Melt Flow Rate (MFR / MFI / MVR): ISO 1133 and ASTM D1238, and the 6 Additive Families That Change It

Melt flow rate (MFR) is the mass of a molten plastic, in grams, that an extrusion plastometer pushes through a 2.095 mm die in 10 minutes at a fixed temperature and load, and 6 additive families move that number in a formulation. The same test is called melt flow index, melt index and MVR depending on the data sheet, so which number is actually being compared? ISO 1133-1 and ASTM D1238-26 define the method, and every value on this page carries the temperature and load it was measured at, because the number means nothing without them.

Antioxidants and processing stabilizers hold the melt flow rate of a polyolefin steady as it moves through repeated extrusion, while organic peroxides raise it on purpose in a process called visbreaking. Chain extenders and hydrolysis stabilizers pull the number back down in recycled polyesters and PLA, and compatibilizers and impact modifiers shift it through grafting and blending rather than through a simple dosage curve. Each mechanism is described below with the sourced dosage or effect that produced it, in the order Table 1 and Table 4 both follow.

Plastic additives change melt flow rate through six separate mechanisms, from stabilization to grafting to blending. This page works through the terminology split between MFR, MFI and MVR, the ISO 1133 and ASTM D1238 method with its per-polymer conditions, the 6 additive families and their sourced dosages, the multiple-pass extrusion protocol that turns the test into a processing-stability rating, what a high or low reading means on the production floor, how the number behaves in recycled plastic, and where the test stops being useful. The complete index of plastic additives on this site groups every family behind those six mechanisms.

Conditions for polymers other than PP and PE are listed in Table 3, with their verification status, because they are not yet confirmed against the primary standard.

What Is Melt Flow Rate?#

Melt flow rate is the mass of polymer melt, in grams per 10 minutes, extruded through a standard 2.095 mm die under a fixed load and temperature, as defined by ISO 1133-1 and ASTM D1238-26. The test reduces a polymer's flow behavior at a single, very low shear rate to one number, and that number depends entirely on which temperature and load a laboratory chooses for the run.

If the value depends entirely on the chosen temperature and load, what does it actually describe? ASTM D1238 answers this directly in its own significance statement:

Melt flow rate is empirical rather than fundamental because it tracks molecular weight and melt viscosity rather than measuring either one directly: a resin with shorter average chains flows faster under a given load, and a resin with longer chains flows slower under that same load. Formulators read the number for three separate jobs: identifying which grade of a resin has arrived in a shipment, checking incoming pellets against a purchase specification, and rating how well an antioxidant package survives repeated processing, the use this page returns to in the multiple-pass section below.

MFR, MFI, MVR and melt index: what each abbreviation means#

MFR, MFI and melt index are three names for the same measurement, the melt mass-flow rate in grams per 10 minutes, while MVR is the melt volume-flow rate in cubic centimetres per 10 minutes.

Data sheets from different eras and different regions default to different names for the same reading. Modern ISO 1133 certificates print MFR, the melt mass-flow rate, while older data sheets often still print MFI, the melt flow index, because ASTM used that name for decades before ISO harmonised the term. Polyethylene converters call the value melt index or MI, a habit that goes back to the earliest ASTM committee work on polyolefins. MVR, the melt volume-flow rate, is a different measurement rather than a different name for the same one: it reports the volume of melt that passes through the die, tracked directly by piston displacement, instead of the mass of a cut-off cooled and weighed afterward. A grade that lists both an MFR and an MVR value at the same temperature and load lets a processor work out the melt density that connects the two, a conversion described later in this section.

Is melt flow rate the same as melt flow index?#

Yes: melt flow index is the older name for what ISO 1133 calls the melt mass-flow rate, so MFI and MFR are the same value in the same unit, g/10 min. The comparison that actually changes the number is MFR against MVR, not MFR against MFI, because MVR reports a volume rather than a mass and converting between the two needs the melt density at the test temperature, a value most commodity data sheets do not publish. A certificate that lists MFI 12 g/10 min and one that lists MFR 12 g/10 min under the same 230 °C / 2.16 kg condition describe the identical result.

How melt flow rate relates to molecular weight and melt viscosity#

Melt flow rate moves in the opposite direction to molecular weight and melt viscosity: a polymer whose chains have been cut flows faster and gives a higher MFR, and a polymer whose chains have been joined flows slower and gives a lower one. Shorter chains slide past each other with less entanglement, so the melt offers less resistance at the die under a given temperature and load, and longer chains resist that same flow because they stay entangled for longer. Why then do polypropylene and polyethylene move in opposite directions during the same extrusion?

Polypropylene and polyethylene answer that question differently because oxidation attacks their backbones in different ways. In polypropylene, oxidation attacks the tertiary carbon present on every other backbone atom, and the resulting radical undergoes beta-scission, cutting the chain and raising MFR with every extrusion pass. Polyethylene has no tertiary carbon on its backbone, so its radicals crosslink and branch instead of scissioning, which lowers melt index and builds the gels that later show up as fisheyes in film. Both routes are two faces of the same polymer degradation, the chain reaction that antioxidant packages are formulated to interrupt, and that reaction is also read by FTIR carbonyl index, oxidative induction time and mechanical testing alongside melt flow rate.

How Is Melt Flow Rate Measured? ISO 1133 and ASTM D1238#

Melt flow rate is measured under two standards, ISO 1133-1 and ASTM D1238, whose current edition is D1238-26, and ASTM states that the two "address the same subject matter, but differ in technical content." The earlier D1238-23a edition is superseded, so a certificate that still cites it references an outdated version of the method. Because the two standards diverge in technical content, a value measured under ISO 1133 and a value measured under ASTM D1238 are not automatically interchangeable, even at the same nominal temperature and load.

ISO 1133-1 covers the general method through two measurement routes, Method A and Method B, and ISO 1133-2 extends the test to materials whose melt properties change during the preheat dwell, such as PET and polyamide. What does the ASTM D1238 standard measure? It measures the rate at which a thermoplastic melt flows through a specified die under a specified temperature and load, expressed as mass per 10 minutes under Method A or as volume per 10 minutes under Method B.

The extrusion plastometer: barrel, piston, die and load#

A melt flow rate test runs on an extrusion plastometer, a heated steel barrel with a weighted piston above it and a die 8.000 mm long and 2.095 mm in diameter below it. Running the test follows the same six steps regardless of polymer:

1. Dry the pellets if the polymer is hygroscopic, since undried PET or PA absorbs moisture that hydrolyses the melt and inflates the reading.
2. Set the barrel to the polymer's test temperature, for example 230 °C for polypropylene or 190 °C for polyethylene.
3. Charge the barrel with the sample and let it preheat before loading begins.
4. Load the piston with the specified dead weight, 2.16 kg being the most common load across commodity polymers.
5. Cut the extrudate at timed intervals and weigh each cut under Method A, or record the piston's displacement directly under Method B.
6. Report the result in g/10 min together with the temperature and load, for example "12 g/10 min (230 °C / 2.16 kg)".

Every reported value is meaningless without its condition, because the same pellet gives a different number at a different temperature or under a different load. A laboratory never quotes a bare melt flow rate figure on its own; it quotes the figure together with the exact condition it was measured under, and any comparison across two data sheets starts by checking that the two conditions match.

Test conditions by polymer: temperature and load#

Each polymer has its own melt flow rate condition, and the two used most often are 230 °C with a 2.16 kg load for polypropylene and 190 °C with a 2.16 kg load for polyethylene.

Conditions marked "not published here" sit in the our sources's standard-industry-knowledge tier and were not confirmed against the primary text of ISO 1133 or ASTM D1238 in the source check of 22 September 2026. Consult each polymer hub for its current processing package.

Why can a polycarbonate value and a polypropylene value never be compared? Because each polymer needs a temperature above its own melting or softening point and a load suited to its own typical viscosity, values from two different polymers, or even two conditions on the same polymer, sit on unrelated scales. Melt flow rate is empirical, so a number without its matching temperature and load carries no comparative meaning at all, whatever the polymer.

Melt volume-flow rate (MVR) and its conversion to MFR#

Melt volume-flow rate (MVR) reports the same flow as a volume, in cubic centimetres per 10 minutes, and converts to MFR only when the melt density at the test temperature is known. ISO 1133-1 Method B measures piston displacement directly, so it yields MVR without a separate weighing step, while Method A yields MFR directly by weighing the timed cut-offs. MFR equals MVR multiplied by the melt density at the test temperature, and because that melt density differs from the solid density printed on a typical data sheet, the two figures cannot be swapped using a room-temperature specific gravity.

Hydrolysis stabilizers illustrate why the two readings are tracked side by side in polyester and PLA grades. Stabaxol P 110, a carbodiimide hydrolysis stabilizer from Lanxess, reduces the MVR of PLA by 20 to 30 % against a once-extruded, unstabilised control, and the comparison only holds because both figures come from the same test condition.

How do you calculate melt flow index?#

Melt flow index is calculated by weighing the extrudate cut over a timed interval and scaling it to 10 minutes: MFR = m x 600 / t, where m is the collected mass in grams and t is the interval in seconds. A 3.170-gram cut collected over a 30-second interval, for example, scales to 63.4 g/10 min under that formula. The result is always reported with its temperature and load, because the same pellet gives a different number under a different condition.

How Do Additives Change Melt Flow Rate? The 6 Families#

Six additive families change the melt flow rate of a compound: antioxidants and processing stabilizers, organic peroxides, chain extenders, hydrolysis stabilizers, compatibilizers and coupling agents, and impact modifiers and other polymeric additives.

• Antioxidants and processing stabilizers
• Organic peroxides
• Chain extenders
• Hydrolysis stabilizers
• Compatibilizers and coupling agents
• Impact modifiers and other polymeric additives

Fillers, colorants and lubricants also shift the reading in a formulation, but our source library holds no sourced dosage or effect for their contribution to melt flow rate, so this page names only the 6 families with a documented dosage or a documented direction of change. Each works through a different mechanism, from interrupting an oxidation cycle to grafting a functional group onto the backbone, and Table 4 lists the direction, mechanism and sourced dosage for every one, in the order the six sections below follow.

A formulator choosing among the 6 families can filter candidates by polymer and function with the plastic additive selector, the site's interactive tool for matching an additive family to a process.

1. Antioxidants and processing stabilizers: melt flow retention#

Antioxidants hold the melt flow rate of a polyolefin steady through processing, because they interrupt the autoxidation cycle before it cuts polypropylene chains or branches polyethylene ones. Primary antioxidants, the hindered phenols, scavenge the peroxy radicals that drive chain scission, and secondary antioxidants, the phosphites and phosphonites, decompose the hydroperoxides those radicals leave behind before they can propagate further. Commodity polypropylene already carries a base stabilisation of less than 400 ppm phenolic antioxidant straight from the reactor, and that base package is what a compounder tops up for a specific process.

A binary blend of Irganox 1010 at 0.05 to 0.4 wt% and Irgafos 168 at 0.05 to 0.2 wt%, in a phosphite-to-phenol ratio of 1:1 to 4:1, is the standard package for polyolefins, and the phenolic and phosphite classes used across the industry are compared on antioxidants for plastics. A sourced study on vitamin E in HDPE found that 200 ppm of the tocopherol retained melt flow index over 3 extrusion passes where 200 ppm of Irganox 1010 at the same dosage did not, a result that points at differences in volatility and radical-transfer efficiency between the two phenolic chemistries.

2. Organic peroxides: raising melt flow rate on purpose#

Organic peroxides raise the melt flow rate of polypropylene deliberately, a process called visbreaking or controlled rheology, in which peroxide radicals cut the longest chains and narrow the molecular-weight distribution. Why does the same peroxide chemistry crosslink polyethylene and cut polypropylene? The tertiary carbon on every other backbone atom of polypropylene gives the radical an easy site to fragment from, while polyethylene's straighter backbone favors radical recombination into crosslinks and long-chain branches instead.

In reactive extrusion, dosages from 0 to 600 ppm of DHBP visbreak polypropylene, and the melt index diverges between screw designs above 400 ppm, a sign that shear history starts to compete with the peroxide chemistry at that level. Staple-fibre CR-PP typically runs at 200 ppm. The half-lives and decomposition temperatures behind this chemistry, including DHBP's 115 °C 10-hour half-life, sit alongside the other peroxide classes used in plastics on organic peroxides for polymers.

The reactive-extrusion route that turns this chemistry into a commercial CR-PP grade is set out on visbreaking (CR-PP). Not every peroxide raises melt flow rate: Perkadox PM-60ST-GR lowers the MFI of recycled polypropylene and raises its melt strength instead, by building long-chain branches rather than cutting them, the clearest proof that peroxide chemistry in PP can run in either direction depending on which grade is chosen.

3. Chain extenders: rebuilding molecular weight in rPET and PLA#

Chain extenders lower the melt flow rate of a recycled polyester because their multifunctional epoxide groups re-link chains that hydrolysis and shear have cut. Joncryl ADR-4368, a styrene-acrylic multifunctional epoxide with a weight-average molecular weight of 6,800 g/mol, an epoxy equivalent weight of 285 g/mol and roughly 9 epoxy groups per molecule, reacts with the carboxyl and hydroxyl end groups that chain scission leaves behind.

In rPET, a dosage of 0.5 to 1.5 wt% Joncryl ADR keeps gel content at or below 2 %, while pushing the dosage to 3 wt% produces about 32 % gel, so the reaction overshoots past a certain loading and starts crosslinking rather than simply extending. The epoxide and dianhydride classes used across this chemistry are covered on chain extenders for polymers, alongside the polymers they rebuild.

A 2024 study in the International Journal of Biological Macromolecules found that 1 phr of epoxidized cardanol oleate raised the weight-average molecular weight of PLA from 15.3 to 17.1 x 10^4 g/mol and cut its melt flow rate from 9.9 to 5.0 g/10 min, the clearest demonstration in the dataset that chain extension and melt flow rate move together. Our source library carries two conflicting dosage ranges for Joncryl ADR in PLA, so this page prints only the rPET range until that conflict is resolved.

4. Hydrolysis stabilizers: stopping melt volume-flow rate drift in polyesters#

Hydrolysis stabilizers keep the melt volume-flow rate of a polyester from drifting upward, because the carbodiimide scavenges the acid end groups that catalyse chain scission in the melt. Undried PET or PA pellets absorb enough moisture to hydrolyse during the barrel dwell, so drying comes before every melt flow rate test on these polymers, and a result that looks unexpectedly high is often a drying failure rather than a formulation problem.

Stabaxol P 110, a carbodiimide hydrolysis stabilizer supplied by Lanxess, reduces the MVR of PLA by 20 to 30 % against a once-extruded, unstabilised control. The carbodiimide grades and dosages used across polyester and PLA chemistries are covered on hydrolysis stabilizers, the family page for this mechanism.

5. Compatibilizers and coupling agents: grafting shifts the melt flow rate#

Maleic-anhydride-grafted compatibilizers arrive with a high melt flow rate of their own, because the peroxide that grafts the anhydride onto polypropylene also cuts the backbone by beta-scission. The grafting reaction runs at 180 to 190 °C, and beta-scission competes directly with the grafting step, so molar mass falls and MFR rises sharply as the maleic anhydride content climbs.

Commercial PP-g-MAH grades carry roughly 0.5 to 1.5 % maleic anhydride, and POLYBOND 3200 carries 0.8 to 1.2 %. The graft levels by blend pair for this family, along with the polymer pairs each grade is designed to couple, are set out on compatibilizers.

6. Impact modifiers and other polymeric additives: the blend rule#

Impact modifiers and other polymeric additives shift the melt flow rate of a compound toward their own, because they are polymers with their own MFI rather than small molecules dissolved in the matrix. LOTADER AX8900, an ethylene terpolymer carrying 24 wt% methyl acrylate and 8 wt% glycidyl methacrylate, has an MFI of 6 g/10 min at 190 °C / 2.16 kg, a melting point of 65 °C and a density of 0.94 g/cm3.

No blend-rule formula in our source library predicts the exact compound value from the two component values, so a compounder verifies the blended melt flow rate by testing rather than by calculation. The grade data by polymer for this family are set out on impact modifiers, the page covering how these polymeric additives are selected.

How Does Multiple-Pass Extrusion Use MFR to Rate an Antioxidant Package?#

A multiple-pass extrusion test rates a processing stabilizer by extruding the same compound up to five times and measuring the melt flow rate after each pass, so the size of the drift becomes the rating. How much drift counts as a failed pass? No standard sets a numeric limit, because the acceptance criterion is set by the converter's own specification, and the value is read as a comparison against an unstabilised control run through the same trial.

Binary blends of Irganox 1010 and Irgafos 168 at 0.1 to 0.3 wt% of the blend held the melt index of recycled polypropylene over 5 passes at 250 °C and of recycled HDPE over 5 passes at 220 °C, in trials Songwon published in its 2025 mechanical-recycling product sheet. A P-EPQ type phosphonite at 0.05 to 0.1 wt% reduced gel counts and stabilised the melt index of recycled LLDPE over the same 5-pass protocol. The phosphonite used in that LLDPE trial is covered on phosphite and phosphonite antioxidants, alongside the hydrolysis behaviour that sets phosphonites apart from phosphites.

An unstabilised control climbs steadily across the five passes, while a properly stabilised compound holds close to its starting value, a pattern Songwon's published chart shows qualitatively without this reference reading off individual data points.

Yellowness index is read alongside melt flow rate after passes 1, 3 and 5 at 230 to 260 °C for polypropylene, so the colour cost of each pass is tracked on the same samples. The full package that survives 5 passes without losing melt flow rate is set out on antioxidants for polypropylene, the page carrying the complete phenolic and phosphite selection guide for this polymer.

What Does a High or Low Melt Flow Rate Mean for Processing?#

A high melt flow rate means a low molecular weight and a low melt viscosity, so the grade fills thin sections easily, and a low melt flow rate means long chains that resist flow but hold a parison or a bubble. The two readings trade off against each other: a resin fast enough to fill a thin-wall mould before it freezes is rarely strong enough to hold a blow-moulded parison without sagging, and a resin viscous enough to hold that parison is rarely fast enough for a thin-wall part. This page does not quantify that trade-off in mechanical terms, because no sourced MFR-against-mechanical-property dataset exists in our source library; the direction of the trade-off, not its magnitude, is what a grade selection rests on.

Values compare only at the same temperature and load; melt flow rate remains an empirically defined parameter, not a fundamental one.

An unexpected shift in melt flow rate between production lots is itself a diagnostic reading. A rising value in polypropylene points at chain scission, and a falling value in polyethylene points at crosslinking or branching, both signs that the additive package or the processing history has changed rather than the base resin. A low-flow grade struggling at the die is usually corrected with polymer processing aids, the fluoropolymer and non-fluorinated additives that reduce friction at the die wall rather than change the bulk melt flow rate.

Choosing a grade by melt flow rate for injection moulding, extrusion and film#

A grade should be chosen by matching its melt flow rate to the shear the process applies: thin-wall injection moulding needs the highest flow, and blow moulding and pipe extrusion need the lowest. Four process-to-flow pairings guide that choice:

• Thin-wall injection moulding and fibre spinning need the highest melt flow rate, so the melt fills long, thin flow paths before it freezes.
• General injection moulding and sheet extrusion run on medium melt flow rate grades, balancing fill speed against part strength.
• Blow moulding and pipe extrusion need a low melt flow rate, so the parison or the pipe wall holds its shape before it sets.
• Film and cast-sheet lines sit close to the medium band, trading flow for the melt strength the web needs to survive drawdown.

The package built specifically for thin-wall parts is covered separately on additives for injection molding, the application page for that process.

Common melt-flow defects and their additive causes#

A melt flow rate that drifts between lots points at the additive package before it points at the polymer: a rising value in polypropylene means chain scission, a falling value with gels in polyethylene means crosslinking, and an inflated MVR in PET usually means wet pellets. Three symptom-to-cause pairings cover most of the drift a quality lab sees:

• Rising MFR in polypropylene signals chain scission and an exhausted stabiliser package.
• Falling melt index with visible gels in polyethylene signals crosslinking and branching, most often in LLDPE and HDPE made with chromium catalysts.
• Inflated MVR in PET or PA signals wet pellets, since undried polyester hydrolyses in the barrel and inflates the reading.

Talc filler adds a fourth, subtler cause in filled polypropylene: it adsorbs antioxidant, which shortens the package's working life and can later show up as an unexpected MFR rise in a filled compound that tested fine unfilled. The full symptom-to-cause matrix for these and other defects is set out on troubleshooting additive-related defects in plastics.

Melt Flow Rate in Recycled Plastics#

Melt flow rate carries more weight in a recyclate than in a virgin grade, because the value records how much processing history the material has already absorbed. A virgin pellet has typically passed through an extruder once, at the resin producer, while a recyclate has already been through a first-use moulding or extrusion cycle plus at least one reprocessing pass, and each pass leaves its mark on the melt flow rate reading.

EN 13476-3 Annex D lists the agreed specification items for polyolefin recyclate: oxidative induction time, melt flow rate, ash content, foreign polymer detected by DSC or FTIR, odour and VOC, plus intrinsic viscosity for rPET. Restabilisation dosages by polymer, including the binary antioxidant blends and the 5-pass practice used to qualify them, are set out on additives for recycled plastics, the formulation guide for this material stream.

Recycled polyethylene: falling melt index and rising gel counts#

Recycled polyethylene moves the opposite way to recycled polypropylene: its melt index falls as chains branch and crosslink, and the gel count in film rises at the same time. Branching is most pronounced in LLDPE and HDPE made with chromium catalysts, because catalyst residue can itself promote crosslinking during reprocessing. A P-EPQ type phosphonite at 0.05 to 0.1 wt% reduced gel counts and stabilised the melt index of recycled LLDPE over a 5-pass protocol, evidence that the gel count and the melt index reading are two symptoms of the same branching reaction. The gel count that rises with the falling melt index is covered on gels and fisheyes in plastic film.

rPET: why melt volume-flow rate and intrinsic viscosity are read together#

Recycled PET is graded by intrinsic viscosity rather than melt flow rate, because the polyester changes during the dwell in the barrel and the measured MVR partly records that change. Intrinsic viscosity bands run by application: textile fibre 0.40-0.70 dL/g, BoPET film 0.60-0.70 dL/g, water and general bottles 0.70-0.78 dL/g, carbonated soft-drink bottles 0.78-0.85 dL/g, tyre cord 0.72-0.98 dL/g and engineering or monofilament grades 1.00-2.00 dL/g. Chain extenders for PET and rPET rebuild the molecular weight that both readings track, at the same 0.5 to 1.5 wt% dosage range used earlier in this page for gel-controlled rPET.

What Melt Flow Rate Cannot Tell You#

ASTM D1238 states the limit itself:

Four limits follow directly from that statement:

• Shear-rate coverage. The test reads one point at a very low shear rate, far below the shear an injection-moulding gate applies.
• Cross-standard comparison. ISO 1133 and ASTM D1238 results are not automatically interchangeable, because the two standards differ in technical content.
• Cross-polymer comparison. A different temperature and a different load mean two polymers never share a common scale.
• Degradation mechanism. A melt flow rate that moved says nothing about which reaction moved it, so confirming chain scission or crosslinking needs FTIR carbonyl index, oxidative induction time, yellowness index and mechanical testing alongside it.

None of these four limits make the test less useful for its actual job, tracking one formulation against itself over time or against a specification, but they do rule it out as a universal comparison tool across standards, polymers or degradation mechanisms.

Why melt flow rate does not predict melt fracture or melt strength#

Two grades with the same melt flow rate can behave differently at the die, because melt fracture appears at high shear and melt strength is an extensional property that a single low-shear point does not capture. Melt fracture and sharkskin appear at the die lip under high shear, well outside the low-shear window the plastometer test measures.

Melt strength is a separate, extensional property, measured by drawing the melt rather than pushing it through a capillary, and Perkadox PM-60ST-GR proves the two properties are independent: the peroxide lowers the melt index of recycled polypropylene while raising its melt strength at the same time, through long-chain branching rather than chain scission. Melt strength enhancers address that separate, extensional property directly, for foaming, thermoforming and blow moulding applications where a low melt flow rate alone is not enough.

Which Other Tests Are Run Alongside Melt Flow Rate?#

Melt flow rate is never read alone: a processing-stability trial pairs it with oxidative induction time and yellowness index, a recyclate specification adds ash and foreign-polymer checks, and a polyester grade is fixed by intrinsic viscosity instead. Six companion tests appear most often alongside a melt flow rate result, each closing a gap the plastometer test leaves open:

Every method in this cluster, from oxidative induction time through additive analysis, is indexed under testing plastic additives, the parent page for this section of the site.

MFR, OIT and yellowness index: the processing-stability triad#

Melt flow rate, oxidative induction time and yellowness index are read together on the same multipass samples, because each one catches a different part of what the stabiliser package did. Multiple extrusion at 230 °C is the reference condition for polypropylene in this triad, and oxidative induction time (OIT) measures how much antioxidant capacity is left in the compound after that processing history. Yellowness index is read after passes 1, 3 and 5 at 230 to 260 °C alongside MFR, so the colour cost of the same passes shows up as yellowness index on the identical sample set.

Intrinsic viscosity for PET and recycled PET#

Intrinsic viscosity replaces melt flow rate as the grade metric for PET, and the bands run from 0.40-0.70 dL/g for textile fibre to 0.78-0.85 dL/g for carbonated soft-drink bottles. ASTM D4603 and ISO 1628-5 set the two standards behind that number, run in solution rather than in the melt, which is why the polyester dwell-time problem that affects MFR does not affect intrinsic viscosity the same way. The bands by application are set out in full on intrinsic viscosity of PET and recycled PET.

Torque rheometry and fusion testing for PVC#

PVC compounds are not graded by melt flow rate: a torque rheometer records fusion time and stability time instead, because the compound degrades in the barrel before it flows freely. ISO 182-1 runs alongside the torque-rheometer measurement as the Congo red stability check on the same PVC formulation, reading the time to hydrogen chloride release rather than a flow rate. Fusion time and stability time are measured by PVC fusion testing.

Melt flow rate and additive analysis#

A melt flow rate result says that the additive package changed, and additive analysis says which additive changed: ASTM D6042-23 quantifies antioxidants and slip agents in polypropylene down to about 2 ppm by LC-UV at 200 nm. ASTM D6953-18 runs the equivalent extraction and quantification for polyethylene. Which additive is present at what level comes from additive analysis and deformulation of plastics, the page that pairs this chemical confirmation with the physical reading melt flow rate provides.

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