Adipic acid grades used across industrial and food manufacturing fall into two broad categories: technical grade, purified to a minimum of roughly 99.7-99.8% for polymer synthesis, and food grade, produced to Food Chemicals Codex (FCC) purity and listed under E355 for use as an acidity regulator. The grade a buyer specifies depends on downstream tolerance for trace metals, color, and ash content, since both grades share the same base chemistry but differ in refinement level and documentation.
Adipic acid (hexanedioic acid, CAS 124-04-9, molecular formula C6H10O4) is a white crystalline dicarboxylic acid with a melting point of approximately 152°C and limited solubility in cold water, improving significantly as temperature rises. It is produced industrially by oxidation of cyclohexane-derived intermediates and is one of the most widely traded aliphatic dicarboxylic acids in the chemical supply chain, valued for its two reactive carboxyl groups that allow it to participate in polycondensation and esterification reactions.
What Is Adipic Acid?
Chemically, adipic acid is a six-carbon straight-chain diacid. Its two terminal -COOH groups react readily with diamines to form polyamide chains and with alcohols to form diesters, which is why it functions equally well as a polymer building block and as a food-grade acidulant. It is non-volatile, thermally stable below its melting point, and mildly acidic in aqueous solution, with a pKa profile that supports controlled pH adjustment in both industrial and food systems.
Adipic Acid Grades and Specifications
Buyers should specify grade explicitly on purchase orders, since technical and food-grade material carry different documentation trails and, in some markets, different regulatory registrations. The table below outlines the typical distinctions procurement and QA teams reference when writing specifications.
| Grade | Typical Purity | Governing Reference | Primary Use |
|---|---|---|---|
| Technical / Industrial Grade | ≥99.7-99.8% | Manufacturer technical data sheet, ASTM-referenced test methods | Nylon 6,6 polymerization, polyurethane resins, plasticizer synthesis |
| Food Grade | ≥99.6% (FCC monograph) | Food Chemicals Codex (FCC); E355 under EU food additive nomenclature | Acidity regulator and leavening component in food formulations |
| Refined / Low-Ash Grade | ≥99.8%, low iron and ash | Customer-specific specification | High-purity polymer applications sensitive to trace metal contamination |
Common QA parameters requested alongside these grades include melting point range, color (APHA/platinum-cobalt scale), moisture content, ash, and iron content, since even trace metal levels can affect polymerization kinetics or color stability in downstream nylon and polyester resin production.
Physical Forms and Packaging
Adipic acid is supplied almost exclusively as a dry crystalline solid, typically as a fine to granular white powder. Standard packaging includes 25kg multi-wall paper bags with a polyethylene liner to protect against moisture pickup, and 500-1,000kg FIBC (bulk) bags for higher-volume industrial buyers. Because the material is hygroscopic to a limited degree and can cake under humid storage conditions, moisture-barrier packaging and dry warehousing are standard practice rather than optional extras.
Applications by Industry
The largest volume application for adipic acid globally is as a monomer for nylon 6,6 fiber and resin, where it is polymerized with hexamethylenediamine. It also serves as a raw material for polyurethane foams and elastomers, where it contributes to polyester polyol backbones, and for adipate ester plasticizers used in flexible PVC compounding. In food manufacturing, adipic acid functions as an acidulant and buffering agent in beverages, gelatin desserts, and baking applications, where its slower, more gradual acid release compared with citric acid supports specific texture and flavor-release profiles. In each application, the underlying chemistry is identical; what changes is the purity threshold and documentation the formulator requires.
Handling, Storage, and QA Documentation
Adipic acid is combustible as a dust and should be stored away from strong oxidizers and open flame sources, with attention to dust control during bulk handling and pneumatic transfer. Bags and FIBCs should be stored in a dry, well-ventilated warehouse, off the floor, and protected from direct moisture exposure to prevent caking or clumping that can complicate downstream dosing equipment. Buyers should request a Certificate of Analysis (COA) confirming purity, melting point, moisture, ash, and color for each lot, along with a current specification sheet and lot traceability documentation. For food-grade material, confirmation of FCC compliance and, where applicable, E355 labeling status should be included in the documentation package before the lot is released to production.
FAQ
What grades of adipic acid are used in food manufacturing?
Food manufacturing uses food-grade adipic acid meeting Food Chemicals Codex (FCC) purity requirements, typically listed under the E355 designation, distinct from the technical grade used in nylon and resin production.
Is adipic acid the same material for nylon production and food use?
The core chemical compound is identical, but the grades differ in purity level, trace metal content, and the documentation (FCC monograph versus technical data sheet) that accompanies each lot.
How should adipic acid be stored to avoid caking?
It should be kept in its original moisture-barrier packaging, in a dry, well-ventilated warehouse away from humidity and heat sources, since the powder is mildly hygroscopic and can cake if exposed to moisture over time.
How DIC Supports This
DIC stocks adipic acid regionally across both technical and food-grade specifications, allowing formulators and polymer producers to source the appropriate grade without carrying excess inventory. Food-grade lots are handled through warehousing suited to sensitive ingredients, with full COA and lot traceability documentation provided on request. For customers with recurring volume needs, vendor-managed inventory (VMI) arrangements can be structured to align delivery schedules with production planning.
