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OCR for page 30
30
4200 4000
y = 0.415x + 3905.5
R2 = 0.2146
4000 Actual 3800
y = -4.835x + 3800
R2 = 0.9761
Yield Strength (psi)
Yield Strength (psi)
3800 3600
y = 3.49x + 3688
3600 3400
Theoretical
y = -4.85x + 3688
3400 3200
VR1 + N10LL VR1 + N35LL
3200 3000
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
4400 4600
y = -0.44x + 4062 y = 3.975x + 4116
4200 R2 = 0.0155 4400 R2 = 0.9135
Yield Strength (psi)
Yield Strength (psi)
4000 4200
3800 y = 1.13x + 3924 4000
VR3 + N10LL
3600 3800 y = 7.62x + 3764
VR2 + N10LL
3400 3600
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
Figure 31. The effect of recycled content on the yield strength of PCR-NAT blends.
However, the yield will be over 4,000 psi, so the NCLS test Blends Made with PIR-HD
will be less severe for this blend. That means that the limit
might be closer to 15%. A total of 12 blends were prepared with PIR-HDPE. Appen-
dix C, Section C.11 contains summary tables for the blend
2. Dramatic improvements in stress-crack resistance can
series, plots of properties versus percentage recycled content,
be obtained by blending the NAT with either LLDPE or
and individual property reports for the 12 blends. Tables con-
MDPE. A failure time of 50 h in the 15% NCTL test can
taining correlation coefficients and predicted versus measured
be obtained with around 45% of added LL and 55% of
properties are found in Tables C-7 and C-8.
added MD.
The blends were
3. Blends between NAT and MDPE are preferred because
the yield stress remains higher for the MD blends. For VR1 + PIR-HD @ 20, 40, 60, AND 80%,
example, the yield stress for 45% LL is around 2,900 psi, VR2 + PIR-HD @ 20, 40, 60, AND 80%,
while the yield stress for 55% MD is around 3,400 psi. The VR3 + PIR-HD @ 20, 40, 60, AND 80%.
AASHTO minimum-density requirement for pipe resins
is 0.948 g/cm3, which correlates to a yield stress of around This series behaved more predictably. The PIR-HD had 3.9%
3,500 psi. color + ash but also a high break strain of 720%. The aver-
4. The addition of only 10% LLDPE does very little to improve age yield stress of 3,157 psi suggests its true density is around
the properties of resulting blends. 0.943 g/cm3 and its 15% NCTL time is around 98 h. This is a very
5. A blend of 50% VR3, 25% NAT and 25% MDPE has prop- good resin for blending because it seems to lack the type of con-
erties very close to a PPI-certified pipe resin. tamination that produced the high scatter in the other blends.
OCR for page 31
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700 800
600 700 y = -2.28x + 639
y = -0.67x + 478
Theoretical 600
500
Break Strain (%)
Break Strain (%)
500
400
400 y = -0.35x + 499.5
300 R2 = 0.0246
300
Actual
200
200
y = 3.04x + 242.5 VR1 + N10LL
100 R2 = 0.8614 100 VR2 + N10LL
0 0
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
800 800
700 700 y = 2.165x + 516
y = -3.76x + 647 R2 = 0.4525
VR3 + N10LL
600 600
Break Strain (%)
Break Strain (%)
500 500 y = 1.77x + 478
400 400
300 300
y = -2.555x + 553
R2 = 0.8663
200 200
VR1 + N35LL
100 100
0 0
0 20 40 60 80 100 120 0 20 40 60 80 100 120
% Recycled % Recycled
Figure 32. The effect of recycled content on the break strain of PCR-NAT blends.
The results of blending and testing with PIR-HD have led M294 resin requirements for corrugated pipe. It was deter-
to the following findings: mined that for simple, two component blends, the maximum
amount of PCR-HDPE is around 15%, while a specific PIR-HD
1. This PIR resin is apparently void of the contaminants found obtained could be used in amounts up to 40%.
in PCR bottles that create high scatter in some properties, More importantly, it was found that through the relation-
particularly break strain. ships discovered during this task, other two and three compo-
2. A resin with a base density of around 0.943 g/cm3 is an nent blends could be designed and optimized for the specific
excellent resin for blending because it has a yield stress of purpose of maximizing the amount of recycled HDPE used.
around 3,150 psi and stress-crack resistance around 100 h. This information will be invaluable to those developing new
3. These test results served to validate the relationships found blends for improved short- and long-term properties of cor-
in the other blends. rugated pipe resins. Contaminants like particles and silicone
4. Blends of virgin resins containing up to 40% PIR-HD had rubber seemed to affect the relationships in a negative way so
yield stresses around 3,500 psi, break strains above 550%, the relationships are probably most useful as guidelines; some
and 15% NCTL times greater than 40 h. This blend would actual testing will still be required.
meet the resin properties found in AASHTO M294 for pipe. It also should be stated that much better recycled blends can
be made than the ones described in this report. The results
A total of 66 blends were prepared and tested to find out herein were limited by the fact that the recycled resins were
how much recycled resin could be used in three PPI-certified blended with PPI-certified pipe resins. The virgin resins only
resins where the final product would still meet the AASHTO had approximately 50 h of NCLS time to begin with. Starting
