24 research outputs found
Recycling Oxidized Model Polyethylene Powder as a Degradation Enhancing Filler for Polyethylene/Polycaprolactone Blends
Polyethylene (PE) powder with different
degrees of oxidation was
prepared to model end-of life polyethylene that has been oxidized
during processing and/or service-life. The nonoxidized and preoxidized
PE powders were blended with PCL to evaluate the possibility to recycle
PE powder in PCL blends. Good elongation at break was reached for
all 25/75 (w/w) PE/PCL films and the elongation at break correlated
well with the carbonyl index of the original PE powder, indicating
that the oxidation of PE increased the interfacial adhesion with PCL
and improved the blend properties. The preoxidized PE powder in combination
with surfactant and pro-oxidant greatly accelerated the degradation
rate of PCL as measured by molecular weight decrease during low temperature
thermo-oxidative aging. This coincided with the fast initial increase
in PE carbonyl index. The degradation accelerating effect was larger
when preoxidized PE was blended with PCL as compared to when nonoxidized
PE was added. However, the degree of preoxidation had minor impact
on PCL degradation rate. Without PE powder the degradation rate of
PCL was not enhanced by the addition of pro-oxidant and surfactant
alone
Green Semi-IPN Hydrogels by Direct Utilization of Crude Wood Hydrolysates
Crude and unmodified
acetylated galactoglucomannan containing wood
hydrolysate (WH) was directly incorporated into a semi-interpenetrating
network (semi-IPN) composed of up to 60% renewable polymers. Semi-IPNs
were produced by a facile and green synthetic pathway through cross-linking
modified carboxymethylcellulose in the presence of at least 30%(w/w)
WH, via free radical copolymerization with acrylic acid and <i>N</i>,<i>N</i>′-methylenebis(acrylamide). FTIR
verified the presence of WH interlaced with CMC in the semi-IPN, and
the highly porous microscopic structure of the networks was confirmed
by SEM. The gelation process of these networks was monitored in situ,
and their individual “gel point” (the <i>G</i>′-<i>G</i>″ crossover) was determined by
in situ rheological measurements. Semi-IPN hydrogels with various
swelling ratios (<i>Q</i> = 20–225) were obtained
within 2.8–20 min of a cross-linking reaction
Ring-Closing Depolymerization: A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2‑Allyloxymethyl-2-ethyltrimethylene Carbonate
Ring-closing depolymerization is
demonstrated to be a powerful
synthetic methodology for the formation of six-membered functional
aliphatic carbonate monomers, providing a rapid, straightforward,
inexpensive, and green route for obtaining six-membered functional
aliphatic carbonate monomers at a scale greater than 100 g. The utility
of this technique was observed via the synthesis of the allyloxy-functionalized
six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene
carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction,
starting from trimethylolpropane allyl ether, diethyl carbonate, and
NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology
is based upon the reversible nature of this class of polymers. The
anionic environment produced by NaH was observed to be sufficient
to mediate the monomer equilibrium concentration; thus, an additional
catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene
(TBD) was demonstrated to be a very active catalyst for the ring-opening
polymerization (ROP) of AOMEC, resulting in a rapid (<i>k</i><sub>p</sub><sup>app</sup> = 28.2 s<sup>–1</sup>) and controlled
polymerization with a low dispersity (<i><i>Đ</i></i> = 1.2). The availability and activity of the functionality
of poly(AOMEC)s were established through subsequent postpolymerization
functionalization via the UV-initiated thiol–ene chemistry
of poly(AOMEC) with 1-dodecanethiol and benzophenone as a radical
initiator. The functionalization proceeded with high control and with
a linear relation between the molecular weight and conversion of the
unsaturation, revealing the high orthogonality of the reaction and
the stability of the carbonate backbone. Hence, as a synthetic methodology,
depolymerization provides a straightforward and simple approach for
the synthesis of the highly versatile functional carbonate AOMEC.
In addition, formation of the monomer does not require any solvents,
reactive ring-closing reagents, or transition-metal-based depolymerization
catalysts, thereby providing a “greener” route for obtaining
functional carbonate monomers and polymers
Simultaneous Polymerization and Polypeptide Particle Production via Reactive Spray-Drying
A method for producing
polypeptide particles via <i>in situ</i> polymerization
of <i>N</i>-carboxyanhydrides during spray-drying
has been developed. This method was enabled by the development of
a fast and robust synthetic pathway to polypeptides using 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) as an initiator for the ring-opening polymerization of <i>N</i>-carboxyanhydrides. The polymerizations finished within
5 s and proved to be very tolerant toward impurities such as amino
acid salts and water. The formed particles were prepared by mixing
the monomer, <i>N</i>-carboxyanhydride of l-glutamic
acid benzyl ester (NCA<sub>Glu</sub>) and the initiator (DBU) during
the atomization process in the spray-dryer and were spherical with
a size of ∼1 μm. This method combines two steps; making
it a straightforward process that facilitates the production of polypeptide
particles. Hence, it furthers the use of spray-drying and polypeptide
particles in the pharmaceutical industry
Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization
The need for polymers for high-end
applications, coupled with the
desire to mimic nature’s macromolecular machinery fuels the
development of innovative synthetic strategies every year. The recently
acquired macromolecular-synthetic tools increase the precision and
enable the synthesis of polymers with high control and low dispersity.
However, regardless of the specificity, the polymerization behavior
is highly dependent on the monomeric structure. This is particularly
true for the ring-opening polymerization of lactones, in which the
ring size and degree of substitution highly influence the polymer
formation properties. In other words, there are two important factors
to contemplate when considering the particular polymerization behavior
of a specific monomer: catalytic specificity and thermodynamic equilibrium
behavior. This perspective focuses on the latter and undertakes a
holistic approach among the different lactones with regard to the
equilibrium thermodynamic polymerization behavior and its relation
to polymer synthesis. This is summarized in a monomeric overview diagram
that acts as a presynthetic directional cursor for synthesizing highly
specific macromolecules; the means by which monomer equilibrium conversion
relates to starting temperature, concentration, ring size, degree
of substitution, and its implications for polymerization behavior
are discussed. These discussions emphasize the importance of considering
not only the catalytic system but also the monomer size and structure
relations to thermodynamic equilibrium behavior. The thermodynamic
equilibrium behavior relation with a monomer structure offers an additional
layer of complexity to our molecular toolbox and, if it is harnessed
accordingly, enables a powerful route to both monomer formation and
intentional macromolecular design
Crucial Differences in the Hydrolytic Degradation between Industrial Polylactide and Laboratory-Scale Poly(L-lactide)
The rate of degradation of large-scale synthesized polylactide
(PLA) of industrial origin was compared with that of laboratory-scale
synthesized poly(L-lactide) (PLLA) of similar molar mass.
The structural discrepancy between the two material types resulted
in a significant difference in degradation rate. Although the hydrolysis
of industrial PLA was substantially faster than that of PLLA, the
PLA material became less brittle and fragmented to a lesser extent
during degradation. In addition, a comprehensive picture of the degradation
of industrial PLA was obtained by subjecting different PLA materials
to hydrolytic degradation at various temperatures and pH’s
for up to 182 days. The surrounding environment had no effect on the
degradation rate at physiological temperature, but the degradation
was faster in water than in a phosphate buffer after prolonged degradation
at temperatures above the <i>T</i><sub>g</sub>. The degree
of crystallinity had a greater influence than the degradation environment
on the rate of hydrolysis. For a future use of polylactide in applications
where bulk plastics are generally used today, for example plastic
packages, the appropriate PLA grade must be chosen based on the conditions
prevailing in the degradation environment
Thiolated Hemicellulose As a Versatile Platform for One-Pot Click-Type Hydrogel Synthesis
A one-pot synthetic methodology for
the thiolation of <i>O</i>-acetyl-galactoglucomannan (AcGGM)
was developed to merge hemicellulose
chemistry with “click” chemistry. This was realized
by the AcGGM-mediated nucleophilic ring-opening of γ-thiobutyrolactone
via the activation of the polysaccharide pendant hydroxyl groups.
The incorporation of thiol functionalities onto the hemicellulose
backbone was visualized by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy
and was assessed by an Ellman’s reagent assay of the thiol
groups. The versatility of the thiolated AcGGM was elaborated and
demonstrated by conducting several postmodification reactions together
with hydrogel formation utilizing thiol–ene and thiol-Michael
addition “click” reactions. The one-pot synthesis of
thiolated AcGGM is a straightforward approach that can expand the
applications of hemicelluloses derived from biomass by employing “click”
chemistry
Innovative Approaches for Converting a Wood Hydrolysate to High-Quality Barrier Coatings
An advanced approach for the efficient
and controllable production of softwood hydrolysate-based coatings
with excellent oxygen-barrier performance is presented. An innovative
conversion of the spray-drying technique into a coating applicator
process allowed for a fast and efficient coating process requiring
solely aqueous solutions of softwood hydrolysate, even without additives.
Compared to analogous coatings prepared by manual application, the
spray-drying produced coatings were more homogeneous and smooth, and
they adhered more strongly to the substrate. The addition of glyoxal
to the aqueous softwood hydrolysate solutions prior to coating formation
allowed for hemicellulose cross-linking, which improved both the mechanical
integrity and the oxygen-barrier performance of the coatings. A real-time
scanning electron microscopy imaging assessment of the tensile deformation
of the coatings allowed for a deeper understanding of the ability
of the coating layer itself to withstand stress as well as the coating-to-substrate
adhesion
Electroactive Hydrophilic Polylactide Surface by Covalent Modification with Tetraaniline
Covalent surface functionalization is presented as a
versatile
tool to increase the hydrophilicity and to introduce the electroactivity
of polyester films. Acrylic acid and maleic anhydride were photografted
onto a polylactide (PLA) surface with a “grafting from”
method to increase the surface wettability, and the subsequent coupling
of conductive aniline oligomer was used to introduce electroactivity
to the PLA surface. The photopolymerization of maleic anhydride and
acrylic acid and the coupling of aniline tetramer (AT) were characterized
by FT-IR, UV, and TGA. The surface morphology of the PLA surface before
and after modification was examined by scanning electron microscopy
(SEM) and atomic force microscopy (AFM). A medium hydrophilic surface
of PLA was achieved by surface modification with maleic anhydride,
acrylic acid, and AT. An electrically conductive surface was obtained
after grafting with AT, and the conductivity increased with increasing
AT content on the surface. The hydrophilic and electroactive surface
of polyesters while retaining their bulk properties offers new possibilities
in biomedical applications, such as bone, cartilage, neural, and cardiovascular
tissue engineering
Innovative Approaches for Converting a Wood Hydrolysate to High-Quality Barrier Coatings
An advanced approach for the efficient
and controllable production of softwood hydrolysate-based coatings
with excellent oxygen-barrier performance is presented. An innovative
conversion of the spray-drying technique into a coating applicator
process allowed for a fast and efficient coating process requiring
solely aqueous solutions of softwood hydrolysate, even without additives.
Compared to analogous coatings prepared by manual application, the
spray-drying produced coatings were more homogeneous and smooth, and
they adhered more strongly to the substrate. The addition of glyoxal
to the aqueous softwood hydrolysate solutions prior to coating formation
allowed for hemicellulose cross-linking, which improved both the mechanical
integrity and the oxygen-barrier performance of the coatings. A real-time
scanning electron microscopy imaging assessment of the tensile deformation
of the coatings allowed for a deeper understanding of the ability
of the coating layer itself to withstand stress as well as the coating-to-substrate
adhesion