A series of biobased epoxy monomers were prepared from diphenolic acid (DPA) by transforming the free acid into n-alkyl esters and the phenolic hydroxyl groups into diglycidyl ethers. NMR experiments ...confirmed that the diglycidyl ethers of diphenolates (DGEDP) with methyl and ethyl esters have 6 and 3 mol % of glycidyl ester. Increasing the chain length of DGEDP n-alkyl esters from methyl to n-pentyl resulted in large decreases in epoxy resin viscosity (700-to-11 Pa·s). Storage modulus of DPA epoxy resins, cured with isophorone diamine, also varied with n-alkyl ester chain length (e.g., 3300 and 2100 MPa for the methyl and n-pentyl esters). The alpha transition temperature of the cured materials showed a linear decrease from 158 to 86 °C as the ester length increases. The Young’s modulus and tensile strengths were about 1150 and 40 MPa, respectively, for all the cured resins tested (including DGEBA) and varied little as a function of ester length. Degree of cure for the different epoxy resins, determined by FTIR and DSC, closely approached the theoretical maximum. The result of this work demonstrates that diglycidyl ethers of n-alkyl diphenolates represent a new family of biobased liquid epoxy resins that, when cured, have similar properties to those from DGEBA.
This paper describes the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol. ...Melt-polycondensation experiments were conducted by a two-stage polymerization using titanium tetraisopropoxide (TiOiPr4) as a catalyst. Polymerization conditions (catalyst concentration, reaction time and second stage reaction temperature) were varied to optimize poly(butylene-FDCA), PBF, and molecular weight. A series of PBFs with different M w were characterized by DSC, TGA, DMTA, X-ray diffraction and tensile testing. Influence of molecular weight and melting/crystallization enthalpy on PBF material tensile properties was explored. Cold-drawing tensile tests at room temperature for PBF with M w 16K to 27K showed a brittle-to-ductile transition. When M w reaches 38K, the Young modulus of PBF remains above 900 MPa, and the elongation at break increases to above 1000%. The mechanical properties, thermal properties and crystal structures of PBF were similar to petroleum derived poly(butylenes-terephthalate), PBT. Fiber diagrams of uniaxially stretched PBF films were collected, indexed, and the unit cell was determined as triclinic (a = 4.78(3) Å, b = 6.03(5) Å, c = 12.3(1) Å, α = 110.1(2)°, β = 121.1(3)°, γ = 100.6(2)°). A crystal structure was derived from this data and final atomic coordinates are reported. We concluded that there is a close similarity of the PBF structure to PBT α- and β-forms.
Biodegradable Polymers for the Environment Gross, Richard A.; Kalra, Bhanu
Science (American Association for the Advancement of Science),
08/2002, Letnik:
297, Številka:
5582
Journal Article
Recenzirano
Odprti dostop
Biodegradable polymers are designed to degrade upon disposal by the action of living organisms. Extraordinary progress has been made in the development of practical processes and products from ...polymers such as starch, cellulose, and lactic acid. The need to create alternative biodegradable water-soluble polymers for down-the-drain products such as detergents and cosmetics has taken on increasing importance. Consumers have, however, thus far attached little or no added value to the property of biodegradability, forcing industry to compete head-to-head on a cost-performance basis with existing familiar products. In addition, no suitable infrastructure for the disposal of biodegradable materials exists as yet.
Petroleum-derived plastics dominate currently used plastic materials. These plastics are derived from finite fossil carbon sources and were not designed for recycling or biodegradation. With the ...ever-increasing quantities of plastic wastes entering landfills and polluting our environment, there is an urgent need for fundamental change. One component to that change is developing cost-effective plastics derived from readily renewable resources that offer chemical or biological recycling and can be designed to have properties that not only allow the replacement of current plastics but also offer new application opportunities. Polyhydroxyalkanoates (PHAs) remain a promising candidate for commodity bioplastic production, despite the many decades of efforts by academicians and industrial scientists that have not yet achieved that goal. This article focuses on defining obstacles and solutions to overcome cost-performance metrics that are not sufficiently competitive with current commodity thermoplastics. To that end, this review describes various process innovations that build on fed-batch and semi-continuous modes of operation as well as methods that lead to high cell density cultivations. Also, we discuss work to move from costly to lower cost substrates such as lignocellulose-derived hydrolysates, metabolic engineering of organisms that provide higher substrate conversion rates, the potential of halophiles to provide low-cost platforms in non-sterile environments for PHA formation, and work that uses mixed culture strategies to overcome obstacles of using waste substrates. We also describe historical problems and potential solutions to downstream processing for PHA isolation that, along with feedstock costs, have been an Achilles heel towards the realization of cost-efficient processes. Finally, future directions for efficient PHA production and relevant structural variations are discussed.
Sophorolipids (SLs) are glycolipids that consist of a hydrophilic sophorose head group covalently linked to a hydrophobic fatty acid tail. They are produced by fermentation of non-pathogenic yeasts ...such as
. The fermentation products predominantly consist of the diacetylated lactonic form that coexists with the open-chain acidic form. A systematic series of modified SLs were prepared by ring opening of natural lactonic SL with
-alkanols of varying chain length under alkaline conditions and lipase-selective acetylation of sophorose primary hydroxyl groups. The antimicrobial activity of modified SLs against Gram-positive human pathogens was a function of the
-alkanol length, as well as the degree of sophorose acetylation at the primary hydroxyl sites. Modified SLs were identified with promising antimicrobial activities against Gram-positive human pathogens with moderate selectivity (therapeutic index, TI = EC
/MIC
= 6-33). SL-butyl ester exhibited the best antimicrobial activity (MIC = 12 μM) and selectivity (TI = 33) among all SLs tested. Kinetic studies revealed that SL-ester derivatives kill
in a time-dependent manner resulting in greater than a 3-log reduction in cell number within 1 h at 2×MIC. In contrast, lactonic SL required 3 h to achieve the same efficiency.
Traditional chemical catalysts for polyester synthesis have enabled the generation of important commercial products. Undesirable characteristics of chemically catalyzed condensation polymerizations ...include the need to conduct reactions at high temperatures (150–280 °C) with metal catalysts that are toxic and lack selectivity. The latter is limiting when aspiring towards synthesis of increasingly complex and well-defined polyesters. This review describes an exciting technology that makes use of immobilized enzyme-catalysts for condensation polyester synthesis. Unlike chemical catalysts, enzymes function under mild conditions (≤100 °C), which enables structure retention when polymerizing unstable monomers, circumvents the introduction of metals, and also provides selectivity that avoids protection–deprotection steps and presents unique options for structural control. Examples are provided that describe the progress made in enzyme-catalyzed polymerizations, as well as current limitations and future prospects for developing more efficient enzyme-catalysts for industrial processes.
Cutinases are polyester hydrolases that show a remarkable capability to hydrolyze polyethylene terephthalate (PET) to its monomeric units. This revelation has stimulated research aimed at developing ...sustainable and green cutinase-catalyzed PET recycling methods. Leaf and branch compost cutinase (LCC) is particularly suited toward these ends given its relatively high PET hydrolysis activity and thermostability. Any practical enzymatic PET recycling application will require that the protein have kinetic stability at or above the PET glass transition temperature (T g, i.e., 70 °C). This paper elucidates the thermodynamics and kinetics of LCC conformational and colloidal stability. Aggregation emerged as a major contributor that reduces LCC kinetic stability. In its native state, LCC is prone to aggregation owing to electrostatic interactions. Further, with increasing temperature, perturbation of LCC’s tertiary structure and corresponding exposure of hydrophobic domains leads to rapid aggregation. Glycosylation was employed in an attempt to impede LCC aggregation. Owing to the presence of three putative N-glycosylation sites, expression of native LCC in Pichia pastoris resulted in the production of glycosylated LCC (LCC-G). LCC-G showed improved stability to native state aggregation while increasing the temperature for thermal induced aggregation by 10 °C. Furthermore, stabilization against thermal aggregation resulted in improved catalytic PET hydrolysis both at its optimum temperature and concentration.
In this work, a series of bio-based chemically recyclable epoxy resins were synthesized from n-alkyl bisferulate esters that do not activate human estrogen receptor alpha (ER alpha ). Viscosities of ...corresponding glycidyl ether n-alkyl bisferulate resins, determined by steady shear rheology, range from 12-9.4 Pa s. Activation energies of flow range from 83-96 kJ mol-1 and are similar to the diglycidyl ether bisphenol A (DGEBA). Thermomechanical properties of diglycidyl ether n-alkyl bisferulate resins cured with isophorone diamine were governed by the length of alpha , omega -diols that link glycidyl ether ferulate units. That is, the glassy phase modulus and alpha transition temperatures range from 3400-2400 MPa (at 25 degree C) and 40-53 degree C (peak of E''), respectively. Furthermore, the onset of thermal degradation (Td5%) varied from 331-300 degree C. Chemical recycling of cured epoxy resins was performed by static immersion in 10 w/w sodium hydroxide aqueous solutions at 60 degree C. Times required for complete conversion of cured resins to water-soluble degradation products was also alpha , omega -diol length dependent and varied from 5 to 65 h. Thus, diglycidyl ether of n-alkyl bisferulate resins provides a viable biobased alternative to BPA epoxy resins as well as the option of chemical degradability and recovery of fillers in composite applications.
This paper reports that the bulk polymerization of l-aspartic acid diethyl ester catalyzed by immobilized CAL-B at 80 °C for 24 h gives primarily (∼95%) α-linked poly(l-aspartate) in 70% yield with ...DP
= 50 and regioselectivity (α/β) = 94 : 6. Plots of log{M
/M
} vs. time and DP
vs. conversion indicate that this polymerization proceeds in a controlled manner by a chain-growth mechanism up to 90% conversion. Thereafter, competition occurs between chain growth and step mechanisms.
The curing kinetics of a family of biobased epoxies derived from n-alkyl diphenolate esters differing in ester side chain length were compared with diglycidyl ether of bisphenol A (DGEBA). Isothermal ...isoconversional analysis and Kamal–Sourour model fitting by differential scanning calorimetry (DSC) were utilized to obtain reaction constants. The biobased epoxides and DGEBA have reaction orders that are comparable while the autocatalytic rate constant of DGEBA was larger than those of the biobased epoxies. As the n-alkyl side chain length of diphenolate esters increased, the autocatalytic rate constant decreased. Furthermore, the non-autocatalytic rate constant for DGEBA is smaller than that of the biobased epoxies. The cause for the difference in rate constants is discussed, and applications are assigned to the epoxies based on curing kinetics.
PDF
