Knowledge Base
Testing Recycled and Sustainable Plastics Glossary and Fact Sheet
Key terms
Chain scission. The breaking of long polymer molecules into shorter chains, reducing molecular weight. Driven by heat, shear, and oxidation during use and reprocessing.
Post-consumer recyclate (PCR). Material recovered from products that have completed their intended use and been collected from end users.
Post-industrial recyclate (PIR). Material recovered from manufacturing scrap, trim, or off-spec product before it reaches a consumer.
Regrind. Reprocessed plastic produced by grinding scrap or rejected parts for reuse, often blended with virgin resin.
Melt flow rate (MFR) / Melt flow index (MFI). The mass of molten polymer extruded through a standard die in a set time. A sensitive indicator of molecular-weight change.
Melt volume rate (MVR). The volume of molten polymer extruded through a standard die in a set time; related to MFR by melt density.
Intrinsic viscosity (IV). A solution-based measure related to molecular weight, important for polymers such as PET. Can be estimated from melt flow data for some polymers.
Tensile strength. The maximum stress a material withstands while being stretched before breaking.
Flexural strength. The maximum stress in a material as it resists bending under a three-point load.
Impact strength. The energy a material absorbs under sudden load before it fractures; a measure of toughness.
Environmental stress cracking resistance (ESCR). A material’s resistance to cracking under the combined action of mechanical stress and a chemical environment.
Density gradient column. A column of liquid whose density increases with depth, used to measure the density of solid plastic specimens to high precision.
Apparent bulk density. The mass of a sample of particles divided by the total volume they occupy, including the void spaces between particles.
Thermo-oxidative degradation. Polymer breakdown caused by the combined effect of heat and oxygen, common during reprocessing.
Standards reference table
| Standard | Scope | Relevance to recycled plastics |
| ASTM D638 | Tensile properties of plastics | Compare strength and elongation of recyclate vs virgin |
| ASTM D790 | Flexural properties of unreinforced and reinforced plastics | Bending strength and stiffness of rigid recycled parts |
| ISO 1133 | Melt mass-flow rate (MFR) and melt volume-flow rate (MVR) | Detects molecular-weight change from degradation |
| ASTM D1238 | Melt flow rate by extrusion plastometer | Processability check and batch consistency |
| ASTM D1505 | Density of solid plastics by density-gradient technique | Confirms composition; flags mixed polymers or fillers |
| ASTM D1895 | Apparent density, bulk factor, and pourability | Bulk handling of recycled powders, pellets, and flakes |
| ASTM D6110 | Charpy impact resistance of notched plastic specimens | Toughness of recycled material under sudden load |
| ASTM D1693 | Environmental stress-cracking of ethylene plastics | Long-term durability of recycled polyethylene |
| ISO 527 / ISO 178 | International equivalents for tensile and flexural testing | Cross-reference for global supplier comparison |
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FAQs
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A virgin-resin datasheet describes the material in a known, controlled state. Recycled material has been through processing, use, and reprocessing, which can shorten polymer chains, lower molecular weight, and introduce contaminants. As a result, properties such as melt flow rate, impact strength, and tensile strength can drift away from the virgin values, and recyclate often shows more batch-to-batch variation. Testing the actual recycled material – rather than assuming the datasheet still applies – is the only reliable way to confirm performance. A melt flow indexer and a universal testing machine are good starting points.
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It depends on the end use, but a core set covers most needs: melt flow rate for processability and degradation; tensile (ASTM D638) and flexural (ASTM D790) for mechanical strength; impact testing for toughness; density for composition; and environmental stress cracking resistance for long-term durability. Testing several of these together gives a fuller picture than any single result and supports clear batch-acceptance criteria.
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Degradation during use and reprocessing tends to shorten polymer chains, which usually raises the melt flow rate because shorter chains flow more easily. A higher or more variable MFR than expected can signal chain scission or contamination, and it directly affects the processing window for molding and extrusion. Measuring MFR to ISO 1133 or ASTM D1238 on incoming material is a fast, sensitive way to catch problem batches before they reach production.
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Yes. The same standard test methods – tensile, flexural, melt flow, impact, density, and ESCR – apply to recycled material, which is what makes direct comparison possible. The practical difference is that recyclate usually needs more frequent testing and a larger sample set to account for batch-to-batch variation. Benchmarking results against both the standard and the equivalent virgin material gives quality and R&D teams a defensible basis for supplier comparison and material acceptance.
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Documented test data turns a sustainability claim into something you can evidence. Recording mechanical, flow, and durability results against recognized standards demonstrates that recycled material meets its specification, which strengthens credibility with customers and helps reduce exposure to greenwashing challenges. In markets where recycled-content labeling is regulated, factual, test-based records become both a compliance tool and a competitive advantage. As your test and measurement partner, Industrial Physics helps quality, R&D, and operations experts build that evidence base.
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