Plastic Deterioration
Plastic Deterioration
(OP)
All,
I am relatively new to the industrial arena, being a civil/environmental most of my career. Therefore some of the questions I have about plastics and polymers may be very elementary, I apologize in advance. I am currently working for a food processing company that uses batch retorts in its process. These retorts process product on injection molded plastic trays (the product is pre-packaged prior to processing). We have noticed a residue on the packaging after processing, and I am attributing it to the plastic in the trays breaking down. The exterior of the trays appears softer than when placed in service and a chalky material is coating the trays.
This is occurring at about six months after being placed in service. I do not know the exact material, but am working on an answer. Coincidental to the deterioration, the condensate in the retort appears to be going more acidic. The retorts run at about 265-280F, and the batch time varies from 1-1.5 hours. The runs are about 16 hours four days a week. The residue left on the product is becoming very problematic.
Would symptoms of material deterioration include the higher pH and chalking? Also, is there a cost effective material that would prevent this, or at least extend the length of time before the deterioration occurs?
Thanks
I am relatively new to the industrial arena, being a civil/environmental most of my career. Therefore some of the questions I have about plastics and polymers may be very elementary, I apologize in advance. I am currently working for a food processing company that uses batch retorts in its process. These retorts process product on injection molded plastic trays (the product is pre-packaged prior to processing). We have noticed a residue on the packaging after processing, and I am attributing it to the plastic in the trays breaking down. The exterior of the trays appears softer than when placed in service and a chalky material is coating the trays.
This is occurring at about six months after being placed in service. I do not know the exact material, but am working on an answer. Coincidental to the deterioration, the condensate in the retort appears to be going more acidic. The retorts run at about 265-280F, and the batch time varies from 1-1.5 hours. The runs are about 16 hours four days a week. The residue left on the product is becoming very problematic.
Would symptoms of material deterioration include the higher pH and chalking? Also, is there a cost effective material that would prevent this, or at least extend the length of time before the deterioration occurs?
Thanks





RE: Plastic Deterioration
RE: Plastic Deterioration
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Plastic Deterioration
An interesting experiment would be to take a few virgin trays and subject them to FT-IR analysis. hAve the lab save the data trace from each tray. Then run the trays through the proccess, retrieve them, and repeat the FT-IR process. The lab can subtract the second trace from the first. The difference would be whatever leached out.
RE: Plastic Deterioration
RE: Plastic Deterioration
Thanks for the replies. I am still working on getting information on the material. Yes, the condensate is water vapor. I should have mentioned that this is a steam retort, so the trays are subject to steam heating in a pressure vessel. I am following through with some recommended testing, but am starting to conclude this is a case of the wrong material for this application. Is there a plastic material that would hold up in this environment, or would I be better to go to stainless trays?
Thanks
RE: Plastic Deterioration
RE: Plastic Deterioration
I finally got the material composition from the MFG. 69% polypropylene resin, 30% talc filler, and 1% elastomeric additive. Does this seem appropriate for a steam retort? We are checking on the stainless option, but have considerable investment in the plastic trays.
RE: Plastic Deterioration
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Plastic Deterioration
Yes, I do believe the residue is talc. We are confirming that. The trays are needed to hold the product while in the retort, but also for transport, so any tray would be start to finish. Would you expect breakdown of the PP with steam? Others here are looking for boiler chemicals as the culprit, but I am becoming convinced that the process itself is degrading the trays (steam retort) without any help from steam additives.
Thanks again, this has been very helpful.
RE: Plastic Deterioration
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Plastic Deterioration
I do not believe the combination of temperature and moisture is the problem here. As far as I know, PP does not hydrolyze. There needs to be a double bonded pendant oxygen molecule, like with nylon, polyester or polycarbonate, to be an initiation site for the hydrolysis to take place. PP is hydrophobic: it repels water. Water and PP simply do not react.
PP is prone to oxidation at elevated temperatures. The higher the temp, the faster it oxidizes. If follows an Arrhenius relationship. There is a rule of thumb that is loosely based on Arrhenius that says for every 10C increase in temp, the rate of degredation would double. The test here would be a melt flow test. As the degredation increases, the molecular weight and viscosity go down, and the melt flow value goes up. Any good polymer testing lab can do this. Send him virgin and used trays and compare the numbers. Oxidation could cause the softening you reported.
16 hrs per day times 4 days a week times 24 weeks is 1536 hrs at 265-280F (130C+). That strikes me as pretty severe for a commodity grade thermoplastic. Assuming the 10 degree rule, thats 1536 hrs * 2^11 or 3,145,728 hours at 20C, or 3641 years. You are essentially conducting an accelerated degredation by oxidation test here. The 10 degree rule is very approximate, but if its off by 100 times, you are still putting 36 years of degredation into 6 mos. Thats pretty nasty!
Take new and old trays han hav TGA run. That test will burn off the organics and leave the talc as an ash residue. If you are loosing a lot of talc, you may see it.
RE: Plastic Deterioration
RE: Plastic Deterioration
Examples:
http://tera.chem.ut.ee/IR_spectra/index.php?option...
http://www.gly.uga.edu/Schroeder/11Schroeder.pdf
RE: Plastic Deterioration
Chris
Chris DeArmitt - PhD FRSC
Plastics & Materials Consulting
www.phantomplastics.com
Plastic Training Seminars
www.plastictraining.com