Writing a Polyethylene Enquiry That Gets Quoted: Specs Buyers Must Include

An enquiry for polyethylene that lacks density, melt flow rate condition, comonomer identity, additive package, and compliance jurisdiction is returned as provisional or priced against the broadest possible grade slate. Polyethylene is not a single material class; it spans high-density, medium-density, linear low-density, low-density, and ultra-high-molecular-weight resins. A quotable request specifies the processing route, the acceptance test methods, the volume, and the packaging. Without these fields, the supplier must request clarification before a fixed quote can be issued. The following sections define the specifications buyers must include if a polyethylene enquiry is to receive a fixed, technically valid quotation.

What Resin Identification Data Are Required Before Polyethylene Pricing Can Be Fixed?

The grade family must be stated precisely. High-density polyethylene spans 0.941–0.965 g/cm³ when tested according to ASTM D1505 or ISO 1183-1. Medium-density polyethylene occupies 0.926–0.940 g/cm³; linear low-density polyethylene typically falls between 0.916 g/cm³ and 0.940 g/cm³; low-density polyethylene is usually 0.910–0.925 g/cm³. For LLDPE, the comonomer is not a minor descriptor. Butene, hexene, and octene comonomers change dart impact, tear, and puncture resistance at equal density and melt index. Metalocene-catalyzed octene LLDPE and Ziegler-catalyzed butene LLDPE can differ widely in film toughness, heat-seal response, and organoleptics. The catalyst technology should be named where known because it influences molecular weight distribution and additive response.

Ultra-high-molecular-weight polyethylene is specified by viscosity number or molecular weight, not melt flow rate. The enquiry should state whether the resin is a homopolymer, a copolymer, or a blend. If the grade contains post-consumer recyclate, the percentage, source, and decontamination certification under the relevant food-contact regulation must be supplied. A request that states only “PE” or “general purpose PE” has no specification boundary and cannot be quoted as a single grade.

For a polyethylene quotation to be comparable across suppliers, the melt flow rate must be tied to a standard condition. The default is 190°C with 2.16 kg load under ASTM D1238 or ISO 1133-1:2022. High-load melt index is measured at 190°C/21.6 kg and is used for high-viscosity HDPE grades. An HDPE pipe grade may show 0.20 g/10 min under 2.16 kg and 6–12 g/10 min under 21.6 kg. If the condition is omitted, the number cannot be compared. The flow rate ratio, typically MFR 21.6 kg divided by MFR 2.16 kg, is a practical marker of molecular weight distribution. Narrow-MWD metallocene resins show lower flow rate ratios than broad-MWD autoclave LDPE. Flow rate ratio is not a direct rheological measurement, but it helps the supplier select the correct grade when the processing route is known.

Rheological Specifications That Control Screw Design and Die Pressure

Unless the processing route is defined, the melt flow rate window is not meaningful. Injection moulding requires low-viscosity flow at high shear; film extrusion requires melt strength and bubble stability; extrusion blow moulding requires parison hang strength; rotational moulding requires powder flow and low-viscosity coalescence. The enquiry should state the specific process and, where possible, the machine type and screw configuration. For a single-screw extruder with L/D 24:1 to 30:1, grade selection changes if the screw is barrier or grooved-feed. On blown film lines with die diameters above 250 mm, narrow-MWD LLDPE may require a polymer processing aid to manage melt fracture and reduce die pressure. Melt fracture onset is grade-dependent; published data for specific commercial formulations is limited. The quoted MFR describes low-shear viscosity, but extrusion and injection moulding occur at shear rates typically between 100 s⁻¹ and 10,000 s⁻¹. A narrow-MWD LLDPE and a broad-MWD LDPE may have identical MFR but different viscosity at high shear. Capillary rheometry according to ASTM D3835-16 should be requested when the converter has a critical die pressure or melt temperature limit. The rheology test should report apparent viscosity at 100 s⁻¹, 500 s⁻¹, and 1,000 s⁻¹ and the test temperature, because shear thinning is resin-specific.

Because specimen preparation changes polymer orientation, mechanical acceptance data require test standards and sample history. Tensile yield stress and elongation at break are determined by ASTM D638-14 or ISO 527-2:2012. Flexural modulus is determined by ASTM D790-17 or ISO 178:2019. Notched impact is not directly equivalent between ASTM D256-10 and ISO 179-1:2020 because specimen dimensions and notch radii differ. For film, dart drop impact is specified by ASTM D1709 and tear resistance by ASTM D1922 or ISO 6383-2:1983. Environmental stress crack resistance is tested by ASTM D1693 for HDPE bottles and containers. The buyer must state whether each value is typical or guaranteed; a typical value is not a batch release criterion. Compression-moulded plaques prepared to ASTM D4703-16 and injection-moulded specimens prepared to ISO 294-1 do not always give identical results because of orientation and cooling-rate differences.

When Additive Loadings and Regulatory Declarations Must Be Stated in the Enquiry

In most polyethylene quotations, additives influence price, density, MFR, and conformity. Slip, antiblock, antioxidant, acid scavenger, UV stabilizer, antistatic, and processing aid loadings must be declared by chemical class and percentage. If a colour masterbatch is requested, the carrier resin and let-down ratio should be defined because they shift the final MFR and density. Antioxidant packages are frequently a blend of primary phenolic antioxidants and secondary organophosphite processing stabilizers, often at total loadings below 0.3 wt%. Acid scavengers such as zinc stearate or calcium stearate are used at low levels to neutralize catalyst residues. Additives should not be described by trade name alone unless a confidentiality agreement is in place. For UV-stabilized outdoor applications, hindered amine light stabilizer and UV absorber loadings must be tied to an accelerated weathering test, such as ASTM D2565 or ISO 4892-2, and the acceptance limit must define the change in tensile elongation or yellowness index after exposure.

An enquiry that requests “food-contact PE” without naming the jurisdiction is insufficient. For the United States, 21 CFR 177.1520 governs olefin polymers used in contact with food, subject to end-use limitations and migration testing under 21 CFR 175.300 where coatings are involved. In the European Union, Regulation (EU) No 10/2011 applies, and a declaration of compliance must identify overall migration limit and specific migration limits for additives. Drinking-water contact may require NSF/ANSI 61 or WRAS. Medical applications may require USP 661.1 or ISO 10993-1. RoHS compliance is governed by Directive 2011/65/EU, and REACH SVHC declarations should be separately requested. A supplier cannot truthfully confirm all of these if the enquiry does not name the final article and contact conditions.

Specify the Processing Route, Not Only the Grade Family

A grade selected by MFR alone may fail on a specific converting line. For extrusion blow moulding, the resin must maintain parison shape at the desired die swell. Die swell is influenced by molecular weight distribution and long-chain branching and is measured by capillary rheometry according to ASTM D3835-16. For blown film, bubble stability and frost line height require a balance of shear viscosity and extensional viscosity. For cast film, higher MFR is often accepted, but the seal initiation temperature and hot-tack strength must be specified for packaging grades. For pipe extrusion, the resin must be classified for long-term hydrostatic strength, not only density and MFR. The request should state the target pipe classification, such as PE 80 or PE 100, and the relevant hydrostatic design basis from ISO 9080 or ASTM D2837. Slow crack growth resistance is commonly assessed by notched pipe test methods such as ISO 13479 or the Pennsylvania notch test ASTM F1473. Failure to specify slow crack growth resistance can lead to a quotation for an ordinary HDPE grade that is not suitable for long-term pressure service.

Blown film enquiries should define the required dart drop, Elmendorf tear in machine and transverse directions, film gauge, and optical properties if haze and gloss are controlled. Haze is measured by ASTM D1003; gloss at specific angles by ASTM D2457 or ISO 2813. A film resin with low haze and high gloss may require a narrow-MWD metallocene LLDPE or a specific LDPE blend, but these choices also affect bubble stability and die pressure. When optical properties are omitted, the supplier can only quote a general-purpose film grade.

For rotational moulding, the enquiry should specify whether the resin is supplied as powder or micropellet, particle size distribution, bulk density, and dry-flow characteristics. A powder with poor dry-flow can bridge in the mould and produce uneven wall thickness. Apparent density and pourability are evaluated by ASTM D1895. The particle size distribution is commonly reported as the fraction retained on specific sieves, such as 35 mesh (500 µm) and 200 mesh (75 µm). Without these data, a rotomoulder cannot confirm whether the powder will flow under process conditions.

For wire and cable jacketing, oxidative induction time is a key specification. Oxidative induction time is measured by ASTM D3895 or ISO 11357-6. The buyer should state the required minimum OIT at 200°C or the oxidative induction temperature. Carbon-black dispersion is assessed by ASTM D5596 for polyethylene compounds used in cable jacketing. A missing OIT requirement can lead to a quotation for a general-purpose HDPE that does not protect the cable jacket against long-term thermal oxidation.

For delivered costing, packaging configuration and volume affect the quotation. Polyethylene is offered in 25 kg bags, 500–1,250 kg bulk sacks, octabins, and bulk railcars. The enquiry must state annual tonnage and the preferred delivery format. Pellets stored below dew point can accumulate surface condensation; therefore, transfer lines and silos may require dry air purging at relative humidity above 60%. If the buyer requires a specific moisture content, the test method and limit must be identified. Without packaging and volume data, the quotation cannot include fixed logistics.

At incoming inspection, the buyer should specify which properties are release criteria and which are typical data. Compression-moulded specimens prepared to ASTM D4703-16 and injection-moulded specimens prepared to ISO 294-1 do not always give identical tensile and impact results because of orientation and cooling-rate differences. Conditioning under 23°C and 50% relative humidity is standard, but polyethylene is not typically condition-sensitive; still, the conditioning interval should be declared. When an enquiry lists each property with the corresponding test standard, specimen preparation, unit, and acceptance limit, the supplier can quote against the specification rather than against a generic datasheet. If the enquiry remains at the level of “PE film,” the quotation is necessarily broad and may not survive an incoming-inspection comparison.