Phthalic Anhydride (PA): Applications and Procurement as a Key Raw Material for Plasticisers, Alkyd Resins and Coatings

Phthalic anhydride (PA) is produced by catalytic oxidation of ortho-xylene and is one of the highest-volume anhydrides. Its two carboxyl groups allow esterification and polycondensation, making it a feedstock for plasticisers, alkyd resins, unsaturated polyester and coatings — often described as the "backbone raw material of paints and plastics".

Core Application 1: Phthalate Plasticisers

Phthalic anhydride esterifies with alcohols to give plasticisers such as DOP, DBP and DINP. These are indispensable components of PVC soft products (cables, artificial leather, films), giving flexibility and low-temperature performance. When selecting, watch the environmental and regulatory restrictions on phthalate plasticisers (for example REACH limits on phthalates).

Core Application 2: Alkyd Resins (the Mainstay of Coatings)

Phthalic anhydride is the largest raw material for alkyd resins. Polycondensation with polyols such as glycerol, trimethylolpropane (TMP) and neopentyl glycol (NPG) yields general-purpose coating resins widely used for anti-corrosion and decorative paints on machinery, buildings and furniture. Drying speed, hardness and weatherability of alkyd resins depend directly on the alcohol component combination.

Core Application 3: Unsaturated Polyester Resin (UPR)

Phthalic anhydride co-condenses with maleic anhydride and diols to give UPR, the matrix resin for FRP, engineered stone, sanitary ware and anti-corrosion equipment. In synergy with maleic anhydride (MA), it determines resin stiffness, toughness and cure speed.

Key Procurement Indicators

Watch anhydride content, initial melting point, molten colour (platinum-cobalt), free acid and thermal stability (prone to sublimation and caking). In hot seasons, transport and storage must protect against moisture, high temperature, caking and hydrolysis. We recommend requesting recent-batch COA and retaining samples. Haiyu Zhonglong can provide specification sheets for phthalic anhydride and other anhydride/coating raw materials with samples from 1kg/25kg. Submit an Online Inquiry or Contact Us; more products in the Product Centre.