Modified EVOH Copolymer Crosslinking for Hot Water Resistance

The patent removes harmful crosslinking agents and crosslinking aids from the EVOH system entirely. Instead, it uses intrinsic hydroxyl groups on the EVOH polymer chains to form crosslinks through controlled reaction with epoxy compounds during extrusion, followed by post-crosslinking. This extraction of harmful substances resolves the contradiction by achieving crosslinking without additives that would remain as harmful residues.

The EVOH polymer serves its own crosslinking needs by utilizing its inherent hydroxyl groups to react with epoxy compounds. The polymer backbone itself provides the reactive sites necessary for crosslinking, eliminating the need for external crosslinking agents. This self-service approach allows crosslinking to proceed without introducing harmful additives that would compromise health safety.

The patent performs preliminary modification of EVOH with epoxy compounds during the extrusion process before the actual crosslinking step. The epoxy compounds react with hydroxyl groups on EVOH chains to introduce reactive sites, but complete crosslinking is delayed until after shaping. This preliminary action prepares the polymer for crosslinking without causing premature gelation during melt-kneading, resolving the operational difficulty.

The crosslinking process is divided into two distinct stages: (1) preliminary modification during extrusion where epoxy compounds are introduced and partially react with EVOH hydroxyl groups, and (2) post-crosslinking after shaping where complete crosslinking occurs. This segmentation separates the preparation phase from the crosslinking phase, preventing gelation during melt-kneading while still achieving the desired hot water resistance.