Biodegradable polymeric multi-layer substrate

摘要

A biodegradable polymeric multi-layer substrate comprises a first layer of a polymeric material, a second layer of a polymeric material different to the polymeric material of the first layer and at least one intermediate tie layer between the first and second layers, the at least one tie layer comprising a mixture of at least two different polymeric materials, wherein the melt flow index and melt viscosity of the at least two polymeric materials within the tie layer are similar. The substrate may be transparent. The first layer may be an outer layer substantially of PLA and the second layer may be an inner layer substantially of PVOH, the tie layer containing substantially PLA and PVOH and the PVOH of the tie layer having a higher MFI and lower melt viscosity than the PVOH of the inner layer. The substrate may comprise a third layer of a polymeric material substantially of PLA, the inner layer substantially of PVOH being between the two outer layers and the outer layers of substantially PLA having different melt temperatures. One outer layer of substantially PLA or a tie layer may contain higher melting point polymers such as cellulose, cellulose esters, PHA, PHB and/or PHBV. A peelable sealing layer may be provided over an outer substantially PLA layer. The polymer of the second layer may be PVOH having a degree of hydrolysis of at least 88% and one of the polymers of the tie layer(s) may be PVOH having a degree of hydrolysis of less than 88%. By matching the melt flow index and melt flow viscosity of the polymeric materials forming the tie layer(s), the homogeneity of the tie layer(s) may be enhanced and bonding to adjacent layers improved. The multi-layer substrate may be used for bags, food trays, lidding films for food trays, sandwich packs, window packs or postal envelopes.