A material label on a resin bag does not, by itself, show what entered a molded part. For an overseas sourcing program, the buyer should decide what must be known about the approved resin route, any reclaim generated during molding, and the finished lots that may contain it. That decision should be written before quotation or trial production, because a supplier cannot apply a meaningful regrind rule when the permitted source, percentage basis, part risk, and approval owner are undefined.
Requirements are the controlled obligations in the drawing, material specification, purchase order, quality agreement, applicable market rules, or customer-specific documents. Recommendations are evidence requests that help the buyer compare suppliers when those documents are silent. Neither a general material certificate nor a supplier statement that it uses “closed-loop regrind” proves that a particular molded-part lot meets its intended use. The suitable controls depend on the resin grade, geometry, runner and tool architecture, machine and material-handling route, end market, and contract terms.
Approve a defined regrind route, not a percentage in isolation: identify the source, eligibility, handling, blend basis, part-specific verification, and written authority for any exception.
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1. Set the material boundary before asking for records
Start with one controlled material statement for each part revision. It should name the resin manufacturer and exact grade when they are buyer-controlled, colorant or additive condition where relevant, permitted alternatives, and whether regrind is prohibited, conditionally permitted, or outside the current approval. Define the traceability unit that supports the actual decision: for example, a finished-part lot, production order, run, or shipment. The aim is not to demand every machine setting or a supplier’s proprietary formulation. It is to make it possible to identify the approved material route used for the parts under review and to contain affected product if a question arises.
Use precise terms. In-house regrind from identified sprues, runners, trim, or eligible molded rejects is not automatically the same as externally supplied post-industrial material, post-consumer recycled content, purge, start-up scrap, or mixed reclaim. UL Solutions distinguishes in-house molding scrap reused at the molder from material sent to another molder, where traceability is compromised and the material becomes a post-industrial mechanically recycled source.[3] The buyer should require the supplier to declare the proposed category and source rather than treating all recovered polymer as one interchangeable input.
A recommendation for lower-risk parts may be a finished-lot link to the material and regrind status. A requirement for a safety-relevant, regulated, load-bearing, appearance-critical, or tightly specified part may be more detailed, but only when the product specification or risk assessment supports it. ISO 22095 provides a framework for chain-of-custody terminology and models, while cautioning that a chain-of-custody system alone does not verify a material or product claim.[2] The acceptance record must therefore connect material information to the actual part requirements, not merely confirm that a record exists.
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2. Specify which regrind is eligible and how it remains identifiable
If regrind is permitted, the buyer should define the eligibility boundary before production. Useful questions are: Which source materials may be reclaimed? Must the source be the same approved grade, color, filler condition, and program? Are start-up parts, rejected parts, purge, off-color material, or material from another tool excluded? May reclaimed material be transferred between sites? The answer should be project-specific. A blanket instruction to use “clean regrind” does not resolve source history, accidental mixing, thermal exposure, moisture pickup, or whether a rejected part was rejected for a material-related reason.
Request a supplier work instruction that covers collection, container labeling, segregation, grinder cleaning or line clearance, storage, material preparation, and disposition of non-eligible scrap. For a representative TPU grade, Covestro permits a limited amount of regrind only where end-use requirements allow, and calls for clean, uncontaminated material from defined sources, proper drying, blending with virgin resin, and finished-part testing; it also warns that limits and suitability are grade- and application-specific.[4] That guidance is not a universal percentage or rule for other polymers. The resin maker’s current instructions and the buyer’s part requirements should govern the proposed route.
Make reprocessing history visible. A regrind container can be labeled with a source lot or run, part and material identifier, color or additive condition, date, status, and the number of permitted regrind cycles if the project uses such a control. Where the supplier combines virgin and regrind material, it should record the agreed blend basis and the run or finished lot that received it. The buyer does not need to prescribe a universal label format; it needs an agreed method that prevents unapproved material from being mistaken for approved material.
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3. Compare supplier controls against the same approval matrix
Ask every bidder to complete the same material-and-regrind matrix. It makes hidden differences visible: one supplier may propose a cold-runner reclaim loop, another a hot-runner system with little reclaim, and a third an externally purchased recycled compound. These are not equivalent routes even when the quoted part material has the same generic polymer name. The matrix is a procurement tool, not a substitute for a resin supplier recommendation, part testing, or a regulated-product assessment.
The buyer should turn the final column into explicit release gates. A supplier may recommend a different control where it can explain the risk and supply comparable evidence. No supplier should treat a missing buyer instruction as permission to introduce regrind, change its source, or ship a lot with incomplete material status.
| Decision area | Buyer should specify or compare | Supplier evidence to request | Acceptance or approval point |
|---|---|---|---|
| Approved material route | Exact grade or permitted grade family, manufacturer or source policy, color/additive condition, and whether regrind is prohibited or allowed. | Controlled material list, current data-sheet reference, proposed material-flow description, and declared exclusions or assumptions. | Buyer approves the defined material route before trial or production; an unlisted substitute needs the agreed change path. |
| Regrind eligibility | Allowed source categories and exclusions, including the status of runners, trim, start-up scrap, rejected parts, purge, off-color material, and external reclaim. | Regrind work instruction, source labels or examples, segregation and grinder-cleaning controls, and non-eligible scrap disposition. | Approve only the sources that are identified and supported by the material and part-risk review. |
| Maximum use and blend basis | Whether a maximum is required, how the percentage is calculated, and whether it applies to a shot, run, finished lot, or another stated basis. | Mixing or feed-control record, declared calculation basis, actual run record, and any supplier or resin-maker limitation relevant to the proposal. | Approve the project-specific limit and basis before sampling; do not infer either from a generic recycled-content claim. |
| Material condition | Handling, storage, drying or conditioning expectations where relevant to the selected resin and use case. | Material-preparation record, container status, line-clearance evidence, and exception or disposal record when material condition cannot be confirmed. | Accept the record only in combination with the defined part inspection or functional evidence; preparation records alone do not prove performance. |
| Part-lot linkage and exceptions | Required link from the molded-part lot to its material and regrind status, record retention, retrieval target, and notification triggers. | Lot or run record, inspection or release record, deviation report, and a controlled sample of backward retrieval if risk justifies it. | Release the lot only when required material status and any deviation disposition are complete under the quality agreement. |
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4. Request evidence that supports the sample and production decision
Before a mold trial, request a concise, revision-controlled evidence pack: the buyer material specification; the supplier’s declared material route; the regrind instruction and percentage basis if applicable; tool and runner configuration relevant to reclaim; the planned sample identification; and the proposed inspection or functional checks. If the supplier relies on a resin maker’s permitted regrind guidance, request the exact grade document and confirm that its conditions are applicable to the proposed use. Do not accept a broad statement about the resin family as evidence for an unnamed grade or a different end-use condition.
For sample approval, require the supplier to identify what the sample represents. Record the part and drawing revision, tool or cavity coverage where relevant, machine or production condition as agreed, virgin and regrind status, material lot or source record as required, and inspection or functional results against the agreed criteria. A sample made with no regrind does not automatically validate a later production lot that contains it. Conversely, a sample containing approved regrind does not approve a new source, a higher percentage, an altered colorant, or a different reprocessing route.
For routine supply, use a record set that is proportionate to risk. It can include the finished-part lot, material identity, regrind status or declared percentage basis, release disposition, quantity, and shipment identifier, plus inspection results when contracted. NIST’s manufacturing traceability framework emphasizes organizing, linking, and querying traceability data across stakeholders; a buyer can request a retrievable evidence chain without demanding unrestricted access to a supplier’s systems.[1] Agree a mock retrieval for higher-risk programs, including scope, response time, confidentiality limits, and pass criteria.
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5. Approve changes and deviations before they become material history
Write material and regrind triggers into the purchase specification or quality agreement. Examples that may require prior written notification or approval include a grade, manufacturer, distributor, additive, colorant, external recycled-content source, permitted regrind percentage, regrind eligibility rule, grinder or material-handling route, mold runner change, mold repair that changes reclaim source, production-site transfer, or a new reprocessing step. The correct response may be document review, new samples, targeted testing, revalidation, or a new release decision. It should be based on the affected requirement and contract, not on an assumption that every change has the same consequence.
When material identity, source eligibility, blend basis, or preparation record is missing, the supplier should segregate the affected material and product, investigate the scope, and seek the agreed disposition before shipment. A concession should identify the affected lots, actual condition, evidence reviewed, proposed containment, authorizing role, and expiry. It should not convert an unverified material route into a permanent approval. UL notes that recycled-plastic evaluation paths and ongoing quality assurance can depend on source identification and consistency, illustrating why a recycled-content statement and a part-performance conclusion need separate evidence.[3]
Keep the final approval revision-specific. The buyer’s release should identify the part and material baseline, permitted regrind rule, evidence reviewed, deviations accepted, applicable lot or period if limited, and future re-approval triggers. This creates a practical shared reference for procurement, quality, engineering, and supplier-management teams. It does not guarantee mold life, dimensional performance, cycle time, price, certification, or product compliance; those outcomes remain dependent on the actual resin, geometry, tool architecture, machine, market, verification method, and commercial terms.
Practical takeaway
Before you move
to the next review.
- Define the exact resin route, permitted alternatives, color or additive condition, traceability unit, and the written authority that can approve a material exception.
- State whether regrind is prohibited, conditionally permitted, or allowed only from named in-house sources; exclude or approve each other recovered-material category explicitly.
- Request the supplier’s regrind work instruction, source and container identification method, segregation and grinder-cleaning controls, material-preparation record, and non-eligible scrap disposition.
- Approve a project-specific maximum and percentage basis only after reviewing the named resin guidance, proposed source route, part requirements, and representative sample or verification plan.
- Set written gates for trial, first-sample, routine-lot release, deviations, and material or regrind changes, including the records, approver, and retrieval or notification expectations.
FAQ
Common questions
Is in-house regrind the same as recycled resin purchased from another supplier?
No. In-house reclaim can have a more direct source link when it is collected and controlled within the molding route, while externally supplied recycled material may have a different source history, processing history, and evidence route. Define the material category, source controls, applicable resin guidance, and required part verification separately. Neither route should be assumed suitable solely because it is described as recycled or closed loop.
What regrind percentage should a buyer allow for an injection molded part?
There is no universal percentage. The permitted amount, if any, should be based on the exact resin grade, source and condition of the reclaim, pigment or filler system, geometry, runner architecture, end-use requirements, applicable market rules, and contract. Ask the supplier to state its calculation basis and supporting evidence. Record a written project limit only when the responsible engineering and quality authorities approve it.
What records prove a molded part used only approved material?
The required proof depends on the agreed traceability level, but it normally links the controlled part revision and material route to a finished-part lot or run, then to its release record. Where regrind is allowed, add the declared source eligibility, status or percentage basis, and any required preparation record. A resin certificate, a bag label, or a generic supplier statement is not enough unless it connects to the lot being accepted.
When should a regrind-control change require buyer approval?
Set the triggers in advance. Prior written review is commonly appropriate when a change could affect the approved material route or a controlled part requirement, such as a new regrind source, percentage, grade, colorant, outside recycler, handling route, tool runner arrangement, or site. The supplier should notify the buyer under the agreement, assess the affected risks, and propose proportionate evidence before implementing the change.
References
Source material
- [1] National Institute of Standards and Technology (NIST), “Supply Chain Traceability Principles: A Manufacturing Meta-Framework” (NIST IR 8536)
- [2] ISO, “ISO 22095:2020 Chain of custody — General terminology and models”
- [3] UL Solutions, “Recycled Plastics Testing and Certification”
- [4] Covestro, “Texin 570D: Processing and Regrind Guidance”
This guide is general information for early procurement and engineering discussion. It does not replace product-specific DFM, qualification, validation, regulatory assessment or legal advice.