IR Absorbers and Reheat Additives: 4 Functions, Mechanisms, Dosage and Selection

IR absorbers are plastic additives that absorb infrared radiation inside the polymer and convert it into heat, and the same label covers 4 jobs that share nothing but that physics. A reheat additive works at single-digit ppm in a PET preform, while a heat-shielding absorber in a polycarbonate roof panel is there to stop heat from getting in, so which one does a formulator actually need?

The 4 functions run in order of commercial weight, and each carries its own chemistry. PET preform reheat uses carbon black at 0.1 to 8.0 ppm, titanium nitride capped at 20 mg/kg, reduced tungsten oxide and iron phosphide. Heat shielding for glazing and film uses lanthanum hexaboride, caesium tungsten oxide and antimony tin oxide. Thermic greenhouse film uses IR-absorbing mineral fillers and EVA copolymer layers whose exact types suppliers do not publish. Laser transmission welding and laser marking use antimony tin oxide and related absorber particles that take up 1,064 nm. Only the reheat function has substances with their own entries in Annex I of Regulation (EU) No 10/2011.

This reference covers the three infrared bands the four functions work in, the difference between an IR absorber and an IR-transmitting plastic, how a reheat additive shortens preform heat-up and why it shifts preform colour, the four reheat chemistries with CAS numbers and FCM entries, ppm dosage against regulatory ceilings, a 6-step selection route, how performance is measured without a dedicated standard, the EU and US position, the suppliers behind the named grades, the six substances in the directory, and the recycling trade-off the same absorption creates.

The table below sets the 4 IR absorber functions side by side by the radiation they absorb, the absorber chemistries used, the level at which they work and the part they sit in.

Only the reheat function has substance-specific entries in Annex I of Regulation (EU) No 10/2011.

What Is an IR Absorber in Plastics?#

An IR absorber is a plastic additive that absorbs infrared radiation the host polymer itself barely absorbs and converts it into heat inside the part, which is useful when the goal is faster heating and a problem when the goal is a cool part or a sortable package. Why does one additive class cover both a bottle plant's energy bill and a greenhouse grower's night-time heat loss? The class is grouped by the physics rather than by the application, so any particle that takes up infrared light belongs in it, whether the heat it releases is wanted, tolerated or fought.

The term only makes sense against its mirror image, and it travels under three names: an IR absorber, an infrared absorber and, where the absorption band is specified, a NIR absorber. IR absorbers are one of the 43 families of plastic additives on this site, and they sit beside the IR-reflective inorganic pigments that answer the same heat problem the opposite way: Shepherd Color states that IR-reflective pigments in PVC siding and profiles reduce the warping and twisting caused by heat build-up. The reheat function carries the commercial names: reheat additive, fast-reheat additive, reheat agent or RHC, and it absorbs the halogen-lamp near-infrared used to heat PET preforms before stretch blow moulding. That same absorption, moved into a black package, is what stops an automatic sorter from identifying the polymer.

Near, mid and far infrared: which band each additive works in#

The 4 IR absorber functions work in three different parts of the infrared spectrum: near infrared for PET reheat and for solar control, 1,064 nm for laser welding and laser marking, and long-wave infrared at 7 to 14 micrometres for thermic greenhouse film. Two of those three bands carry a number in the primary sources, and the third does not.

Near infrared is the qualitative band. Quartz halogen lamps in a preform reheat oven emit it, sunlight carries its heat load in it, and no source we have verified states band edges in nanometres for either the reheat or the solar-control case. The 1,064 nm value is exact: it is the dominant industrial wavelength of Nd:YAG and fibre lasers, and polyethylene, polypropylene, TPU and epoxy barely absorb there, which is why an absorber is added at all. The long-wave band at 7 to 14 micrometres (7,000 to 14,000 nm) is the thermal radiation that soil and plants emit after sunset, and a thermic film is designed around it.

IR absorber vs IR-transmitting plastic: the difference#

An IR absorber and an IR-transmitting plastic are opposite specifications: the absorber is an additive that takes infrared energy up inside the polymer, while an IR-transmitting plastic is a base material chosen so that infrared passes straight through it, as it must in the cover part of a laser-welded assembly. One is something added, the other is something selected, and laser transmission welding needs both in the same joint: the upper part transmits 1,064 nm, the lower part absorbs it.

That distinction settles the two questions the term attracts most often. An infrared signal does pass through plastics that were not given an absorber, which is why remote-control windows are moulded from unfilled polymer, and an infrared camera reads the surface temperature of a plastic part rather than seeing through it, because the surface is what radiates. Neither question is about an additive, and the table below separates the four specifications that get confused with each other.

4 Functions of IR Absorbers in Plastics#

IR absorbers do 4 jobs in plastics: they speed up the reheating of PET preforms, they shield glazing and film from solar heat, they hold night-time heat inside a greenhouse film, and they let one plastic part absorb a laser beam that passes through another. The order below runs from the largest commercial use to the smallest, and every table, list and image on this page keeps it. Only the first function has named supplier grades, published ppm levels and its own entries in the EU Union list. The other three are described in trade literature and patents without a single published loading level, which is a fact about the sources rather than an editorial preference.

1. Reheat additives for PET preforms#

A reheat additive is an infrared-absorbing particle dosed into PET at single-digit ppm so that a preform reaches blowing temperature faster under the quartz halogen lamps of a stretch blow moulding machine. The additive is also sold as a fast-reheat additive, a reheat agent or RHC, and the 4 chemistries with a documented PET reheat use are listed below.

• Carbon black, CAS 1333-86-4, the original reheat absorber and still the only one with a published dose range: Brian W. Pengilly at Goodyear patented the carbon-black route in 1983 and 1984 (US 4,408,004 and US 4,476,272, priority 24 February 1982) at 0.1 to 8.0 ppm.
• Titanium nitride, CAS 25583-20-4, a golden-yellow transition-metal nitride used as nanoparticles and authorised in the EU only in PET, up to 20 mg/kg, under FCM 807.
• Reduced tungsten oxide, WOn with n = 2.72 to 2.90, CAS 39318-18-8, a non-stoichiometric metal oxide listed as FCM 1064 with a specific migration limit of 0.05 mg tungsten per kg of food.
• Iron phosphide, CAS 12751-22-3, listed as FCM 607 and restricted to PET polymers and copolymers.

A reheat additive never travels alone. Bottle-grade PET carries reheat additives alongside toners, colorants and oxygen barriers, and a heat-set grade adds crystallisation aids, so the reheat particle is one of five or six ingredients competing for the same clarity budget. A bottle-grade PET package also carries oxygen scavengers for plastic packaging where shelf life is the constraint, and, in some bottles, barrier additives for plastic packaging such as MXD6 or nanoclay where carbon dioxide loss is. Antimony, cobalt and phosphorus residues found in the same resin analyses are polymerisation catalyst and toner residues rather than absorbers, and no source we have verified describes an antimony compound as a reheat additive.

2. Heat-shielding (solar-control) IR absorbers for glazing and film#

A heat-shielding IR absorber is a metal boride or doped metal oxide dispersed in a transparent plastic so that the part still passes visible light but absorbs the near-infrared part of sunlight, which is how solar-control glazing and window film keep heat out. Three chemistries carry this function in the primary literature: lanthanum hexaboride (LaB6, CAS 12008-21-8, EC 234-531-6, MW 203.8 g/mol), caesium tungsten oxide (CWO, CAS 52350-17-1, EC 466-380-9) and antimony tin oxide (ATO, CAS 128221-48-7).

The identity of the caesium compound is unresolved and is written here as it stands. CAS 52350-17-1 is the ECHA-registered caesium tungsten oxide, and PubChem maps that number to Cs2WO4, while the near-infrared shielding grades sold to film and glazing producers are the non-stoichiometric tungsten bronze CsxWO3 with x of about 0.33, offered under CAS 189619-69-0. The mapping between the registered identity and the commercial NIR grade is unconfirmed. The larger gap is quantitative: no loading level, host-polymer dosage or performance value for any of these three absorbers in a plastic appears in a primary source we have verified, so supplier data sheets remain the only route to a starting formulation.

No loading level for these three absorbers in a plastic appears in a primary source we have verified.

3. Thermic IR additives for greenhouse film#

A thermic IR additive keeps a greenhouse warm at night by absorbing the long-wave infrared at 7 to 14 micrometres that soil and plants radiate after sunset, instead of letting it escape through the film. The heat that a tunnel gains during the day leaves as thermal radiation once the sun sets, and a film that stops that radiation holds the heat inside the tunnel overnight without any heating input.

The additives that do this are the least documented of the four functions. IR-absorbing mineral fillers and EVA copolymer layers carry the effect in LDPE, LLDPE and EVA films, and the exact mineral types and their loadings are not published by suppliers, so no chemistry and no dosage is stated here. What suppliers do publish is the intended optical asymmetry: Avient describes its Cesa IR additives as allowing short-wave infrared solar heating while preventing the cooling effect of longer-wave emissions, which is the same trade the film itself makes between day and night. The rest of the greenhouse package, from UV stabilisation to anti-drip, is on additives for greenhouse film.

4. IR absorbers for laser transmission welding and laser marking#

In laser transmission welding the beam passes through one part and is absorbed by the other, so the lower part carries an IR absorber that turns 1,064 nm laser light into the heat that melts the joint. Polyethylene, polypropylene, TPU and epoxy absorb almost nothing at 1,064 nm, the dominant industrial wavelength of Nd:YAG and fibre lasers, so neither welding nor marking happens in an unmodified polyolefin without help. Antimony tin oxide is the absorber documented for this wavelength: it takes the beam up and heats the polymer immediately around each particle.

Laser marking runs on the same absorption and ends in a different place. Heat concentrated at an absorber particle carbonises the polymer to give a dark mark or foams it to give a light one, which is a colour-generation problem rather than a joining problem, and the absorber chemistries used to mark plastics are on laser marking additives.

How Do Reheat Additives Work in PET Stretch Blow Moulding?#

A reheat additive works in 4 steps: the preform enters the reheat oven, the absorber particles take up near-infrared light that clear PET would let pass, they convert it to heat inside the wall, and the preform reaches blowing temperature sooner or at a lower lamp setting. The 4 steps below happen between the preform feed and the blow station of a two-stage line.

1. Feed the injection-moulded preform into the reheat oven, where quartz halogen lamps radiate near infrared onto its outer surface.
2. Absorb that near infrared on the dispersed particles, which is energy clear PET transmits rather than takes up.
3. Convert the absorbed radiation to heat at each particle, which warms the surrounding polymer through the wall thickness rather than only at the skin.
4. Reach blowing temperature earlier at the same lamp setting, or reach it at the same time with the lamps turned down.

In the Goodyear patent example, 2.5 ppm of carbon black raised the temperature reached after 80 seconds of infrared heating from 201 °F to 215 °F (94 °C to 102 °C) while Hunter haze stayed below 3.0 (US 4,408,004). That is a laboratory comparison at a fixed exposure time and a fixed level, not a line result, and in a plant the gain appears as a shorter oven residence time or a lower lamp power at equal output. The full bottle, fibre and film package for this polymer is on additives for PET resin.

Why faster preform heat-up cuts blow-moulding energy#

The energy saving comes from the oven, not the mould: Avient reports up to 25 % lower blow-moulding energy for its ColorMatrix SmartHeat RHC reheat additive at a dose of 0.02 to 0.075 % of the resin. The reheat oven is the largest electrical load on a two-stage stretch blow moulding line, because it takes a room-temperature preform to about 100 °C in seconds, and any radiation the polymer fails to absorb leaves as waste heat.

Three plant-level gains follow from the same absorption, and each is a different currency.

• Electrical energy per bottle, which is the figure Avient attaches its up-to-25 % claim to, and the only quantified energy claim in our sources.
• Line output, because a preform that reaches blowing temperature sooner allows a shorter oven residence time and therefore a faster cycle; the whole bottle package is on additives for plastic bottles.
• Process window, because the wall heats more evenly through its thickness, which reduces the surface overheating that causes preform pearlescence at high lamp settings.

No energy figure from any other supplier is held in our sources, so the 25 % value belongs to one named grade rather than to the additive class.

Why reheat additives make preforms grey, blue or yellow#

Every reheat additive is a particle that absorbs light, so it costs some clarity: a carbon-black-based grade shifts the preform grey, and the Association of Plastic Recyclers notes that reheat additives can turn PET flake dark or yellow, thereby reducing its value. An absorber that takes up near infrared inevitably takes up some visible light as well, and the shift grows with the loading, which is why the patent range stops at 8.0 ppm and prefers 1.5 to 3.5 ppm.

The trade is managed rather than eliminated. In the Goodyear example the optical cost stayed inside Hunter haze below 3.0 at 2.5 ppm, which shows that the constraint is kept by holding the level in single-digit ppm rather than by a corrective chemistry. Bottle-grade PET also carries toners, which are colorants for plastics used to correct exactly this kind of shift. No b*, L* or colour-shift value for any commercial reheat grade appears in our sources, so the direction of the effect is established and its magnitude is not, and the optical cost is read with haze and clarity measurement on moulded plaques or on the preform wall.

Which IR Absorbers Are Used? Chemistry, CAS Numbers and Food-Contact Entries#

Four absorber chemistries are used as reheat additives in PET: carbon black (CAS 1333-86-4), titanium nitride (CAS 25583-20-4), reduced tungsten oxide (CAS 39318-18-8) and iron phosphide (CAS 12751-22-3), and each has its own entry in Annex I of Regulation (EU) No 10/2011. The three heat-shielding absorbers sit in a different regulatory position entirely and are compared in the table under the heat-shielding function above.

Carbon black carries two completely different levels on this site, and mixing them is the single most common error on this topic: it works as a reheat additive at 0.1 to 8.0 ppm, and it is permitted at up to 2.5 % w/w in the polymer when it is used as a pigment or a UV screen under FCM 411. Those two numbers differ by a factor of about 3,000, and the 2.5 % ceiling is a food-contact maximum for the pigment use, never a reheat dose.

Titanium nitride is the clearest nanomaterial case in the family: FCM 807, Ref 93485, authorises "titanium nitride, nanoparticles" only in PET, up to 20 mg/kg, with the explicit condition that there is no migration of nanoparticles, and in PET the substance exists as agglomerates of 100 to 500 nm built from primary particles of about 20 nm. Reduced tungsten oxide carries a specific migration limit of 0.05 mg tungsten per kg of food under FCM 1064, with the unusual provision that verification of SML compliance is not required when it is used as a reheat agent in PET. FCM 607 has the narrowest wording of the four and permits iron phosphide only in PET polymers and copolymers.

Particle size in this table is the primary or agglomerate size stated in the cited source; the general definition is on particle size.

How Much IR Absorber Does PET Need? Dosage in ppm#

Reheat additives work at single-digit ppm: the carbon-black patent range is 0.1 to 8.0 ppm with 1.5 to 3.5 ppm preferred, titanium nitride is capped at 20 mg/kg in the EU, and Avient doses its ColorMatrix Joule RHB dispersion to about 5 ppm in carbonated-soft-drink resin. The titanium nitride ceiling of 20 mg/kg equals 20 ppm by mass, which puts the regulatory maximum for that substance within a factor of three of the highest patented carbon-black level.

Two distinctions decide whether a number in this section is usable. A regulatory ceiling is a maximum use level for food-contact conditions and is never a recommended dose, so the table below keeps evidenced levels and legal ceilings in separate columns. A product dose is not an active dose either: Avient's 0.02 to 0.075 % figure for ColorMatrix SmartHeat RHC is the dose of a formulated liquid, and its Joule RHB dispersion is 10 % active in monoethylene glycol, so the absorber itself arrives at a fraction of the quoted number. Reheat additives sit at the very bottom of the scale of additive dosage levels in plastics, below the ppm-level antioxidants and three orders of magnitude below a filler.

A regulatory ceiling is a maximum use level for food-contact conditions, never a recommended dosage. Convert ppm to cost per tonne with the additive dosage and cost-in-use calculator.

Where the additive is dosed: reactor, melt, liquid or masterbatch#

A reheat additive reaches the resin by one of four routes, and the choice is made by whoever owns the step: the resin producer doses at the reactor, and the preform moulder doses a liquid or a masterbatch at the machine. The four routes are listed below with the evidence attached to each.

• Reactor dosing, where the absorber enters during polymerisation: Avient states that ColorMatrix Joule RHB, a 10 % active dispersion in monoethylene glycol with particles below 10 µm, is added at late esterification or early polymerisation and has a 180-day shelf life.
• Melt dosing at the resin plant, where the absorber is introduced into the polymer melt rather than the reactor, which keeps the reheat level a property of the purchased resin grade.
• Liquid dosing at the preform machine, where SmartHeat RHC is dosed like a liquid color concentrate, at the machine: Avient states a 60 to 90 day shelf life, EU, FDA and Mercosur food-contact status, APR accreditation and EPBP approval, and restricts the grade to transparent preforms in two-stage injection stretch blow moulding.
• Masterbatch dosing, where preform moulders that do not buy pre-dosed resin use an additive masterbatch metered at the throat.

Dispersion decides whether any of the four routes works, because the reheat effect depends on particle size: at 2 or 3 ppm a handful of agglomerates carries the entire dose, and an agglomerated absorber gives haze without heat-up.

How Do You Select an IR Absorber? 6 Steps#

Select an IR absorber in 6 steps: name the function, fix the wavelength band, set the optical limit, check the food-contact route, choose the dosing point, then check what the additive does to the recycling stream. The order matters, because a decision taken at step 4 can invalidate a chemistry chosen at step 1.

1. Name the function first, because a reheat additive, a solar-control absorber and a thermic film filler share nothing but a label.
2. Fix the band: near infrared for reheat and solar control, 1,064 nm for laser work, 7 to 14 µm for thermic film.
3. Decide how much optical loss the part can carry, and set the haze or colour target before choosing a chemistry.
4. Check the food-contact route in every target market, because in PET only carbon black, titanium nitride, reduced tungsten oxide and iron phosphide hold Annex I entries.
5. Choose the dosing point, whether reactor, liquid at the machine or masterbatch, and check dispersion, because at single-digit ppm the particle size decides the effect.
6. Check the recycling consequence against the APR and EPBP guidance before a commercial launch.

A formulator should treat steps 4 and 6 as gates rather than preferences, because both are decided outside the plant. The general framework these six steps specialise is on how to select plastic additives.

How Is IR Absorber Performance Measured?#

IR absorber performance is judged on three axes at once: how much faster the part heats at an equal lamp setting, how much clarity and colour it costs, and whether the package still passes the recycling sorting thresholds. No ASTM or ISO standard written specifically for reheat efficiency appears in our sources, and no spectrophotometric near-infrared transmission method for plastics does either, so the industry measure is a plant or laboratory heat-up comparison at an equal lamp setting, against a control resin of the same grade.

The optical and sorting axes, by contrast, use ordinary published methods: colour and haze are read with standard colour and haze instrumentation, and near-infrared sortability is read against the Association of Plastic Recyclers thresholds. Every method named below is indexed under testing plastic additives.

How Are IR Absorbers Regulated?#

IR absorbers are regulated in 3 layers: chemical registration under REACH and TSCA, food-contact clearance under Regulation (EU) No 10/2011 or 21 CFR in the United States, and the recycling design rules that decide whether a package containing them is accepted. All three instruments are summarised in plastic additive regulations, and the first layer is the one where the four reheat absorbers are best documented.

Registration status differs sharply across the family, and the wording matters. Carbon black is registered under REACH in the 1,000,000 to 10,000,000 tonnes per year band and sits on the CoRAP substance-evaluation list; titanium nitride holds 4 active full dossiers and is not an SVHC (ECHA CHEM, checked 22 September 2026); reduced tungsten oxide holds 13 active dossiers and caesium tungsten oxide 2. For lanthanum hexaboride and antimony tin oxide, no active registration was found under this identity in an ECHA CHEM query, which is a statement about the search rather than a finding of non-compliance. What a registration number does and does not prove is explained on REACH and plastic additives.

EU food contact: FCM numbers, SMLs and the nanoparticle restriction#

In the EU, four IR absorbers have their own entries in Annex I of Regulation (EU) No 10/2011: carbon black as FCM 411, iron phosphide as FCM 607, titanium nitride nanoparticles as FCM 807 and reduced tungsten oxide as FCM 1064. Each entry carries its own restriction, and no two are written the same way.

Carbon black is the most heavily conditioned. FCM 411, Ref 42080, permits a maximum use level of 2.5 % w/w in the polymer and attaches purity conditions: primary particles of 10 to 300 nm aggregated to 100 to 1,200 nm, toluene extractables of at most 0.1 % measured to ISO 6209, and benzo(a)pyrene at most 0.25 mg/kg of carbon black. FCM 807 is the site's clearest example of a nanomaterial authorised with a condition on the nanoform itself: it permits titanium nitride nanoparticles only in PET, up to 20 mg/kg, with the condition that there is "no migration of nanoparticles". FCM 1064 sets a specific migration limit of 0.05 mg tungsten per kg of food and waives verification of SML compliance for the PET reheat use, and FCM 607 restricts iron phosphide to PET polymers and copolymers. Above these sit the generic limits that apply to everything: a generic SML of 60 mg/kg and an overall migration limit of 10 mg/dm². The full table of specific migration limits covers every additive on this site. The heat-shielding absorbers are caught by Annex II metal limits instead of their own entries, at 0.05 mg/kg for the sum of europium, gadolinium, lanthanum and terbium and 0.04 mg/kg for antimony. The Union list and its conditions are explained on EU 10/2011, and the simulants and contact conditions used to demonstrate compliance are on migration testing.

United States and other markets#

In the United States only carbon black has a named food-contact entry among the reheat absorbers: 21 CFR 178.3297 clears high-purity furnace black at up to 2.5 % by weight of the polymer, with total polycyclic aromatic hydrocarbons at most 0.5 ppm and benzo[a]pyrene at most 5.0 ppb. The same section also lists channel-process carbon black, made by impingement from stripped natural gas, without a numeric limit. No FDA entry was found for titanium nitride, reduced tungsten oxide or iron phosphide, which is a gap in the record rather than a prohibition. The conditions of use a PET food-contact article is matched against run from A to H in 21 CFR 176.170(c) Table 2, from high-temperature heat-sterilised to frozen or refrigerated and reheated in the container, and the 21 CFR sections are mapped on FDA food contact rules.

One California listing attaches to carbon black and is routinely misread. Carbon black is listed under California Proposition 65 as "carbon black (airborne, unbound particles of respirable size)" for cancer since 21 February 2003, and IARC classifies it in Group 2B, so the listing addresses respirable airborne particles rather than carbon black bound in a plastic. Avient states that its SmartHeat RHC grade holds EU, FDA and Mercosur food-contact status; Mercosur, Japan and China are compared on food contact rules worldwide.

Who Makes IR Absorbers and Reheat Additives?#

Avient is the only supplier with named reheat additive grades in our source library: ColorMatrix SmartHeat RHC, a liquid dosed at the preform machine, and ColorMatrix Joule RHB, a dispersion dosed into the resin reactor. The company was formed as PolyOne on 31 August 2000 from Geon and M.A. Hanna, acquired the Clariant masterbatch business in 2020, and runs the Cesa, OnColor, ColorMatrix, Smartbatch and Hydrocerol brand lines, of which Cesa also carries the Cesa IR additives used in thermic agricultural film.

Carbon black reaches the same application through a different supply chain. Its three documented producers, Cabot, Orion Engineered Carbons and Birla Carbon, sell it as a pigment and UV-screening grade rather than as a reheat product, so its reheat use is a dosage question inside the resin plant. Ampacet appears in this family for the inverse problem: REC-NIR-BLACK is a carbon-black-free black masterbatch, COTREP-certified for PP and HDPE rigid packaging. No independent market size for this family is published in our sources, and other suppliers are active on this market whose products we have not verified. Company profiles are in the directory of plastic additive manufacturers and suppliers.

No independent market size for IR absorbers or reheat additives is published in our sources, and this family has no supplier directory page yet.

Complete List of IR Absorber Substances (6 Pages)#

The 6 IR absorber substances documented on this site are listed below with their CAS number, function, typical level and EU food-contact entry, in the order of the 4 functions. Iron phosphide is listed as a seventh row because it holds an EU entry without yet having a page of its own.

All 435 substance pages sit in the plastic additives database, where each absorber is cross-linked to its polymer, test and regulation pages.

Do IR Absorbers Harm Plastic Recycling?#

IR absorbers sit on both sides of the recycling question: the Association of Plastic Recyclers rates reheat additives as Requires Testing because they can turn PET flake dark or yellow, while Avient states that its SmartHeat RHC grade is APR accredited and EPBP approved. Requires Testing is a conditional category rather than a rejection, and it puts the burden on the brand owner to demonstrate that a specific formulation survives the recycling stream without devaluing the flake.

Colour is the mechanism behind that caution, and the EPBP guideline treats additives that lower L* as limited in compatibility. The stakes rise with the recycled-content targets: the PPWR, Regulation (EU) 2025/40, requires 30 % recycled content in contact-sensitive PET and in single-use plastic beverage bottles from 2030 and 50 % in contact-sensitive PET from 2040, and applies from 12 August 2026, so any additive that lowers the value of PET flake now competes against a legal demand for that flake. The wider design rules are on how additives affect plastic recyclability.

Why carbon black makes black packaging invisible to NIR sorters#

The property that makes carbon black a reheat additive is the property that makes black packaging unrecyclable: it absorbs near infrared, so the sorter's near-infrared beam gets nothing back and the package is routed to residue. Automatic sorters identify polymers by their near-infrared reflectance spectrum, which is a fingerprint of the polymer's own absorption bands, and a standard carbon-black colourant absorbs across that region so completely that no fingerprint returns.

One mechanism, two consequences: at 2 ppm in a preform the absorption is an energy saving worth up to a quarter of the oven load, and at pigment level in a black tray it is the reason the tray never reaches a recycling stream. The Association of Plastic Recyclers sets the threshold numerically in SORT-S-01, where a black or dark colour fails at L* below 40 or at a near-infrared reflectance of 10 % or less. The answer is a carbon-black-free black: NIR-sortable black colorants, of which Ampacet REC-NIR-BLACK is COTREP-certified for PP and HDPE rigid packaging.

Does recycled PET already contain reheat additive?#

Recycled PET arrives with an unknown reheat-additive load: a 2022 bottle-to-bottle review published in Polymers found that Asian post-consumer recyclate often contains none, while United States water and carbonated-soft-drink recyclate contains less than heat-set recyclate. No percentage or ppm value for the reheat content of any recyclate stream is published in our sources, so the variable is qualitative and stream-specific.

That variability is a formulation problem rather than a compliance problem. Heat-set grades are designed with reheat and crystallisation aids as part of the grade, so a heat-set-rich recyclate carries more absorber into the next preform than a water-grade stream does, and a converter blending recyclate into a clear bottle inherits both the absorber and its colour shift without a declared level. Recyclate formulations are usually corrected with chain extenders for PET and rPET as well, to restore the intrinsic viscosity lost in reprocessing, and food-contact recyclate is governed by recycled plastics regulations rather than by the reheat additive's own entry.

Is an IR absorber the same as an IR-blocking window film?#

Partly: an IR-blocking window film is a finished product, and a heat-shielding IR absorber such as lanthanum hexaboride or caesium tungsten oxide is one of the additives dispersed inside it. The film also owes its performance to its substrate, its thickness and any reflective coating, so the absorber sets the near-infrared absorption while the product sets everything else.

Does a thermic greenhouse film keep heat in or out?#

In: a thermic film is designed to let short-wave solar infrared through during the day and to stop the long-wave infrared that soil and plants radiate at night from leaving. Avient describes its Cesa IR additives in exactly those terms, as allowing short-wave infrared solar heating while preventing the cooling effect of longer-wave emissions, which is why the function is named for heat retention rather than heat rejection.

What "IR absorber" means outside plastics#

Outside plastics, "IR absorber" usually means an IR-absorbing coating or an optical thin-film absorber, and "infrared absorption" usually means the spectroscopy method used to identify a material rather than anything added to one. Those meanings belong to coatings technology, optics and analytical chemistry, and none of them describes an additive compounded into a polymer.