Desiccant Masterbatch: 3 Types, Mechanisms, Dosage and Selection

Desiccant masterbatch is a concentrate of a water-binding mineral in a carrier resin that captures moisture inside a damp or recycled polymer while it melts, and suppliers dose it at 1 to 5 % of the compound. Water that is still in the resin when it reaches the die turns to steam at extrusion temperature, so which mineral binds it, and how much of it does a wet recyclate need?

Moisture control is a processing job rather than a stabilisation job, which is why the family sits with the processing modifiers. Desiccants are one of the 7 processing modifiers among the 43 families of plastic additives, next to lubricants, polymer processing aids, mold release agents, slip agents, antiblock additives and dispersing agents, and they reach the processor in one form only, as a concentrate.

This page defines desiccant masterbatch and separates it from resin drying, explains chemisorption and physisorption and why a desiccant binds less water inside a polymer than on its own, describes the 3 actives in order, names the polymers and processes that use the concentrate, gives the dosage rules and the arithmetic that matches a dose to a measured moisture content, lists what to measure, sets out the food-contact status of calcium oxide and names the producers. It covers desiccants used inside the polymer, not sachet desiccants, not household moisture absorbers and not the oxazolidine moisture scavengers used in polyurethane coatings and sealants.

The 3 desiccants used in plastics differ in how they bind water, in whether they can release it again, and in what our sources establish about their behaviour inside a polymer.

Mechanism and reversibility follow Sängerlaub and colleagues at the Fraunhofer Institute for Process Engineering and Packaging (Materials, 2019). Suppliers of commercial desiccant masterbatch do not disclose which active they use or at what loading, so this page states no concentrate composition.

What Is Desiccant Masterbatch?#

Desiccant masterbatch is a concentrate of a water-binding mineral, usually calcium oxide, in a polyolefin carrier resin, added at the machine so that the mineral captures moisture inside the melt instead of letting it turn to steam. A masterbatch is a concentrate of a pigment or an additive in a carrier resin that the processor lets down into the base polymer, and the desiccant version differs from a colour or a filler concentrate only in what the carrier is carrying.

Three further names describe the same product in supplier literature: moisture scavenger masterbatch, moisture absorbent masterbatch and anti-moisture masterbatch. Every desiccant grade is sold as masterbatch, never as a loose powder for the converter to meter by hand, and the two brand lines documented in our sources are Cesa Dry from Avient and Polydry from Plastiblends.

Calcium oxide is not a single-purpose mineral, which is the second reason this family is easy to mistake for something else. The same oxide works as an acid scavenger, because it is a base, and as the moisture and carbon dioxide absorber in active packaging, so one CAS number appears in 3 places on this site with 3 different jobs. Which faults does the trapped moisture cause if the mineral does not capture it?

Which moisture defects does desiccant masterbatch prevent?#

Moisture left in the resin turns to steam in the extruder and shows up as visible faults in the part, and the defect count on the film or the moulding is the acceptance test the supplier literature uses. Our source library holds no verified catalogue of those faults, so this page names none: the defect lists published by masterbatch producers carry no primary source behind them. One supplier claim on this point is documented. Avient states that its Cesa Dry grades also help protect metal tools from oxidation, which is a second benefit rather than a defect, and other extrusion faults are covered under troubleshooting additive-related defects.

Desiccant masterbatch and resin drying: what each one does#

Desiccant masterbatch and a resin dryer solve two different problems: the masterbatch binds residual water in polyolefins, which do not react with it, while a dryer removes water from polyesters, polyamides and polycarbonate before that water can cleave the chain. Water damages a polyolefin physically and a condensation polymer chemically, and no additive reverses the chemical route once it has run.

Hydrolytic degradation cleaves ester, amide and carbonate bonds, and the polymers it affects are PET, polycarbonate above 70 °C in humid conditions, PA and PLA. In PET, excess moisture reduces molecular weight by chain scission, so the loss sits in the resin itself rather than in the surface of the part. The countermeasures run in a fixed order: drying first, then the carbodiimides and other hydrolysis stabilizers that protect the chain, and chain extenders that rebuild molecular weight after it has already fallen.

Polyolefins carry no hydrolysable bond, which is why the same water is a processing nuisance in polyethylene and a material loss in PET. That asymmetry decides every selection question on this page: desiccant masterbatch is the primary tool in PE and PP, and it is not a substitute for drying in PET, PA, PC or PLA.

Drying targets in ppm and dryer dew points are not published in our sources and are therefore not stated here.

How Does Desiccant Masterbatch Work?#

Desiccant masterbatch works in 3 steps: the carrier melts and disperses the mineral through the compound, the mineral meets water at its particle surface, and it binds that water either chemically, as calcium oxide does, or physically in a pore system, as silica gel and zeolite do. The third step separates the 3 actives, and it decides whether the captured water can come back.

Water reaches the particle by diffusion through the molten polymer, which is why a desiccant inside a compound behaves differently from the same mineral in a sachet. Dispersion is therefore the precondition for the other two steps: a mineral that stays agglomerated presents a fraction of its surface to the melt, so the carrier resin and the let-down ratio matter as much as the choice of active.

Chemisorption and physisorption: two ways to bind water#

Calcium oxide binds water chemically and permanently: it reacts to calcium hydroxide, so the water cannot be released again at extrusion temperature, while silica gel and zeolite hold water physically in their pores and can give it back. The reaction is a single step.

CaO + H2O → Ca(OH)2

Stefan Sängerlaub and colleagues at the Fraunhofer Institute for Process Engineering and Packaging drew this distinction explicitly in their 2019 comparison of desiccant films in Materials, and it is the peer-reviewed anchor for a difference that supplier literature leaves out. Physisorption holds the water molecule in a pore by physical forces alone, without changing the chemical identity of either partner, which is why a silica gel sachet can be regenerated in an oven and a spent calcium oxide particle cannot.

Reversibility is not an academic distinction in melt processing. An irreversible binder cannot re-release its water further down the screw, or during storage of the finished pellet, and that is the practical argument for calcium oxide inside a polymer rather than around it.

Why a desiccant binds less water inside a polymer than on its own#

A desiccant loses much of its capacity once it is embedded in a polymer: silica gel dispersed in LDPE keeps up to two-thirds less water-vapour capacity than the same silica gel on its own, on the measurements of Sängerlaub and colleagues (Materials, 2019). The polymer is the reason. Water has to diffuse through the matrix before it reaches a particle the melt has coated, so the particle works against a transport limit that does not exist in an open sachet.

No capacity figure for a commercial desiccant masterbatch is established in our sources, and none can be derived from the LDPE result, because the loading, the particle size and the carrier resin of a commercial grade are all undisclosed.

3 Types of Desiccant Used in Plastics#

The 3 desiccants used inside plastics are calcium oxide, which binds water chemically, and silica gel and zeolite, which hold it physically in a pore system. Calcium oxide leads the list because it is the only one of the 3 our source library ties to desiccant masterbatch by name, and silica gel and zeolite are recorded as its two alternatives.

Commercial desiccant masterbatch is sold without a declared composition, so a technical data sheet, or a direct question to the supplier, is the only way to learn which of the 3 a given grade contains. Identity, CAS numbers, dosage and regulatory status for every additive on this site are in the plastic additives database.

1. Calcium oxide (CaO)#

Calcium oxide (CAS 1305-78-8, EC 215-138-9), also sold as quicklime, is the desiccant that commercial masterbatch chemistry is built on: it reacts with water to calcium hydroxide and cannot release it again. The mineral is an alkaline-earth metal oxide with the formula CaO and a molar mass of 56.08 g/mol, a white solid that melts at 2,613 °C, with 2,570 °C also reported, and a density of 3.34 g/cm³. Burnt lime, unslaked lime, calcia and oxocalcium name the same substance.

In plastics the oxide is documented in recycled PE and PP, in film, raffia tape and woven sacks, and in calcium-carbonate-filled polyethylene. Its level is always given as a masterbatch level rather than as a mineral level, because the CaO content of commercial concentrates is not disclosed by the suppliers who sell them.

Calcium oxide carries two further functions in the same polymers, which is why one CAS number appears under 3 headings on this site. As a basic oxide it is one of the acid scavengers for polymers, alongside zinc oxide and magnesium oxide, where its basicity rather than its affinity for water does the work. In active packaging it works as a moisture and carbon dioxide absorber inside the pack rather than inside the wall of the part. Its food-contact position is settled on both sides of the Atlantic and is set out in full further down this page.

2. Silica gel#

Silica gel holds water physically in its pores, which makes the binding reversible: it is the standard sachet desiccant, and our source library records it as one of the two alternatives to calcium oxide inside a polymer. Reversibility is the first trade-off. A silica gel particle can be regenerated, and it can also give its water back when the compound is reheated, which is the opposite of what a melt-processing desiccant is asked to do.

Capacity is the second trade-off. Dispersed in LDPE, silica gel keeps up to two-thirds less water-vapour capacity than pure silica gel, on the same 2019 Fraunhofer measurements, and that penalty applies to every physisorbing mineral that has to work through a polymer matrix. No substance page exists for silica gel on this site, because the map records it as an alternative to calcium oxide rather than as a plastics additive in its own right.

3. Zeolite (molecular sieve)#

Zeolite, sold in this use as a molecular sieve, adsorbs water into a crystalline pore structure and is the third desiccant found in polymer systems. Like silica gel it works by physisorption, so the binding is reversible, and our source library records it as an alternative to calcium oxide rather than as the named active of a commercial masterbatch grade. No in-polymer water capacity for zeolite is established in our sources.

The same mineral appears in a second role in recyclate. Zeolite grades are used among odor absorbers and odor control additives for recycled polyolefins, where the pore structure holds volatile odour compounds instead of water, and a dosage documented for odour control says nothing about moisture capacity.

Which Polymers and Processes Use Desiccant Masterbatch?#

Desiccant masterbatch is used almost entirely in recycled and filled polyolefins: our source library documents calcium oxide desiccant masterbatch in recycled PE and PP film, in raffia tape and woven sacks, and in calcium-carbonate-filled polyethylene. Recyclate is the case that defines the family, and the full additive package for that material, from restabilization to odour control and compatibilization, is on additives for recycled plastics.

Reclaimed material is washed, ground and stored as a solid before it is reprocessed, and supplier literature describes wash water, ambient humidity and label residue as the routes. None of those routes is quantified in our sources, so the table below names the polymer and the process rather than a moisture figure.

Moisture routes into recyclate and filled compounds are described in supplier literature. Our source library documents the use of calcium oxide desiccant masterbatch in recycled PE and PP film, raffia and sacks and in calcium-carbonate-filled polyethylene.

Filled compounds are the second case, and they matter because the mineral arrives with its own handling history. Calcium carbonate brought in by filler masterbatch raises the mineral content of a film compound that is often already recycled, which is why the desiccant and the filler concentrate are frequently specified in the same recipe.

Virgin polyolefins sit at the other end of that matrix, because a dry virgin resin carries little water and needs no desiccant at all.

Blown and cast film is the process where the whole question converges, since a film line shows a steam fault immediately while a thick-walled moulding hides it. The rest of the film package, from slip and antiblock to antifog, is on additives for packaging film.

How to select and trial a desiccant masterbatch in 6 steps#

Select a desiccant masterbatch in 6 steps: confirm the polymer, measure the moisture, ask which active the grade uses, set the dose from the moisture content, check carrier compatibility, then trial on the machine. The order matters, because step 1 removes most of the wrong applications before any supplier is contacted.

1. Confirm that the polymer is a polyolefin and not a hydrolysis-sensitive polyester, polyamide or polycarbonate.
2. Measure the moisture content of the incoming resin or recyclate, because it is the input to the only dosing rule published for this family.
3. Ask the supplier which active the grade contains, on which carrier resin, and at what loading.
4. Set the dose from the measured moisture content, starting from the supplier dosing rule and staying inside the published 1 to 5 % band.
5. Check carrier compatibility and the effect on melt flow rate and on the rest of the additive package.
6. Trial on the machine and judge the result by the defect count on the part, not by the data sheet.

The general method behind these steps is on how to select plastic additives, and a formulator should run steps 1 and 2 before asking a supplier for a recommendation. Step 3 is the one most converters skip: a grade whose active is not named cannot be compared with any other grade.

How Much Desiccant Masterbatch Is Needed? Dosage and Let-Down Ratio#

Suppliers dose desiccant masterbatch at 1 to 5 % of the compound, and Plastiblends gives a rule of 1 % of masterbatch for every 0.15 % of moisture in the polymer. Both numbers are supplier values: Mascom publishes the 1 to 5 % band and Plastiblends the dosing rule for its Polydry line, and no independent or standardised dosing table for this family exists in our sources.

Units carry the whole answer here, so they are stated with every number. The dose is a weight percentage of the finished compound, not parts per hundred resin, and the two are not interchangeable: wt% is the phr of the additive divided by the total phr, multiplied by 100, and the unit rules for every family are on conversion to wt%, ppm and let-down ratio.

Let-down ratio expresses the same quantity as a ratio of base resin to concentrate, which is how a gravimetric dosing unit is set. A dose of 2 % of the compound is a let-down ratio of about 49:1 and a dose of 5 % is about 19:1, the convention that also applies to a colour or a filler concentrate.

One number is missing from every published source: the water a concentrate can actually bind per kilogram. Typical levels for every additive family are collected on additive dosage levels in plastics, and here the level stays a supplier band rather than a calculated requirement.

How is the dose matched to the moisture content?#

The dose follows the measured moisture: at the Plastiblends rule of 1 % per 0.15 %, a recyclate carrying 0.30 % water takes about 2 % of desiccant masterbatch, and one carrying 0.45 % takes about 3 %. The 3 lines below are arithmetic from the supplier rule, not a supplier recommendation.

• 0.15 wt% moisture in the resin gives about 1 % masterbatch, a let-down ratio of about 99:1.
• 0.30 wt% moisture gives about 2 % masterbatch, about 49:1.
• 0.45 wt% moisture gives about 3 % masterbatch, about 32:1.

The arithmetic stops at the top of the published band. A moisture content that would call for more than 5 % of masterbatch is a signal to dry the material or to change the incoming stream rather than to raise the dose, because no supplier in our sources publish a level above 5 %, and at that level the carrier resin becomes a formulation change in its own right. Check any concentrate dose against the mass balance with the let-down ratio calculator.

How is desiccant masterbatch stored and handled?#

Desiccant masterbatch is itself hygroscopic, so Mascom advises using an opened bag within 16 to 24 hours. The reason follows from the mechanism: a chemisorbing pellet that binds ambient humidity on the shelf reaches the machine with part of its capacity already spent, and that part cannot be recovered by drying the concentrate.

Three handling rules follow from the 16 to 24 hour window, and a converter should hold all 3.

• Keep bags sealed until the run starts.
• Dose from a closed hopper rather than an open one.
• Return unused pellets to a sealed container immediately after the run.

How Is Moisture and Desiccant Performance Checked?#

Desiccant performance is judged by 3 checks: the count of visible defects in the part, the melt flow rate of the compound (ISO 1133-1 and ASTM D1238, current edition D1238-26), and thermogravimetric mass loss (ISO 11358). Melt flow rate is measured at 190 °C and 2.16 kg for polyethylene and at 230 °C and 2.16 kg for polypropylene, and it is an empirical value rather than a fundamental property, so it is read as a before-and-after comparison on the same material rather than as an absolute.

The fourth measurement is the one the whole dosing rule depends on. Moisture content is measured on the incoming resin or recyclate before the dose is set, and no moisture-determination standard is established in our source library, so this page names none and the method has to be agreed with the laboratory that runs it. An unknown concentrate itself can be identified by additive analysis and deformulation.

How Is Calcium Oxide Regulated in Food-Contact Plastics?#

Calcium oxide is authorised for food-contact plastics on both sides of the Atlantic: it is FCM No 395 (Ref 41520) on the Union list of Regulation (EU) No 10/2011, listed as an additive with no specific migration limit, and it is generally recognised as safe under 21 CFR 184.1210 in the United States. Under Regulation (EC) No 1907/2006 it is registered with 100 active dossiers under EC 215-138-9, and it is not on the REACH Candidate List.

Union list values were verified against the consolidated text of Regulation (EU) No 10/2011 of 16 March 2025. Calcium oxide: CAS 1305-78-8, EC 215-138-9.

No specific migration limit does not mean no limit at all. The generic SML of 60 mg/kg and the overall migration limit of 10 mg/dm² still apply to the finished article, and how the Union list works, including what an additive entry does and does not authorise, is explained on EU 10/2011.

The hazard profile belongs to the raw powder rather than to the finished plastic. Notifications aggregated by PubChem include H315, H318 and H335, with H314 in some notifications, and these are aggregated notifier entries rather than a harmonised classification under Regulation (EC) No 1272/2008.

In the United States the status is a GRAS listing rather than a premarket approval. Calcium oxide is generally recognised as safe under 21 CFR 184.1210, and every 21 CFR section that carries a plastic additive is mapped on FDA food contact rules.

Active packaging is the one place where the position is genuinely open. The EU list of authorised active and intelligent substances under Regulation (EC) No 450/2009 had not been adopted as of 22 September 2026, with only a register of applications in place, so the same authorisation gap affects oxygen scavengers for plastic packaging and every other active system that works inside the pack rather than in the wall.

Who Makes Desiccant Masterbatch? Suppliers, Brands and Grades#

Desiccant masterbatch is made by additive masterbatch producers rather than by mineral companies, and the two brand lines documented in our sources are Cesa Dry from Avient and Polydry from Plastiblends. Concentrate makers across every additive family are compared on masterbatch manufacturers, and a desiccant grade normally sits in the same catalogue as the antistatic, antifog and processing concentrates rather than in a product line of its own.

Only companies documented in our source library are listed. Send an enquiry through the supplier finder for a wider quote list.

No market size, growth rate or price for desiccant masterbatch is established in our sources, and no reliable published figure for the category exists, so this page names producers without ranking them. Concentrate volumes for the wider category are tracked on the masterbatch market page.

Company profiles, plant locations and brand lines for every family are in the directory of plastic additive manufacturers and suppliers. Ampacet is documented as a global masterbatch producer and nothing more specific, which is why the table above says exactly that.

An enquiry for this product needs 5 items, because not one of them appears on a public data sheet: the active mineral, the carrier resin, the loading of the active, the moisture capacity and the food-contact declaration. A supplier who answers all 5 can be compared with a second supplier.

The visible supply base is concentrated in India, Vietnam and China, where most product pages and marketplace listings for it originate, and Indian producers across every family are listed with plastic additive suppliers in India. Only companies documented in our source library are named here, so the regional makers that rank on this query are not reproduced without a verifiable source.

What Desiccant Masterbatch Cannot Do: Limits, Alternatives and Lookalikes#

Desiccant masterbatch fixes steam-driven processing faults in polyolefins, and it does not fix hydrolysis, does not replace a dryer for PET or nylon, and does not carry anything close to the water capacity of a sachet desiccant. Hydrolysis is one route in polymer degradation, alongside the thermal, thermo-oxidative, photo-oxidative and thermo-mechanical routes, and it is the one route a desiccant cannot address, because the damage falls on the chain rather than on the part surface. Capacity is the second limit, and it is quantified: silica gel keeps up to two-thirds less water-vapour capacity dispersed in LDPE than loose in a sachet, which makes a concentrate a processing aid rather than a storage desiccant.

Which additives are confused with desiccant masterbatch?#

4 product classes are regularly mistaken for desiccant masterbatch: oxazolidine moisture scavengers for polyurethane coatings, carbodiimide hydrolysis stabilizers, acid scavengers and foaming agent masterbatch. Each of the 4 shares a word with this family and does something different.

• Oxazolidine moisture scavengers, sold for polyurethane coatings, sealants and adhesives, which lie outside the plastics border of this site and are not covered here.
• Carbodiimide hydrolysis stabilizers, which protect the ester bond against the water that is present instead of removing that water.
• Acid scavengers, a family that shares calcium oxide as a substance while using its basicity rather than its affinity for water.
• Foaming agent masterbatch, which creates a cell structure on purpose and is the opposite function to a desiccant.

Two consumer meanings complete the list, and neither belongs inside a polymer compound: silica gel sachets and household moisture absorbers sit next to the goods rather than in the wall of the part.

Does desiccant masterbatch affect recycling and food contact?#

Desiccant masterbatch is what makes some recyclate processable at all, because binding water lets a converter run a higher share of washed flake and filled compound without steam faults. Recycled PE and PP film, raffia and woven sacks are the documented uses, and they are the streams where moisture, odour and a partly consumed stabilizer package arrive together, which is why a desiccant is usually specified next to a restabilization package and an odour absorber.

Food contact is not a barrier on the substance side. Calcium oxide is on the Union list as FCM No 395 and is generally recognised as safe in the United States, and the limits that bind are the overall migration limit of 10 mg/dm² and the generic SML of 60 mg/kg on the finished article. No APR, EPBP or RecyClass position on desiccant masterbatch is established in our sources, so this page states none, and how each additive family affects sorting and reprocessing is set out under design for recycling.

Desiccant masterbatch FAQs#

Three questions decide most enquiries about this family, and each of the 3 answers below is limited to what our sources establish: whether the concentrate can replace a dryer, whether the Asian trade name means the same product, and whether the mineral itself is hazardous.

Does desiccant masterbatch replace a resin dryer?#

For polyolefins it can, and Avient states that its Cesa Dry grades eliminate the need to predry resin, but for PET, nylon, polycarbonate and PLA it does not: those polymers hydrolyse, and the water has to be removed before processing rather than bound during it. The statement about Cesa Dry is a supplier claim about specific grades, so it is confirmed on the machine and against the defect count rather than assumed for the whole category.

Is desiccant masterbatch the same as defoaming masterbatch?#

In parts of Asia the two names are used for the same moisture-binding concentrate, where "defoaming" describes the absence of steam bubbles rather than an anti-foaming agent. Our source library does not carry that equivalence as a verified fact, so it is reported here as trade usage rather than as chemistry. What the name certainly does not describe is a foaming agent masterbatch, which creates a cell structure on purpose.

Is calcium oxide in plastics hazardous?#

Calcium oxide is authorised for food-contact plastics in the EU and the United States, and the hazard belongs to the raw powder rather than to the finished article. Notifications aggregated by PubChem include skin irritation (H315), serious eye damage (H318) and respiratory irritation (H335), with H314 in some notifications, and these are aggregated notifier entries rather than a harmonised classification. They describe how a compounder handles the mineral, not how a moulded part behaves in service.