Reactively Modified Poly(lactic acid): Properties and Foam Processing

Abstract

Summary: 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 modification 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.

Advantages of polycarboxylic over dicarboxylic anhydrides in the melt modification of PPC

“…Instead this behavior suggests that the improved mechanical properties may arise from branching from at least three PPC chains tethered to a PDAH molecule (Figure 2c). This hypothesis is also supported from previous work on chain extension in PLA in which the addition of polyfunctional chain extenders with isocyanide or epoxy moieties result in branched polymer structures [10,11]. Maleic anhydride reinforces the polymer at low loadings but softens the polymer at higher level.…”

Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review

“…Several processing technologies for PLA have been developed for large-scale production lines, depending on the intended application, including drying and extrusion [8,84], injection molding [85][86][87], injection stretch blow molding [2,88,89], casting (film and sheet) [89][90][91], extrusion blown film [92][93][94], thermoforming [47,95,96], foaming [97][98][99][100][101][102], fiber spinning [103][104][105][106][107], electro spinning [108][109][110][111][112][113][114][115][116], blending [117][118][119][120], compounding [11,[121][122][123][124] and nanocompositing [125][126]…”

Effect of gas saturation conditions on the expansion ratio of microcellular poly(lactic acid)/wood-flour composites

“…Recently the production of microcellular-foamed structures in the polymer through a batch and continuous foaming processes has addressed several of the hindrances associated with PLA [4,[12][13][14][15][16][17][18][19][20]. Over the past years, several in-depth studies have examined the effects of the processing conditions and formulations on the foamability of PLA in a batch process [4,[12][13][14][15][16][17][18][19][20]]. Fujimoto and coworkers described the foam processing of neat PLA and two different types of PLA/layered silicate nanocomposites using supercritical CO 2 as a foaming agent [12].…”

“…In fact, Hu et al [15] reported that lower saturation pressure (up to 2.8 MPa) leads to more uniform microcellular structures whereas foam structures become inhomogeneous with an increase in saturation pressure, owing to the rapid diffusion of CO 2 out of the polymer. Attempts have also been made to enhance the foamability of PLA by controlling the melt rheology of PLA through increasing the molecular weight to compensate for the molecular weight decrease caused by processing degradation and to increase the melt viscosity [19,20]. PLA modified with chain extenders showed enhanced melt viscosity and elasticity, resulting in the production of foamed PLA with smaller cell size, higher cell-population density, and lower foam density compared to the unmodified counterpart [19,20] In addition to the ingredients used in the PLA formulations, processing variables also affect the foamability of PLA.…”

“…Attempts have also been made to enhance the foamability of PLA by controlling the melt rheology of PLA through increasing the molecular weight to compensate for the molecular weight decrease caused by processing degradation and to increase the melt viscosity [19,20]. PLA modified with chain extenders showed enhanced melt viscosity and elasticity, resulting in the production of foamed PLA with smaller cell size, higher cell-population density, and lower foam density compared to the unmodified counterpart [19,20] In addition to the ingredients used in the PLA formulations, processing variables also affect the foamability of PLA. Investigations have shown that the foaming time and/or the foaming temperature are important process variables for controlling the density and porous morphology of PLA foams owing to their effects on the visco-elastic properties of the polymer [4].…”