1,721,050 research outputs found
Polyhydroxyalkanoates production with mixed microbial cultures: from culture selection to polymer recovery in a high-rate continuous process
No full textPolyhydroxyalkanoates (PHA) production with mixed microbial cultures (MMC) has been investigated by means of a sequential process involving three different stages, consisting of a lab-scale sequencing batch reactor for MMC selection, a PHA accumulation reactor and a polymer extraction reactor. All stages were performed under continuous operation for at least 4 months to check the overall process robustness as well as the related variability of polymer composition and properties.By operating both biological stages at high organic loads (8.5 and 29.1gCOD/Ld, respectively) with a synthetic mixture of acetic and propionic acid, it was possible to continuously produce PHA at 1.43g/Ld with stable performance (overall, the storage yield was 0.18 COD/COD). To identify the optimal operating conditions of the extraction reactor, two digestion solutions have been tested, NaOH (1m) and NaClO (5% active Cl2). The latter resulted in the best performance both in terms of yield of polymer recovery (around 100%, w/w) and purity (more than 90% of PHA content in the residual solids, on a weight basis). In spite of the stable operating conditions and performance, a large variation was observed for the HV content, ranging between 4 and 20 (%, w/w) for daily samples after accumulation and between 9 and 13 (%, w/w) for weekly average samples after extraction and lyophilization. The molecular weight of the produced polymer ranged between 3.4×105 and 5.4×105g/mol with a large polydispersity index. By contrast, TGA and DSC analysis showed that the thermal polymer behavior did not substantially change over time, although it was strongly affected by the extraction agent used (NaClO or NaOH). © 2013 Elsevier B.V
Biodegradation of chemically-modified flax fibers in soil and ‘in vitro’ with selected bacteria.
No full textThe extent and rate of degradation of flax (Linum usitatissimum) fibers, both in the native state and after surface chemical modification (acetylation or polyethylene glycol, PEG, grafting), was investigated under laboratory conditions in two different biodegrading environments.
Degradation of the fibers under aerobic conditions by the action of the microorganisms present in soil is assessed with the ASTM 5988-96 method by monitoring carbon dioxide evolution. ‘In vitro’ biodegradation experiments were carried out by exposing the fibers to a pure culture of Cellvibrio fibrovorans bacteria and measuring the mass loss as a function of time.
In spite of the complexity of the system, the results of degradation in soil were satisfactorily reproducible, although the absolute rates were found to change in different experiments using the same soil. The degradation rate of acetylated fibers in soil nearly equals that of unmodified fibers, whereas in the pure culture acetylated fibers biodegrade slower than native fibers. The opposite happens with the PEG-grafted fibers, which degrade slower than unmodified flax in soil and at a comparable rate upon ‘in vitro’ exposure to the bacterial culture. The different biodegradation kinetics observed in the two biodegrading environments were attributed to differences of biocenoses, abiotic factors and biodegradation assessing methods. Nevertheless, the final extent of biodegradation was the same for modified and unmodified fibers both in soil and in the pure culture, showing that the surface chemical modifications applied do not significantly affect biodegradability of the flax fibers
METHOD OF CONTROLLING THERMAL DEGRADATION OF ANIONICALLY TERMINATED POLYMERS AND MATERIALS OBTAINED
No full textThe invention relates to a polymer having improved thermal stability and to a method for preparing said polymer that enables control of its thermal degradation and stability via chemical structure of the polymer end groups. Further the invention relates to a blend comprising said polymer. Finally, the invention relates to use of said polymer or blend for the preparation of polymeric materials for applications in medical, environmental, agricultural and advance materials
Structure-property relations in polymers from renewable resources
No full textThe present research project focuses its attention on the study of structure-property relations in polymers from renewable sources (bio-based polymers) such as polymers microbially produced, i.e. polyhydrohyalkanoates (PHAs) or chemically synthesized using monomers from renewable sources, i.e. polyammide 11 (PA11). By means of a broad spectrum of experimental techniques, the influence of different modifications on bio-based polymers such as blending with other components, copolymerization with different co-monomers and introduction of branching to yield complex architectures have been investigated.
The present work on PHAs focused on the study of the dependence of polymer properties on both the fermentation process conditions (e.g. bacterial strain and carbon substrate used) and the method adopted to recover PHAs from cells. Furthermore, a solvent-free method using an enzyme and chemicals in an aqueous medium, was developed in order to recover PHAs from cells. Such a method allowed to recover PHA granules in their amorphous state, i.e. in native form useful for specific applications (e.g. paper coating).
In addition, a commercial PHA was used as polymeric matrix to develop biodegradable and bio-based composites for food packaging applications. Biodegradable, non-toxic, food contact plasticizers and low cost, widely available lignocellulosic fibers (wheat straw fibers) were incorporated in such a polymeric matrix, in order to decrease PHA brittleness and the polymer cost, respectively.
As concerns the study of polyamide 11, both the rheological and the solid-state behavior of PA11 star samples with different arm number and length was studied. Introduction of arms in a polymer molecule allows to modulate melt viscosity behavior which is advantageous for industrial applications. Also, several important solid-state properties, in particular mechanical properties, are affected by the presence of branching.
Given the importance of using ‘green’ synthetic strategies in polymer chemistry, novel poly(-amino esters), synthesized via enzymatic-catalyzed polymerization, have also been investigated in this work
Electrospun Polymeric Scaffolds with Enhanced Biomimetic Properties for Tissue Engineering Applications
No full textThis PhD Thesis is focused on the development of fibrous polymeric scaffolds for tissue engineering applications and on the improvement of scaffold biomimetic properties. Scaffolds were fabricated by electrospinning, which allows to obtain scaffolds made of polymeric micro or nanofibers. Biomimetism was enhanced by following two approaches: (1) the use of natural biopolymers, and (2) the modification of the fibers surface chemistry.
Gelatin was chosen for its bioactive properties and cellular affinity, however it lacks in mechanical properties. This problem was overcome by adding poly(lactic acid) to the scaffold through co-electrospinning and mechanical properties of the composite constructs were assessed. Gelatin effectively improves cell growth and viability and worth noting, composite scaffolds of gelatin and poly(lactic acid) were more effective than a plain gelatin scaffold.
Scaffolds made of pure collagen fibers were fabricated. Modification of collagen triple helix structure in electrospun collagen fibers was studied. Mechanical properties were evaluated before and after crosslinking. The crosslinking procedure was developed and optimized by using - for the first time on electrospun collagen fibers - the crosslinking reactant 1,4-butanediol diglycidyl ether, with good results in terms of fibers stabilization. Cell culture experiments showed good results in term of cell adhesion and morphology.
The fiber surface chemistry of electrospun poly(lactic acid) scaffold was modified by plasma treatment. Plasma did not affect thermal and mechanical properties of the scaffold, while it greatly increased its hydrophilicity by the introduction of carboxyl groups at the fiber surface. This fiber functionalization enhanced the fibroblast cell viability and spreading.
Surface modifications by chemical reactions were conducted on electrospun scaffolds made of a polysophorolipid. The aim was to introduce a biomolecule at the fiber surface. By developing a series of chemical reactions, one oligopeptide every three repeating units of polysophorolipid was grafted at the surface of electrospun fibers
Novel Polymeric materials for life sciences applications through biocatalytic routes and nanotechnology
No full textBy circumventing many difficulties of conventional synthetic chemistry, biocatalysis represents an
innovative and very flexible route to the synthesis of macromolecules and to their modification after
synthesis. The NSF-BBM Center of Biocatalysis at Brooklyn Polytechnic University has utstanding expertise in the development of new methods for enzyme-catalyzed polymer synthesis.The US Group has established a synergic cooperation with the Polymer Science Group at Bologna University (UNIBO), based on complementarities of their scientific skills. Stemming from the encouraging results of the ongoing collaboration, this new Project aims at using enzymatic catalysis to explore new environmentally friendly routes to polymers to be employed as constituents of innovative porous supports for cell growt
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