11 research outputs found
Enhancement of Energy Density in the BOPP-Based Sandwich-Structured Film by the Synergistic Effect of BaTiO<sub>3</sub>@Polyaniline Hybrid Dielectric Fillers
A series
of polyaniline-coated BaTiO3 (BaTiO3@PANI) hybrid
dielectric fillers were prepared through the in situ
oxidative polymerization of aniline. The morphology of the hybrid
fillers can be controlled by the ratio of aniline and BaTiO3 particles. Mulberry-like and coreâshell BaTiO3@PANI composite particles are prepared successfully. The two kinds
of dielectric fillers were introduced into the poly(vinylidene fluoride)
(PVDF) matrix separately or simultaneously. The dielectric loss can
be suppressed by the synergetic effect of these two hybrid fillers
while enhancing the dielectric constant at the same time. The finite
element simulation results showed that the surface morphology of adjacent
hybrid fillers played an important role in the dielectric performance.
The fillers were introduced in the biaxially oriented polypropylene
(BOPP)-based sandwich-structured film; specifically, the outer layer
was BOPP and the middle layer was the composites consisting of chlorinated
polypropylene (CPP)/PVDF blends and the hybrid fillers. The energy
storage density of the sandwich-structured film was improved significantly
compared to that of the BOPP film. The highest discharge energy density
was 7.31 J/cm3 at 450 MV/m, and the chargeâdischarge
efficiency was 77.3% with 30 wt % hybrid fillers in the middle layer
Nonisothermal Crystallization Behavior and Enhanced Heat Resistance and Impact Toughness of Poly(lâlactic acid) with Bimodal Molecular Weight Distribution
Poor heat resistance and toughness put some limitations
on the
applications of polyÂ(lactic acid), one of the most promising eco-friendly
polymers. Herein, bimodal polyÂ(l-lactic acid) (PLLA) was
prepared by melt-blending high- and low- molecular-weight PLLAs, and
the nonisothermal crystallization behavior, heat resistance, and mechanical
properties of bimodal PLLA were investigated. Low-molecular-weight
PLLA (L-PLLA) improves the crystallization capability of bimodal PLLA.
The double melting behavior is reasonably explained by the meltingârecrystallization
mechanism. Octamethylenedicarboxylic dibenzoylhydrazide, a typical
heterogeneous nucleating agent, significantly enhances the crystallization
rate and crystallinity of PLLA. The maximum crystallinity of 100%
L-PLLA is as high as 54.4%, and the heat deflection temperature (HDT)
of the bimodal PLLA containing 95% L-PLLA is up to 151 °C, while
the impact strength drops sharply to 17.2 kJ/m2 due to
the large crystallite size. d-Sorbitol (DS) exhibits a completely
different mechanism from heterogeneous nucleation, that is, a lower
crystallization rate but elevated crystallinity and crystallization
temperature. The DS-modified sample realizes an excellent balance
between heat resistance (HDT up to 136 °C) and impact strength
(47.9 kJ/m2) via a self-toughening effect by increasing
the crystallinity and reducing the crystallite size
Separated Immobilization of Incompatible Enzymes on Polymer Substrate via Visible Light Induced Living Photografting Polymerization
The use of the mixed catalytic system
with several enzymes can
provide multiple benefits in terms of the cost, simplification of
a multistep reaction, and effectiveness of complex chemical reactions.
Although study of different enzyme coimmobilization systems has attracted
increasing attention in recent years, separately immobilizing enzymes
which can not coexist on one support is still one of the great challenges.
In this paper, a simple and effective strategy was introduced to separately
encapsulate incompatible trypsin and transglutaminase (TGase) into
different polyÂ(ethylene glycol) (PEG) network layer grafted on low-density
polyethylene (LDPE) film via visible light induced living photografting
polymerization. As a proof of concept, this dual-enzyme separately
loaded film was used to catalyze the synthesis of a new target antitumor
drug LTV-azacytidine. The final results demonstrated that this strategy
could maintain higher activities of both enzymes than the mixed coimmobilization
method. And the mass spectra analysis results demonstrated that LTV-azacytidine
was successfully synthesized. We believe that this facile and mild
separately immobilizing incompatible enzyme strategy has great application
potential in the field of biocatalysis
Direct One-Pot Synthesis of Chemically Anisotropic Particles with Tunable Morphology, Dimensions, and Surface Roughness
Previously,
synthesis of anisotropic particles by seeded polymerizations
has involved multiple process steps. In conventional one-pot dispersion
polymerization (Dis.P) with a cross-linker added, only spherical particles
are produced due to rapid and high cross-linking. In this Article,
a straightforward one-pot preparation of monodisperse anisotropic
particles with tunable morphology, dimensions, surface roughness,
and asymmetrically distributed functional groups is described. With
a cross-linker of divinylbenzene (DVB, 8%), ethylene glycol dimethacrylate
(EGDMA, 6%), or dimethacryloyloxybenzophenone (DMABP, 5%) added at
40 min, shortly after the end of nucleation stage in Dis.P of styrene
(St) in methanol and water (6/4, vol), the swollen growing particles
are inhomogeneously cross-linked at first. Then, at low gel contents
of 59%, 49%, and 69%, corresponding to the cases using DVB, EGDMA,
and DMABP, respectively, the growing particle phase separates and
snowman- or dumbbell-like particles are generated. Thermodynamic and
kinetic analyses reveal that moderate cross-linking and sufficient
swelling of growing particles determine the formation and growth of
anisotropic particles during polymerization. Morphology, surface roughness,
sizes, and cross-linking degrees of each domain of final particles
are tuned continuously by varying start addition time and contents
of cross-linkers. The snowman-like particles fabricated with DVB have
a gradient cross-linking and asymmetrical distribution of pendant
vinyl groups from their body to head. The dumbbell-like particles
prepared using DMABP have only one domain cross-linked; i.e., only
one domain contains photosensitive benzophenone (BP) groups. With
addition of glycidyl methacrylate (GMA) or propargyl methacrylate
(PMA) together with DVB or EGDMA, epoxy or alkynyl groups are asymmetrically
incorporated. With the aid of these functional groups, carboxyl, amino,
or thiol groups and PEG (200) are attached by thiolâene (yne)
click and photocoupling reactions
Entrapment of Xylanase within a Polyethylene Glycol Net-Cloth Grafted on Polypropylene Nonwoven Fabrics with Exceptional Operational Stability and Its Application for Hydrolysis of Corncob Hemicelluloses
Enzyme
immobilization is a core technique of enzymatic biochemical
engineering because it can remarkably reduce the cost of enzymes and
improve the enzyme recovery procedure. The most crucial issues for
enzyme immobilization include (1) maintaining its activity, both in
the immobilization process and in the batchwise catalyst course; (2)
separating the immobilized enzyme from the reaction mixture; and (3)
the readiness and cost of the immobilization process. Herein, we report
a new strategy to immobilize xylanase within a hydrophilic and nonswelling
polyethylene glycol (PEG) net-cloth grafted on a polypropylene nonwoven
fabric (PP<sub>NWF</sub>) membrane by a visible light-induced surface
graft cross-linking polymerization. The xylanase was in situ entrapped
within the PEG net-cloth. The nonswelling PEG net-cloth can effectively
maintain the xylanase without leakage in long-term operation. As for
the hydrolysis of corncob hemicelluloses, the experimental results
showed that the as-formed immobilized xylanase retained 80% of its
original activity after being reused for 25 cycles and 60% after 50
cycles, which is far better than that of other immobilization methods
by entrapment. Notably, this simple in situ entrapment of enzymes
on routine polymeric matrix would lead to an easy industrial production
at low cost, while the form of end-products as a sheet can be readily
separated from the reaction mixture and reused for batchwise production.
After immobilization, the xylanase showed no significant shift in
pH or temperature optima as compared with its free form. These results
suggest that the immobilization of xylanase within the PEG net-cloth
grafted on PP<sub>NWF</sub> is promising for industrial applications
because of its long-term operation stability and convenient recovery
for reuse
Ammonium-Functionalized Hollow Polymer Particles As a pH-Responsive Adsorbent for Selective Removal of Acid Dye
In this work, a novel
type of ammonium-functionalized hollow polymer particles (HPP-NH<sub>3</sub><sup>+</sup>) with a high density of ammonium groups in the
shell has been specially designed and synthesized. Benefiting from
both the high surface area and from the high density of positively
charged ammonium groups, the as-prepared HPP-NH<sub>3</sub><sup>+</sup> can serve as a selective adsorbent for the removal of negatively
charged acid dye (e.g., methyl blue <i>a</i>-MB). The equilibrium
adsorption data of <i>a</i>-MB on the HPP-NH<sub>3</sub><sup>+</sup> were evaluated using Freundlich and Langmuir isotherm
models, and Langmuir isotherm exhibited a better fit with a maximum
adsorption capacity of 406 mg/g. Most importantly, because of the
presence of dual functional groups (ammonium and carboxyl groups),
the HPP-NH<sub>3</sub><sup>+</sup> showed a significant pH-dependent
equilibrium adsorption capacity, which increased dramatically from
59 mg/g to 449 mg/g as the solution pH decreased from 9 to 2. This
uniqueness makes the dye-adsorbed HPP-NH<sub>3</sub><sup>+</sup> can
be facilely regenerated under mild condition (in weak alkaline solution,
pH 10) to recover both <i>a</i>-MB and the HPP-NH<sub>3</sub><sup>+</sup>, whereas the recovery of conventional adsorbents is
commonly performed under particularly severe conditions. The regenerated
HPP-NH<sub>3</sub><sup>+</sup> can be reused for dye removal and the
dye removal efficiency remained above 98% even after five adsorptionâdesorption
cycles. Because of its high adsorption capacity, pH-sensitivity, easy
regeneration, and good reusability, the HPP-NH<sub>3</sub><sup>+</sup> has great potential for the application in the field of water treatment,
controlled drug release, and pH-responsive delivery
UV-Induced ThiolâEne âClickâ Surface Grafting Polymerization on BOPP Substrate and Its Postmodifying for Hydrophilic and Antibacterial Applications
This
paper proposed a novel and versatile surface modification
route by integrating UV light-mediated thiolâene âclickâ
surface grafting polymerization and postmodification via the reactions
of the surface thiol groups. At first, poly(thiol ether) layers with
tunable thiol group density, up to 8.2 Ă 102 ea/nm3 for cross-linked grafting layers, were grafted from biaxially
oriented polypropylene (BOPP) film. Then, the surface âSH groups
reacted with epoxy compounds to introduce quaternary ammonium salt.
With the immobilized quaternary ammonium salt and coordinated Zn2+ ions, the modified film demonstrated 99.98% antibacterial
rate against Staphylococcus aureusafter
soaking in DI water for 21 days and in a highly alkaline environment
(0.1 M NaOH aqueous solution) for 3 days, and the surface water contact
angle decreased to 39°. At last, the polymethacrylate chains
were also successfully grafted from the surface thiol groups of the
cross-linked poly(thiol ether) under visible light irradiation. With
2-(dimethyldodecylammonium) ethyl methacrylate as the grafting monomer,
the modified BOPP film had shown a 99.99% antibacterial rate against
both Escherichia coliand S. aureus. Meanwhile, with 2-methacryloxyethyl
phosphoryl choline as grafting monomer, the modified surface showed
an excellent antibioadhesion of living S. aureus, and the surface water contact angle was as low as 48°
Image_1_Involvement of 5-HT1A receptors of the thalamic descending pathway in the analgesic effect of intramuscular heating-needle stimulation in a rat model of lumbar disc herniation.JPEG
BackgroundIntramuscular (IM) heating-needle therapy, a non-painful thermal therapy, has been found to exert an analgesic effect via the thalamic ventromedial (VM) nucleus, solely by reducing the triggering threshold for descending inhibition; this could be modulated by intracephalic 5-hydroxytryptamine-1A (5-HT1A) receptors, rather than via the regular analgesia pathway. In this study, the effect and the potential serotonergic mechanism of IM heating-needle stimulation at 43°C were explored in the case of the pathological state of lumbar disc herniation (LDH).MethodsA modified classic rat model of LDH, induced via autologous nucleus pulposus implantation, was utilized. IM inner heating-needles were applied at the attachment point of skeletal muscle on both sides of the L4 and L5 spinous processes. WAY-100635 and 8-OH-DAPT, 5-HT1A receptor antagonist and agonist, were separately injected into the bilateral thalamic mediodorsal (MD) and VM nucleus via an intrathalamic catheter. Nociception was assessed by bilateral paw withdrawal reflexes elicited by noxious mechanical and heat stimulation.ResultsIM heating-needle stimulation at a temperature of 43°C for 30 or 45 min significantly relieved both mechanical and heat hyperalgesia in the rat model of LDH (P 0.05). Injection of 8-OH-DAPT into the thalamic MD nucleus exerted no modulating effects on either mechanical or heat hyperalgesia (P > 0.05).ConclusionIM heating-needle stimulation at 43°C for 30 min may activate 5-HT1A mechanisms, via the thalamic VM nucleus, to attenuate hyperalgesia in a rat model of LDH. This innocuous form of thermal stimulation is speculated to selectively activate the descending inhibition mediated by the thalamic VM nucleus, exerting an analgesic effect, without the involvement of descending facilitation of the thalamic MD nucleus.</p
Emulsion copolymerization of vinyl chloride with poly (ethylene glycol) methyl ether methacrylate
In this work, we reported a novel emulsion copolymerization of vinyl chloride monomer (VCM) with amphipathic monomer poly (ethylene glycol) methyl ether methacrylate (PEGMA) by using sodium dodecyl sulfate (SDS) as emulsifier and K2S2O8/NaHSO3 as redox initiator. Owing to the multifunctionality of PEGMA that can serve as co-monomer and âemulsifierâ, the emulsion copolymerization is achieved successfully and the interesting results demonstrate quite different features such as:(1) the stable P[(VC)-co-(PEGMA)] latex is obtained only when the mass ratio of PEGMAâ>â10% (to total monomer mass), (2) a small amount of ionic emulsifier SDS is required to achieve a stable latex, and (3) the mechanism of the micellar formation is different from the typical emulsion polymerization. Unexpectedly, the obtained copolymer formed high content of gel fraction which is mainly caused by the chain transfer reaction of the PVC growth chain radical to the hydrogen atom of the methylene from alkoxy (-OCH2CH2-) of the PEGMA oligomer chain. However, it could be inhibited effectively by the addition of chain transfer agent 2-mercaptoethanol (2-MCE). Subsequently, the properties of as-obtained P[(VC)-co-(PEGMA)] copolymer are evaluated carefully and it exhibited unique features such as self-plasticization, lower Tg (decreased from 83.1 to 59.6 °C), higher heat resistance (increased from 270 to 290 °C), hydrophilic, and high transparent in comparison to pure PVC. These outstanding features of the P[(VC)-co-(PEGMA)] copolymer offered a potential route for the functional modifications of PVC and broadened its further use.</p
Copolymers of Vinyl Acetate and Vinyl Carboxylates Bearing Branched C<sub>7</sub>âC<sub>9</sub> Chains: Synthesis, Alcoholysis, and Properties
This
contribution reported the radical copolymerization of vinyl
acetate (VAc) with vinyl carboxylates bearing branched C7âC9 chains, including vinyl neononanoate (VV-9),
vinyl neodecanoate (VV-10), and vinyl 2-ethylhexanoate (VV-EH), and
the VAc units of the as-prepared copolymers were subsequently hydrolyzed
to vinyl alcohol units in a base medium. With reactivity ratios of r1 = 0.94 (VV-9) and r2 = 0.96 (VAc), the copolymerization of VV-9 and VAc demonstrates
an ideal azeotropic copolymerization. By simply adjusting the initial
feed ratios, terpolymers of VV-9, VAc, and vinyl alcohol (PVVOH) with
different compositions have been successfully prepared. As a proof-of-concept,
their application as modifiers to improve the adhesive, hydrophilic,
and oxygen barrier properties of low-density polyethylene (LDPE) was
evaluated. When the PVVOH with 40 wt % VV-9 units was blended with
LDPE, the dispersed PVVOH phase formed microdomains with a size of
about 1 ÎŒm, and there was no observable two-phase structure.
The water contact angles of the PVVOH/LDPE blends were reduced from
103.7 ± 0.9° to 51.1 ± 1.3° and retained after
being soaked in water at ambient conditions for 30 days. PVVOH is
also effective in improving the adhesion between LDPE and aluminum
alloys. With the addition of 25 wt % PVVOH (20 wt % VV-9), the ultimate
shear strength of the lap joint was effectively enhanced from 3.60
± 0.17 MPa (pristine LDPE) to 4.87 ± 0.02 MPa. Furthermore,
the addition of 20 wt % PVVOH reduced the oxygen transmission rates
(OTR) of LDPE film from 145.3 to 52.2 cm3·mm·mâ2·dayâ1·barâ1