene has been reported by Dunn 
et al [4]. Gains in thermal stability associated 
with the addition of NA can be exploited in 
applications where clarity and radiation 
resistance may not be important considerations. 
Acknowledgement: The article was financial 
supported from the National Programs for 
Fundamental Researches the year of 2004-2005 
of the Ministry of Science and Technology 
(Vietnam) to this research is highly appreciated.  
REFERENCES 
1. H. N. Beck, H. D. Ledbetter. J. Appl. 
Polym., 9, 2131 - 2142 (1985). 
2. Differential Scanning Calorimeter Operating 
Manual, Perkin-Elmer Corporation, 
Norwalk, Connecticut, May 2000. 
3. A. K. Zarah, F. Yoshii, K. Makuuchi, I. 
Ishigaki. Polymer 30, 1425 - 1432 (1989). 
4. T. S. Dunn, E. E. Williams, J. L. Williams. 
Radiat. Phys.&Chem., 19, 287 - 290 (1982). 
 


A DSC/TGA STUDY OF THE HETEROGENEOUS NUCLEATION OF  CRYSTALLIZATION IN POLYPROPYLENE COPOLYMER

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A DSC/TGA STUDY OF THE HETEROGENEOUS NUCLEATION OF CRYSTALLIZATION IN POLYPROPYLENE COPOLYMER

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