Life cycle assessment of bio-based synthetic fibers: the case of polyester substitutes

Numerous studies have shown that the textile sector has a high fossil-fuel dependency, emits excessive amount of greenhouse gases and uses vast amount of water. Currently, polyester (fossil-based) makes up about a half of the industry's fiber production and the volumes are expected to increase. Polyester fiber is traditionally made out of polyethylene terephthalate (PET) polymer. In order to break from the fossil-fuel dependency, textile industry has the possibility to use alternative feedstock for the polyester by reverting to bio-sourcing – strategy where the product's carbon backbone comes partially or fully from the bio-based feedstock. The polyester fiber can be entirely substituted in its current uses by three such bio-based substitutes: bio-based PET fiber as a drop-in substitute (chemically identical to the fossil counterpart); polytrimethylene terephthalate (PTT) fiber as an intra-family substitute with properties comparable to PET fiber and nylon; and polylactic acid (PLA) fiber as a novel fiber without a fossil counterpart and with properties comparable to PET fiber. All of these fibers are produced from the homonymous polymers via melt spinning and their carbon backbone comes partially or entirely from bio-based feedstock. The environmental effects of this feedstock substitution have not been studied abundantly, in spite of the existing political will to prioritize bio-based products, e.g. as the European Green Deal does. This project therefore performs a comparative, cradle-to-gate life cycle assessment of the conventional polyester fiber and these substitutes taking into account state-of-the-art production process. In order to do so Life cycle inventories (LCI) were modelled for 6 different scenarios for bio-based PET, 2 for bio-based PTT and 1 for PLA and were based on public literature and ecoInvent data. Impact assessment was performed by applying two methods – Swiss Ecological Scarcity and European Environmental Footprint, representative of the Swiss environmental policy and of a more scientific classification of environmental and health impacts respectively. The study finds that all three bio-based fibers are produced from the first-generation feedstock (crops). Currently, only the partially bio-based PET and PTT polymers are commercialized, such that the prevailing monomer, purified terephthalic acid (PTA) remains fossil-based for both. Then, monoethylene glycol (MEG) is produced from sugarcane or corn and 1,3-propanediol (PDO) from corn respectively. PLA is a fully bio-based polymer, produced from corn. Bio-sourcing for polyester is found to offer a limited improvement in a small number of impacts (with negligible contribution to the overall score) while causing substantial additional environmental burdens elsewhere (per kg of fiber). Namely, none of the bio-based alternatives perform better than the fossil-based PET fiber on the overall score. However, the partially bio-based PTT fiber may be a viable substitute for nylon (based on lower overall score). In the absence of carbon crediting for bio-based feedstock, climate impacts are found to be worse for the alternatives than the conventional polyester. Eutrophication, acidification, water scarcity impacts and land use rise with fiber's bio-content and largely stem for the agricultural practices (up to 88%, 74%, 97% and 100% respectively). It was also seen that PTA necessitates more precise modeling to raise the certainty of conclusions for the respective fully bio-based PET and PTT scenarios. At this stage, bio-based alternatives have a worse environmental performance than fossil-based polyester. The environmental performance of the bio-based fibers may be increased with alternative feedstock options or with improved agricultural practices.

Processing of Sustainable Cellular Biocomposites

Carole Boissard

Petroleum-based polymers and composites are commonly used in a wide variety of application fields. However ecological concerns, increasing oil prices and dwindling natural resources explain why nowadays industrial and public interest is more than ever focused on new bio-based – “greener”- products. In order to find viable substitutes for petroleum-based materials, major efforts are devoted to the development of sustainable solutions combining fully compostable matrices and fibres from renewable resources. Polylactide (or polylactic acid) (PLA) is currently one of the most versatile biodegradable polymers derived from renewable resources such as non-food crops of corn or sugar cane. Its transformation into foamed cellular structures would decrease its density and at the same time may improve its specific mechanical properties. This could provide cost-effective and sustainable products for packaging and construction. In the context of developing “green” foams, the focus in the present work has been on a solvent-free process based on physical foaming with supercritical carbon dioxide (ScCO2) as a foaming agent. This foaming process includes thermally driven but kinetically controlled phenomenon. Solubility and diffusion of the gas in the molten polymer, cell nucleation and growth, as well as stabilization of the final foam structures were studied for neat and composite materials. At low processing temperatures and low depressurization rates, homogeneous structures were obtained thanks to a balance between cell growth mechanisms and cell stabilization, thus limiting uncontrolled cell coalescence. The density of the resulting polylactide foams ranged from 0.12 to 0.3 g/cm3 with corresponding compression moduli of 6 to 73 MPa respectively. The processing windows were strongly dependent on the rheological melt properties of the PLAs. PLA is generally considered to be a high strength, high modulus thermoplastic but its brittleness has limited its industrial use. PLA was therefore combined with wood fibres (WF) and microfibrillated cellulose (MFC) in order to improve its mechanical performance without compromising its environmental impact. Two compounding methods, a wet mixing papermaking-like process and a solvent casting process were investigated for the production of WF/PLA and MFC/PLA biocomposites. Degradation of PLA occured during wet-mixing, due to the water used as a dispersant, and to several heating steps applied during compounding. Improvement of the drying and processing conditions and/or the replacement of water by isopropanol limited this degradation. The presence of cellulose fibres considerably modified foaming mechanisms; gas solubility was decreased and the coefficient of diffusion increased, leading to lower quantities of CO2 available for foaming. In addition, stiffness of the fibre network impeded full expansion of the polymer matrix. Thus smaller cells were created. Densities from 0.15 (neat PLA) to 0.37 and 0.55 g/cm3 and moduli ranging from 35 (neat PLA) to 125.5 and 373 MPa were obtained by the addition of 5wt% WF and MFC respectively. Addition of a chain extender enabled viscosity of the matrix to be increased causing increased orientation of the fibre network during flow and hence fibre alignment in the cell walls. Density was thus decreased by 95 % to 0.017 g/cm3 and compression modulus decreased to 0.32 MPa for 5wt% WF composite. Cell wall shrinkage was observed in the neat PLA foams obtained with the chain extender. This was reduced by adding wood fibres while maintaining similar density and modulus. Cellulose fibres act as an extra scaffold in the cellular structures. Industries are currently considering the use of these materials for applications in packaging e.g. as cushioning materials, or in architecture as display panels, or as sandwich core materials for the replacement of expanded polystyrene, polyvinyl chloride or polyurethane foams.

EPFL2012

Synthesis of Functional Polyesters via Baylis-Hillman Polymerization

Sanhao Ji

Aliphatic polyesters receive increasing attention over the last years driven by their application as biodegradable substitutes for conventional commodity thermoplastics and applications in the biomedical field, where amongst the family of biodegradable polymers, aliphatic polyesters possess the leading position as a consequence of the ready metabolization of the degradation products in most cases. This has led to a wide spread use of polyester homo- and copolymers in drug delivery, surgical implants, and functional materials in tissue engineering. In general, polyesters have a high level of commercial importance, and a variety of well known processing technologies are available. To tune the properties of these materials, e.g. their degradation behavior and to add further functionality, there is significant interest in synthetic strategies which can be used to prepare side-chain functionalized polyesters with variable architectures. This Thesis explores the feasibility of a novel approach towards functional polyesters that is based on the Baylis-Hillman reaction, which involves the base catalyzed condensation of an aldehyde and an acrylate building block to produce an α-methylene-β-hydroxycarbonyl compound. As the Baylis-Hillman polymerization does not require the use of side chain protected monomers, this route may represent an interesting alternative strategy for the preparation of functional polyesters. An attractive feature of the Baylis-Hillman polymerization is that it generate polymer with reactive hydroxyl and vinyl groups, which can be used in a subsequent step for post-modification or prepare functional crosslinked scaffolds. This Thesis consists of four chapters. The different synthetic strategies that have been used for the preparation of multi-functional polyesters and the Baylis-Hillman reaction are reviewed in Chapter 1. Chapter 2 investigates the feasibility of the Baylis-Hillman polymerization of diacrylates and dialdehydes to prepare side-chain functional polyesters and explores the subsequent post-polymerization modification of these polymers to further enhance their functionality. Using 1,3-butanediol acrylate and 2,6-pyridinecarboxaldehyde as monomers and DABCO as catalyst, polymers with a degree of polymerization of up to 25 were prepared. These polymers are attractive as they contain chemically orthogonal side-chain hydroxyl and vinyl groups that can be further modified. In first experiments, it was demonstrated that the side-chain hydroxyl and vinyl groups can be quantitatively post-modified with phenyl isocyanate, respectively, methyl-3-mercaptopropionate. Chapter 3 explores the feasibility of the Baylis-Hillman reaction for the synthesis of hyperbranched polyesters. This Chapter describes an efficient and novel approach to functional hyperbranched polyesters via an A2 + B3 approach based on the Baylis-Hillman reaction. Using trimethylolpropane triacrylate and 2,6-pyridinedicarboxaldehyde as monomers and 3-quinuclidinol as the catalyst, polymer swith a degree of branching between 0.36 and 0.8, and a molecular weight of up to 28,100 were prepared. The effects of monomer ratio and addition mode on the final molecular weight, polydispersity index and degree of branching were studied. In order to demonstrate the potential of this polyester as a reactive polymer, the hydroxyl, vinyl groups and pyridine residues were post-modified with phenyl isocyanate, methyl-3-mercaptopropionate and methyl iodide. Chapter 4 aims to further explore the scope and versatility of the Baylis-Hillman polymerization and studies the preparation of side-chain functional polyesters by polymerization of 1,3-butanediol diacrylate with meta- and para-phthalaldehyde, which are two commercially available dialdehyde building blocks.

EPFL2011

Chemistry and Analysis of Nanoparticle-Modified Living Cells

Tanja Thomsen

Conventional therapeutics are often limited by their targeting ability, resulting in harmful and potential fatal side-effects for the patients. Recently, new strategies have been developed to improve target specificity of drugs in order to generate more efficient therapeutics. An innovative concept, examined in this thesis, is the use of cells as therapeutic carriers. This concept termed cell-mediated drug delivery, relies on the intrinsic targeting properties of cells to transport the therapeutic drug to the target location. The conjugation of nanoparticles, loaded with drugs or adjuvants, to the surface of cells enables the transport to the desired location and increases the local drug concentration, reducing the required therapeutic leading to further attenuation of side effects. Chapter 1 introduces the concept of cell-mediated drug delivery. It highlights the advantages of using cells decorated with nanoparticles as carriers for therapeutics as opposed to free (polymer) nanoparticles. Examples of various covalent and non-covalent nanoparticle conjugations strategies are discussed and an overview of all approaches, which have been used previously to attach nanoparticles to the cell surface, is presented. The importance of a thorough in vitro characterization of nanoparticle-modified cells is emphasized. The use of common characterization techniques such as flow cytometry, UV-Vis and fluorescence spectroscopy, fluorescence and electron microscopy, and radiolabeling is discussed in detail and examples of qualitative and quantitative in vitro analysis of nanoparticle- modified cells are reviewed. Chapter 2 contains an extensive in vitro analysis of cell-nanoparticle conjugates using fluorescent- and fluorescent label-free methods. The stability of nanoparticles loaded with cargo attached to cells was investigated by encapsulating three different green fluorescent dyes into nanoparticles and tracking the fluorescence signal over 24 h. Two of the dyes revealed a complete loss of fluorescence of a time period of 24 h, whereas a third entrapped dye and a covalently attached dye did not have a decrease in fluorescence over 24 h. Finally, we developed a fluorescent label-free method as an alternative to characterize nanoparticle-decorated cells without the need for any fluorescent label. Chapter 3 systematically explores conjugation chemistries to immobilize two platforms of functional biodegradable polymer nanoparticles (PEG-PLA (poly(ethylene glycol) - poly(lactide)) nanoparticles and carboxylic PLA nanoparticles) on T cells as potential carrier across the blood-brain barrier (BBB). We compared a series of covalent and non-covalent immobilization strategies by flow cytometry (FACS), confocal microscopy, and impact on cell proliferation and cellular viability. We found that T-cell surface coupling of nanoparticles is dependent on the ratio of nanoparticles to cells and that higher ratios led to more particles attached to cells. Furthermore, the most efficient strategy to attach nanoparticles was via ligand-receptor interactions (lectin - sialic acid and biotin - NeutrAvidin). In addition, nanoparticle-decorated T cells were investigated for their ability to cross an in vitro mouse BBB model under static conditions in a two-chamber assay. Decorating the cells with nanoparticles does not affect their ability to bind ICAM-1 (a protein involved in the transmigration process) or to cross the model biological barrier.

EPFL2020