DSC GELATION MEASUREMENT : INFLUENCE OF PIPE FORMULATION ON RESULT

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DSC GELATION MEASUREMENT INFLUENCE OF PIPE
FORMULATION ON RESULT

• Joël Fumire
• Research Technology SBU Vinyls

São Paulo, 2005
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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.

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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
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DSC measurement

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

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DSC measurement
mW

• 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)

DSC
Heat Flow
B
A
Tg
B-onset
A-onset
30
50
70
90
110
130
150
170
190
210
230
Temperature
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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

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Parameters

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

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Parameters

• The main target is not
• 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)

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Evolution of gelation
Gelation as measured by the DSC method
(transformation of crystallites) appears rather
late compared to a standard plastograph gelation
test.
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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

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Parameters (1st serie)
Was milled at 180C
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Sample preparation
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Parameters (2nd serie)
All milled at 180C
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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

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ParametersRelation between B onset and gelation
Gelation
100
2nd series
R² 0.3608
90
80
70
60
50
40
170
175
180
185
190
195
200
B onset (C)
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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

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Alternative method

• Another method was extensively used within our
  company to assess the level of gelation of window
  profiles

Elongation at rupture measured at 100C in a
tensile test
Elongations measured are in the range 200 (bad
gelation) to 300 (good gelation) or higher (too
strong gelation)
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Alternative method

• Correlation is rather satisfactory
• DSC could lead to a lack of precision in high
  gelations
• Elongation at 100C 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
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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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Thank you for your attention !