Reactively modified poly(lactic acid): properties and foam processing

In order to produce modified poly(lactic acid) (PLA) resins for applications requiring high melt viscosity and elasticity (e.g., low-density foaming, thermoforming), a commercial PLA product has been reactively modified in melt by sequentially adding 1,4-butanediol and 1,4-butane diisocyanate as low-molecular-weight chain extenders. By varying amounts of the two chain extenders associated to the end group contents of PLA, three resulted samples were obtained. They were then structurally characterized by FTIR spectroscopy and molecular structure analysis. Their thermal, dynamic mechanical thermal properties and melt viscoelastic properties were investigated and compared along with unmodified PLA. The results indicated that chemical modifi- cation may be characterized as chain scission, extension, crosslinking, or any combination of the three depending on the chain extender amounts. The increase of PLA molecular weight could be obtained by properly controlling amounts of two chain extenders. The samples with increased molecular weights showed enhanced melt viscosity and elasticity. Such property improvements promised a successful application for modified PLA in a batch foam processing by producing foams with reduced cell size, increased cell density and lowered bulk foam density in comparison with plain PLA foam.