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37
developing recycled resins for corrugated pipe. There is little
doubt that stress-crack resistance is the key property for the
successful use of recycled materials in corrugated pipe.
Long-Term Properties
The results of the short-term tests have shown that it will
not be too difficult to make blends with recycled contents over
50% that will meet the property requirements of AASHTO
M294. By far, the biggest challenge with recycled materials is
controlling and minimizing the effects of contamination. Once
more, the effects of contaminants will not be seen in short-
term tests, but instead will present themselves through a lim-
ited service lifetime of the pipe. This makes an understanding
of the long-term properties of the pipe critical to the success-
ful use of recycled resins in pipe.
Since these are all longer-term tests, not all of the 15 pipe
formulations could be evaluated. Therefore, six samples were
selected based mainly on the percentage of recycled content
and the type of recycled content (colored or natural). The for-
mulations selected were as follows:
· B1 - 100% VR1.
· A2 - 85% VR1 + 15% MCR.
· L5 - 50% VR1 + 20% MD + 30% MCR.
· A5 - 40% VR1 + 30% MD + 30% NAT.
Figure 38. Fathead specimen. · B3 - 20% VR1 + 40% MD + 24% MCR + 16% NAT.
· B5 - 40% MD + 36% MCR + 24% NAT.
These formulations vary from 0% to 60% recycled content,
AASHTO M294 Properties and there is one formulation with only natural recycled con-
It is useful to see how the trial pipe formulations per- tent. Some of their properties are given in Table 15. The prop-
formed as measured by the AASHTO M294 requirements of erties were measured on compression-molded plaques from
a cell class of 435400, and the additional requirements of a the pipes.
percentage carbon black between 2% and 5%, a NCLS value This group of formulations is believed to be a good repre-
on a plaque from the pipe of 18 h, and an OITemp of 220°C. sentation of the recycled pipe formulations that might be used.
The results for the 15 pipe samples are shown in Table 14. Notice that A2, L5, and B5 have properties outside of the
There were six samples that did not meet the density require- current M294 requirements for virgin, uncompounded resins
ment when the measured density was corrected for carbon (shown in bold in Table 15).
black. This is an issue with the contaminants interfering with
the accuracy of the test. If one uses the yield stress to calculate
Long-Term Tensile Strength by SIM
the density, only two samples, B3 and B5, do not meet the
requirement, and these were designed to be lower in density. The long-term tensile yield strength (Stage I) was deter-
There were eight samples that were low in carbon black, but mined by the SIM for TTS. It was used to determine the 50 and
this was a manufacturing mistake that can be easily adjusted. 100 year tensile strengths of the six candidate pipe formulations.
And, finally, there were two samples that did not meet the SIM tests were performed at three levels of stress: 1000 psi,
suggested 10 h of NCLS time on molded plaques from pipe. If 1500 psi, and 2000 psi.
one applies the new criteria of 24 h on plaques from pipe, then The test specimens were placed under the appropriate load
six of the 15 would not comply. It is clear from these results then a series of 10,000 second (166 min) creep rupture tests
that more attention needs to be placed on the NCLS test when were performed on the same specimen and separated by 7°C
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Table 12. BFF test results on 15 pipe samples at 80ºC/650 psi
in D.I. water.
Sample Formulation Failure Time (h)
(COV)
A1 100% VR1 175 25 (14%)
A2 85% VR1 + 15% MCR 157 45 (29%)
A3 85% VR1 + 15% NAT 123 17 (14%)
A4 50% VR1 + 20% MD + 30% MCR 130 35 (27%)
A5 40% VR1 + 30% MD + 30% NAT 245 11 (4%)
B1 100% VR1 188 36 (19%)
B2 50% VR1 + 20% MD + 30% MCR 155 62 (40%)
B3 20% VR1 + 40% MD + 24% MCR + 16% NAT 149 43 (29%)
B4 50% MD + 50% NAT 108 23 (21%)
B5 40% MD + 36% MCR + 24% NAT 145 29 (20%)
L1 Solplast Pipe Resin 56 9 (16%)
L2 50% VR2 + 20% MD + 30% MCR 150 35 (23%)
L3 100% VR2 147 81 (55%)
L4 100% VR1 181 35 (19%)
L5 50% VR1 + 20% MD + 30% MCR 190 53 (28%)
Table 13. Effect of residual surfactant on BFF failure times.
Time to Failure (h) at 80ºC/650 psi
Sample/ (COV)
Formulation September October October March
2008 2008 2009 2010
A1 175 31 226 46
VR1 (18%) (20%)
B1 188 44 215 97 411 ± 135 414 ± 97
VR1 (23%) (45%) (33%) (23%)
L4 181 42 211 46
-- --
VR1 (23%) (22%)
A4 130 42 148 73
VR1+MD+MCR (33%) (50%) -- --
50/20/30
B2 169 68 234 52
VR1+MD+MCR (40%) (22%) -- --
50/20/30
L5 190 65 255 54 431 ± 86 334 ± 117
VR1+MD+MCR (34%) (21%) (20%) (35%)
50/20/30
A2 157 ± 56 257 ± 85
VR1+MCR (36%) -- (33%) --
85/15
A5 253 ± 14 323 ± 70
VR1+MD+NAT (6%) -- (22%) --
40/30/30
B3 166 ± 36 330 ± 66
VR1+MD+MCR+NAT (22%) -- (20%) --
20/40/24/16
B5 145 ± 35 280 ± 95 228 ± 141
MD+MCR+NAT (24%) -- (34%) (62%)
40/36/24
L1 56 ± 9 -- 201 ± 39 208 ± 73
Proprietary (16%) (19%) (36%)
Note: "--" = data not available.
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39
Table 14. AASHTO M294 requirements for 15 trial pipe samples.
Sample Density1 MFI Flexural Yield % Carbon NCLS OITemp
Modulus Stress Black
M294 4 3 5 4 25% >18 hrs >220°C
A1 4 4 5 5 1.6 28 257
A2 3 3 5 5 1.4 21 256
A3 5 3 5 5 2.2 <18 257
A4 4 3 5 5 0.5 18 256
A5 4 3 5 5 1.5 29 260
B1 4 4 5 5 2.0 26 253
B2 4 3 5 5 2.0 18 253
B3 3 3 5 4 2.0 30 256
B4 4 3 5 5 1.4 19 257
B5 3 3 5 4 1.9 19 256
L1 4 3 5 5 2.1 <18 240
L2 4 3 5 5 1.5 28 256
L3 4 4 5 6 1.5 39 256
L4 3 3 5 6 2.5 29 254
L5 3 5 5 2.6 26 256
1
Measured density corrected for percentage carbon black.
Note: MFI = melt flow index.
Table 15. Select index properties of final six candidate formulations.
Property Sample
B1 A2 L5 A5 B3 B5
1
Density 0.951 0.943 0.946 0.948 0.948 0.952
(g/cm3)
MI 0.13 0.15 0.17 0.21 0.27 0.34
(g/10 min)
% Color 2.0 1.4 2.6 1.5 2.0 1.9
% Ash 0.0 0.3 0.3 0.2 0.3 0.4
% PP 0.0 0.7 1.8 0.3 1.7 2.2
Flexural 148,210 152,607 142,618 140,065 128,361 128,758
(psi)
Yield (psi) 3,865 3,775 3,922 3,623 3,251 3,311
Break Strain 165 168 108 159 300 351
(%)
NCLS (h) 25.5 21.2 25.9 28.6 29.8 19.2
OIT (mib) 49 39 78 96 93 75
BFF Test2 411 257 382 323 330 254
(h)
1
Corrected for % color
2
At 80ºC and 650 psi of stress.
