Effect of FR-20 [Mg(OH)2] amount on mechanical properties and burning
resistance of PVC.
1. Objective
Investigate the effect of Santicizer 148 additions and of replacing the regular
CaCO3 or Kaolin by FR 20 on the burning and mechanical properties of two
types of PVC with different molecular weights ( K=70 & K=67).
2. Experimental
2.1 Formulations
The formulations are described in Table 2. The amounts of different components
are shown as weight percentages.
Table 1 - Particle characteristics of batches FR-20 grade 100 D
Property
FR-20 100
D
Surface Area (m²/g)
(BET)
7.3
D50 (Coulter) (µm)
2.1
D90 (Coulter) (µm)
4.5
Table 2 PVC Formulations
Ingredients 1
2
3
4
PVC K=67 Epivyl 37P
-
-
-
5
6
7
8
8b
9
10
11
-
55.4 55.4 51.0 51.0 51.0 48.0 45.0
PVC K=70 59.8 59.8 54.3 50.7 47.6 Epivyl 43
-
-
-
-
-
-
Trimellitate 29.3 10.1 8.1
6.1
5.7
-
-
-
-
-
-
-
DIDP
-
-
-
-
32.1 12.7 10.7 10.7 10.7 9.1
Santicizer
148
-
19.2 18.5 18.8 17.6 -
19.4 18.9 18.9 18.9 18.7 17.6
Kaolin
6
6
-
-
-
-
-
-
-
-
-
-
CaCO3
-
-
-
-
-
8.3
8.3
-
-
7.6
-
-
FR 20-100 D
94-060
-
14.7 20.3 25.2 -
-
15.3 -
7.6
20.2 -
FR-20-100 D
96-058
-
-
-
-
-
-
-
15.3 -
-
25.2
Sb2O3
3.7
3.7
3.3
3.1
2.9
3.1
3.1
3.1
3.1
3.1
3.0
2.8
Lead
dibasic
phtalate
0.6
0.6
0.5
0.5
0.5
0.6
0.6
0.5
0.5
0.5
0.5
0.45
Dibasic
lead
stearate
0.3
0.3
0.27 0.25 0.24 0.28 0.28 0.25 0.25 0.25 0.24 0.22
Bisphenol
A
0.3
0.3
0.27 0.25 0.24 0.28 0.28 0.25 0.25 0.25 0.24 0.22
-
8.6
Formulation 1 / 11 were prepared from PVC of various K values (see Table 2)
produced at Frutarom Acco.
2.2 Mixing
Before mixing the formulations in the Brabender, a premixing stage was carried
out by means of a mechanical mixer at about 150 rpm.
The mixing conditions in the Brabender were as follows: temperature of the
mixing chamber for formulations based on Epivyl 43 (K=70) was 175°C and for
formulations based on Epivyl 37P (k=67) 160°C. The mixing speed was 50 rpm.
The other conditions are shown in tables 3.1 and 3.2.
Table 3.1 - Mixing conditions - formulations based on PVC with k=70
Formulation 1
1a¹
2
2a¹
3
3a¹
4
5
No.
No. of runs
4
4
4
4
4
4
4
4
Melt
temperature
(°C)
186
186
184
184
186
186
184
186
Mixing time
(min)
5
5
5
5
5.5
5
4.5
5
Torqe (N.m)
15.1
15.6
13.4
14.2
15.2
13.9
16
16.3
Standard
deviation
(N.m)
0.58
0.29
0.52
0.17
0.28
0.35
0.33
0.48
¹Formulations marked with an "a" were compression molded at 165°C (see par.
2.3 below)
Table 3.2 - Mixing conditions of formulations based on PVC with k=67
Formulation 6
7
8
8b
9
10
11
No.
No. of runs
5
5
5
3
5
5
5
Melt
temperature
(°C)
170
170
170
172
170
170
175
Mixing time
(min)
5
5.5
5.5
5
5
5
5
Torqe (N.m)
12.3
11.8
13.3
13.1
13.1
13.6
11.6
Standard
deviation
(N.m)
0.53
0.12
0.59
0.31
0.32
0.53
0.27
Torque increased, as expected, with the content of filler and the molecular weight
of the polymer. Quite unexpectedly, the formulation containing about 25% FR-20
[Mg(OH)2] from batch 96-058
(formulation 11 - Table 2) exhibited a very low torque as compared with the
formulation containing only about 20% Mg(OH)2 (formulation 10 - Table 2) but
belonging to batch 94-060. However, formulations containing about 15%
Mg(OH)2 (8 and 8b - Table 2) showed very similar torque values (13.34±0.59
N.m vs. 13.07±0.31 N.m). It appears therefore that while the small differences
between the two batches have no impact on mechanical properties, they still
affect the processability of the compound, especially at high filler loadings.
2. 3. Samples preparation
The compression molding was performed at 185°C for formulations based on
PVC K=70 and 165°C for formulations based on PVC K=67 on a 30 tonnes Dr.
Collin's press. The formulations marked with "a" in Table 2 above were
compression molded at 165°C. The pressure was 100 bar and was maintained
both during the hot (1 min) and cooling (6 min) stages. The temperature of the
mold by the end of the compression cycle reached about 35°C.
Plates with a thickness of 1.6 mm were prepared for the UL-94 test. Plates with a
thickness of 3.2 mm were prepared for the LOI and tensile tests. Prior to each
test the samples were conditioned for 3 days at room temperature inside sealed
PE bags.
At increased compression molding temperatures (185°C) as used in our previous
work it was noticed a discoloration of the material, due seemingly to the low
thermal stability of Santicizer 148. The color of the plates changes to a slight
yellow-light brown if a second compression molding was performed on the same
material.
2.4 Tests description
2.4.1. UL-94 burning test
The burning tests were conducted according to UL-94 for vertical samples. The
tested samples were 127x12.5x1.6 mm.
2.4.2 LOI test
The LOI tests were conducted in the Applicative Plastics Lab of BCL accordingly
to work instructions 06-95-20/13. Samples dimentions were 120x5.5x3.2 mm. No
smoke tests were performed because the smoke chamber was out of function.
2.4.3. Tensile tests
The tensile tests were performed on an Instron machine model 5567 according to
ASTM D-638 using a 1000% mechanical extensometer. The specimens were
dumbell shaped, type IV specimens. The test was conducted at room
temperature at a crosshead speed of 70 mm/min.
3. Results and Discussion
3.1. UL-94 burning test
Only representative formulations with and without FR-20 (at max. content), i.e.
formulation 1 vs. formulation 5 and formulation 6 vs. formulation 10 were tested.
Since no significant differences were observed, no other formulations were
checked by UL-94 test.
5 samples from each formulation were tested. Burning time after the first ignition
was defined as t1 and the burning time after the second ignition was defined as
t2 . Table 4 summarizes the results of tests (maximum burning time, and the total
burning time, which is the sum of all the burning times of the 5 samples).
No tested samples drip or ignite the cotton. Consequently, all the formulations
tested were classified as V-0.
Table 4 - Results of UL-94 tests
Formulation No.
1
5
6
10
Maximum burning 2
time
(t2 or t1 )
(sec)
0
3
1
Total burning time 3
(t2 + t1)
(sec)
0
10
3
3.3 LOI test
LOI test result of all formulations are shown at tables 5 and 6 and figure 2.
Table 5 - LOI test results of PVC K=70 formulations
Formulation 1
2
2a
3a
No.
LOI (%)
30.9-31.4 27.9
28
4
5
33.0-33.2 33.4-33.6 33.7-34.4
Table 6 - LOI test results of PVC K=67 formulations
Formulation 6
7
8
9
No.
10
LOI (%)
30.5-30.9 32.5-32.7
27.1-27.4 26.1-26.3 30.1
29.1
11
The addition of Mg(OH)2 to PVC by replacing a part or the whole amount of the
regular filler (CaCO3 or Kaolin) leads to a significant increase of the LOI. It seems
that this increase is more significant for the K=67 polymer. Substitution of only
half of the original amount of CaCO3 by Mg(OH)2 (7.5% magnesium hydroxide)
leads to almost the same increase in LOI as by substituting the entire amount of
CaCO3 by magnesium hydroxide. This seems to confirm previous results
reported by us in an earlier internal communication. It appears that the two
investigated polymers behave differently in regard to the effect of magnesium
hydroxide additions on the LOI:
- The LOI values of formulations based on the higher molecular weight PVC are
higher than
of formulations based on the lower molecular weight PVC;
- Formulations based on Epivyl 43 (K=70) reached an LOI plateau already at
15% Mg(OH)2
while formulations based on Epivyl 37P (K=67) exhibited a continuous increase
in LOI.
Caution should however be exercised in regard to this statement since most of
the
increasing trend is actually a result of the LOI value of formulation 11 based on a
different
Mg(OH)2 batch.
Summarizing, while for K67-based formulations, an increase of 1 unit of LOI is
obtained by a little less than 4% FR-20, for K70-based formulations the effect of
FR-20 content on the LOI is far from being linear.
An additional observation is related to the effect of Santicizer 148. It appears that
additions of Santicizer 148 or replacement of a part of regular plasticizer (either
trimellitate or DIDP) by Santicizer 148 leads for both investigated systems to a
decrease of LOI (compare formulations 1 and 2, and 6 and 7, respectively, in
Tables 3.1 and 3.2).
3.3 Mechanical properties
The mechanical properties at tension of the tested formulation are summarized at
tables 7 and 8 and in figures 3 and 4.
No significant differences were noticed between various formulations in terms of
elongation to break: it varies between 220 and 280%. No definite trend of the
variation of the strain at break with the filler loading and/or molecular weight of
the polymeric matrix could be identified. However, other mechanical properties
are strongly affected by the concentration of Mg(OH)2 and the molecular weight
of PVC. As expected, the tensile strength of the compound decreases fast with
the concentration of the filler while the elastic modulus increases. Interestingly,
the most affected formulations are those based on PVC with a higher molecular
weight (K=70) while formulations based on Epivyl 37P showed an almost
constant tensile strength in the whole range of filler loadings (0 - 25%).
With respect to the additions of Santicizer 148 instead (or together with)
trimellitate, it may be noticed that this plasticizer appears to be much more
effective than trimellitate: the elastic modulus of formulation 2 dropped to half the
corresponding value of the formulation 1 as a result of replacing about 2/3 of the
trimellitate by Santicizer. Similarly, the elongation at yield increased almost 3-fold
as a result of the same change in formulation (see Table 7). Santicizer 148
appears to have a similar plasticizing efficiency when compared with DIDP.
The compression molding temperature affects markedly the mechanical
properties of the compounds. Increasing the temperature from 165°C to 185°C,
while maintaining all the other parameters constant, leads to a significant
weakening of the polymers (compare formulations 1a, 2a, 3a processed at 165°C
with formulations 1, 2, 3 processed at 185°C - Tables 7 & 8). The tensile strength
decreases by up to 18%, the elastic modulus increased slightly and the
elongation to break increased by up to 20%. This seems to indicate that some
kind of system deterioration takes place at a higher processing temperature.
However, this conclusion deserves more systematic investigations.
Table 7 - mechanical properties of PVC K=70 formulations
Formulation
1
1a
2
2a
3
3a
4
Property
5
Yield Stress
(MPa)
4.33
4.41
5.90
8.67
6.09
9.90
9.88
7.11
S.D² (MPa)
1.33
0.93
0.39
0.95
0.22
1.56
1.26
0.44
Yield Strain
(%)
12.43 9.63
32.77 44.85 28.43 55.17 50.55 30.72
S.D.
(%)
4.62
2.15
Stress at
break
(MPa)
21.61 24.68 19.04 23.06 16.88 20.02 18.11 14.57
S.D.
(MPa)
0.43
3.96
0.92
0.54
6.49
0.59
1.23
0.99
17.47 11.25 0.67
0.71
0.63
0.37
Strain at break 313.5 249.3 297.1 257.2 256.6 259.6 221.4 236.8
(%)
S.D.
(%)
13.2
18.7
12.2
28.2
Elast. modulus 40.85 44.55 20.83 22.78 23.9
(MPa)
23.45 25.2
28.0
S.D.
(MPa)
1.49
1.51
2.34
Energy to
break
(J)
21.10 20.66 16.68 17.05 14.04 16.3
4.03
S.D.
0.98 2.65
(J)
²S.D. = standard deviation
13.5
0.71
1.24
18.7
0.36
1.6
32.2
0.22
2.70
20.5
1.49
2.75
14.03 12.55
0.96
1.86
Table 8 - mechanical properties of PVC K=67 formulations
Formulation
6
7
8
8b
9
10
11
Property
Yield Stress
(MPa)
5.41
4.49
4.71
4.72
4.79
5.18
7.06
S.D² (MPa)
1.02
0.51
0.68
1.45
0.85
0.89
1.28
Yield Strain
(%)
48.85 44.11 38.67 37.0
S.D.
(%)
13.91 7.59
Stress at
break
(MPa)
15.65 14.89 13.38 14.58 14.12 13.85 13.53
S.D.
(MPa)
0.49
0.47
8.95
0.41
39.65 36.63 48.71
13.14 8.61
0.26
0.31
8.38
0.35
12.98
0.43
Strain at break 282.1 266.04 251.2 259.5 242.5 279.7 276.0
(%)
S.D.
(%)
8.6
11.17 7.4
Modulus
(Young)
(MPa)
14.38 11.84 14.04 14.49 13.82 16.68 17.98
S.D.
(MPa)
0.59
Energy to
break
(J)
12.98 10.86 10.40 11.01 9.4
11.59 11.57
S.D.
(J)
0.85
0.35
0.57
0.71
0.62
0.60
9.2
0.53
0.74
13.4
0.51
0.80
5.2
0.24
10.7
1.2
12.98
4. Conclusions and Recommendations
- Replacement of the regular filler (CaCO3 or Kaolin) by FR-20-100D leads in all
cases to a significant increase in LOI and elastic modulus, with almost no impact
on the elongation to break.
- FR-20 is a powerful smoke suppressant enabling to reduce the smoke density
by a factor of 3 to 9 for loads of 15 and 25 % respectively. The maximum rate of
smoke evolution is also reduced significantly.
- The tensile strength of formulations including FR-20-100D decreases markedly
with the concentration of the filler when the polymeric matrix was PVC with a
higher molecular weight. However, the tensile strength of formulations based on
the lower molecular weight PVC (Epivyl 37P) was almost unaffected by the filler
loading.
- Formulations based on different (although similar) filler batches exhibit similar
mechanical properties, but markedly different processability and burning behavior
(LOI). Therefore, we would recommend to undertake a systematic study of the
effect of particle size and size distribution on the processability and properties of
compounds containing Mg(OH)2.
- The LOI reaches a plateau of 33-34% for FR-20 loadings in excess of 15%
when the polymeric matrix was Epivyl 43. However, when the PVC in
formulations was Epivyl 37P, the LOI values increased steadily with FR-20
concentration reaching about 32-33% for 25% FR-20 loading. It is therefore
recommended to limit the additions of FR-20-100D to 15% in formulations based
on higher molecular weight PVC and to continue to look for an optimum loading
of FR-20-100D in formulations based on the lower molecular weight PVC.
- It appears that Santicizer 148 has a rather detrimental effect on the LOI and
thermal
stability of resulting compounds.
Signed by: Moshe Link
Approved by: Dr. Samuel Bron