Most storage guides emphasize keeping plasticizers free from contamination. In my experience supporting PVC compounders, I trace more batch rejections to temperature excursions than to contamination. A drum stored in direct sunlight for a week causes more processing problems than trace moisture ingress ever will.
Every 10C temperature rise doubles the degradation rate of plasticizers. This Arrhenius relationship means a plasticizer stored at 35C degrades twice as fast as one stored at 25C. Temperature control deserves more attention than contamination prevention in your storage facility planning.
Temperature Control Requirements
Store plasticizers between 15-25C for optimal stability. Most manufacturers specify an upper limit of 35C, but I recommend staying below 30C whenever possible. Above this threshold, oxidation accelerates noticeably.
The 10C rule works in both directions. Research published in Nature Communications confirms that with a typical activation energy of 50 kJ/mol for plastic degradation, every 10-degree temperature rise doubles the degradation rate. This applies to oxidation, hydrolysis, and additive migration alike.
Temperature stability matters as much as absolute temperature. One collector community member put it well: “As important as temperature is the stability of temperature. Items that have been in a loft, changing from minus in winter to 40+ in the summer, but with an average of 14, do not hold up well.” Fluctuations cause more damage than consistent cool storage.
Cold storage presents a trade-off. Museum conservators found that PVC dolls stored at 11-12C for ten years developed lubricant bloom on surfaces. Despite this cosmetic issue, they returned objects to cool storage because “plasticiser loss could cause long term stability issues.” For industrial storage, the lesson is clear: avoid temperature cycling rather than pursuing the coldest possible conditions.
What does this mean practically? Install temperature monitoring in your storage area. A simple datalogger that records highs and lows reveals excursions you would otherwise miss. If you see this defect pattern – viscosity drift between batches – check your storage temperature history first.
Handling and Transfer Procedures
Temperature affects viscosity dramatically, which directly impacts pumping and transfer operations. DOTP viscosity increases from 63 mPa.s at 25C to 410 mPa.s at 0C – a 6.5x increase. Winter operations require longer transfer times and potentially heated lines.
DOP has a freezing point of 4C, making it problematic for cold-climate operations without heated storage. DOTP freezes at -48C, offering much better cold-weather handling. If your facility experiences cold winters, this difference alone may justify a plasticizer switch.
Before adding to the mixer, ensure your plasticizer has equilibrated to processing temperature. Cold plasticizer added directly to a hot mixer creates localized viscosity variations that affect dispersion. Allow drums or IBCs to sit at room temperature for 24-48 hours after receiving winter shipments.
For bulk storage, steel is the recommended container material according to Eastman’s handling guidelines. Steel provides reliable chemical compatibility for both monomeric and polymeric plasticizers. Polyethylene may be acceptable for specific products, but verify compatibility with your supplier before use.
Secondary containment should hold 110% of your largest container volume. For IBC operations, this typically means a bunded area capable of containing a full 1000-liter spill.
Storage Requirements by Plasticizer Family
Different plasticizer types have distinct storage needs. Generic guidelines miss these critical differences.
Phthalates (DOP, DINP, DIDP): Store at 15-35C maximum. DOP is particularly temperature-sensitive with its 4C freezing point. Shelf life under proper storage is approximately 18 months for DOP.
Terephthalates (DOTP): More forgiving with an effective temperature range of -50C to 120C in use, and a -48C freezing point that eliminates cold-weather solidification concerns. Shelf life extends to 10-15 years under proper conditions – significantly longer than phthalate alternatives. DOTP-specific storage guidelines cover additional temperature management details, but the core principle remains: maintain similar temperature ranges to phthalates for optimal viscosity.
Adipates (DOA, DIDA): These cold-resistant plasticizers maintain flexibility at temperatures as low as -40C in the finished product. Storage requirements are comparable to general phthalates. Shelf life is approximately 2 years.
Trimellitates (TOTM, TINTM): Required for high-temperature applications – 90C continuous use needs trimellitates, and 105C cables require trimellitates or polymeric plasticizers exclusively. Storage conditions are similar to other families, but these products command premium pricing, making proper storage protection especially important.
Cold-resistant plasticizers like DOA or DOS typically function as auxiliary plasticizers at 5-20% of the main plasticizer content. Store these separately with clear labeling to prevent formulation errors.
Quality Verification Before Use
Visual inspection catches obvious problems but misses temperature-induced degradation. A plasticizer can appear normal while having undergone oxidation that affects processing.
One failure analysis case illustrates this risk. A manufacturer submitted two plastic parts for comparison – one functioning properly, one that fractured during use. FTIR spectroscopy revealed the failed part contained significantly less dioctylphthalate than the functioning counterpart. The reduced plasticizer content compromised the material’s integrity. This loss can occur through improper storage as easily as through processing errors.
ASTM D1045 specifies the standard tests for plasticizer quality: acid number, ester content, specific gravity, color, refractive index, and water content. For incoming material verification, I recommend at minimum:
- Visual check: Color should match the supplier’s specification. Yellowing indicates oxidation.
- Viscosity: If you have a viscometer, compare against the certificate of analysis. Temperature-degraded plasticizer often shows viscosity increase.
- Acid number: Elevated acid number confirms oxidation has occurred.
For critical applications, request the manufacture date on your certificate of analysis. Calculate remaining shelf life based on storage conditions since production.
Conclusion
Temperature control forms your first line of defense for plasticizer quality. Monitor storage temperatures continuously rather than assuming conditions remain stable. Verify material condition before use, especially after seasonal temperature swings or extended storage.
Storage checklist:
- Install temperature datalogger in storage area
- Set alert thresholds at 30C high and 5C low
- Review temperature history weekly
- Equilibrate cold shipments 24-48 hours before use
- Check viscosity and color against COA for any material stored over 6 months
- Maintain FIFO inventory rotation with clear date labeling
Temperature excursions are silent failures. Contamination you can see; degradation from heat exposure reveals itself only when processing goes wrong.