Properties of Recycled PP over Virgin

[alex_idone]

Hi everybody, anyone knows the difference of physical and thermal properties of Recycled PP and VPP? Properties such as Elastic Modulus, Poissons ratio, shear modulus, Density, Thermal Conductivity and Specific Heat. Will there be a big difference of these parameters between recycled PP and VPP? Thanks

[DwightDixon]

How badly degraded the PP properties will be is, of course, dependent on how bad the degradation of the polymer length and exhaustion of the antioxidant package is. The properties you listed are some of the least effected. Impact strength, elongation, and resistance to heat aging are usually the first to go.

[alex_idone]

THANKS...The PP is not very much degraded, it was only recycled once. is it okay to assume that the elastic modulus will be almost the same since both tensile strength and elongation decreased a little bit?

[Len]

THANKS...The PP is not very much degraded, it was only recycled once. is it okay to assume that the elastic modulus will be almost the same since both tensile strength and elongation decreased a little bit?

Show me your data, not your conclusions about tensile and elongation (T&E) and I'll be better able to comment. Some loss in tensile and elongation may not effect elastic modulus results, but too great a loss in either could easily point to other degradation problems.

What was your T&E before and after recycling? What is the SDev. and Mean for the data sets? Why are you concerned w/ Elastic Modulus?

Len

[DwightDixon]

Elastic modulus is measured in the more linear portion of T&E curve. It is not directly related to the ultimate tensile strength or elongation at failure. The elastic modulus can influence how the part works (flexibility/stiffness) but not how it fails. The ultimate properties (at failure) are the things which degrade first. I would say you should do quantitative failure mode testing, as well as functional testing of the product, to determine if the recycled product gives you an adequate factor of safety. Due to the use of regrind, there may be some increase in the scatter of data as well.

[alex_idone]

Previous Data (average) Tensile = 26.6 N/sq mm; Elongation 183%
After recycling (average) Tensile = 23.5 N/sq mm; Elongation 121%
Len; will the data be enough to comment on? thnx

I'm interested on the elastic modulus to check the factor of safety on the stress analysis (COSMOS, SOLID WORKS).
Thanks for the advise Dwight

[Len]

I'd need to see the stress/strain curves to compare elastic modulus. Dwight is correct in this regard. The straight line portion of the stress/strain, tensile curve just before the sample begins to yield, is an indication of elastic modulus.

However, base on the limited results you mention, I'd say the recycling process is causing some degradation in the polymer. I think, a loss of >100 psi tensile or >50% elongation is reason for concern.

Len

[DwightDixon]

The material properties are definitely degraded, but it still may be good enough for the application dependent on the margin of safety of the original design and the usage. I do not believe the use of COCMOS or Solid Works is going to tell you whether it is acceptable. These programs are intended to help you design, not determine if the product will pass the use tests. You need to destructively test (recording the analog value of the failure mode) a statistically sufficient number of products made from virgin and recycled material and make a marketing decision if the customers will still find the product acceptable.

[PhoenixInc]

You may consider blending in virgin with recycled if you just can't quite hit the specs you need without.