Bead foam technology with a double crystal-melting peak structure has been well established for polyolefins. The double crystal melting peak structure, which is required in the molding stage of the bead foams, generates a strong sintering among the foamed beads and maintains the overall foam structure. In this research, despite the PLA’s poor foaming behavior and its slow crystallization kinetics, we successfully developed expanded PLA (EPLA) bead foams with double crystal melting peak structure and the inter-bead sintering behavior was verified through steam chest molding. For this purpose, the generation and evolution of double crystal melting peak structure in different PLA materials is simulated in a high-pressure differential scanning calorimeter (HP-DSC). The simulation results shows that the formation of double crystal melting peak with different peak ratios can be controlled by varying the processing parameters (i.e., saturation pressure, temperature, and time) during the saturation. The PLA bead foams characterization showed that the high melting temperature crystals generated during the saturation and the low melting temperature crystals formed during the cooling and foaming can significantly affect the foaming behavior of PLA bead foams. Moreover, the crystallization kinetics of different PLA materials are systematically investigated in presence of dissolved gas. It is shown that the different crystallization kinetics (i.e., crystal nucleation and growth rate) that can be induced at various gas pressures can significantly influence the PLA’s foaming behavior (i.e., cell nucleation and expansion behavior).

Bead foam technology with a double crystal-melting peak structure has been well established for polyolefins. The double crystal melting peak structure, which is required in the molding stage of the bead foams, generates a strong sintering among the foamed beads and maintains the overall foam structure. In this research, despite the PLA’s poor foaming behavior and its slow crystallization kinetics, we successfully developed expanded PLA (EPLA) bead foams with double crystal melting peak structure and the inter-bead sintering behavior was verified through steam chest molding. For this purpose, the generation and evolution of double crystal melting peak structure in different PLA materials is simulated in a high-pressure differential scanning calorimeter (HP-DSC). The simulation results shows that the formation of double crystal melting peak with different peak ratios can be controlled by varying the processing parameters (i.e., saturation pressure, temperature, and time) during the saturation. The PLA bead foams characterization showed that the high melting temperature crystals generated during the saturation and the low melting temperature crystals formed during the cooling and foaming can significantly affect the foaming behavior of PLA bead foams. Moreover, the crystallization kinetics of different PLA materials are systematically investigated in presence of dissolved gas. It is shown that the different crystallization kinetics (i.e., crystal nucleation and growth rate) that can be induced at various gas pressures can significantly influence the PLA’s foaming behavior (i.e., cell nucleation and expansion behavior).

No description available.

Yes / The “sliding graft copolymer” (SGC), in which many linear poly-ε-caprolactone (PCL) side chains are bound to cyclodextrin rings of a polyrotaxane (PR), was prepared and employed to toughen brittle polylactide (PLA) with methylene diphenyl diisocyanate (MDI) by reactive blending. The SGC was in situ crosslinked and therefore transformed from a crystallized plastic into a totally amorphous elastomer during reactive blending. Meanwhile, PLA-co-SGC copolymer was formed at interface to greatly improve the compatibility between PLA and SGC, and the chain extension of PLA also occurred, were confirmed by FTIR, GPC, SEM, and TEM. The resulting PLA/SGC/MDI blends displayed super impact toughness, elongation at break and nice biocompatibility. It was inferred from these results the crosslinked SGC (c-SGC) elastomeric particles with sliding crosslinking points performed as stress concentrators and absorbed considerable energy under impact and tension process. / This work was supported by the National Natural Science Foundation of China (50933001, 51221002 and 51320105012).

Le polylactide (PLA) est un polymère à la fois biodégradable et biosourcé focalisant l'attention des chercheurs pour le remplacement des plastiques conventionnels. A la température ambiante, le PLA est fragile et nécessite d’être modifié par plastification physique afin d’augmenter sa ductilité, mais dans le même temps sa rigidité chute fortement. Une alternative à cette plastification physique est la plastification par extrusion réactive. L’extrusion réactive du PLA avec l’acrylate de poly(éthylène glycol) (acrylPEG) donne lieu à un PLA plastifié nommé pPLA. Cette thèse a pour objectifs l’identification de la structure du pPLA et l’étude de son évolution lors de transformations thermomécaniques d’étirage et de recyclage. La structure du pPLA a été analysée par une approche multi-échelles et multidisciplinaire. L’acrylPEG polymérisant et formant des inclusions, est partiellement greffé au PLA et partiellement libre. De plus, les réactions conduisent à une légère réticulation de la matrice. La présence de plastifiant conduit à un bon équilibre entre rigidité et ductilité. Les mécanismes de déformation du pPLA sous étirage ont montré que les mécanismes d’orientation moléculaire sont prépondérants par à l’endommagement, qui lui prédomine dans le PLA. L’analyse du recyclage thermomécanique du pPLA a mis en évidence une dégradation du matériau dépendant du type de procédé utilisé. L’utilisation de la compression à chaud est le procédé le plus défavorable, conduisant à une dégradation plus importante du pPLA par rapport au PLA. Ces travaux ont permis de développer des méthodologies de caractérisation permettant une meilleure identification structurale des biopolymères / Polylactide (PLA), a biodegradable and bio-based polymer, raised researchers’ attention to replace conventional plastics. At room temperature, PLA is brittle and requires physical plasticization that increases its ductility but at the same time drastically decreases its stiffness. As an alternative, plasticization by reactive extrusion was recently developed. The reactive extrusion of PLA with acrylated poly(ethylene glycol) (acrylPEG) as plasticizer yields a plasticized PLA named pPLA. This thesis aims at identifying the structure of this pPLA and studying its evolution engendered by thermomechanical transformations as drawing and recycling. First, pPLA’s structural features are analyzed by a multi-scale and multi-disciplinary approach. pPLA is characterized by partially grafted and partially free inclusions of the polymerized plasticizer and a slightly crosslinked PLA matrix. These plasticizer inclusions lead to a material with a good stiffness-ductility balance. Second, the deformation mechanisms of pPLA upon drawing indicate that chain orientation mechanisms are predominant compared to damage, the latter dominating deformation in PLA. Third, the thermomechanical recycling of pPLA shows that degradation is dependent on the type of processing step. Compression-molding is detrimental to pPLA inducing after recycling a higher degradation compared to PLA. This thesis releases new characterization methodologies enabling a better identification of biopolymer structural features

The development of biodegradable plastics from sustainable sources is at the forefront of chemical research. One such example is the production of polylactide (PLA) via the ring-opening polymerisation (ROP) of the cyclic ester lactide (LA). Current industrial metal initiators utilised for the ROP of LA do not allow control over the stereochemistry of the resulting product. This thesis will investigate various initiators containing a variety of ligand sets for the ROP of rac-LA. Chapter 1 introduces the ROP of rac-LA, the mechanisms utilised and the methods employed for characterisation of PLA. A review of the current literature of recent developments in the production of PLA via various metal initiators is also included. Chapter 2 reports the development of a series of group (IV) complexes containing various amine tris(phenolate) ligands, where the sterics and electronics have been varied. Such complexes were trialled for the ROP of rac-LA as well as the ROP of trimethylene carbonate (TMC). The ability of such initiators to produce copolymers of rac-LA/TMC and rac-LA/isosorbide was also investigated and discussed. Chapter 3 describes the synthesis of a range of group (IV) complexes containing Salalen ligands. The sterics of the ligands have been varied and the ability of the initiators to initiate the ROP of rac-LA in a stereocontrolled fashion has been investigated. Furthermore, the complexes have been trialled for the degradation of PLA into methyl lactate, an important starting material in the production of LA. Chapter 4 investigates the development of Al(III) Salalen complexes for the ROP of rac-LA, where the sterics and electronics of the ligand have been varied. Kinetic investigations have been carried out to aid the understanding of the polymerisation process. Chapter 5 provides details of the reaction procedures for the synthesis of ligands, complexes and polymers. Kinetic procedures are also reported together with details of the analytical techniques employed.

Biodegradable polyesters represent a class of extremely useful polymeric materials for many applications. Among these polyesters, the biodegradable and biocompatible, polylactide is very promising for many applications in both medical and industrial areas. Other biodegradable polymers such as polytrimethylene carbonate, polybutyrolactone, polyvalerolactone, and polycaprolactone can be blended or copolymerized with polylactide to fine tune the properties to fit the needs for their applications. The properties of these polymers and copolymers depend upon the tacticity of the polymers which can be directly controlled by the catalysts used for polymer production. Therefore, it has been of great interest to develop new selective catalytic systems for the ring-opening polymerization of lactide and other cyclic monomers. This dissertation focuses on developing new zinc and aluminum complexes and studying their selectivity and reactivity of these complexes for the ring-opening polymerization of lactide and other cyclic monomers, i.e. trimethylene carbonate, beta-butyrolactone, delta-valerolactone, and epsilon-caprolactone. Herein, aspects of the ring-opening polymerization of lactide and other cyclic monomers utilizing novel zinc and aluminum complexes will be discussed in detail. In the process for the ring-opening polymerization of lactide, chiral zinc half-salen complexes derived from natural amino acids have shown to be very active catalysts for producing polymers with high molecular weight and narrow polydispersities at ambient temperature. The chiral zinc complexes were found to catalyze rac-lactide to heterotactic polylactides with Pr values ranging from 0.68-0.89, depending on the catalyst and reaction temperature employed during the polymerization process. The reactivities of the various catalysts were greatly affected by substituents on the Schiff base ligands, with sterically bulky substituents being rate-enhancing. Furthermore, a series of both chiral and achiral aluminium half-salen complexes have been synthesized and characterized. These aluminum complexes all showed moderate selectivity to the ring-opening polymerization of rac-lactide to produce isotactic polylactide with Pm value up to 0.82 in toluene at 70 degrees C. Moreover, some of the studied aluminum complexes displayed epimerization of rac-lactide to meso-lactide during the polymerization process. Kinetic studies for the ring-opening polymerization of lactide utilizing these zinc and aluminum complexes are included in this dissertation. Along with these studies, the copolymerization of lactide with epsilon-caprolactone and delta-valerolactone will also be presented.

Biodegradable, biocompatible polylactide (PLA) synthesized from renewable resources has attracted extensive interests over the past decades and holds great potential to replace many petroleum-derived plastics. With no loss of biodegradability and biocompatibility, we highly toughened PLA using a novel bioelastomer (BE)–synthesized from biomass diols and diacids. Although PLA and BE are immiscible, BE particles of ∼1 μm in diameter are uniformly dispersed in the matrix, and this indicates some compatibility between PLA and BE. BE significantly increased the cold crystallization ability of PLA, which was valuable for practical processing and performance. SEM micrographs of fracture surface showed a brittle-to-ductile transition owing to addition of BE. At 11.5 vol%, notched Izod impact strength improved from 2.4 to 10.3 kJ/m2, 330% increment; the increase is superior to previous toughening effect by using petroleum-based tougheners.

Yes / Co-crystallization of polymers with different configurations/tacticities provides access to materials with enhanced performance. The stereocomplexation of isotactic poly(L-lactide) and poly(D-lactide) has led to improved properties compared with each homochiral material. Herein, we report the preparation of stereocomplex micelles from a mixture of poly(L-lactide)-b-poly(acrylic acid) and poly(D-lactide)-b-poly(acrylic acid) diblock copolymers in water via crystallization-driven self-assembly. During the formation of these stereocomplex micelles, an unexpected morphological transition results in the formation of dense crystalline spherical micelles rather than cylinders. Furthermore, mixture of cylinders with opposite homochirality in either THF/H2O mixtures or in pure water at 65 °C leads to disassembly into stereocomplexed spherical micelles. Similarly, a transition is also observed in a related PEO-b-PLLA/PEO-b-PDLA system, demonstrating wider applicability. This new mechanism for morphological reorganization, through competitive crystallization and stereocomplexation and without the requirement for an external stimulus, allows for new opportunities in controlled release and delivery applications. / University of Warwick, Swiss National Science Foundation and the EPSRC. The Royal Society - an Industry Fellowship to A.P.D. The Engineering and Physical Sciences Research Council (EP/G004897/1) - funding to support postdoctoral fellowships for A.P.B. as well as funding for J.S. and M.A.D. through the Warwick Centre for Analytical Science (EP/F034210/1). The Science City Research Alliance and the HEFCE Strategic Development Fund - funding support. Some items of equipment that were used in this research were funded by Birmingham Science City, with support from Advantage West Midlands and part-funded by the European Regional Development Fund.

Yes / We report the crystallization-driven self-assembly of diblock copolymers bearing a poly(L-lactide) block into cylindrical micelles. Three different hydrophilic corona-forming blocks have been employed: poly(4-acryloyl morpholine) (P4AM), poly(ethylene oxide) (PEO) and poly(N,N-dimethylacrylamide) (PDMA). Optimization of the experimental conditions to improve the dispersities of the resultant cylinders through variation of the solvent ratio, the polymer concentration, and the addition speed of the selective solvent is reported. The last parameter has been shown to play a crucial role in the homogeneity of the initial solution, which leads to a pure cylindrical phase with a narrow distribution of length. The hydrophilic characters of the polymers have been shown to direct the length of the resultant cylinders, with the most hydrophilic corona block leading to the shortest cylinders. / EPSRC and the University of Warwick, the Swiss National Science Foundation - Early Postdoc Mobility fellowship (Grant no PBNEP2-142949 to A.P.B.). The Warwick Research Development Fund. Some items of equipment funded by Birmingham Science City: Innovative Uses for Advanced Materials in the Modern World (West Midlands Centre for Advanced Materials Project 2), with support from Advantage West Midlands (AWM) and part funded by the European Regional Development Fund (ERDF).