Carbon fibers having unique morphologies, from hollow circular to gear‐shaped, are produced from a novel melt‐processable precursor and method. The resulting carbon fiber exhibits microstructural and ...topological properties that are dependent on processing conditions, rendering them highly amenable to myriad applications.
Here we report utilizing a tailored feedstock to synthesize mechanically robust thermoplastic polyurethanes at very high lignin contents (65-75 wt%). The molecular weight and glass transition ...temperature (T sub(g)) of lignin were altered through cross-linking with formaldehyde. The cross-linked lignin was coupled with diisocyanate-based telechelic polybutadiene as a network-forming soft segment. The appearance of two T sub(g)'s, around -35 and 154 degree C, for the polyurethanes indicates the existence of two-phase morphology, a characteristic of thermoplastic copolymers. A calculated Flory-Huggins interaction parameter of 7.71 also suggests phase immiscibility in the synthesized lignin polyurethanes. An increase in lignin loading increased the modulus, and an increase in crosslink-density increased the modulus in the rubbery plateau region of the thermoplastic. This path for synthesis of novel lignin-based polyurethane thermoplastics provides a design tool for high performance lignin-based biopolymers.
Agroforestry systems provide smallholder farmers with opportunities to broaden their income base. However, as planting trees can come at the cost of reduced crop yield because of competition for ...resources, farmers need to understand the consequences of tree growing on crop productivity. This paper explores the impacts of
Acacia auriculiformis
on agricultural crop productivity during the first three cropping seasons in Gunungkidul, Java, Indonesia; maize then soybean was planted in each season. We also sought to understand whether water competition was a factor in determining productivity in this agroforestry system, as this environment is characterised by a long (~ 6-month) dry season. A randomised complete block design with five replications was used, with three treatments, monoculture
A. auriculiformis
trees, monoculture agricultural crops, and an agroforestry plot that combined the trees and crop. At the final measure, at age 27 months, the trees were 7.4 and 6.9 m in height and 7.2 and 7.1 cm in diameter in the monoculture and in the agroforestry systems respectively, and treatment had no significant effect on the tree height or diameter. Grain yield of soybean was not affected by treatment in any of the three growing seasons, but both grain and stover yields of maize were significantly lower in the agroforestry system than in the monoculture in the third growing season. Differences in soil water deficit, and pre-dawn and mid-day leaf water potentials in
A. auriculiformis
and soybean were generally not significant between treatments in all three growing seasons. land equivalent ratios for the
A. auriculiformis
agroforestry system decreased from the 1st to the 3rd growing seasons but remained > 1.3. As fertilizer was applied it was assumed that there was no nutrient limitation. It was therefore concluded that tree shading was primarily responsible for reductions in productivity, and that this affect was greater on maize than soybean grain yield.
Wide-angle X-ray scattering observations of alpha-cyclodextrin (CD)-poly(ethylene glycol) (PEG) inclusion complexes (ICs) have shown for the first time that two crystalline columnar modifications ...(forms I and II) are produced in the process of their formation. This was made possible by precise azimuthal X-ray diffraction scanning of oriented IC samples. Form I is characterized by CDs threaded onto PEG chains and arranged along channels in the order head-to-head/tail-to-tail, while form II is formed by unbound CDs also arranged into columns in a head-to-tail and also possibly a head-to-head/tail-to-tail manner, probably as a result of template crystallization on the form I IC crystals. It was shown that similar structural peculiarities are inherent for channel structures based on ICs obtained with PEG with a wide range of molecular weights (MWs). The characteristic feature of ICs based on PEG, especially with MW > 8000, is the presence of unbound polymer in the composition of the complex. The amount of unbound PEG was shown to rise with increasing MW of PEG, resulting in greater imperfections in the IC crystalline structure. The polyblock structure of ICs based on alpha-CD and PEG was therefore proposed.
We have demonstrated the potential of meso- and microporous carbons in controlled release applications and targeted oral drug delivery. We have employed two mesoporous and two microporous carbons for ...the sustained release of one water-soluble drug (antipyrine) and one water-insoluble drug (indomethacin), using these as models to examine the controlled release characteristics. The micro-/mesoporous carbons were characterized as having a BET surface area of 372-2251 m
2
g
−1
and pore volume 0.63-1.03 cm
3
g
−1
. The toxicity studies with
E. coli
bacterial cells did not reveal significant toxicity, which is in accordance with our previous studies on human cells with similar materials. Mucin adsorption tests with type III pork mucin demonstrated 20-30% mucin adsorption by the carbon samples and higher mucin adsorption could be attributed to higher surface area and more oxygen functionalities. Antipyrine and indomethacin loading was 6-78% in these micro-/mesoporous carbons. The signatures in thermogravimetric studies revealed the presence of drug molecules within the porous moieties of the carbon. The partial shifting of the decomposition peak of the drug adsorbed within the carbon pores was caused by the confinement of drug molecules within the narrow pore space of the carbon. The release profiles of both drugs were examined in simulated gastric fluid (pH = 1.2) and in three other release media with respective pH values of 4.5, 6.8 and 7.4, along with varying residence times to simulate the physiological conditions of the stomach, duodenum, small intestine and colon, respectively. All the release profiles manifested diffusion controlled sustained release that corroborates the effective role of micro-/mesoporous carbons as potential drug carriers.
We have demonstrated the potential of meso- and microporous carbons in controlled release applications and targeted oral drug delivery.
The formation of polymer-cyclodextrin inclusion compounds of polycarbonate (PC), poly(methylmethacrylate) (PMMA) and poly(vinylacetate) (PVAc) guests with host γ-cyclodextrin (γ-CD) have been ...successfully achieved. Coalesced bulk polymer samples were obtained by removal of γ-CD from their inclusion compounds (ICs). The chemical and crystalline structures of ICs and coalesced PC, PMMA and PVAc were studied by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). The thermal transitions, thermal stability, and degradation mechanisms of the samples were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and direct insertion probe pyrolysis mass spectrometry (DIP-MS). FTIR findings indicated that the chain conformations of the bulk polymers were altered when they were included inside the CD channels and extended chain conformations were retained when coalesced from their ICs. Significant improvements were observed in the thermal transitions observed for the coalesced polymers, with glass transitions shifted to higher temperatures. The TGA results reveal that the thermal stabilities of coalesced polymers increased slightly compared to the corresponding as-received polymers. The DIP-MS observations indicated that the thermal stability and degradation products of the polymers are affected once the polymers chains are included inside the γ-CD-IC cavities.
Cyclomaltohexaose (alpha-cyclodextrin, alpha-CD) can form inclusion complexes (ICs) with polymer molecules in the columnar crystal structure in which alpha-CD molecules stack to form a molecular ...tube. Complementary water vapor sorption and wide-angle X-ray diffractomery (WAXD) were performed on oligomer/alpha-CD ICs to determine their structures and stabilities. To discern the effect of guest molecule hydrophobicity on water adsorption isotherms, polyethylene glycol (PEG, MW = 600 g/mol) and hexatriacontane (HTC) guests were used. Sorption isotherms for PEG/alpha-CD IC are similar to those obtained for pure alpha-CD and PEG, suggesting the presence of dethreaded PEG in the sample. WAXD collected before and after water vapor sorption of PEG/alpha-CD IC indicated a partial conversion from columnar to cage crystal structure, the thermodynamically preferred structure for pure alpha-CD, due to dethreading of PEG. This behavior does not occur for HTC/alpha-CD IC. Sorption isotherms collected at 20, 30, 40, and 50 degrees C allowed the calculation of the isosteric heats of adsorption and the integral entropies of adsorbed water which are characterized by minima that indicate the monolayer concentration of water in the ICs.
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Rapid recrystallization of cyclomaltohexaose (α-cyclodextrin, α-CD) from aqueous solution resulted in formation of the columnar crystal structure of α-CD containing only water as the ...guest molecule. Complementary water vapor sorption and wide-angle X-ray diffractometry (WAXD) experiments were performed on the α-CD columnar structure to elucidate the crystal structure present at varying sorption levels. Equilibrium isothermal water vapor sorption experiments at 40
°C revealed that the α-CD columnar structure is unstable above a water activity of approximately 0.67. This was confirmed by WAXD diffractograms collected over time, which further revealed that α-CD columnar structure undergoes a phase transformation to the cage structure after approximately 0.25
h at 40
°C and a water activity of 1.0.
α-Cyclodextrin (α-CD), a cyclic oligosaccharide, can form inclusion complexes (ICs) with polymer molecules in which α-CD molecules stack in the columnar crystal to form a molecular tube. Physical ...mixtures of α-CD powder and oligomeric liquids such as poly(ethylene glycol) (PEG) have been shown to spontaneously form an IC, which is accompanied by a solid-state α-CD phase transformation from the cage to the columnar crystal structure. In this paper, the phase transformation is tracked with wide-angle X-ray diffraction as a function of temperature, atmospheric water vapor content and the type of guest molecule. A first-order kinetic model is used to describe the kinetics of complexation. The time required to completely complex PEG200 (200g/mol) at low water activities is greater than 300h, whereas only a few hours are necessary at high water activities. Solid-state complexation of α-CD with a hydrophobic guest molecule (hexatriacontane, HTC), is also reported here for the first time. Slower complexation kinetics are observed for α-CD with HTC compared to PEG600 (600g/mol).
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