scholarly journals Synergistic Enzyme Mixtures to Realize Near-Complete Depolymerization in Biodegradable Polymer/Additive Blends

2021 ◽  
Author(s):  
Christopher DelRe ◽  
Boyce Chang ◽  
Ivan Jayapurna ◽  
Aaron Hall ◽  
Ariel Wang ◽  
...  
Keyword(s):  
Chemical Modification ◽  
Degradation Rate ◽  
Morphological Changes ◽  
Strong Dependence ◽  
Monomer Conversion ◽  
Chain Scission ◽  
Polymer Additive ◽  
Processive Enzyme ◽  
Random Scission ◽  
Host Polymer

AbstractEmbedding catalysts inside of plastics affords accelerated chemical modification with programmable latency and pathways. Nanoscopically embedded enzymes can lead to near complete degradation of polyesters via chain-end mediated processive depolymerization. The overall degradation rate and pathways have a strong dependence on the morphology of semi-crystalline polyesters. Yet, most studies to date focus on pristine polymers instead of mixtures with additives and other components despite their nearly universal uses in plastic production. Here, additives are introduced to purposely change the morphology of polycaprolactone (PCL) by increasing the bending and twisting of crystalline lamellae. These morphological changes immobilize chain-ends preferentially at the crystalline/amorphous interfaces and limit chain-end accessibility by the embedded processive enzyme. This chain end redistribution reduces the polymer-to-monomer conversion from >95% to less than 50%, causing formation of highly crystalline plastic pieces including microplastics. By synergizing both random chain scission and processive depolymerization, it is feasible to navigate morphological changes in polymer/additive blends and to achieve near complete depolymerization. The random scission enzymes in the amorphous domains create new chain ends that are subsequently bound and depolymerized by processive enzymes. Present studies further highlight the importance to consider host polymer morphological effects on the reactions catalyzed by embedded catalytic species.

scholarly journals Phosphated Avocado Seed: A Renewable Biomaterial for Preparing a Flame Retardant Biofiller

2021 ◽  
Author(s):  
DAVID Zuluaga-Parra ◽  
L.F Ramos-deValle ◽  
Saul Sanchez ◽  
J.R. Torres-Lubián ◽  
J.A. Rodríguez-Gonzalez ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Chemical Modification ◽  
Flame Retardant ◽  
Photoelectron Spectroscopy ◽  
Morphological Changes ◽  
Ethylene Vinyl Acetate ◽  
Chemically Modified ◽  
Air Atmosphere ◽  
Thermal Stability Of ◽  
Avocado Seed

Abstract The cellulose and starch present in the avocado seed can be chemically modified to obtain biofillers with fire retarding characteristics. The resulting composites could be used as substitute of the corresponding halogenated composites. For this, the avocado seed was first washed, dehydrated and pulverized, and thereafter, chemically modified with phosphoric acid in the presence of urea. This was studied using infrared spectroscopy, nuclear magnetic resonance and X-Ray photoelectron spectroscopy, in order to determine the resulting chemical structure and confirm the presence of the proposed functional groups. In addition, scanning electron microscopy and elemental analysis were used, respectively, to establish the resulting morphological changes, as well as the elements present on the surface of the modified material. Thermogravimetric analysis was also carried out in order to establish the thermal stability of the material and predict the effect on the flame retardancy due to the mentioned chemical modification. Further tests established that the obtained modified structure and morphology of the avocado seed was highly dependent on the method used to dehydrate the pulverized avocado seed. It was also determined that chemical modification greatly increased the thermal stability of the avocado seed in air atmosphere. The flame-retardant effect of the modified avocado seed was assessed in polyethylene/ethylene-vinyl-acetate (PE/EVA) composites via cone calorimeter tests. These results showed that the modified avocado seed decreased the peak of the heat release rate (pHRR) by 50% and the total heat released (THR) by 15%. This phosphated avocado seed could be a good option as a renewable biofiller for polymer composites with enhanced flame-retardant properties.

Partition of tert-dodecyl mercaptan in systems containing styrene, polystyrene, and polybutadiene. Its effect on the macromolecular characteristics of high-impact poly styrene

e-Polymers ◽  
2007 ◽  
Vol 7 (1) ◽  
Author(s):  
Natalia Casís ◽  
Carla Vanesa Luciani ◽  
Diana Alejandra Estenoz ◽  
Marisa Martinelli ◽  
Miriam Strumia ◽  
...  
Keyword(s):  
Total Concentration ◽  
Strong Dependence ◽  
Monomer Conversion ◽  
Theoretical Work ◽  
High Impact ◽  
Proton Nuclear Magnetic Resonance ◽  
Molecular Weights ◽  
H Nmr ◽  
Dodecyl Mercaptan ◽  
Good Agreement

AbstractThis work investigates the distribution between phases of tert-dodecyl mercaptan (t-DDM) in systems containing styrene (St), polystyrene (PS), and polybutadiene (PB) with the aim of studying its effect on the molecular macrostructure of High-Impact Polystyrene (HIPS) produced via the bulk process. Experimental work involved the study of several St/PS/PB/t-DDM blends, and of 2 polymerizations of St in presence of PB (with and without t-DDM). Blends were prepared with increasing PS/St ratios to emulate monomer conversions of 7, 9, 11, 13, and 15%, employing 2 base PSs of different molar masses, and several total concentrations of t-DDM. Measurements by Proton Nuclear Magnetic Resonance (1H NMR) indicate that t-DDM is almost evenly distributed between the phases at room temperature. In addition, for samples taken along the 2 investigated polymerizations, monomer conversion, grafting efficiency, and free PS molecular weights were measured. Theoretical work involved first to model the species partitions through the Flory-Huggins theory [1]; and then, to combine such partition model with a polymerization model extended from that by Casís et al. [2]. Theoretical estimations were in good agreement with experimental determinations. Simulations suggest that t-DDM partition coefficients exhibit a weak dependence with temperature, but a strong dependence with its total concentration. Also, the combined partition/polymerization model indicates that the free PS contained in the occlusion regions exhibits lower molecular weights than that in the continuous matrix.

Enhanced Spin-capturing Polymerization and Radical Coupling Mediated by Cyclic Nitrones

2012 ◽  
Vol 65 (8) ◽  
pp. 1110 ◽  
Author(s):  
Kayte Ranieri ◽  
Matthias Conradi ◽  
Pierre-Yves Chavant ◽  
Veronique Blandin ◽  
Christopher Barner-Kowollik ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Strong Dependence ◽  
Monomer Conversion ◽  
Functional Polymers ◽  
Spin Trapping ◽  
Coupling Reactions ◽  
Trapping Rate ◽  
Cyclic Nitrones ◽  
Radical Coupling ◽  
Addition Rate

A series of cyclic nitrones have been tested for their spin-trapping activity in the enhanced spin-capturing polymerization of styrene and in nitrone-mediated radical coupling reactions. rac-2-Isopropyl-2,3-dimethyl-1-oxy-2,3-dihydro-imidazol-4-one was found to be the most efficient nitrone. The specific polystyrene macroradical addition rate to this nitrone was determined to be 8.0 × 103 L mol–1 s–1, which is by a factor of 10 higher than for previously studied compounds. Via enhanced spin-capturing polymerization, polymers in the range of oligomers to 30000 g mol–1 were obtained. A strong dependence of molecular weight on monomer conversion was observed, which can be explained by the high trapping rate. In nitrone-mediated radical coupling, almost ideal coupling of bromine-functional polymers was obtained and the successful introduction of the residual alkoxyamine functionality confirmed.

STIMULI RESPONSIVE MORPHOLOGICAL CHANGES OF PNIPA POLYMER BRUSHES SYNTHESIZED ON SILICON SUBSTRATE

2013 ◽  
Vol 01 (02) ◽  
pp. 1350003
Author(s):  
MUHAMMAD NURUL HUDA ◽  
A. N. M. HAMIDUL KABIR
Keyword(s):  
Conformational Changes ◽  
Polymer Brushes ◽  
Morphological Changes ◽  
Polymer Brush ◽  
Gel Permeation Chromatography ◽  
Monomer Conversion ◽  
Stimuli Responsive ◽  
Air Bubble ◽  
Force Microscopy ◽  
Stimulus Response

High-density polymer brushes were grown from the silicon surface by atom transfer radical polymerization of Poly(N-isopropylacrylamide) (PNIPA) at different polymerization conditions. PNIPA brushes were prepared using Copper (I) Chloride/tris(2-(dimetylamino)ethyl)amine (Me6TREN) as a catalytic system in DMSO at 20°C. Free polymer formed during the brush formation was characterized by gel permeation chromatography. The grafting densities up to 0.52 chains/nm2 were obtained. The layer thickness of polymer brush increases with the increase of conversion of the monomer conversion as well as polymerization time. Atomic force microscopy and air bubble contact angle under pH solution were employed to study the surface morphology, reversible conformational changes of and stimulus-response behavior. PNIPA brushes exhibited a different nanomorphology after treatment with different pH solution. It also revealed a unique reversible wetting behavior with pH. The reversible properties of the PNIPA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.

Helical Spring Stress Relaxometer

1957 ◽  
Vol 30 (3) ◽  
pp. 889-894
Author(s):  
J. P. Berry
Keyword(s):  
Stress Relaxation ◽  
Practical Importance ◽  
Chain Scission ◽  
Routine Test ◽  
Test Procedures ◽  
First Order ◽  
Time Graph ◽  
Aging Conditions ◽  
Force Time ◽  
Random Scission

Abstract Changes in the tensile properties of rubber are obviously of great practical importance. Consequently, measurements of the change in force required to maintain or produce a given extension under controlled conditions of temperature and atmosphere have frequently been made and have advanced our understanding of the physical process of crystallization and of the chemical reactions responsible for thermal aging to the extent that they may become routine test procedures. The decrease in the force required to maintain a constant extension during the period of aging (stress relaxation) has been the most common measurement, in part because rubber elasticity theory predicts an equality between the fractional decrease in force and the fraction of the network chains originally supporting the stress which have become ineffective. Stress-relaxation behavior may characterize the type of scission reaction occurring; for example, the stress relaxation of most vulcanizates can be interpreted as a first-order scission of crosslinks, and not as a random scission of monomeric units in the chains between crosslinks. Stress-relaxation results, however, do not provide all the necessary information on network changes—the final properties of the rubber depend not only on crosslink or chain scission but to a comparable degree on crosslink formation during aging, which does not affect the force at constant extension. To examine this second effect requires measurements on the intermittent stretching of an unstrained sample to a constant extension. Parallel measurements of force at constant and intermittent extension under identical aging conditions are therefore required. The several designs of apparatus already described have usually been rather complicated and require practice and skill in use. A simple apparatus developed in these laboratories, which can readily be used for routine operations, is described in the following paragraphs. The fractional change in force is read directly from a vernier scale on the instrument, and may be immediately plotted on a force-time graph, preferably as log10 (force/forcet=0) vs. time (cf. Reference 3).

scholarly journals Degradation of Some Pesticides in Avian Embryos

1999 ◽  
Vol 47 (1) ◽  
pp. 117-122
Author(s):  
L. Várnagy
Keyword(s):  
Analytical Chemistry ◽  
Japanese Quail ◽  
Degradation Rate ◽  
Normal Development ◽  
Morphological Changes ◽  
Avian Embryos ◽  
Chemistry Data ◽  
Immersion Technique ◽  
Air Space

On day 9 or 12 of the hatching period different pesticides (parathion, methylparathion, carbendazim, 2,4-D-amine Na, phosmethylane) were applied in ecotoxicological trials. The formulations were either injected into the air space of pheasant, quail or hen eggs or hen eggs were treated by the immersion technique. The residues of pesticides were measured in samples on days 13, 14 and 16 of incubation of chicken and pheasant embryos, while the Japanese quail embryos were analysed on days 10-14 of incubation. Analytical chemistry data showed a varying degradation rate of the compounds in avian embryos of the same species. The residues directly affect the embryos, disturbing their normal development and causing pathophysiological and morphological changes.

Chemorheology of Irradiation-Cured Natural Rubber. I. Stress Relaxation Mechanisms for Various Curing Systems in Natural Rubber at High Temperature

1975 ◽  
Vol 48 (2) ◽  
pp. 141-153 ◽  
Author(s):  
S. Tamura ◽  
K. Murakami
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Main Chain ◽  
Chain Scission ◽  
Chemical Structures ◽  
Carbon Carbon Bonds ◽  
Interchange Reaction ◽  
Thermal Scission ◽  
Physical And Chemical ◽  
Random Scission

Abstract 1. There was no difference of stress relaxation, either in air or in nitrogen, between DCP cures (Sample 1) and irradiation cures (Sample 2). This suggests that these vulcanizates have the same physical and chemical structures. In air Samples 1 and 2 underwent random scission of only the main chain. 2. In the case of irradiation-TMTD cures (Samples 4 and 5), the stress decay was also based on oxidative scission of the main chain. The number of moles of main chain scission, qm(t), was independent of the ratio ρ (of Nc(0)) based on the carbon—carbon bonds to Nm(0) based on the mono- and disulfide links). However, qm(t) was larger than that of Sample 2. The oxidative scission of the main chain seemed to be accelerated by mono- and disulfide. It was found from comparison of Samples 4 and 5 that TMTD cures (Sample 3) underwent random scission on the main chain. The stress relaxation in nitrogen for Samples 3, 4, and 5 was due to thermal scission of the crosslink. 3. The stress relaxation, either in air or in nitrogen, of accelerated-sulfur-cures (Sample 6) and irradiation-sulfur cures (Samples 7 and 8) was expressed by the sum of two exponential terms. The stress relaxation in air of Samples 6, 7, and 8 could be explained by the interchange reaction of polysulfide links and the random scission on the main chain. The stress decay in nitrogen of these vulcanizates was based on both interchange of polysulfide links and thermal scission of crosslinks. The rate of the interchange reaction in air was very closely consistent with that in nitrogen. 4. The apparent activation energy of oxidative scission of the main chain was about 21 kcal/mol for Samples 2, 6, 7, and 8 and 27 kcal/mol for Samples 3, 4, and 5.

scholarly journals Reduction of graphene oxide and graphene quantum dots using nascent hydrogen: The investigation of morphological and structural changes

2020 ◽  
Vol 5 (1) ◽  
pp. 1-4
Author(s):  
Svetlana Jovanovic ◽  
Olaf C. Haenssler ◽  
Milica Budimir ◽  
Duška Kleut ◽  
Jovana Prekodravac ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Graphene Oxide ◽  
Chemical Composition ◽  
Electrical Properties ◽  
Chemical Modification ◽  
Structural Changes ◽  
Morphological Changes ◽  
Graphene Quantum Dots ◽  
Structure And Morphology

AbstractIn order to modify both chemical and electrical properties of graphene-based nanomaterials, we conducted the chemical modification of graphene oxide (GO) and graphene quantum dots (GQDs). The reaction of the reduction with nascent hydrogen was conducted on both materials. The structure and morphology of produced chemically reduced GO and GQDs were analyzed. While the chemical composition of both GQD and GO changed significantly, GO showed also significant changes in morphology as opposite to GQDs where were morphological changes were not observed.

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