How to Test Hot-Melt Adhesive Powder by Sieve Analysis

A hot melt adhesive powder sieve analysis method should incorporate a representative sample, agreed sieve procedure, and report that accounts for the material weighed in. A particle-size percentage alone leaves too much unanswered. Which aperture retained it? What happened to the pan fraction? Did the report normalize away missing powder?

This guide is for specifying and interpreting the test for industrial adhesive powder. It includes a worked example of a mass ledger and procurement checklist. It doesn’t replace the validated procedure of the laboratory or the complete standard that it follows. To select a production grade, begin with the separate adhesive powder particle-size selection guide.

Method scope: what a sieve result can and cannot prove

Sieve analysis measures the mass separated by specified apertures under stated test conditions. It can describe size fractions and assist in comparing lots. It doesn’t define adhesive chemistry, bond strength, or production suitability. Those decisions require material identity and appropriate evidence of use as well as a meaningful particle-size report.

ASTM D1921-25’s public scope covers dry sieving of plastic materials supplied as powder, granules or pellets. It gives an approximate lower measurement limit of 38 µm. That boundary pertains to this test method; it is not a claim that all finer powder is unmeasurable.

“These test methods are used to determine particle size distribution and therefore are useful for determining lot-to-lot uniformity.”

Is sieve analysis right for your material?

This method can work if powder can be reproducibly separated at the appropriate apertures. Assess the material and the method prior to use. If powder sticking, agglomeration or a fine fraction makes a meaningful separation impossible, assume that a sieve label doesn’t necessarily answer the question and ask the laboratory to provide a method to demonstrate a more suitable means.

State the product format first. Industrial coatings, transfer printing powder and continuous adhesive films fulfill different purchasing requests. The film, powder, web and pellet comparison helps with that distinction before a laboratory request is made. Keep the test with the material you’ll actually buy.

Prepare a representative powder sample

A test portion must represent the defined material being assessed. Obtaining a test sample and splitting it into test portions are two different operations, and must both be recorded. Recovering every gram from the sieve stack can demonstrate a complete mass balance, but cannot prove that the original scoop represented the lot.

ISO 14488:2007 on sampling and sample splitting addresses representative test samples from particulate bulk material, with a defined confidence level. Its public summary is particularly relevant to particle-size measurement. It does not, however, provide a sampling plan for your specific adhesive grade.

• Define the lot, containers and sampling locations covered by the result.
• Document how the laboratory sample was combined, handled and subdivided.
• Record the powder’s received condition and any authorized conditioning.
• Retain enough identified material for the agreed repeat or dispute procedure.

Imagine we have a hypothetical receipt inspection. In this example, the procurement team sends the lab a pouch from the top of an opened bag. The operator divides that pouch carefully, obtains consistent results and reports good mass recovery. These observations support the handling of the pouch. However, they can’t validate sampling of other bags or different locations. The correct next step is to review the sampling record, not to congratulate the lab for proving whole-shipment uniformity. The same pouch could be sampled again, and the sampling limitation may be reproduced. Agree what population the report represents before using it to accept the delivery.

Keep grade and chemistry on the sample label. A copolyamide adhesive powder specification and a copolyester powder specification shouldn’t lose their identity when they reach the balance.

Specify sieve apertures and the test setup

Aperture and sieve identification, along with the condition of the apparatus, should be specified together. The aperture describes the separation being attempted, while the sieve identification identifies the measuring equipment. The shaker and balance records should also be indicated. Though equipment used for separation may vary, the details of the setup should be documented.

ASTM E11-24 is concerned with the construction and inspection of woven wire sieve cloth. Its stated apparatus aperture range extends from 125 mm down to 20 µm. Purchasing a conforming sieve does not validate the powder procedure by itself.

What is the function of a vibratory sieve shaker?

Vibratory motion of the sieve shaker moves the sample and repeatedly exposes particles to sieve openings. Note the settings of the vibrating sieve shaker as part of the test method along with loaded mass, stack and endpoint. Behavior of separation can vary with motion. Assess comparability before treating results from a replacement shaker as equivalent.

In reports moving into purchasing, don’t substitute the recorded aperture with “fine” or “medium.” Retain the number specification for TPU adhesive powder grades as closely as for EVA adhesive powder grades. Marketing categories aren’t measurement settings.

Run the agreed sieve analysis procedure

Use the authorized procedure for the identified powder and apparatus. It should define preparation, sample load, sieve arrangement, motion, endpoint and weighing. The sequence that follows is a checklist of this procedure and isn’t a substitute for operating instructions. A convenient duration borrowed from another material isn’t evidence that this powder has reached its end point.

The public method outline (D1921) distinguishes a multi-sieve approach from an abbreviated approach using selected sieves. The full materials and methods procedure must be available to the laboratory using it. Keep the materials and methods record with the results. General balance and instrument guides are an aid in organizing the work, but can’t provide missing acceptance criteria.

1. Confirm the record. Match sample identity, method revision and authorized preparation.
2. Check the apparatus. Identify the clean sieves, pan, cover and balance; record empty masses.
3. Weigh the charge. Record the actual material introduced, including any transfer discrepancy.
4. Apply the procedure. Use its stack, motion and endpoint; record interruptions and deviations.
5. Weigh every fraction. Preserve each retained mass and the pan result with their sieve identities.
6. Reconcile the report. Calculate recovery and distributions, then apply the agreed validity and acceptance rules.

Don’t manipulate the sample in a manner that would affect the reported data merely to make a sample pass more easily. A melting point specification is not permission to set the drying temperature. Keep grade instructions, lab procedures, and site handling requirements together.

Calculate retained fractions and mass recovery

Calculate mass recovery against the original charge and state the denominator used for each size fraction. Recovered mass distribution and the original charge distribution address different questions. Both should be shown if they aid in the evaluation. Never allocate the missing mass to the pan. Never describe recovery as production yield.

The principle of mass-fractions follows the public description of dry sieving. The following 2-Denominator Sieve Ledger is an editorial reporting aid and not a prescribed ASTM calculation sheet. The masses shown are for illustration; none of the masses describes a lot of Teng Yang.

2-Denominator Sieve Ledger

For your records, replace A-D with the actual nominal apertures. Determine net retained mass for each as loaded sieve mass minus empty mass. Sum all recovered fractions, including the pan. Compute recovery (%) = recovered mass/ initial charge × 100. Express ratio as a percentage. For a fraction, calculate mass/ total recovered mass, or mass/initial charge, depending on the method nominated for report. Test your gram weighing system.

In this illustrative test, adding 4.00 g + 25.00 g + 45.00 g + 24.00 g + 1.00 g gives 99.00 g. Recovery is therefore 99.00 ÷ 100.00 × 100 = 99.00%. Sieve C contributes 45.00% of the original charge, or 45.00 ÷ 99.00 × 100 = 45.45% of recovered material after rounding. Neither statement repairs the missing 1.00 g. The normalized entries total 99.99% when individually rounded, although their unrounded sum is 100%. Preserve sufficient calculation precision and state the rounding rule. This example demonstrates accounting, not a 99% acceptance criterion.

In this case, the unaccounted mass equals the measured pan mass. Therefore, determining where it went is important for the fine tail. Cumulative passing also requires an established basis; that is, adding up the measured material passing the nominated aperture, not assuming missing material is passing. Examine validity using the method approved by all concerned; if it’s valid, then judge the lot.

Troubleshoot blinding, clumps and poor recovery

Investigate a surprise fraction before identifying a change of material. Some of the issues that affect results may include blocked openings, retained residues, clumps, transfer losses, and incorrect recordings. Examine the sample and the apparatus. Repeating an altered test without documenting the change may produce a different number while leaving the cause unresolved.

In a historical flour study, USDA researcher Keshun Liu found that test conditions affected sieving performance. This indicates that the conditions of the test should be assessed as opposed to transferring flour settings to thermoplastic adhesive powder. Powder-specific preparation still needs its own basis.

What are the disadvantages of sieve analysis?

Fractions obtained by sieving are limited and results are dependent on the shape of particles, agglomeration and how they’re handled. Very fine or stubborn powders may require an alternative method. Sieving is useful if the measurement answers the specification. Document why an alternative method addresses the specification better before replacing it.

Instrument guidance from Haver & Boecker identifies inadequate cleaning as a cause of carryover between tests. A beautiful, smooth distribution curve can’t compensate for unknown residual powder.

Compare sieving with air jet and laser diffraction

Match the measurement question prior to comparing results obtained using different methods. Mechanical sieving separates and weighs fractions; air-jet sieving uses airflow to assist separation and dispersion; laser diffraction interprets scattered light. A matching particle-size label doesn’t guarantee a corresponding population. Record the preparation and the reporting basis along with the instrument name.

ISO 13320:2020 addresses laser diffraction and instrument qualification, while its public scope excludes requirements for specific materials. A percentile derived from laser diffraction should not replace a sieve mass fraction on an agreed purchase specification.

Let’s say a plant identifies troublesome clumps, but a dispersed laboratory measurement resembles an acceptable lot. The laboratory may have measured the smaller particles after the clumps broke apart, while the plant handled the powder as received. Particle Technology Labs provides an example where a material, in this case an unnamed material, was found to contain problematic soft agglomerates by gentle sieving, which dispersed measurements didn’t. That is a useful counterexample, not proof that every hot-melt powder behaves this way. Decide which state is of concern to the plant: delivered agglomerates, dispersed particles, or some other defined state. Then, qualify a procedure that retains the feature that’s of concern to the plant in relation to the purchasing decision.

• Compare like preparation and explain any deliberate differences.
• State whether results are mass-based, volume-based or another representation.
• Ask for paired measurements on relevant material before changing the contractual method.
• Avoid a universal correction factor between sieving and laser diffraction.

Set lot acceptance rules before the shipment

Agree the evidence and decision rule before deciding whether a lot conforms. Although a test may be well recorded, it may not be appropriate for making a shipment decision. Verify sampling, method validity and specification limits, and ensure appropriate treatment of boundary results. Lack of information may require clarification or an agreed repeat; it doesn’t automatically prove that the powder is defective.

The relation of uncertainty to conformity decisions is treated in ISO/IEC Guide 98-4:2012, and it differentiates between acceptance limits and specification limits. Ask the laboratory how it deals with a measurement result that is close to a specification limit. This guide supplies no universal uncertainty allowance or mandatory guard band for adhesive powder.

Lot-Report Release Matrix

Use this proposed matrix in a test request. Enter the acceptance limits in the matrix. The matrix doesn’t provide default limits.

Keep the measurement report distinct from a safety sheet or a generic product description. The role of each document is described in the guide to powder safety, technical and lot-analysis documents. The title of a report is less important than its content and evidence.

Keep method revisions and production trials connected

Retain the method revision with the lot record and assess the performance of the application separately. Modified method and updated record may affect comparability. Neither proves the adhesive changed. For the purchasing decision, determine whether substantial differences exist between methods and whether further application trials or paired results are warranted.

The current public listings identify D1921-25 and E11-24; ISO 14488:2007 remains listed with an amendment. Record the applicable edition and amendment rather than using a bare standard number. A website’s update date alone does not explain a changed test requirement.

Teng Yang’s industrial adhesive powder range states copolyamide, copolyester, TPU and EVA. The webpage also states they don’t publish first-party laboratory particle size distributions for this powder range. Therefore, identify who will perform the test and provide the report prior to placement of an order that relies on the test report.

Keep the identity of the substrates, adhesive formulation, method of application and criteria for bonding, along with a powder report, for a production trial. A laboratory’s analytical record will indicate if the measured size distribution meets their spec. The production trial would also confirm if the adhesive and process provide the required bond.

Frequently asked questions