Choosing a polymer antioxidant package for polyolefins is a formulation decision, a process-control decision, and a supply-risk decision at the same time. Polyethylene and polypropylene can encounter heat, oxygen, shear, catalyst residues, recycled feedstock, and repeated melt histories from resin production through compounding and final conversion. An additive package that protects one extrusion pass may not preserve color, melt flow, odor, or mechanical properties after recycling, long residence time, or demanding service.
For this reason, procurement teams should not compare Antioxidant 1010, Antioxidant 1076, and Antioxidant 168 only by price, assay, or product name. These materials perform different functions. Hindered phenols are commonly used as primary antioxidants, while phosphites such as 168 are secondary antioxidants and processing stabilizers. Their combined performance can be synergistic, but the useful ratio and dosage depend on the polymer, process, other additives, regulatory requirements, and intended lifetime.
This guide is intended for polyolefin resin producers, compounders, masterbatch manufacturers, recyclers, converters, technical buyers, and quality managers. It explains how to build a qualification program around actual polymer performance. Examples from commercial technical literature illustrate principles; they are not universal dosage recommendations. Final approval requires controlled trials in the buyer's resin, equipment, and complete formulation.
Executive Buying Summary
A technically sound purchasing program begins with the degradation risk, not with an additive catalog. Define whether the main challenge is melt processing, long-term heat exposure, color retention, recycled-content variability, outdoor use, food-contact documentation, low odor, extraction resistance, or several of these at once.
The usual roles can be summarized as follows:
- Antioxidant 1010 is a high-molecular-weight hindered phenolic primary antioxidant widely considered for long-term thermal stabilization and relatively low volatility.
- Antioxidant 1076 is a hindered phenolic primary antioxidant with different molecular structure, compatibility, mobility, and application behavior from 1010.
- Antioxidant 168 is a phosphite secondary antioxidant used mainly to decompose hydroperoxides during processing and to support color and molecular-weight retention.
- A phenol/phosphite blend can provide broader protection than either component alone because it interrupts different parts of the oxidation cycle.
These descriptions are functional starting points, not proof of equivalence between suppliers. Buyers should qualify the exact grade, origin, physical form, specification, and formulation. An identical CAS number does not guarantee identical particle form, impurity profile, hydrolytic history, handling, or application performance.
A defensible decision should answer five questions. Does the package protect melt flow or rheology through realistic heat histories? Does it control initial color and color development? Does it deliver the required long-term stability after processing consumption? Is it compatible with pigments, fillers, light stabilizers, acid scavengers, and the resin? Can the supplier demonstrate consistent quality, traceability, regulatory support, and reliable logistics?
The Industry Pain Points Behind Antioxidant Failure
The first pain point is under-stabilization. Insufficient protection can allow chain scission in polypropylene, crosslinking or branching tendencies in some polyethylene conditions, discoloration, odor formation, loss of elongation, surface defects, or unstable processing. The failure may not be obvious during initial pellet inspection. It can emerge during customer conversion or after thermal aging.
The second pain point is indiscriminate over-dosing. More antioxidant is not automatically better. Excess additive can increase cost and may contribute to blooming, deposits, odor, color, migration, printing or sealing problems, or compliance complexity. Antioxidants are consumed by reactions and can interact with other formulation components. The optimum is a validated performance window, not the highest practical addition level.
The third problem is confusing processing stability with long-term stability. A phosphite can be highly effective during melt conversion, while a hindered phenol supports radical scavenging and longer protection. A package that produces excellent initial color may still be inadequate for elevated-temperature service. Conversely, a formulation designed only for long-term aging may lose too much stabilizer or molecular integrity during repeated extrusion.
The fourth problem is approving a laboratory sample without studying commercial lots. Moisture, particle size, physical form, residual impurities, assay, and packaging can influence dosing and performance. Phosphites also require careful protection from moisture. A qualification based on one fresh sample may not represent a shipment stored or transported under different conditions.
Finally, buyers sometimes rely on a standard product number as if it were a complete specification. Product identity must be supported by analytical methods, release limits, traceability, application data, and change control. Procurement needs evidence that connects chemical identity to manufacturing consistency.
How Polyolefin Oxidation Develops
Polymer oxidation is commonly described as a radical chain process with initiation, propagation, and termination. Heat, shear, oxygen, light, metal contamination, and pre-existing hydroperoxides can contribute to radical formation. Polymer radicals react with oxygen to form peroxy radicals. These can abstract hydrogen from polymer chains, generating hydroperoxides and new radicals. Hydroperoxides can decompose into additional reactive species, accelerating degradation.
The practical effects depend on polymer structure and conditions. Molecular-weight change alters melt viscosity and mechanical performance. Chromophores and oxidation products can create yellowing, odor, taste, or volatile emissions. The material may appear acceptable after one mild pass but deteriorate more rapidly during later processing because oxidation intermediates have accumulated.
Antioxidants interrupt this cycle through different mechanisms. Primary antioxidants react with radical species. Secondary antioxidants convert hydroperoxides into less reactive products before those hydroperoxides decompose into new radicals. This division of work explains why combinations are often valuable.
Antioxidants are not regenerative shields with infinite capacity. They are consumed or transformed. Processing temperature, oxygen availability, residence time, surface-area exposure, shear, contamination, and previous history affect how much remains for later service. Therefore, the retained stabilizer state after extrusion can matter as much as the initial dosage.
Primary Antioxidants: The Roles of 1010 and 1076
Sterically hindered phenols are a major class of primary antioxidants for polymers. They donate hydrogen to reactive radicals and form more stable phenoxy species, interrupting propagation. Their structure influences volatility, compatibility, extraction resistance, mobility, melting behavior, and processing.
Antioxidant 1010 is often selected where low volatility and long-term thermal stabilization are important. Its relatively high molecular weight can support permanence in many polymer systems. It is frequently used in polyethylene, polypropylene, engineering polymers, elastomers, adhesives, and other organic substrates, subject to application-specific approval.
Antioxidant 1076 is also a widely used hindered phenol. Its structure and physical properties differ from 1010, so formulators may choose it for compatibility, handling, processing, or performance reasons. It should not be treated as a drop-in replacement merely because both are primary antioxidants.
Comparing 1010 and 1076 requires the same resin, additive package, thermal history, and specimen preparation. Useful endpoints include initial color, melt-flow change, oxidation induction behavior, long-term oven aging, retained mechanical properties, extraction or migration where relevant, odor, and deposits. The preferred result may differ between thick molded parts, film, fibers, recycled compounds, and high-temperature components.
Secondary Antioxidants: Why 168 Matters During Processing
Antioxidant 168 is a phosphite secondary antioxidant. Its principal role is to react with hydroperoxides formed during autoxidation, reducing their ability to generate further radicals. Commercial technical literature commonly positions phosphites as processing stabilizers and highlights their synergy with hindered phenols.
During extrusion and molding, this function can help limit molecular-weight change and discoloration. However, performance is formulation-specific. Processing temperature, water exposure, acid scavenger, catalyst residues, pigments, fillers, and residence time can influence results. The material's condition before dosing also matters because phosphite chemistry can be affected by hydrolysis.
A certificate stating assay alone may not predict processing behavior. Relevant supplier controls can include appearance, assay by an agreed method, melting range, volatile matter, solution clarity or transmission where appropriate, acid value or related hydrolysis indicators, and application-specific color. Buyers should agree on which measures correlate with their process.
The Hengyi Antioxidant 168 technical data describes the product as a processing stabilizer used with primary antioxidants. It is useful for initial screening, while the buyer's multiple-pass extrusion and analytical work should determine final dosage and suitability.
Why Phenol and Phosphite Combinations Are Synergistic
Synergy arises because the additives address complementary stages of oxidation. A hindered phenol helps remove radical propagators, while a phosphite decomposes hydroperoxides. Protecting the polymer also reduces the burden on the primary antioxidant; protecting the primary antioxidant during processing can leave more useful capacity for storage and service.
This does not mean that one fixed ratio is universally correct. Technical suppliers offer blends with different phenol-to-phosphite ratios because processing severity and long-term requirements vary. A resin producer making a general-purpose pellet, a converter reprocessing scrap, and a manufacturer of a long-life hot-water component need different optimization.
The correct comparison is a response surface. Test a controlled range of total antioxidant loading and component ratio. Plot melt-flow retention, color, oxidation induction, aging, and cost. A useful package sits in a robust region where normal dosing and process variation do not push production beyond limits.
Selecting a Package for PE and PP Applications
Polypropylene
Polypropylene can undergo chain scission during thermo-oxidative processing, often observed as an increase in melt-flow rate. Multiple extrusion passes provide a practical stress test. A successful package limits the change in melt flow, color, and mechanical behavior under defined conditions. Fiber and thin-wall applications may require particularly careful color and processing control because high surface area or severe conversion can expose weaknesses.
HDPE and LLDPE Film
Film producers evaluate gels, odor, color, die deposits, sealing, optical appearance, and stable extrusion. Polyethylene degradation behavior differs from polypropylene and may include molecular growth or crosslinking under some conditions. The test program should measure melt flow or rheology in the direction relevant to the resin rather than assuming every polymer fails the same way.
Injection and Blow Molding
Long residence time, scrap regrind, hot runners, and repeated startup cycles can challenge stabilization. Molded plaques should be compared at identical thickness and processing history. For blow molding, molecular architecture is critical to melt strength, so rheological change may be more informative than color alone.
Recycled Polyolefins
Recycled feedstock arrives with unknown or variable previous stabilization, contamination, and oxidation history. Adding a standard dose without characterizing the feed can produce inconsistent results. Use incoming melt flow, carbonyl or oxidation indicators where available, color, odor, contamination, and controlled reprocessing to design restabilization. Antioxidants cannot restore polymer chains that are already irreversibly damaged.
Filled and Pigmented Compounds
Fillers and pigments may contain moisture, metals, acidic or basic sites, surface treatments, and absorbed contaminants. These can change stabilizer demand or interactions. Carbon black, titanium dioxide, organic pigments, mineral fillers, flame retardants, and recycled content should be included in the qualification formulation. Testing antioxidants in unfilled resin alone can miss the commercial risk.
Critical Formulation Interactions
Acid scavengers can support processing by neutralizing acidic residues, but their type and level can affect other additives. Light stabilizers and UV absorbers address photodegradation through different mechanisms and are not interchangeable with thermal antioxidants. Lubricants, slip agents, antistats, nucleating agents, peroxide residues, and pigments can change dispersion, migration, color, or analytical results.
Gas fading is a specific color concern associated with reactions involving certain phenolic structures and nitrogen oxides in the environment. The risk depends on antioxidant, polymer, pigments, exposure, and storage. Where sensitive white or pastel products are involved, conduct an appropriate gas-fade or warehouse-exposure comparison rather than relying on a generic non-yellowing claim.
Phenolic antioxidants can also interact with some colorants or create color bodies after reaction. Color must be measured after realistic processing and aging, not only on the additive powder. A supplier should ask about the complete additive and pigment package before recommending a grade.
Testing Matrix for Technical Qualification
| Performance question | Useful method or observation | Why procurement should care |
|---|---|---|
| Is molecular weight protected? | Melt-flow rate plus capillary or oscillatory rheology | Predicts process and property consistency |
| Is processing color controlled? | L*, a*, b*, yellowness after each extrusion pass | Quantifies initial and developing color |
| Is oxidation resistance retained? | OIT or other agreed thermal-oxidation method | Compares remaining stabilization under set conditions |
| Does long-term protection work? | Oven aging with defined failure criteria | Tests service-related thermal endurance |
| Are mechanics retained? | Tensile, elongation, impact or application-specific tests | Connects chemistry to usable performance |
| Is dosage consistent? | Validated additive assay or extraction method | Verifies compounding and supplier consistency |
| Is 168 in acceptable condition? | Agreed assay, acid/hydrolysis indicator and appearance | Helps identify moisture-related deterioration |
| Will the package create defects? | Plate-out, deposits, odor, volatile and blooming observations | Protects conversion and customer acceptance |
| Is the material consistent? | Same application protocol across several lots | Tests commercial reproducibility |
Methods must be documented completely. Melt-flow rate requires temperature and load. OIT requires a named method, specimen, atmosphere, heating program, and endpoint. Color needs instrument geometry, illuminant, observer, background, and sample thickness. Oven aging requires temperature, airflow, specimen geometry, and failure definition.
OIT can be useful for comparative quality control, but it is not a universal service-life predictor. Different antioxidants may produce different OIT responses, and specimen preparation can affect results. Use it alongside processing and aging tests rather than as the only acceptance criterion.
Building a Multiple-Pass Extrusion Trial
Multiple-pass extrusion is one of the most informative tools for a processing-stabilizer package. Begin with a well-characterized polymer and compare an unstabilized or minimally stabilized control, the incumbent package, and candidates. Keep resin lot, feeder calibration, screw configuration, temperature profile, screw speed, throughput, residence time, cooling, and pelletizing constant.
Take samples from the first pass and subsequent passes selected to represent the commercial risk. Three to five passes are common comparative designs, but the appropriate number depends on the polymer and purpose. Record melt temperature, torque, pressure, output, odor, smoke, strand behavior, pellet appearance, and equipment deposits.
After every pass, measure melt flow and color. Add rheology if small molecular changes are commercially important. Mold or extrude standard specimens for mechanical testing and OIT. Retain sealed samples. The objective is not to create an artificial winner at extreme conditions; it is to reveal how packages diverge as thermal history accumulates.
Interpret trends rather than isolated readings. In polypropylene, a rapid melt-flow increase can indicate chain scission. A stable initial color followed by strong yellowing may show that processing protection is being exhausted. A high OIT with unacceptable deposits is not a commercially balanced result. Technical and operations teams should agree on the complete pass criteria before seeing supplier identities.
Long-Term Heat Aging and Real Service Conditions
Long-term heat-aging tests expose specimens at a controlled temperature and inspect them at intervals. Failure may be defined by embrittlement, cracking, loss of tensile elongation, color limit, or another application-specific endpoint. Because specimen thickness and airflow affect oxygen exposure, comparisons require identical geometry.
Accelerated aging is comparative. It should not be converted casually into an exact field lifetime. Actual service includes variable temperature, stress, chemicals, light, washing, extraction, and oxygen. Where failure has high consequence, correlate accelerated work with appropriate real-use or field data.
The processing trial and aging trial must be connected. Testing a freshly mixed specimen can overstate protection if commercial material loses antioxidant during extrusion. Prepare aging specimens from pellets or articles that have experienced the intended processing history.
Color, Yellowing, Odor, and Volatiles
Color is often the first customer-visible signal. Measure the additive powder and the processed polymer, but prioritize the final article. Initial color, color after repeat processing, thermal aging, UV exposure, and gas-fade exposure answer different questions.
Odor and volatile requirements are application-specific. Packaging, automotive interiors, household goods, and medical-related products may have stricter expectations than general industrial parts. Do not describe a material as odorless without a defined method and threshold. Use sensory panels or analytical screening appropriate to the product and applicable requirements.
Deposits may originate from antioxidant, degradation products, lubricants, pigments, or interactions. A controlled blank and reference formulation help isolate the cause. Examine die lips, vents, molds, chill rolls, and downstream equipment over sufficient production time.
Hydrolysis, Storage, and Handling of Phosphites
Phosphite processing stabilizers require appropriate moisture protection. Hydrolysis can change product condition and performance. Packaging integrity, warehouse humidity, temperature, opened-bag practices, transport history, and shelf life therefore belong in the qualification program.
Incoming inspection should look for damaged bags, caking, unusual odor or appearance, and deviations in agreed analytical controls. Keep packages sealed until use, follow supplier storage instructions, apply first-in-first-out management, and avoid returning contaminated material to original containers.
For international supply, review bag liner, pallet protection, container humidity risk, shipment duration, and seasonal conditions. A low-cost source can become expensive if phosphite arrives out of condition or creates feeding inconsistency. Retained samples from receipt and production support root-cause analysis.
Separate Components Versus One-Pack Blends
Purchasing 1010 or 1076 and 168 separately gives formulators ratio flexibility. It can also create additional weighing, feeding, inventory, dust, and dosage-error risk. A pre-blended one-pack can improve handling and dosing consistency if blend uniformity and segregation are controlled.
The economic comparison should include feeder count, labor, cleanup, dust management, inventory, batch errors, production changeover, and working capital. A one-pack is not automatically homogeneous under all transport and conveying conditions. Buyers should evaluate particle-size compatibility, bulk density, flow, segregation, and concentration uniformity from different package locations.
Approve the exact blend composition and tolerances. Request the component identities, nominal ratio, release controls, and change-notification terms to the extent commercially available. A proprietary blend still needs enough technical and compliance documentation for the buyer to assess suitability.
Supplier Documentation and E-E-A-T Evidence
A reliable supplier should provide a current technical data sheet, safety data sheet for the destination, specification, certificate-of-analysis format, test methods or method references, manufacturing origin, packaging, storage, shelf life, lot coding, and change-notification policy. Application-specific regulatory documentation must be reviewed by qualified compliance personnel. A generic statement does not prove suitability for every food-contact, medical, automotive, or electrical use.
Ask how identity and assay are confirmed, how impurities and color are controlled, how reference standards are managed, and how out-of-specification results are investigated. For blends, ask how uniformity is validated. For 168, discuss moisture protection and relevant hydrolysis controls.
Technical credibility is also shown by application support. A responsible supplier will ask about polymer grade, catalyst system, processing temperature, residence time, recycle passes, pigments, fillers, light stabilizers, article geometry, service temperature, and compliance market. It should recommend a trial range rather than promise a universal dosage.
Hengyi's antioxidants product hub and antioxidants for plastics and masterbatch page provide initial product context for 1010, 1076, and 168. Buyers should combine product documentation with retained samples, representative commercial lots, and their own application protocol.
Total Cost Rather Than Price per Kilogram
Antioxidants are used at relatively low concentration, so small differences in additive price may have limited impact on finished-product cost compared with scrap, downtime, customer rejection, or reduced service life. Calculate cost per acceptable metric ton of compound or converted product.
Include dosage, freight, duties, inventory, testing, feeder losses, dust collection, packaging disposal, output, energy, deposits, cleaning, off-color scrap, and complaint risk. If a higher-performing package allows lower total dosage, fewer components, more recycled content, or a wider process window, quantify the benefit through trial data.
Avoid claiming savings from supplier data alone. A commercial trial should establish the baseline and confidence range. Procurement can then negotiate against measured value while quality protects the approved technical window.
Common Troubleshooting Patterns
Melt Flow Changes Too Rapidly
Confirm actual additive concentration, feeder calibration, resin lot, process temperature, oxygen exposure, residence time, and previous heat history. Compare the primary/secondary balance and retained antioxidant. Check whether contamination or peroxide is present before simply increasing dosage.
Polymer Yellows During Processing
Separate initial additive color from reaction color and polymer degradation. Review phenol/phosphite ratio, phosphite condition, acid scavenger, nitrogen-oxide exposure, pigments, catalyst residues, temperature, and residence time. Use controlled plaques and instrumental color after each pass.
OIT Is Low but Processing Looks Acceptable
The processing stabilizer may have protected melt conversion while leaving insufficient long-term capacity, or the OIT method may respond differently to the package. Verify method, specimen history, and primary-antioxidant level. Add aging and mechanical tests before changing formulation.
Powder Cakes or Feeds Inconsistently
Inspect moisture exposure, packaging, storage, particle form, bulk density, electrostatic behavior, and conveying. Compare unopened retained material with the affected bag. For one-packs, test segregation and component uniformity.
Deposits or Blooming Appear
Review compatibility, total loading, molecular weight, additive interactions, cooling, migration, and surface temperature. Identify the deposit analytically where possible. An antioxidant may be involved, but lubricants, slip agents, fillers, and degradation products are alternative sources.
B2B Supplier Qualification Scorecard
A balanced scorecard can assign 40% to application performance, 20% to analytical quality and lot consistency, 15% to documentation and compliance support, 15% to supply reliability, and 10% to total cost. Adjust the weights for application risk.
Application performance should include multiple-pass processing, color, rheology, OIT or agreed oxidation metric, aging, and defects. Quality scoring should include representative lots, method alignment, impurity or hydrolysis controls, blend uniformity, and traceability. Supply evaluation should address qualified capacity, lead time, packaging, contingency plans, and shipment accuracy.
Do not approve only a supplier name or CAS number. Approve the grade, physical form, manufacturing origin if relevant, specification revision, package or blend ratio, and intended application. State what changes trigger notification and requalification.
Procurement and Trial Checklist
- Define polymer, catalyst system, formulation, process temperatures, residence time, recycle passes, service environment, and compliance market.
- Identify whether processing stability, long-term heat stability, color, odor, extraction resistance, or several requirements drive the project.
- Request specification, TDS, SDS, sample COA, methods, origin, packaging, storage, shelf life, and change policy.
- Compare an incumbent, controls, and candidates using one resin lot and a written multiple-pass protocol.
- Test more than one representative commercial lot when volume and consequence justify it.
- Measure melt flow and/or rheology, color, oxidation stability, aging, mechanics, deposits, and odor as relevant.
- Validate the complete formulation including pigments, fillers, recycled content, light stabilizers, and acid scavengers.
- Calculate total cost per acceptable finished unit.
- Retain additive, compound, and finished specimens with complete batch and process records.
Frequently Asked Questions
What is the difference between Antioxidant 1010, 1076, and 168?
1010 and 1076 are hindered phenolic primary antioxidants that scavenge radical species. 168 is a phosphite secondary antioxidant that decomposes hydroperoxides and is particularly associated with processing stabilization. Their structures and application behavior differ, so substitution requires testing.
Why combine Antioxidant 1010 or 1076 with 168?
The combination addresses complementary parts of the oxidation cycle. The phosphite helps control hydroperoxides during processing, while the hindered phenol provides radical-scavenging and longer-term protection. The useful ratio is formulation- and process-specific.
What dosage should be used in polypropylene or polyethylene?
There is no universal dosage. Resin type, catalyst residues, processing severity, recycled content, pigments, service life, and compliance constraints determine the useful range. Screen a controlled concentration and ratio matrix, then confirm it in production.
Is OIT enough to qualify an antioxidant package?
No. OIT is a comparative method under defined conditions. Combine it with multiple-pass extrusion, melt-flow or rheology, color, long-term aging, mechanical properties, and defect observations. Different chemistries may not rank identically in every test.
How should multiple-pass extrusion be evaluated?
Keep material and processing conditions constant, sample after defined passes, and track melt flow, rheology, color, pressure, torque, odor, deposits, and final properties. Compare trends against an incumbent and pre-agreed limits.
Can more antioxidant always improve service life?
No. Performance may plateau, and excessive additive can create cost, migration, blooming, deposits, odor, color, or compliance problems. Optimize a robust window rather than maximizing concentration.
Why does Antioxidant 168 require moisture control?
Phosphites can be affected by hydrolysis. Packaging integrity, storage, transport, opened-bag handling, and analytical condition can influence processing performance. Follow supplier guidance and define appropriate incoming controls.
Are products with the same CAS number interchangeable?
Not automatically. Assay, impurities, color, physical form, particle distribution, moisture history, packaging, blend uniformity, and manufacturing consistency can differ. Approve a specific grade and supplier through analytical and application testing.
Should a buyer use separate antioxidants or a one-pack blend?
Separate components provide ratio flexibility. One-packs can reduce weighing, feeding, dust, and inventory complexity. Compare blend homogeneity, segregation, dosing accuracy, cost, formulation flexibility, and documentation.
What information should be included in a supplier inquiry?
Provide polymer grade, process, temperature, number of heat histories, current package and dosage, pigments or fillers, recycled content, target color and stability, compliance market, annual volume, destination, and current failure mode.
Conclusion: Qualify the Package as a Performance System
A polymer antioxidant package for polyolefins should be purchased as a verified stabilization system, not as three interchangeable commodity numbers. Primary hindered phenols and secondary phosphites perform different jobs, and their synergy depends on ratio, dosage, resin, process, and the complete additive environment.
The strongest procurement decision combines mechanism-based formulation, multiple-pass extrusion, color and rheology trends, oxidation and aging data, commercial-lot consistency, documentation, logistics, and total cost. This approach reduces the risk of solving an initial-color problem while creating a service-life problem—or selecting a low-price additive that increases conversion cost.
To discuss an antioxidant qualification project, use the Hengyi contact page and share the polymer, processing temperature, number of extrusion passes, current formulation, target performance, annual demand, and destination. This information supports a more relevant 1010, 1076, 168, or blended-package evaluation and sample plan.
Technical References
- BASF, Antioxidants for plastics: primary hindered phenols, secondary phosphites and thioesters, and synergistic combinations.
- BASF, Irgafos 168 Technical Information: processing stabilization and hydroperoxide decomposition.
- BASF, polyolefin packaging case study using multiple-pass extrusion and rheological evaluation. Results are formulation-specific.
- SONGWON, Recent Aspects of Polypropylene and Polyethylene Stabilization and polymer stabilizer technical portfolio.
