{"id":4227,"date":"2026-06-27T05:25:13","date_gmt":"2026-06-27T05:25:13","guid":{"rendered":"https:\/\/kitech-recycling.com\/blog\/polymer-recycling-methods\/"},"modified":"2026-06-27T05:25:13","modified_gmt":"2026-06-27T05:25:13","slug":"polymer-recycling-methods","status":"publish","type":"post","link":"https:\/\/kitech-recycling.com\/pt\/blog\/polymer-recycling-methods\/","title":{"rendered":"Reciclagem de Pol\u00edmeros: M\u00e9todos, Tecnologias e Tend\u00eancias da Ind\u00fastria em 2026"},"content":{"rendered":"
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Updated June 2026 \u00b7 Reviewed by the Kitech technical team.<\/p>\n

Polymer recycling is the recovery and transformation of discarded plastic into usable material, and it can take the form of an endless circle (closed loop) or a one-way trip to fuel, and the path you follow – whether mechanical, chemical, or advanced – depends on where you start: your plastic feedstock, its family of resins, the degree of contamination, and current recycling laws (especially those set to kick in 2026).<\/p>\n

We provide here a roadmap to the four major recycling categories and their attendant technologies, which plastics actually get recycled, and emerging regulatory frame works from the trenches of equipment manufacturers.<\/p>\n

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Simply stated: Polymer recycling generally falls into four types, often defined as primary<\/strong>, secondary<\/strong> (both mechanical), tertiary<\/strong> (chemical), and quaternary<\/strong> (energy recovery), by standards like ASTM D5033 or classifications used by industry groups such as the ISO 15270 family.<\/p>\n

The most common method for processing the bulk of plastic waste, mechanical recycling, re-melts thermoplastics<\/strong>; chemical recycling involves deconstructing some plastics back to their basic elements. However, global recycling rates are dismally low, around 9% \u2014 and the recycling category of a material, rather than its resin code alone, determines whether you can achieve something approaching a circular economy.<\/p>\n<\/div>\n

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Polymer Recycling at a Glance<\/h3>\n
\n\n\n\n\n\n\n\n\n
The Polymer Recycling Method Family Tree: the four categories, what each does, and its typical output (per ASTM D5033 \/ ISO 15270).<\/caption>\n
Category<\/th>\nMechanism<\/th>\nOutput<\/th>\n<\/tr>\n<\/thead>\n
Primary<\/td>\nMechanical (clean scrap)<\/td>\nSame-grade product (closed-loop)<\/td>\n<\/tr>\n
Secondary<\/td>\nMechanical (mixed\/used)<\/td>\nLower-grade product (downcycling)<\/td>\n<\/tr>\n
Tertiary<\/td>\nChemical \/ depolymerization<\/td>\nMonomers or feedstock<\/td>\n<\/tr>\n
Quaternary<\/td>\nEnergy recovery (combustion)<\/td>\nHeat \/ electricity<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

The 4 Core Categories of Polymer Recycling (Method Family Tree)<\/h2>\n
\"The<\/figure>\n

These four routes apply across the full span of polymer types \u2014 from commodity polymers and other thermoplastic polymers to cross-linked thermoset polymers and engineered polymer composites \u2014 and they govern whether a polymer blend or a single polymer can re-enter production and recycling rather than disposal. The recycling of plastic is rarely one tidy recycling solution; in practice it spans recycling and upcycling across renewable and sustainable supply chains. A frequent and costly mistake is counting quaternary energy recovery as recycling on a sustainability report: it overstates circularity, fails an audit, and invites greenwashing scrutiny.<\/p>\n

You\u2019ll encounter four distinct groups of recycling technologies: primary, secondary, tertiary, and quaternary. While standards can differ in classification, the most consistent taxonomy comes from a peer-reviewed standards mapping<\/a> and ASTM D5033: Primary recycling occurs when the same resin is mechanically reworked into products with similar properties to the original material, completing a closed-loop system. Secondary recycling occurs when used, possibly mixed, plastics are mechanically reworked into products with lower performance requirements (also known as downcycling).<\/p>\n

Tertiary recycling consists of chemically breaking the plastic down into monomers (for potential monomer synthesis) or converting it into feedstock for the chemical industry. Finally, quaternary recycling converts energy through the controlled combustion of plastic waste.<\/p>\n

What often confounds readers-including industry veterans-is the different ways the two major recycling standards define these categories. The ASTM D5033 standard categorizes routes numerically from 1 to 4. Conversely, the ISO 15270 family defines categories by action type (mechanical, chemical, energy recovery) while combining what ASTM distinguishes as \u2018primary\u2019 and \u2018secondary\u2019 under a single heading \u201cmechanical recycling,\u201d differentiating them only by output quality.<\/p>\n

The transition within ISO standards-its 2008 single-point guide is being replaced by a series (Parts 3, 4, and a new 2025 Part 5 for organics\/biological)-has introduced a fifth category to be formally considered: industrial composting for certifiable \u201ccompostable\u201d plastics. Home composting, however, is outside<\/em> the purview of plastic recycling per se.<\/p>\n

\n
\ud83d\udca1<\/span> Key takeaway<\/strong><\/div>\n

The widely adopted waste hierarchy ranks the four types as follows, favoring high-value use of resources: \u2022 Primary (closed-loop mechanical): the best.<\/p>\n

\u2022 Secondary (downcycled mechanical) \u2022 Tertiary (chemical) \u2022 Quaternary (energy recovery): the least preferable alternative to landfill, and a useful check on vendors mislabeling incineration as \u201crecycling.\u201d\n<\/p><\/div>\n

Which Polymers Can Actually Be Recycled? (Resin Recyclability Decoder)<\/h2>\n
\"Which<\/figure>\n

A resin’s chemical structure and thermal stability decide its fate. In practice, only PET (#1) and HDPE (#2) are recycled at meaningful rates \u2014 about 29% of bottles in the U.S. \u2014 while PVC, polystyrene, and most #7 polymer materials are challenging to recycle and leave a buyer with few recycling options, because some polymers tolerate repeated reprocessing and most others simply do not.<\/p>\n

The Resin Identification Code \u2014 the chasing arrows with a number inside \u2014 tells you what the material is, not whether it\u2019s recyclable. Only the first two resin codes-#1 Polyethylene Terephthalate (PET) and #2 High-Density Polyethylene (HDPE)- are reliably recovered in any significant quantity in most streams.<\/p>\n

In the U.S., recycling rates for PET beverage bottles stand at 29.1%, while for natural HDPE beverage bottles it is 29.3%<\/a> (U.S. EPA 2018 data)-far exceeding the overall U.S. rate of 8.7% for plastics waste. All lower resin codes are largely contaminants within a sorted bale destined for recycling equipment.<\/p>\n

The \u201cResin Recyclability Decoder\u201d table shows you the commonality of recycling by each plastic code, and what sort of processing each typically undergoes.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Resin Recyclability Decoder: which polymer classes are recycled, by what method, into what (US 2018 EPA bottle rates where applicable).<\/caption>\n
Resin class (code)<\/th>\nReal-world recyclability<\/th>\nDominant method & output<\/th>\n<\/tr>\n<\/thead>\n
PET (1)<\/td>\nWidely recycled (~29% bottles)<\/td>\nMechanical \u2192 rPET flake\/fiber; chemical \u2192 monomer<\/td>\n<\/tr>\n
HDPE (2)<\/td>\nWidely recycled (~29% bottles)<\/td>\nMechanical \u2192 pipe, lumber, bottles<\/td>\n<\/tr>\n
PVC (3)<\/td>\nRarely curbside \u2014 stream contaminant<\/td>\nLimited mechanical; trace PVC ruins rPET<\/td>\n<\/tr>\n
LDPE\/LLDPE (4)<\/td>\nStore drop-off film only<\/td>\nMechanical \u2192 film, liners<\/td>\n<\/tr>\n
PP (5)<\/td>\nIncreasingly accepted (>60% US households, 2025)<\/td>\nMechanical \u2192 crates, automotive<\/td>\n<\/tr>\n
PS (6)<\/td>\nRarely recycled<\/td>\nLimited; depolymerization \u2192 styrene emerging<\/td>\n<\/tr>\n
PLA (7, bioplastic)<\/td>\nNot curbside; contaminates PET<\/td>\nIndustrial composting (organic route), not mechanical recycling<\/td>\n<\/tr>\n
PC (7, polycarbonate)<\/td>\nNiche; chemically recyclable<\/td>\nMethanolysis \u2192 BPA (95\u201396%)<\/td>\n<\/tr>\n
ABS (7, engineering)<\/td>\nLimited (e-waste, sortation-dependent)<\/td>\nMechanical regrind; density separation<\/td>\n<\/tr>\n
Multilayer \/ composite (7)<\/td>\n~5% recyclable conventionally<\/td>\nChemical (feedstock) only; immiscible bonded layers<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Rates: U.S. EPA Plastics Material-Specific Data (2018).<\/p>\n<\/div>\n

\u201cThermoset Plastic Recycling 101.\u201d The deeper divide is chemical, not numerical: thermoplastics (PET, PE, PP, PS) have linear chains that re-melt, so they can be mechanically recycled; thermosets<\/strong> (polyurethane foam, epoxy, flame-retardant and fiber-reinforced composites) are locked into a covalently cross-linked 3D network and cannot be re-melted at all<\/a>. That’s why a guide claiming \u201cthermosets are non-recyclable\u201d is half right and half outdated-they can\u2019t be melt-recycled, but chemical routes exist (polyurethane foam glycolysis recovers polyol, the most mature thermoset route), and reprocessable vitrimers are an active research frontier. To go deeper on the resin families, see our breakdown of the types of recyclable plastic and resin codes<\/a> and why thermosetting plastic behaves differently<\/a> from thermoplastics.<\/p>\n

Can thermoset plastics be recycled?<\/h3>\n

Not by melting. Thermosets such as polyurethane foam and epoxy are permanently cross-linked, so they can’t be re-melted and reshaped the way a PET bottle can. They’re recycled by chemical routes instead-polyurethane foam glycolysis recovers usable polyol, and that’s currently the only industrially mature thermoset chemical-recycling path.<\/p>\n

Otherwise thermosets are ground into filler or sent to energy recovery.<\/p>\n

Picture a reclaimer receiving a mixed curbside bale. The PET bottles and natural HDPE jugs have buyers; the PVC blister packs, the metallized snack film, and a stray polystyrene tray don’t.<\/p>\n

Worse, the operator can’t simply melt them together-PE, PP, PS, PA, and PET are largely immiscible and won’t co-melt into a usable resin. So the first real recycling decision happens at the sort, not the extruder, and it’s driven by what each resin\u2019s end market will actually pay for. Buyers exploring resin-specific lines often start with HDPE recycling<\/a>, ABS recycling<\/a>, or recycled LDPE<\/a>.<\/p>\n

Mechanical Recycling: How It Works (and Where It Hits a Wall)<\/h2>\n
\"Mechanical<\/figure>\n

Mechanical recycling of plastic is the dominant form of material recycling, but every pass drives polymer degradation \u2014 chain scission shortens polymer chains and erodes the thermal and mechanical properties batch after batch. A single lot of clear PET bottle flake shows the path in practice: its first mechanical loop can still yield food-grade rPET, but by the third or fourth remelt the falling intrinsic viscosity pushes it down into fiber and strapping, then into non-food uses \u2014 the same plastic three rungs down the value ladder within a few years.<\/p>\n

Mechanical recycling is the workhorse that handle the overwhelming majority of recycled plastic worldwide. It re-melts and reforms thermoplastics without breaking their chemical structure-at least in theory. In practice the polymer changes a little every pass, and that’s the wall every operator eventually meet.<\/p>\n

What are the stages of mechanical plastic recycling?<\/h3>\n

A mechanical recycling line runs four purpose-built stages: size reduction, washing and contaminant removal, drying and moisture control<\/a>, then pelletizing. On Kitech lines the chain runs as follows, with each stage sized to the feedstock’s particle size, contamination level, and moisture content, and the equipment matched to a throughput of 300 to 3,000 kg\/h so no single step becomes the bottleneck.<\/p>\n

    \n
  1. Shredding (size reduction):<\/strong> single- or two-shaft crushers cut waste to uniform 10-50 mm granules; motor power runs 15 kW for light film up to 200 kW for heavy HDPE drums and rigid ABS.<\/li>\n
  2. Washing:<\/strong> hot caustic washes at 60-85 \u00b0C dissolve adhesives and organic residue; friction washers spin at 900-1,200 RPM to abrade surface dirt; float-sink tanks separate by density (PET sinks above 1.0 g\/cm\u00b3, PP\/PE caps float).<\/li>\n
  3. Drying:<\/strong> centrifugal dryers and screw-press dewatering pull moisture from ~40% down to below 3%-miss this and the extruder produces bubbles and weak pellets.<\/li>\n
  4. Pelletizing:<\/strong> single- or two-stage extruders with 80-120 mesh melt filters remove fine contaminants and form clean pellets ready for the next molder.<\/li>\n<\/ol>\n

    Two of these stages decide output quality, see our deep dive on float-sink separation in plastic recycling<\/a> and how drying and moisture control protect pellet quality.<\/p>\n

    \n\ud83d\udcd0 Engineering Note: why mechanical recycling downcycles<\/strong><\/p>\n

    Each remelt cycle scissions polymer chains and reduces molecular weight. Bottle-grade PET going through four melt extrusion passes under controlled circumstances lost up to ~19% of intrinsic viscosity (from a nominal ~0.80 to ~0.65 dL\/g), ~29% of elongation at break, while crystallinity increased from 23% to 29.5% — the stuff gets brittle\/stiff.<\/p>\n

    That’s \u201cdowncycling\u201d as the process go, which leaves a number of demanding applications in other material uses. it’s why the plastic recyclate has to be diluted with virgin polymer or a barrier is put around it.<\/p>\n<\/div>\n

    There are two field factors that mean more to plastics recycling than the chemical textbooks ever could; firstly, mechanical recycling isn’t, strictly speaking, entirely a physical process-chain-scission of polypropylene, branched chains in polyamide, transesterification of PET\/polycarbonate during melt processing makes it a \u201cmaterial\u201d recycle for others; secondly, feedstock composition is the real capacity limitation: as low a level as fractions of percent of PVC in a PET load means a HCl emission will degrade the product; therefore, the material sort and composition management will be equipment issues on the load handling side, not afterthought process elements; the melt is recovered for the balance to be made up by chain extenders or by diluting with virgin resin.<\/p>\n

    Chemical Recycling: Breaking Polymers Back to Building Blocks<\/h2>\n
    \"Chemical<\/figure>\n

    Going beyond mechanical recycling, feedstock recycling \u2014 including the recycling of polyolefins and the recycling of polystyrene \u2014 uses heat, catalytic systems, and chemical agents to break polymer networks down to new polymer building blocks, while compatibilization of polymer blends keeps mixed mechanical streams usable.<\/p>\n

    Chemical processes rearrange a polymer\u2019s molecules.<\/p>\n

    Broadly speaking there are two streams here, which the industry doesn’t helpfully markets under one term: one is the chemistry that deconstructs polymers back to monomers (depolymerization, aka chemolysis, or solvolysis) to be re-inserted into plastics manufacturing, while another class is a physical-chemical breakdown process called conversion that takes sorted plastics waste and generates refinery (pyrolysis, gasification) Feedstock: to go back into the chemical plant. (Another niche process called dissolution isn’t covered).<\/p>\n

    For a process overview, the U.S. GAO describes the operating envelopes<\/a>: pyrolysis runs at 300-900 \u00b0C without oxygen to make synthetic crude; gasification runs at 500-1,300 \u00b0C in low oxygen to make syngas; and depolymerization uses heat, chemicals, catalysts, or enzymes, some near 40-70 \u00b0C. Conversion<\/strong> is the most established and furthest along in scaling; depolymerization sits in early pilots and purification is least mature.<\/p>\n

    According to peer-reviewed reviews<\/a>, representative PET depolymerization yields are: glycolysis (160-300 \u00b0C) recovers about 70-90% BHET monomer, methanolysis gives up to ~98% dimethyl terephthalate (DMT), and hydrolysis provides about 78-96% terephthalic acid (TPA) \u2014 exact figures vary with conditions and catalyst. The best enzyme systems work as low as 40-70 \u00b0C at similar yields. Polycarbonate methanolysis recovers ~95-96% BPA.<\/p>\n

    Nylon-6 yields caprolactam up to about 85-90% on total weight.<\/p>\n

    \n
    \u26a0\ufe0f<\/span> The bond that decides everything<\/strong><\/div>\n

    In addition, clean monomer recovery is currently only applicable to some condensation polymers such as PET, polycarbonate, nylon, and PLA because they are designed to contain an ester or amide group that is readily broken (cleavable). Olefin-based products such as the world’s top volume plastics – polypropylene (PP) and polyethylene (PE) – were never designed to contain such a differentially cleavable bond. As such, there is no way to break them down into their respective monomers selectively, so polyolefin recycling to monomer is off the table and the recycling of polymers like PE and PP stays mechanical or fuel-bound.<\/p>\n

    They can only be cracked nonselectively into various hydrocarbons via cracking. Therefore, chemical recycling, as is, will not work for “all plastics”.\n<\/p><\/div>\n

    Pyrolysis itself is a fuel process as much as a plastic process: a 2025 review found it converts 60-80% of plastic into liquid fuel<\/a> (up to 85% in fast pyrolysis at 450-600 \u00b0C), with pyrolysis oil selling at $600-900\/tonne. That basic distinction – feedstock versus fuel – is where the next section live.<\/p>\n

    And for an example of a downstream process related to depolymerization, we recommend a look at solid-state polycondensation for rPET<\/a>.<\/p>\n

    Advanced Recycling & Depolymerization: The Infinite Loop vs the 2026 Reality<\/h2>\n
    \"Advanced<\/figure>\n

    “Advanced recycling,” the process marketed as the circular economy panacea which will create infinite recycling. The patents are indeed there – Carbios with an enzymatic PET process delivering over 90% depolymerization in under 10 hours at 72 \u00b0C; Loop Industries patents glycolysis \/ methanolysis \/ hydrolysis routes to monomer. The reality in 2026 is however far more nuanced than the hype: most polymer recycling companies pursuing advanced polymer recycling have yet to prove the polymer recycling process out at commercial scale.<\/p>\n

    According to one industry estimate cited by Yale Environment 360<\/a>, of 2 million tons of advanced recycling capacity to come online, less than 500,000 tons will actually be new plastic, the remainder used as fuel. The track record is poorer still, with as of January 2025 only eight chemical-recycling plants active in the U.S.; an Indiana facility in the Brightmark pipeline has declared bankruptcy and hasn’t yet reached capacity, and the Department of Energy withdrew a $375 million contract in May 2025 for an Eastman facility, stating that such projects \u201caren’t economically feasible.\u201d The proposed capacity (more than 6 million tons\/year of plastic through 169 projects) remains enormously optimistic about reality.<\/p>\n

    \n

    “There’s a real lack of transparency about how much plastic they’re recycling.”<\/p>\n

    Veena Singla<\/strong>, Senior Scientist, Natural Resources Defense Council<\/cite>\n<\/p><\/blockquote>\n

    Chain-Integrity Spectrum: how deep each method cuts the polymer<\/h3>\n

    Here’s a handy mental model I’ve found — the “Chain-Integrity Spectrum,” reflecting how much impact a process has on the polymer chain: Mechanical recycling preserves chains but degrades them with every pass (finite reuse). Conversion cracks chains into mixed feedstock or fuel (loss of polymer identity). Depolymerization rebuilds chains by recovering virgin-quality monomer (true circularity, assuming it can run).<\/p>\n

    The further right on this chain of methods you get, the better the ideal loop — and the higher the cost, energy, and immaturity, all relative to a naive understanding. The honest truth for a purchasing team in 2026, if they decide this isn’t hype — economics not chemistry is the bottle-neck, because virigin plastic is still cheaper and the demand is still too narrow.<\/p>\n

    Mechanical vs Chemical vs Advanced: A Feedstock-to-Route Decision Tree<\/h2>\n
    \"Mechanical<\/figure>\n

    \u201cWhat\u2019s going into this are three input variables that feed a route decision tree\u2026 how clean and what single resin is your material?\u2026 what’s the polymer family?\u2026 what must that end use polymer qualify for?\u201d – This all leads to a purchasing call rather than just the science.<\/p>\n