DOS and DOA Cold Resistant Plasticizers for Cold Chain PVC Curtains (-40°C Rating)

DOS and DOA Cold-Resistant Plasticizers for Cold Chain PVC Curtains (-40°C Rating)

Can DOS or DOA be used as the only plasticizer in a -40°C PVC curtain? In most cases no. DOS (CAS 122-62-3) and DOA (CAS 123-79-5) are aliphatic dibasic ester plasticizers that are used together with a primary plasticizer, typically at 10-30 phr of the total plasticizer package. Their job is to keep the compound flexible when the primary plasticizer is approaching its own low-temperature limit. The exact ratio has to be confirmed with a low-temperature brittleness test on your own formulation.

What low temperature actually does to a plasticized PVC strip

A freezer-grade PVC strip curtain is a demanding application because the material is expected to stay soft, transparent and repeatedly flexing while the ambient temperature sits between -18°C and -40°C. As temperature falls, a plasticized PVC compound passes through a sequence that ends in either stiffening or brittle fracture. Two mechanisms drive that sequence.

The first is the intrinsic mobility of the plasticizer itself. A plasticizer with a branched or aromatic structure starts to lose mobility at a relatively high temperature, so the free volume available to the PVC chains contracts earlier and the strip becomes stiff. The second is crystallization and migration-related loss: under sustained cold and flexing, plasticizer that is poorly anchored in the compound can migrate to the surface or become locally ordered, which shows up as a surface bloom, loss of clarity or a crack that starts at the flex line.

Cold chain curtains therefore need a plasticizer package with a low glass transition contribution combined with good permanence in the compound. That combination is the reason DOS and DOA are specified rather than a single general purpose plasticizer.

Why aliphatic dibasic esters behave differently

DOS and DOA are linear aliphatic diesters. Their straight-chain structure keeps the molecule free of the bulky aromatic ring, which lowers the temperature at which molecular motion becomes restricted. The practical result is measurable in two routine tests: low-temperature brittleness (the temperature at which the specimen fractures under impact) and cold bend or cold flexing, which reflects how the strip behaves when it is pushed through day after day.

DOA is often the first choice when the required temperature is moderate and the formulation also has to stay economic, while DOS is the reference when the specification calls for the coldest flexing behaviour. The two are frequently blended so that the package combines a lower brittleness temperature with a sensible balance of cost and permanence.

Designing a curtain compound around a target cold rating

Cold chain curtains are usually specified with a required service temperature rather than a formulation, so the design process starts from that number and works backwards.

Where a curtain is used in a food handling area, the formulation also has to be reviewed against the food contact rules that apply in the destination market, and against the migration or extraction requirements that come with them. DOS and DOA are addressed by different regulatory frameworks depending on the country, so the compliance position should be confirmed for the specific market before the design is frozen.

Common defects and what they usually indicate

Dosage and process notes

DOS and DOA are liquid and add to a normal mixing sequence without special equipment. The usual approach is to treat them as part of the plasticizer package and adjust the primary plasticizer downwards as the cold-resistant fraction is introduced, so that total loading stays where the hardness target requires it. Because both esters are less efficient plasticizers by weight than a general purpose primary, replacing primary plasticizer one-for-one will usually harden the compound; the offset is normally more than one to one and is best found by a short trial series.

Low-temperature performance should never be judged from a single test. The brittleness test gives the fracture threshold, cold bend or flexing shows fatigue behaviour under repeated movement, and both should be run on strip produced under the actual process conditions. Curtains that pass a laboratory brittleness test can still fail in service if the flex point is designed with a sharp radius or if the strip is exposed to a mixture of cold and grease.

Frequently asked questions

Are DOS and DOA the same as DOA-based general purpose plasticizers? No. They are aliphatic dibasic esters used for low-temperature performance, not general purpose primary plasticizers, and they are normally used as part of a package with a primary plasticizer.

Which of the two is better for -40°C? DOS is the more common starting point when the target is the coldest rating. DOA is often used where the requirement is moderate or where cost balance is a priority. The final answer depends on the trial result for your specific compound.

Can the curtain be made with 100% DOS or DOA? Technically it can be formulated, but the balance of cost, processing behaviour and permanence usually makes a blend with a primary plasticizer the better solution.

Do I need to change the stabilizer? The stabilizer system usually stays in place, but its level may need review because the processing temperature profile and the transparency requirement interact with the plasticizer change.

How do I confirm the right ratio? Run a low-temperature brittleness series at three or four ratios, then verify the best candidate with a cold bend test on the finished strip.

Request a sample and a recommendation

Our team can recommend a starting ratio for your target temperature and send a 1kg complimentary testing sample dispatched worldwide via DHL or FedEx for your own trial. Grade reference: DOS / DOA (CAS 122-62-3 / 123-79-5). Trial order MOQ is 1 MT, and bulk shipments are loaded as 23 MT flexitank containers from Ningbo or Shanghai.