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

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.

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

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)

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

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

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

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)

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%

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.

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

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.

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.

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

Parameters Relation between B onset and gelation 100% 2nd series R² = 0.3608 90% 80% 70% 60% 50% 40% 170 175 180 185 190 195 200 B onset (°C)

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

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)

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 = 92.052e0.0147x 370 R² = 0.8031 320 270 220 170 120 40 50 60 70 80 90 100

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

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