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60 60
50 50
VR1 + N10LL VR2 + N10LL
NCTL Failure Time (hrs)
NCTL Failure Time (hrs)
40 y = 45.8e-0.0273x 40
y = 38.5e-0.0255x
Theoretical
30 30
20 20
-0.0178x
y = 20.592e
10 R2 = 0.6512 10 y = 29.985e-0.0245x
Actual R2 = 0.9712
0 0
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
60 60
50 50 VR1 + N35LL
VR3 + N10LL
NCTL Failure Time (hrs)
NCTL Failure Time (hrs)
-0.0271x
y = 36.2e
40 40
30 30 y = 45.8e-0.0085x
20 20 y = 43.269e-0.0093x
R2 = 0.9297
10 y = 31.843e-0.027x 10
R2 = 0.983
0 0
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
Figure 33. The effect of recycled content on the 15% NCTL of PCR-NAT blends.
with similar resins with 100 or 150 h of NCLS time would Each plant made a sample from 100% virgin resin 1 and a
allow for much more recycled content to be used. 50/20/30 blend of VR1, MDPE, and MCR.
Additionally, there are new bi-modal resins with densities Sample L1 was a proprietary pipe resin formulated by the
that meet M294 requirements and that have thousands of recycled-resin supplier. This was included as a representation
hours of stress-crack resistance. It would be valuable to see of the type of resin that could be supplied by the recycled-resin
the effects of adding these resins to recycled content. companies.
Phase 3--Pipe Made from Short-Term Properties
Recycled-Resin Blends
Index Test Results
Trial Pipe Manufacturing
After the 15 sample pipes were manufactured, their prop-
A total of 15 trial pipe samples were prepared at three dif- erties were measured on compression-molded plaques made
ferent manufacturing plants, designated Plants A, B. and L. from the pipe. All the plaques were made in accordance with
Five, 20-feet-long samples were made from each formulation ASTM D4703 at a cooling rate of 15°C/min. Complete reports
for a total of 1,500 feet of pipe. The formulations made at the are given for each pipe formulation in Appendix D, Sec-
three plants are shown in Table 8. tion D.11. This section will focus on specific properties that
Each of the three plants used the same lots of PCR-MCR and may be important for future specifications. A summary of
PCR-NAT from a single supplier. Each plant used a different the short-term properties is shown in Table 9.
lot of the VR1 and each plant used their own carbon black The density of base resins for AASHTO M294 pipe must
master batch. The MDPE used was also from the same lot. be between 0.948 and 0.955 g/cm3. This is cell class 4 accord-
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Table 8. Trial pipe formulations.
Sample % VR1 % Virgin % PCR-MCR % PCR-NAT
LMDPE
A1 100 0
A2 85 0 15 0
A3 85 0 0 15
A4 50 20 30 0
A5 40 30 0 30
B1 100 0 0 0
B2 50 20 30 0
B3 20 40 24 16
B4 0 50 50
B5 0 40 36 24
L11 0 0 0 0
L2 50 (VR2) 20 30 0
L3 100 (VR2) 0 0 0
L4 100 0 0 0
L5 50 20 30 0
1
Proprietary formulated pipe resin containing about 50% recycled content.
ing to ASTM D3350. When directly measured, all but four Yield Stress = 81, 250 × Density - 73, 500
of the samples had densities higher than the upper limit of
0.955 g/cm3. This was caused by the presence of carbon black where yield stress is expressed as psi and density as g/cm3.
and particles that are certainly denser than HDPE. However, Both values are shown in Table 9. It is believed that the
according to ASTM D3350, these values can be corrected for density measured in a gradient density column and corrected
the percentage carbon black, according to the relationship for percentage carbon black is inaccurate because of the pres-
Dcorr = D - 0.0044C, where C is the percentage carbon black. ence of particles and PP. Their presence will influence the
Density values can also be determined from other material measured value. Also, the direct density measurement might
properties, such as the yield stress or flexural modulus. The be influenced by the very small size of the test specimen. A
equation relating density to yield stress is piece around 1/16 in. × 1/16 in. is often the size tested. If this small
Table 9. Short-term properties for 15 trial pipe samples.1
Property Sample
A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 L1 L2 L3 L4 L5
Density 2
(g/cm3 ) 0.952 0.943 0.963 0.952 0.948 0.951 0.948 0.948 0.948 0.952 0.950 0.950 0.952 0.946 0.946
Density 3
(g/cm3 ) 0.952 0.951 0.952 0.950 0.948 0.952 0.949 0.945 0.948 0.945 0.949 0.951 0.955 0.955 0.953
Melt Index
(g/10 min) 0.12 0.15 0.16 0.19 0.21 0.13 0.22 0.27 0.36 0.34 0.20 0.33 0.36 0.12 0.17
% Carbon
Black 1.6 1.4 2.2 0.5 1.5 2.0 2.0 1.9 1.4 1.9 2.1 1.5 1.5 2.5 2.6
% Ash 0.1 0.3 0.2 0.4 0.2 0.0 0.4 0.3 0.1 0.4 0.7 0.4 0.0 0.0 0.3
% PP 0.0 0.7 0.2 1.4 0.3 0.0 1.9 1.7 1.0 2.2 2.5 2.4 0.0 0.0 1.8
Yield
Stress (psi) 3851 3775 3863 3710 3623 3865 3638 3251 3523 3311 3631 3751 4079 4145 3922
% Break
Strain 183 168 139 241 159 163 343 300 190 351 277 195 252 93 108
OIT (min) 49 39 38 32 96 49 54 93 110 75 13 78 78 70 78
1
All properties measured on compression molded plaques made from the pipe.
2
Measured density corrected for percentage carbon black.
3
Density calculated from yield stress.
