1. DSC GELATION MEASUREMENT : INFLUENCE OF PIPE FORMULATION ON RESULT
Joël Fumire
Research & Technology SBU Vinyls
São Paulo, 2005

2. Introduction Considering the fact that …
The level of gelation of PVC determines the mechanical properties of the finished item
The level of gelation has a significant influence on subsequent processing (biorientation or corrugation)
A few methods exist since a long time : MCT, SEM homogeneity, short die melt rheology, etc… none of them was considered as totally satisfactory.

3. Introduction Considering the fact that …
The measurement by DSC method seems to realise a good compromise between accuracy, universal application and cost
But : some authors found limitations to the application of the method related to the composition of the item
THIS IS THE REASON FOR OUR INVESTIGATION

4. DSC measurement Apparatus : DSC TA 2920 from TA Instruments
Operating instruction : 20 mg of sample in Al capsule,
Heating speed : 20°K/min measurement range : 50 to 220 °C (conventionnally)

5. DSC measurement
Endotherm A is the endotherm after Tg and up to the minimum at Tm (processing temperature)
Endotherm B is taken from this Tm up to 220 °C (conventionnaly)
Gelation level is calculated as : G = A / (A + B) mW
DSC
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
Heat Flow B A Tg
B-onset
A-onset 30 50 70 90
110
130
150
170
190
210
230
Temperature

6. DSC measurement This method is not yet an international standard
Standardisation group ISO TC138/SC5/WG2 is working on this topic with designation : ISO 18373
The operation instruction adopted in this work is close to the existing draft

7. Parameters The main parameters investigated are :
Type of stabilisation (Pb, Ca-Zn, Sn)
Amount of filler
Presence of impact modifier
Level of lubricant

8. The main target is not : The main target is : Parameters
to assess the effect of additives to promote gelation
The main target is :
To check if some additives affect the DSC thermogram (shape or amplitute of endotherm)

9. Evolution of gelation
Gelation as measured by the DSC method (transformation of crystallites) appears rather late compared to a standard plastograph gelation test.
Degree of gelation versus plasticising time 10 20 30 40 50 60 70 2 4 6 8 12
Time (min)
Torque (Nm)
60%
55%

10. Sample preparation
The formulation is of the pipe-type, i.e. low level of additives but highly lubricated and the samples are gelified on a 2-roll mill
Table 1 1 2 3 4 5 6 7 8
PVC K66
100
Solid tin one-pack
Lead one-pack
2.4
Ca-Zn one-pack
2.8
Liquid tin stab.
0.8
Internal lubricant
0.3
0.6
Lubricant
CC filler 15 30
Acryl Impact modif.
TiO2 pigment
0.25
C pigment
0.025
Characteristic
Lead
Acryl.
Ca-Zn réf.
lubricant
filler 15
filler 30
Liqu-Tin
Tin-O.P.

11. Parameters (1st serie) Was milled at 180°C
DSC -Tm
140
150
160
170
180
190
200
Lead
Acryl.
Ca-Zn
réf.
lubricant
filler 15
filler 30
Liqu-Tin
Tin-O.P.
Effect of formulation on gelation level
40%
50%
60%
70%
80%
90%
Lead
Acryl.
Ca-Zn réf.
lubricant
filler 15
filler 30
Liqu-Tin
Tin-O.P.
DSC - Gelation level

12. Sample preparation Table 2 PVC Solid Tin O.P. Lead stab. Ca-Zn stab.
Characteristic
Table 2
PVC
Solid Tin O.P.
Lead stab.
Ca-Zn stab.
Liqu. Tin
Int. Lubr.
Lubric.
CC filler
CC coarse filler
Precip. Filler
pigment 1
100
2.4
0.6 3
0.25
0.025
2.8
0.3 6 4 5 7 2 8
Lead
filler 6
intern.
coarse
filler
Precip.CC
Tin OP.
tin+
coarse f.

13. Parameters (2nd serie) All milled at 180°C Tm Gelation 140 150 160 170
190
200 Pb
Filler 6
Intern. Lubric
Coarse filler
PCC
Tin
tin+c.f.
All milled at 180°C
40%
50%
60%
70%
80%
90%
Gelation Pb
Filler 6
Intern. Lubric
Coarse filler
PCC
Tin
tin+c.f.

14. Parameters
The variants of additives did generally not introduce a different shape of endotherm
Only the ox-PE wax (lubricant) introduced an additional peak at 130 °C

15. Parameters Relation between B onset and gelation
100%
2nd series
R² =
90%
80%
70%
60%
50%
40%
170
175
180
185
190
195
200
B onset (°C)

16. Parameters
The processing temperaure can be checked with good accuracy but on these small machines this value is not totally correlated with the gelation level
The shape of the endotherm was generally not affected by the composition (except by PE-wax)
The sample with Pb stabilisation shows higher endotherms than the average
For the sample with modifier and highly lubricated the energy/g of the endotherm was lower than the average

17. Elongation at rupture measured at 100°C in a tensile test
Alternative method
Another method was extensively used within our company to assess the level of gelation of window profiles :
Elongation at rupture measured at 100°C in a tensile test
Elongations measured are in the range 200% (bad gelation) to 300% (good gelation) or higher (too strong gelation)

18. Alternative method Correlation is rather satisfactory
DSC could lead to a lack of precision in high gelations
Elongation at 100°C is also a precise method but the measurement is more labor intensive and equipment is more expensive.
420
y = e0.0147x
370
R² =
320
270
220
170
120 40 50 60 70 80 90
100

19. Conclusions
Normal levels of additives have no adverse affects on the measurement with this standard procedure (even with high levels of fillers)
In some cases, the processing temperature is not a reliable way of expressing the gelation level
The method is correctly correlated with other methods of assessing the gelation level
The method appears to be enough robust to be used as quality control of extrusion

20. Thank you for your attention !