Poly(melkzuur) : karakterisatie en verbetering

In the last decades, scientists and industrial partners were pushed to search for substitutes of petroleum-based plastics due to economic and social reasons related to environmental pollution and overexploitation of finite fossil resources. Poly(lactic acid) (PLA), a synthetic thermoplastic aliphatic polyester, is one of the most commercially interesting options, because, apart from being bio-based, bio-degradable and compostable, it can be processed with equipments usually used for conventional plastics and its mechanical properties are relatively good with respect to other biopolymers. However, despite the many attractive qualities, there are still some aspects of PLA which need to be improved so that it can compete with conventional polymers. In this context, the aim of this work was to tune PLA material properties in order to make its production more profitable, by decreasing production costs and enlarging the application spectrum. We are convinced that this can be done by optimizing PLA crystallization behavior and melt strength. Two methods to modify the crystallization behavior of PLA were presented: (1) the addition of bio-based nucleating agents and (2) the application of flow The nucleating of amino acids and poly(amino acids) (L-alanine, poly-DL-alanine, glycine and polyglycine) effect was confirmed. In the case of polyglycine, low concentrations were sufficient to obtain a significant acceleration due to an increased nucleation density. The critical experimental flow conditions under which the crystallization process is accelerated and significant changes in morphology take place were determined with parameters from molecular rheology and the criterion of the applied mechanical work. There was a fair coincidence between the calculated critical values for orientation and the transitions experimentally measured. Rather than focusing on crystallization and melt enhancement separately, it was proposed to solve both issues at once, since it is economically interesting and more practical. Six PLA-based additives with various characteristics such as architecture, stereoregular composition and molecular weight were screened to find a match. The additive called AD4a had the desired double enhancing effect. This was accredited to the combination of long chain branching and the presence of HoSCo crystals formed during the extrusion step. In conclusion, this work presented two additives which can be used to tune PLA crystallization and strain hardening behavior. Polyglycine is interesting for applications were only slow crystallization rates are an issue, such as injection molding where shorter cooling cycles are wished. For example, the addition of 0.5wt% of polyglycine decreased the crystallization time at 130°C of neat extruded LMw PLA from 2115s to 761s. This means that an injection molding cycle at 130°C could be more than 20 minutes shorter. On the other hand, the PLA-based additives (AD4b) could be used in film blowing applications were both crystallization and melt strength need to be tunable to obtain the desired transparency and thickness of the film. It was also shown that the Entrance Flow Method (EFM) was the most satisfactory and adequate technique to detect melt strength enhancement and it was used, in combination with Cogswell’s analysis, to determine the extensional viscosity of two PLA model systems.Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III Samenvatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII Notation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XI Chapter 1: Introduction Context : Environment & Economics . . . . . . . . . . . . . . . . . . . . . . . 1 Biopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Classification based on bio-properties . . . . . . . . . . . . . . . . . . . 2 Classification based on feedstock . . . . . . . . . . . . . . . . . . . . . . 4 Poly(Lactic Acid) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 What is PLA? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 PLA Life cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Chirality and Homo-stereocomplexation . . . . . . . . . . . . . . . . 6 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Motivation & Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Chapter 2: General Experimental Section Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Measurement Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Differential Scanning Calorimetry. . . . . . . . . . . . . . . . . . . . . . . 15 Gel Permeation Chromatography . . . . . .. . . . . . . . . . . . . . . . . 16 Rotational Shear Rheometry . . . . . . . . . . .. . . . . . . . . . . . . . . . 17 Capillary Shear Rheometry . . . . . . . . . . .. . . . . . . . . . . . . . . . . 18 Shear Deformation and Temperature Control . . . . . .. . . . . . . . 19 Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Drying Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Sample Mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Sample Geometry Preparation . . . . . . . . . . . . . . . . . . . . . . . . 20 Quiescent Non-isothermal Protocol . . . . . . . . . . . . . . . . . . . . . 20 Quiescent Isothermal Crystallization Protocol . . . . . . . . . . . . . 20 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Chapter 3: Crystallization Enhancement Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Quiescent Crystallization in Absence of Nucleating Agents . . . . . 30 Quiescent Crystallization in Presence of Nucleating Agents . . . . 31 Flow Induced crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Experimental Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Techniques & Measurement Conditions . . . . . . . . . . . . . . . . . . 42 Protocols & Analyses . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 42 Results & Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Quiescent Crystallization in Absence of Nucleating Agents . . . . 47 Quiescent Crystallization in Presence of Nucleating Agents . . . . 52 Flow-induced Crystallization . . . . . . . . .. . . . . . . . . . . . . . . . . . 63 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Chapter 4: Melt Strength Measurement Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 State of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Melt strength of Semi-crystalline Polymers . . . . . . . . . . . . . . . . 86 Melt Strength Enhancement Techniques . . . . . . . . . . . . . . . . . . 88 Melt Strength Measurement Techniques . . . . . . . . . . . . . . . . . . 91 Exploratory Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Entrance Flow Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Experimental section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Measurement Techniques & Protocols . . . . . . . . . . . . . . . . . . . 103 Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Analogy Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Analogy Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Chapter 5: PLA Enhancement Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Linear molecules as additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Neat Systems of Branched Molecules. . . . . . . . . . . . . . . . . . . . . . . . 124 Branched molecules as additives . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Experimental Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Materials and Sample Preparation . . . . .. . . . . . . . . . . . . . . . . . . 131 Measurement Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Results & Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Effect of Molecular Architecture & Stereochemical Composition. . 135 Effect of the Molecular Weight or M/Im ratio . . . . . . . . . . . . . . . . 146 Effect of the Additive Concentration . . . . . . . . . . . . . . . . . . . . . . . 151 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Chapter 6: Conclusions & Outlook Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 List of Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 nrpages: 194status: publishe