Processing of poly(lactic acid): characterization of chemical structure, thermal stability and mechanical properties

The processing of poly(lactic acid) (injection and extrusion/injection) as well as annealing of processed materials were studied in order to analyze the variation of its chemical structure, thermal degradation and mechanical properties. Processing of PLA was responsible for a decrease in molecular weight, as determined by GPC, due to chain scission. The degree of crystallinity was evaluated by means of differential scanning calorimetry and X-ray diffraction. It was found that mechanical processing led to the quasi disappearance of crystal structure whereas it was recovered after annealing. These findings were qualitatively corroborated by means of FTIR. By analyzing 1H NMR and 13C NMR chemical shifts and peak areas, it was possible to affirm that the chemical composition of PLA did not change after processing, but the proportion of methyl groups increased, thus indicating the presence of a different molecular environment. The thermal stability of the various materials was established by calculating various characteristic temperatures from thermograms as well as conversion and conversion derivative curves. Finally, the mechanical behaviour was determined by means of tensile testing (Young modulus, yield strength and elongation at break).

[1]  X. Colom,et al.  Determination of small interactions in polymer composites by means of FTIR and DSC , 2000 .

[2]  M. L. Lorenzo.  Crystallization behavior of poly(l-lactic acid) , 2005 .

[3]  Simona Bronco,et al.  Thermal degradation of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) and their blends upon melt processing , 2009 .

[4]  P. Pagès,et al.  Thermal degradation and stability of epoxy nanocomposites: Influence of montmorillonite content and cure temperature , 2008 .

[5]  K. Reichert,et al.  Thermal decomposition of biodegradable polyesters—III. Studies on the mechanisms of thermal degradation of oligo-l-lactide using SEC, LACCC and MALDI-TOF-MS , 1997 .

[6]  Xiaoqiang Yang,et al.  Synthesis and properties of collagen/polylactic acid blends , 2004 .

[7]  J. Mano,et al.  On the kinetics of melting and crystallization of poly(L-lactic acid) by TMDSC , 2005 .

[8]  K. Reichert,et al.  Thermal degradation of poly-L-lactide-studies on kinetics, modelling and melt stabilisation , 1997 .

[9]  J. Saurina,et al.  Changes in Crystallinity of the HDPE Matrix in Composites with Cellulosic Fiber Using DSC and FTIR , 2000 .

[10]  Susan Selke,et al.  An overview of polylactides as packaging materials. , 2004, Macromolecular bioscience.

[11]  Catia Bastioli,et al.  Handbook of Biodegradable Polymers , 2005 .

[12]  T. Osswald,et al.  Materials Science of Polymers for Engineers , 1995 .

[13]  Alain Bourmaud,et al.  Effect of thermo-mechanical cycles on the physico-chemical properties of poly(lactic acid) , 2008 .

[14]  E. Turi,et al.  Thermal characterization of polymeric materials , 1981 .

[15]  M. Sánchez‐Soto,et al.  Curing FTIR study and mechanical characterization of glass bead filled trifunctional epoxy composites , 2007 .

[16]  Donald Garlotta,et al.  A Literature Review of Poly(Lactic Acid) , 2001 .

[17]  Katrin Mackenzie,et al.  Thermal decomposition of biodegradable polyesters—II. Poly(lactic acid) , 1996 .

[18]  F. Carrasco,et al.  Study of curing of layered silicate/trifunctional epoxy nanocomposites by means of FTIR spectroscopy , 2008 .

[19]  A. Södergård,et al.  Stabilization of poly(l-lactide) in the melt , 1994 .

[20]  E. Giménez,et al.  Influence of processing on ethylene-propylene block copolymers: Structure and mechanical behavior , 2004 .

[21]  Ingo Alig,et al.  In-line monitoring of the thermal degradation of poly(l-lactic acid) during melt extrusion by UV–vis spectroscopy , 2008 .

[22]  S. Ray,et al.  New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology , 2003 .

[23]  Catia Bastioli,et al.  Effect of molecular weight and crystallinity on poly(lactic acid) mechanical properties , 1996 .

[24]  R. G. Sinclair.  The Case for Polylactic Acid as a Commodity Packaging Plastic , 1996 .

[25]  Tzong‐Ming Wu,et al.  Fabrication and Characterization of Biodegradable Poly(Lactic Acid)/Layered Silicate Nanocomposites , 2005 .

[26]  Y. Ozaki,et al.  Differences in the CH3⋯OC interactions among poly(l-lactide), poly(l-lactide)/poly(d-lactide) stereocomplex, and poly(3-hydroxybutyrate) studied by infrared spectroscopy , 2005 .

[27]  F. Carrasco,et al.  Fourier transform IR and differential scanning calorimetry study of curing of trifunctional amino‐epoxy resin , 2005 .

[28]  T. Masuko,et al.  Crystallization behaviour of poly(l-lactide) , 1998 .

[29]  R. Shishoo,et al.  Influence of processing parameters on the degradation of poly(L‐lactide) during extrusion , 2001 .

[30]  Ramani Narayan,et al.  Reversible Kinetics and Thermodynamics of the Homopolymerization of l-Lactide with 2-Ethylhexanoic Acid Tin(II) Salt , 1997 .

[31]  Yoshiharu Doi,et al.  Thermal degradation of microbial copolyesters: poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) , 1990 .

[32]  D. Grijpma,et al.  (CO)POLYMERS OF L-LACTIDE .1. SYNTHESIS, THERMAL-PROPERTIES AND HYDROLYTIC DEGRADATION , 1994 .

[33]  Y. Ikada,et al.  Effects of residual monomer on the degradation of DL‐lactide polymer , 1998 .

[34]  J. Lunt.  Large-scale production, properties and commercial applications of polylactic acid polymers , 1998 .

[35]  Y. Shirai,et al.  Thermal stability of poly (L-lactide): influence of end protection by acetyl group , 2004 .

[36]  M. Gupta,et al.  Thermal oxidative degradation of poly-lactic acid , 1982 .

[37]  D. Dionisi,et al.  Thermal stability of polyhydroxyalkanoates , 2006 .

[38]  I. C. Mcneill,et al.  Degradation studies of some polyesters and polycarbonates—2. Polylactide: Degradation under isothermal conditions, thermal degradation mechanism and photolysis of the polymer , 1985 .

[39]  Hengxing Yu,et al.  Modeling of poly(L‐lactide) thermal degradation: Theoretical prediction of molecular weight and polydispersity index , 2003 .

[40]  J. Mano,et al.  Influence of melting conditions on the thermal behaviour of poly(l-lactic acid) , 2005 .

[41]  Yoshito Ikada,et al.  Thermal characterization of polylactides , 1988 .

[42]  Y. Shirai,et al.  Thermal degradation behaviour of poly(lactic acid) stereocomplex , 2004 .