DSC Testing for Plastic Additives: Crystallization Temperature, Nucleation Efficiency and OIT, and the 6 Additive Families It Measures

Differential scanning calorimetry (DSC) measures the heat flowing into or out of a few milligrams of plastic while the specimen temperature is ramped, and it reports the transition temperatures and the enthalpies of fusion and crystallization that 6 additive families are bought to change. ASTM D3418-21 sets that scope and the ISO 11357 series covers the same subject part by part. The same resin gives two different crystallization temperatures before and after a nucleator is added, so which features on a trace belong to the additive and which to the moulding machine?

Each family moves a different feature. Nucleating agents such as NA-11 and clarifying agents such as DMDBS raise the crystallization temperature Tc and shorten the half-time; antioxidants such as Irganox 1010 lengthen the oxidation induction time; plasticizers such as ATBC lower the glass transition temperature Tg; fillers such as talc and glass fibre nucleate as a side effect; and chemical blowing agents such as azodicarbonamide add a decomposition exotherm of 1.36 kJ/g.

This page covers the working principle, the 5 thermal events, the method under ASTM D3418-21 and the ISO 11357 series, how each family moves a number, the two calculations that turn a trace into an additive rating, the value that matters in each polymer, recyclate, and the 5 questions a calorimeter cannot answer. Six families of plastic additives are bought partly for what they do to these numbers.

Table 1. DSC at a glance

Standard editions are the versions current on 18 October 2026. ISO 11357 part numbers are given without an edition year where the edition could not be read from the standard itself.

What Is DSC Analysis of a Polymer?#

DSC analysis of a polymer is the measurement of transition temperatures and the enthalpies of fusion and crystallization by differential scanning calorimetry, the scope ASTM D3418-21 sets for the method and the subject the ISO 11357 series covers part by part. Clause 1.2 applies the method to polymers in granular form and to any fabricated shape from which a specimen can be cut, and clause 1.3 puts the normal operating range from the cryogenic region to 600 °C.

If a milligram of granule runs in a few minutes, what does a formulator learn from it? Five uses account for most industrial scans: grade identification, incoming-goods control, additive screening during development, failure analysis on a part that cracked or warped, and recyclate qualification.

How differential scanning calorimetry works#

A DSC works by heating or cooling a sealed pan of plastic and an empty reference pan at the same controlled rate and recording the difference in the heat each one needs, so every melting, crystallization, glass transition or oxidation event appears as a peak or a step away from the baseline. A run has three steps.

1. Seal a few milligrams of resin or a cut specimen in a pan, with an empty reference pan beside it.
2. Ramp the temperature at a controlled rate under a purge gas, nitrogen for transitions and oxygen for oxidation.
3. Read the peaks and steps against the baseline, where endothermic events absorb heat and exothermic events release it.

Instruments come in heat-flux and power-compensation designs, and either records a difference in heat flow, whereas a differential thermal analyser (DTA) records a difference in temperature.

What is the difference between DSC and TGA?#

DSC measures heat flow and TGA measures mass loss, so a DSC finds the temperatures at which a polymer softens, melts, crystallizes or starts to oxidise, while a thermogravimetric analyser finds the temperatures at which an additive volatilises or a filler stops burning off. Irganox 1010 reaching 5 % mass loss at about 330 to 353 °C is a TGA number about additive volatility, not a DSC transition, measured to ISO 11358. Both instruments are screening steps in additive analysis and deformulation.

The 5 thermal events a DSC curve shows#

The 5 thermal events on a DSC curve are the glass transition, cold crystallization, melting with the enthalpy of fusion, crystallization on cooling with the enthalpy of crystallization, and oxidation.

• Glass transition (Tg): a baseline step from glassy to rubbery, with unplasticized PVC at 82 °C and PET between 67 and 81 °C.
• Cold crystallization: an exotherm on heating, where a polymer quenched too fast to crystallize does so above its Tg, the first-scan feature of PET and PLA.
• Melting (Tm) and the enthalpy of fusion: an endotherm whose peak gives the melting temperature, 160 to 166 °C for isotactic polypropylene, and whose area gives the heat absorbed.
• Crystallization (Tc) and the enthalpy of crystallization: an exotherm on cooling whose peak is the number a nucleator is bought to raise, read at 10 °C/min.
• Oxidation: the exotherm whose onset, measured isothermally in oxygen, is the oxidation induction time.

Crystallinity is calculated from the melting endotherm by normalising the measured enthalpy of fusion against the enthalpy a fully crystalline sample would show. ASTM D3418-21 warns in Note 1 that true heats of fusion require structural investigation and often specialised crystallization techniques, so this page quotes no reference enthalpy in J/g. Nagarajan, Mohanty and Misra at the University of Guelph (2016) raised PLA crystallinity from 10 % to 45 % with 0.25 wt% of LAK-301, and Gao, Masato and co-workers (2022) from 26 % to 63 % with 1 wt% of orotic acid. The full definition of crystallinity sits on its glossary entry.

How do you read a DSC curve?#

Read a DSC curve by identifying the direction of each feature first: a step in the baseline is a glass transition, an endothermic peak is melting, an exothermic peak on cooling is crystallization, and an exothermic peak during an isothermal hold in oxygen is the start of oxidation. The crystallization temperature that gets reported is the peak of the cooling exotherm, not its onset. A glass transition is read from the step, and the convention used (onset, midpoint or inflection) belongs next to the value, because the three do not agree on the same curve.

How Is a DSC Test Run? ASTM D3418 and the ISO 11357 Series#

A DSC test is run by ramping a sealed milligram specimen through a defined heat, cool and reheat programme under ASTM D3418-21, the current ASTM method for transition temperatures and the enthalpies of fusion and crystallization of polymers, or under the matching part of the ISO 11357 series. DSC sits in the thermal group of the methods for testing plastic additives, beside the oxidation and heat-ageing tests. ASTM D3418-21 was last updated on 17 September 2021 and supersedes D3418-15 and D3418-12, so a data sheet that still quotes D3418-08 or D3418-15 is citing a withdrawn edition.

Specimen, pans, purge gas and heating rate#

Four settings decide whether two DSC results can be compared: the specimen, the pan, the purge gas and the ramp rate. ASTM D3418-21 states only that the temperature is changed at a controlled rate and names no specimen mass, so the figures below come from research practice and from instrument makers, Linseis putting the usual run at 10 K/min with a 5 to 10 mg specimen and calibration against indium, tin or lead.

• Specimen: a few milligrams, from granule or cut from a moulded part, the cut face flat against the pan floor.
• Pan: the same pan type across a comparison, because pan contact changes the apparent onset.
• Purge gas: nitrogen for transitions, oxygen or air for oxidation, at a flow recorded with the result; published OIT practice in a 2023 study in Polymers uses 50 mL/min.
• Rate: the same ramp for every specimen, with the crystallization-temperature convention at 10 °C/min on cooling.

Two crystallization temperatures should only be compared when the cooling rate, the specimen mass and the pan type were the same. Linseis also reports an artefact near 100 °C in undried polyethylene, removed by vacuum drying at 80 °C, a supplier observation rather than a clause of either standard.

The heat-cool-reheat programme and why the second heating scan is the one to quote#

The second heating scan is the one to quote because the first still carries the thermal history of moulding or extrusion, and only after a controlled cooling scan has erased it do the melting peak and the melting enthalpy describe the formulation rather than the machine. The programme runs in three stages.

1. Heat past the melting range to erase the thermal history and, for a clarified compound, past the clarifier's dissolution temperature.
2. Cool at a controlled rate and read the crystallization exotherm, whose peak is the Tc a nucleator moves.
3. Reheat at the same rate and read the melting peak, the melting enthalpy and the glass transition.

Residual crystal fragments left by an incomplete first melt act as ideal nuclei and inflate the next cooling scan, the self-nucleation effect the Fillon efficiency scale exploits. Why residual crystal fragments act as ideal nuclei is explained under polymer crystallization and nucleation. Iwasaki and co-workers (2020) found that MDBS at 0.4 wt% dissolves in polypropylene only at about 210 °C, and sorbitol clarifiers need about 220 °C, so a first scan stopping at 200 °C measures undissolved clarifier.

Which standard covers which transition#

Four standards cover the DSC measurements that matter for plastic additives: ASTM D3418-21 for transition temperatures and the enthalpies of fusion and crystallization, the ISO 11357 series for the same subject part by part, ASTM D3895-19 and ISO 11357-6:2018 for oxidation induction time, and ASTM D5885 for high-pressure OIT. Table 2 maps each measurement onto its standard and records how far each reference was verified for this page.

Table 2. Which standard covers which DSC measurement

Editions are the versions current on 18 October 2026. Where an edition year is not shown, the standard's own text was not available to us and only the part number is stated.

Part numbers and edition years decide what a data-sheet value means: a value quoted as "ISO 11357" with no part number does not say whether it is a glass transition from part 2 or a crystallization temperature from part 3, and a value quoted as "D3418" with no edition does not say which of three editions produced it. The specification tables for oxidative induction time (OIT) sit on its own page.

Is ASTM D3418 equivalent to ISO 11357?#

No: ASTM D3418-21 states in its own notes that the method is "similar but not equivalent" to ISO 11357-1, ISO 11357-2 and ISO 11357-3, and the same non-equivalence applies to the OIT pair, ASTM D3895-19 and ISO 11357-6:2018. A specification that names one standard is therefore not satisfied by a result obtained under the other, so an incoming-goods specification and the supplier's data sheet have to name the same standard and the same part. ASTM D1238 and ISO 1133 set the same trap on the melt-flow side.

How Do Additives Change a DSC Curve? The 6 Families#

The 6 additive families a DSC measures are nucleating agents, clarifying agents, antioxidants and processing stabilizers, plasticizers, fillers and reinforcements, and chemical blowing agents, and the nucleating agents are the reason the test became a routine formulation tool at all. A nucleated compound crystallizes at a higher temperature, which shortens cycle time, raises flexural modulus and heat deflection temperature, gives isotropic shrinkage and, above a nucleus-density threshold, improves clarity. Table 3 gives the number each family moves, its direction and a sourced example.

Table 3. How 6 additive families move a DSC number

Values are from the cited studies and supplier documents at the stated dosage in the stated polymer. A DSC result from one resin and one cooling rate does not transfer to another.

1. Nucleating agents: crystallization temperature and half-time#

Nucleating agents raise the crystallization temperature because they give the melt a foreign surface to crystallize on, so the exotherm on a DSC cooling scan appears at a higher temperature and the moulding is ejected sooner. The peak of that exotherm, read conventionally at 10 °C/min, is the primary quick metric of nucleating efficiency, and the crystallization half-time t1/2, the time to reach 50 % relative crystallinity in an isothermal run, replaces it in slow-crystallizing polymers such as PLA and PET.

Simanke and co-workers (2016) found that HPN-68L accelerates crystallization more efficiently than sodium benzoate and DMDBS at 1,000 to 2,200 ppm in polypropylene, and a 2026 review by Hao and co-workers in Molecules records TMB-5 at 0.6 wt% in PET raising Tc by 16.6 °C. Grades, dosage and selection for all nucleating agents sit on the family hub.

Melting point decides whether a nucleator appears on the curve as a separate event. NA-11 melts above 400 °C, so it never dissolves in the polypropylene melt and acts as a particulate nucleator at any melt temperature, which leaves the shifted cooling exotherm as its only signature. ADEKA reports that 0.1 wt% of NA-27 can let a polypropylene part run 10 % thinner at equal load, and Milliken reports UL-validated energy savings of 5 to 8 % for four Hyperform HPN grades.

2. Clarifying agents: dissolution temperature and the Tc jump#

Clarifying agents are melt-soluble nucleators that have to dissolve before they can work, so a DSC heating scan shows their dissolution and the following cooling scan shows the crystallization exotherm jumping to a higher temperature. The chemistry of melt-soluble clarifying agents is covered generation by generation on the hub, from the sorbitol acetals to the benzenetrisamides that Blomenhofer and co-workers at the University of Bayreuth (2005) showed clarify isotactic polypropylene from 200 ppm.

More clarifier is not better, and the DSC is where that becomes visible. Kristiansen, Tervoort and Smith at ETH Zurich (Macromolecules 36:5150, 2003) mapped the DMDBS and isotactic polypropylene system as a monotectic: the maximum Tc increase falls between 0.2 and 1 wt%, optics worsen above 1 wt%, liquid-liquid phase separation appears above 2 wt%, and the cooling rate strongly affects the result. DMDBS (Millad 3988) is the clarifier that phase diagram was measured on. Horvath and co-workers (2014, RSC Advances) add the ceiling: sorbitol clarifiers dissolve in polypropylene only to a few thousand ppm, and the Flory-Huggins interaction parameter correlates with the best optical result the system can reach, which a calorimeter never measures.

3. Antioxidants and processing stabilizers: oxidation induction time#

Antioxidants lengthen the oxidation induction time because the DSC holds the specimen at a fixed temperature in oxygen and the exotherm only starts once the stabilizer is consumed, which makes OIT a direct reading of the active antioxidant left. ISO 11357-6:2018 and ASTM D3895-19 define that measurement, typically between 190 and 220 °C, and which classes contribute to an OIT result is set out under antioxidants for plastics.

The polyolefin baseline is a two-component package at a known split. A phenolic antioxidant such as Irganox 1010 runs at 0.05 to 0.4 wt% with a phosphite such as Irgafos 168 at 0.05 to 0.2 wt%, at a phosphite-to-phenol ratio between 1:1 and 4:1, and recyclate restabilization uses blends of the two at 0.1 to 0.3 wt%. At 200 °C the phenolic can dominate the result while the phosphite does its work on the melt rather than in the calorimeter cell, so an OIT number reads one half of the package more clearly than the other. The percentages in FDA clearances are legal maxima, not dosages.

4. Plasticizers: glass transition and miscibility#

Plasticizers lower the glass transition temperature, and the shape of that step reads something a hardness test cannot: one glass transition means the plasticizer is dissolved in the polymer, two mean it has separated into its own phase. Unplasticized PVC has a glass transition at 82 °C, which is the reason flexible PVC exists, and flexible PVC carries 5 to 65 wt% of plasticizers for plastics.

Miscibility is read from the same step. A 2018 study in RSC Advances tracked PLA with acetyl tributyl citrate (ATBC) and put the solubility limit at about 50 wt% from the Fox-law glass transition, with no phase separation up to 17 wt%, so a single Tg across that range is evidence that the citrate is dissolved rather than dispersed. The definition of the glass transition temperature and its three reading conventions are in the glossary. This page gives no Tg for a plasticized PVC compound at a stated phr, because plasticizer efficiency on this site is compared at Shore A 80, a hardness convention.

5. Fillers and reinforcements: nucleation as a side effect#

Fillers change a DSC curve even when nucleation is not what they were bought for: 6 wt% of talc raises the nucleation density of PLLA about 500 times and cuts the crystallization half-time 7-fold between 100 and 120 °C, a result Kolstad recorded and Gao and Masato cite in their 2024 review. Loading levels for talc in plastics run from 0.5 wt% as a nucleant to 40 % as a bulk filler. Three cases appear on the curve.

• Nucleating fillers: talc and other fine minerals raise Tc and cut the half-time, which is why 2 wt% of talc in a bio-polyester cut t1/2 at 66 °C from 7.69 min to 1.95 min.
• Retarding colorants: nigrosine slows PA66 crystallization by hydrogen-bonding to the polyamide chains, so the cooling exotherm moves the other way.
• Pigments as accidental nucleators: phthalocyanine pigments nucleate polypropylene, one of the causes of differential shrinkage and warpage in coloured parts.

Glass fibre and carbon black act the same way, so a reinforced grade and its base resin give different cooling exotherms before any nucleator is added.

6. Chemical blowing agents: the decomposition exotherm#

A chemical blowing agent adds a feature no polymer transition explains: its own decomposition exotherm, which for azodicarbonamide releases 1.36 kJ/g between 160 and 230 °C as measured by DSC. Decomposition ranges for the other chemical blowing agents are tabulated on the node, with the activators that move them.

Where that exotherm sits decides whether the compound foams or degrades, because it has to fall above the processing temperature and below the degradation temperature of the polymer. The recorded decomposition points for one chemistry spread widely: PubChem lists 225 °C, a review gives pure material at around 210 °C, and the Eiwa Vinyfor grades run 200 to 209 °C. The grade spread for azodicarbonamide (ADCA) and its EU food-contact status are on its substance page, and that spread is why a grade's own trace is the number to work from.

How Is Nucleation Efficiency Calculated from a DSC Scan?#

Nucleation efficiency is calculated from three crystallization temperatures measured on the same polymer, as the fraction of the available window that the nucleator captures.

NE = (Tc,NA - Tc,1) / (Tc,2max - Tc,1) x 100 %

• Tc,1: the crystallization temperature of the unnucleated resin, the bottom of the scale.
• Tc,NA: the crystallization temperature of the nucleated compound.
• Tc,2max: the highest crystallization temperature the polymer reaches when seeded with its own crystal fragments, the top of the scale.

Fillon, Lotz, Thierry and Wittmann at CNRS Strasbourg defined that calorimetric scale in the Journal of Polymer Science Part B in 1993, and the number that makes it useful is the ceiling they measured: commercial isotactic polypropylene nucleators rate at best 60 to 70 % on it. The best products therefore capture about two-thirds of the headroom, so a supplier claim of a large Tc gain has to be read against that ceiling rather than against zero, which is why nucleating agents for polypropylene are compared on efficiency rather than on raw Tc gain.

The top of the scale comes from self-nucleation, and Muller and co-workers (1997) built the related thermal-fractionation technique, successive self-nucleation and annealing, on that behaviour. A Tc gain should be reported with the self-nucleated maximum for the same resin, or it cannot be compared across resins.

How Is OIT Measured by DSC, and Which Specifications Use It?#

OIT is measured by melting the specimen in the DSC under nitrogen, holding it at a fixed temperature between 190 and 220 °C, switching the purge to oxygen or air, and timing the minutes until the oxidation exotherm starts. Pipe, geomembrane and recyclate specifications all use that number as a contractual requirement, which separates OIT from every other DSC output: a crystallization temperature is a development number, an OIT is one a delivery is rejected on.

Isothermal OIT: ASTM D3895 and ISO 11357-6#

The OIT value that appears in a contract is the PE pressure-pipe requirement of at least 20 minutes at 210 °C, set in Table 1 of ISO 4427-1:2019 and EN 12201-1 and measured to ISO 11357-6 in oxygen on 3 test pieces. Footnote g of that table decides disputes: it permits 200 °C or 220 °C only where a clear correlation has been established, and makes 210 °C the reference temperature. The pipe and geomembrane packages behind these numbers are on additives for polyethylene. Table 4 collects the OIT numbers that appear in specifications.

Table 4. OIT values that appear in specifications

The 210 °C requirement is the standard clause. Figures quoted at 200 °C are either an allowed alternative under an established correlation or industry practice, never the requirement.

HP-OIT for geomembranes and the HALS gap#

HP-OIT is the high-pressure version of the test, run at 3.4 MPa of oxygen and 150 °C under ASTM D5885, used when a compound's standard OIT exceeds 30 minutes and the isothermal run stops being practical. GRI-GM13 puts the geomembrane thresholds at 100 minutes of standard OIT or 400 minutes of HP-OIT. The other half of that durability specification is carbon black: PE pressure pipe carries 2.0 to 2.5 % by mass at 10 to 25 nm average primary particle size and dispersion grade 3 or better to ISO 18553, not the 2.0 to 3.0 % GRI-GM13 sets for geomembranes.

The high-pressure test also closes a gap in additive selection. Hindered amine light stabilizers register in HP-OIT but not in a standard OIT run, so a compound well protected by a HALS package can look under-stabilized on a standard OIT and pass on HP-OIT. Where oven ageing at 85 °C for 90 days enters the specification, long-term heat aging and RTI takes over as the lifetime evidence.

Oxidation induction temperature is not oxidation induction time#

Oxidation induction time and oxidation induction temperature are two different measurements that share an abbreviation: the first is a number of minutes at a fixed temperature, defined by ISO 11357-6:2018 and ASTM D3895-19, and the second is a temperature reached during a ramp.

Knoben and co-workers (2025) tracked closed-loop recycled polypropylene with a modified DSC method in an inert atmosphere and report an oxidation induction temperature of 198 °C without antioxidant against 257 °C with antioxidant. That 59 °C spread says nothing about how many minutes either compound would survive at 210 °C, so it cannot be quoted as an OIT, and the same study found that antioxidant re-dosed at every cycle leads to build-up. Antioxidant build-up across closed-loop cycles is covered under restabilization of recycled plastics.

Which DSC Values Matter for Each Polymer?#

The DSC value that matters depends on how fast the polymer crystallizes: polypropylene and polyethylene are read on the crystallization temperature, PET and PLA on the crystallization half-time, polyamides on the crystallization temperature a filler or colorant has shifted, and PVC on the glass transition, because it has no crystallization exotherm. Table 5 gives the reference Tg and Tm for each polymer, as orientation rather than specification.

Table 5. Reference thermal values and what a DSC is run for, by polymer

Values are the knowledge base's reference figures for the neat polymer. Grade, comonomer content and additive package all move them, and where a cell says "not in our source set" no verified value exists and none is invented.

Polypropylene and polyethylene#

Polypropylene is the polymer DSC was made useful for in additive work, because it grows crystals slowly at large undercooling and almost never nucleates on its own, which Gahleitner and co-workers (2011) call an ideal material for controlled nucleation. One cooling scan on an isotactic grade melting at 160 to 166 °C, with a crystallinity of 30 to 60 %, answers the nucleator question. The full PP package is on additives for polypropylene.

Polyethylene behaves the other way round. HDPE and LLDPE crystallize fast, so a DSC on polyethylene is usually run for OIT rather than for a Tc gain, and Seven, Cogen and Gilchrist (2016, Polymer Engineering and Science) describe PE nucleation as bought for clarity, cycle time, warpage and stiffness instead of crystallization speed. The PE film nucleator HPN-210M, based on sodium 4-[(4-chlorobenzoyl)amino]benzoate (CAS 1489170-67-3), is cleared under FDA FCN 1579 up to 0.25 % in polyolefins.

PET and recycled PET#

PET crystallizes so slowly that a DSC cooling scan on the neat resin can show almost no exotherm, which is why crystalline PET trays, engineering PET grades and injection-moulded recycled PET all carry a nucleator. Bottle, fibre and film grades are separated on additives for PET resin, because each one wants a different point on the crystallization curve.

Chemical nucleation of PET is where the calorimeter's blind spot shows. Wang and co-workers (2024, Molecules 30:37) describe sodium benzoate acting through the chain ends, where sodium forms anionic end groups, so the Tc gain arrives with a molecular-weight loss the DSC cannot see. Dibenzylidene sorbitol melts at 224 °C and sodium linoleate at 192 °C, both below the 270 °C at which recycled PET is processed, which causes chain scission.

PLA and other biopolymers#

PLA is the polymer where the crystallization half-time, not the crystallization temperature, decides whether a part can be made: 1 wt% of LAK-301, potassium dimethyl 5-sulfoisophthalate, brings the half-time at 140 °C down from 61 minutes to 1.8 minutes with a maximum crystallinity of 50 %, as Nagarajan, Mohanty and Misra at the University of Guelph measured in 2016. The whole PLA package is on additives for PLA.

Two other results fix the scale of the effect. Gao, Masato and co-workers (2022, Micromachines 13:2186) cut the half-time from 4.1 to 1.8 minutes with 0.2 wt% of TMC-328, and a 99/1 PLLA/PDLA blend with 1 wt% of talc cut the half-time at 110 °C from 25 minutes to 0.4 minutes. Heat resistance needs a nucleator plus a hot mould or an annealing step, with the stereocomplex route reaching a heat deflection temperature of up to 190 °C. Grade-by-grade half-time data sits on nucleating agents for PLA, and boron nitride is cleared up to 1 wt% in PHA under FDA FCN 970.

Polyamides and engineering plastics#

In polyamides a DSC is usually run to find out what the filler and the colorant did to the crystallization exotherm, because glass fibre, talc, ultrafine polyamide nucleators and carbon black all raise the crystallization temperature while nigrosine lowers it. Boucenna (2023) measured that rise in a compound with 30 % glass fibre and 0.4 % carbon black, and nigrosine works the other way by hydrogen-bonding to the polyamide chains. The reference melting points make the shift readable: PA6 melts at 215 to 218 °C with a glass transition at 47 °C, PA66 at 264 °C, PBT at 223 °C and POM at 175 °C. Copper heat stabilizers, nigrosine and the glass-fibre package are on additives for nylon (polyamide).

PVC: why DSC is not the heat-stability test#

A DSC on rigid PVC shows a glass transition near 82 °C and nothing else, because PVC is effectively amorphous and has no crystallization exotherm, which is why PVC heat stability is measured by the Congo red method to ISO 182-1 at 180 °C instead. The method that does measure it is PVC heat stability testing, and TGA is too insensitive to catch early PVC degradation. What the calorimeter still reads well is the glass-transition step, which moves with the plasticizer level and splits in two if the plasticizer has separated.

DSC Testing of Recycled Plastics#

In a recyclate a DSC answers two questions at once: how much active antioxidant is left, from the oxidation induction time, and what else is in the bale, from a melting peak that does not belong to the host polymer. Which packages go back into a bale is set out on additives for recycled plastics. Three readings come off one set of scans.

• Residual antioxidant: the oxidation induction time falls as the stabilizer is consumed over successive extrusions, and it is an agreed specification item for PP recyclate under EN 13476-3 Annex D.
• Foreign polymer: a second melting endotherm is the signature of cross-contamination, and EN 13476-3 Annex D names DSC or FTIR as the method.
• Restabilization effect: Knoben and co-workers (2025) measured an oxidation induction temperature of 198 °C for closed-loop recycled polypropylene without antioxidant against 257 °C with it.

Contamination costs real performance. Five per cent of polypropylene in recycled HDPE cuts slow-crack-growth resistance by up to 40 %, and polyethylene in recycled polypropylene by up to 70 %, so an endotherm found in minutes predicts a failure mode that takes hundreds of hours to measure. ADEKA's CYCLOAID UPR-011 is an antioxidant plus nucleator package for recycled polyolefins, so one compound moves both numbers on the same trace.

What DSC Cannot Tell You#

A DSC cannot answer 5 questions that formulators regularly put to it, and each one has a different instrument behind it.

• Whether the part will last: ASTM D3895 calls OIT a qualitative assessment of stabilization, and PE100+ reports no good correlation between OIT and the brittle failure of PE-MD pipe, so heat ageing and pressure testing remain the lifetime evidence.
• Whether a volatile antioxidant is working: the same standard warns in Note 2 that a volatile stabilizer can give a poor OIT and still perform at service temperature.
• What a nucleator did to molecular weight: chemical nucleation of PET by sodium benzoate cuts chain length, which no thermal transition records.
• How much of the beta form a polypropylene contains: beta content comes from the Turner-Jones WAXD peak-area ratio, not a calorimeter.
• How clear the part is: haze is measured to ASTM D1003-21, and a high crystallization temperature does not guarantee a low value.

Chain length is read by intrinsic viscosity of PET, which is why a PET nucleation trial reporting only a Tc gain has measured half the result.

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Which Other Tests Are Run Alongside DSC?#

A DSC result is read next to 4 other tests, because the thermal trace explains a crystallisation mechanism while the other four measure the property a specification names. The complete map of testing plastic additives and additive-dependent properties shows which test answers which formulation question.

Haze and clarity for clarified polypropylene#

Haze is the number a clarifier is bought for, and it is measured on a different instrument: ASTM D1003-21 puts the specimen in a hazemeter (procedure A) or a spectrophotometer (procedure B) and reports the share of transmitted light scattered by more than 2.5 degrees. Above 30 % haze a material counts as diffusing and is tested to ASTM E2387, and ASTM D1003 is not equivalent to ISO 13468-1 or ISO 14782. Procedures A and B are compared on haze and clarity measurement.

A haze value carries its thickness or it means nothing. ADEKA reports 2.2 % haze at 1 mm for ADK TRANSPAREX against a market low of 3.2 %, third-party verified, and states a Guinness World Records title for 2025. Target haze values by application are on clarified polypropylene, together with the DMDBS window in which Tc and haze move together.

Melt flow rate and intrinsic viscosity#

Melt flow rate is the test that sits closest to a DSC in an incoming-goods specification: a 2023 peer-reviewed polypropylene study ran oxidation induction time to ISO 11357-6 and melt volume-flow rate to ISO 1133-1 on the same material, because one reads the stabilizer and the other the chain length. ISO 1133-1 and ASTM D1238-26 run polypropylene at 230 °C with a 2.16 kg load and polyethylene at 190 °C with the same load, through a die of 8.000 mm by 2.095 mm, and the result is empirical rather than a fundamental property. That pairing of OIT with melt flow rate is what an incoming-goods specification usually copies, and intrinsic viscosity does the equivalent job in PET.

HDT, Vicat and impact strength#

A higher crystallization temperature usually shows up as a higher heat deflection temperature, measured on a different machine entirely: ASTM D648 or ISO 75 load the bar at 0.455 or 1.82 MPa and heat it at 2 °C/min to a 0.25 mm deflection, and the result is explicitly not for design use. Vicat softening under ISO 306 or ASTM D1525-25 runs A50 at 10 N and B50 at 50 N, with ISO 10350 using B50. What a Tc gain is worth in service shows up as heat deflection temperature.

Beta-nucleated polypropylene is the exception. Varga (2002) showed that the beta form has markedly higher impact strength and toughness than alpha polypropylene, so a beta-nucleated grade is judged on impact strength (Izod, Charpy) rather than stiffness, and its beta content comes from a diffractometer.

TGA and additive deformulation#

A DSC is the first instrument in a deformulation, not the last: the standard screening sequence is FTIR-ATR for the polymer, TGA for the volatile, organic, filler and carbon-black fractions, and DSC for the transitions, before anything is extracted. Extraction follows by reflux, Soxhlet or accelerated solvent extraction, then identification by HPLC-UV, LC-MS, GC-MS and pyrolysis GC-MS.

Chromatography closes the identification. Antioxidant and slip additives are quantified by ASTM D6042-23 in polypropylene and ASTM D6953-18 in polyethylene, both down to about 2 ppm, which is where a calorimeter stops and a chromatograph starts. The full sequence is on additive analysis and deformulation of plastics.

Do you need your own DSC, or a test lab?#

An in-house DSC pays for itself where crystallization scans are run on every batch of a nucleated or clarified compound, and an accredited laboratory is the better route where the number goes into a contract or where a high-pressure OIT cell at 3.4 MPa is needed. This page quotes no instrument or test price, because no verified figure exists in our sources. To start from the property rather than from the test, use the additive finder by polymer and function.

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