Development and evaluation of orally disintegrating tablets (ODTs) containing Ibuprofen granules prepared by hot melt extrusion

In the current study Ibuprofen was embedded in a methacrylate copolymer (Eudragit^® EPO) matrix to produce solid dispersions by hot-melt extrusion (HME) processing. The obtained granules were incorporated in orally disintegrating tablets (ODTs). The tablets were developed by varying the ratio of superdisintegrants such as sodium croscarmellose and crosslinked polyvinylpyrrolidone grades while a direct compression process was used to compress the ODTs under various compaction forces to optimize tablet robustness. The properties of the compressed tablets which included porosity, hardness, friability and dissolution profiles were further evaluated and compared with Nurofen^® Meltlet ODTs. The taste and sensory evaluation in human volunteers demonstrated excellence in masking the bitter active and improved tablet palatability.     

Morphology and physical properties of polyethylene/silicate nanocomposite prepared by melt intercalation

Maleated polyethylene (PEMA)/silicate nanocomposites with a different aspect ratio of silicate and maleated PEMA/SiO₂ composite were prepared by melt intercalation. The nanocomposites with a high aspect ratio silicate (montmorillonite) showed a faster decrease in the terminal slope of the storage modulus and a steeper increase in complex viscosity than those with a low aspect ratio silicate (laponite) and SiO₂. The addition of montmorillonite increases the crystallization and the melting temperature of PEMA but decreases above 3 vol % of the silicate content because of the increased viscosity. The nanocomposite with montmorillonite showed the highest yield strength and secant modulus among the composites because of the highest aspect ratio of the filler. It also revealed strong interfacial adhesion with the matrix and orientation during tensile deformation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1454–1463, 2002     

Thermal and flammability properties of polyethersulfone/halloysite nanocomposites prepared by melt compounding

This paper presents a study of polyethersulfone (PES)/halloysite nanotube (HNTs) nanocomposites prepared by melt compounding either through a simple extrusion process or via a water-assisted extrusion procedure. Scanning and transmission electron microscopy techniques are combined with rheological measurements to assess the influence of polymer end groups (–Cl or –OH) and water injection on the HNTs dispersion state. A morphological transition form microcomposite to nanocomposite is achieved when replacing –Cl chain ends of PES by –OH groups, especially when water is injected during processing. By a combination of Soxhlet extraction and thermogravimetric analysis, we show that some PES(OH) chains are covalently bonded onto the aluminosilicate surface during extrusion. A mechanism describing the physico-chemical action of water is presented. The best system in terms of clay dispersion has been retained to characterize PES-HNTs nanocomposites with respect to their thermo-mechanical, thermal and fire (mass loss calorimetry and UL-94) properties. Dynamic mechanical analysis shows a significant enhancement in the storage modulus of halloysite-based nanocomposites when compared to the unfilled matrix. The improved thermal and thermo-oxidative stability of PES in presence of HNTs is mainly attributed to the labyrinth effect provided by individually dispersed nanotubes, which is reinforced during the decomposition process by the formation of a protective charred ceramic surface layer. The mechanism of action of HNTs for fire retardancy of PES presumably arises from a synergistic effect between physical (i.e. ceramic-like structure formation and mechanical reinforcement of the intumescent char) and chemical (i.e. charring promotion) processes taking place in the condensed phase. According to this study, the straightforward and cost-effective melt compounding route could pave the way for future development of high-performance nanoscale polymeric materials combining enhanced thermal properties and excellent flame retardant behaviour.     

Thermal degradation and combustion behavior of the polyethylene/clay nanocomposite prepared by melt intercalation

Studies of thermal and fire-resistant properties of the polyethylene/organically modified montmorillonite (PE/MMT) nanocomposites prepared by means of melt intercalation are discussed. The sets of the data acquired with the aid of non-isothermal TG experiments have been treated by the model kinetic analysis. The extra acceleration of thermal-oxidative degradation of the nanocomposite which has been observed at the first stage of the overall process has been analyzed and is explained by the catalytic effect of the clay nanoparticles. The results of cone calorimetric tests lead to the conclusion that char formation plays a key role in the mechanism of flame retardation for nanocomposites.     

Design and in vitro evaluation of zidovudine oral controlled release tablets prepared using hydroxypropyl methylcellulose

Oral controlled release matrix tablets of zidovudine were prepared using different proportions and different viscosity grades of hydroxypropyl methylcellulose. The effect of various formulation factors like polymer proportion, polymer viscosity and compression force on the in vitro release of drug were studied. In vitro release studies were carried out using United States Pharmacopeia (USP) type 1 apparatus (basket method) in 900 ml of pH 6.8 phosphate buffer at 100 rpm. The release kinetics were analyzed using Zero-order model equation, Higuchi's square-root equation and Ritger-Peppas' empirical equation. Compatibility of drug with various formulations excipients used was studied. In vitro release studies revealed that the release rate decreased with increase in polymer proportion and viscosity grade. Increase in compression force was found to decrease the rate of drug release. Matrix tablets containing 10% hydroxypropyl methylcellulose (HPMC) 4000 cps were found to show a good initial drug release of 21% in the first hour and extended the release upto 16 h. Matrix tablets containing 20% HPMC 4000 cps and 10% HPMC 15000 cps showed a first hour release of 18% and extended the release upto 20 h. Mathematical analysis of the release kinetics indicated that the nature of drug release from the matrix tablets followed non-Fickian or anomalous release. No incompatibility was observed between the drug and excipients used in the formulation of matrix tablets. The developed controlled release matrix tablets of zidovudine, with good initial release (17-25% in first hour) and which extend the release upto 16-20 h, can overcome the disadvantages of conventional tablets of zidovudine.     

Structure and properties of polyamide‐6/vermiculite nanocomposites prepared by direct melt compounding

Polyamide‐6 (PA6)/vermiculite nanocomposites were fabricated through the direct melt compounding of maleic anhydride‐modified vermiculite (MAV) with PA6 in a twin‐screw extruder followed by injection molding. The structure and morphology of the nanocomposites were determined by X‐ray diffraction and scanning and transmission electron microscopy techniques. The results revealed the formation of intercalated and exfoliated vermiculite platelets in the PA6 matrix. Tensile measurement showed that the tensile modulus and strength of the nanocomposites tended to increase with increasing vermiculite content. The thermal properties of the nanocomposites were determined by dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetry measurements. The storage modulus of the PA6–MAV nanocomposites increased to almost twice that of the neat PA6. The thermal stability of the nanocomposites increased dramatically, and this was associated with the addition of vermiculite. The effect of the addition of maleic anhydride on the formation of the PA6–vermiculite nanocomposites was examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2860–2870, 2002     

Crystallization and morphology of iPP/MWCNT prepared by compounding iPP melt with MWCNT aqueous suspension

In this work, isotactic polypropylene (iPP) composites filled with multiwalled carbon nanotubes (MWCNTs) were prepared by compounding iPP melt with MWCNT aqueous suspension using a corotating twin-screw extruder, and the morphology and crystallization behavior of the composites were investigated. Scanning electron microscopy micrographs showed that MWCNTs dispersed individually at nanoscale in the iPP matrix when the MWCNTs concentration was low, though MWCNTs aggregates were detected when the filler concentration increased. The results of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy indicated that the β-form crystal of iPP was induced by MWCNTs at the concentration of 0.1 wt.% which was dispersed individually in the iPP matrix. At higher content, however, MWCNTs acted as α-nucleating agent, and the crystals in the iPP/MWCNT composites showed higher degree of perfection than that of pure iPP though smaller in dimension. Crystallization rate of iPP increased significantly with increasing MWCNT content.     

The morphology and dynamic viscoelasticity for PPS/low-melting temperature glass hybrids prepared by melt blending

Polyphenylene sulfides(PPS) and low-melting temperature glasses(LMTG) were used to prepare a PPS/LMTG organicinorganic hybrid material by melt blending.The etched surfaces of the hybrids were observed by scanning electron microscope (SEM) and the images showed different dispersed phase morphologies compared to traditional filled composites,which maybe induced by shear.Advanced rheometric expanded system(ARES) was used to investigate the rheological behaviors of the hybrids and the results showed that the strain y dependence of dynamic storage modulus G’ for the hybrids with high contents of LMTG did not appear Payne effect.     

Enhanced thermoelectric performance and novel nanopores in AgSbTe2 prepared by melt spinning

We report a melt-spinning spark-plasma-sintering synthesis process of the polycrystalline p-type material composed of AgSbTe₂ coarse grains and evenly formed 5-10 nm pores that occur primarily on the surface of matrix grains. The formation mechanism of nanopores and their influences on the thermoelectric properties have been studied and correlated. Microstructure analysis shows that the as-prepared sample can be regarded as a nanocomposite of matrix and in situ generated nanopores evenly coated on matrix grains. For the single-phase component and the possible energy-filter effect caused by the nanopores, the electrical transport properties are improved. Moreover, the thermal conductivity is significantly reduced by strong phonon scattering effect resulted from the nanopores. The thermoelectric performance of the as prepared sample enhances greatly and a ZT of 1.65 at 570 K is achieved, increasing∼200% compared with the sample prepared by traditional melt and slow-cooling method.     

Composites of polystyrene and surface modified cellulose nanocrystals prepared by melt processing

Cellulose - Cellulose nanocrystals (CNCs) were surface modified with benzoic acid anhydride (BzAnh) at room temperature in 48-h reaction time. FTIR spectroscopy confirmed the high degree of...     

Compatibilisation effect of PP-g-MA copolymer on iPP/SiO2 nanocomposites prepared by melt mixing

In the present study, a series of iPP/SiO₂ nanocomposites, containing 1, 2.5, 5, 7.5, 10 and 15 wt% SiO₂ nanoparticles, were prepared by melt mixing in a twin screw co-rotating extruder. Poly(propylene-g-maleic anhydride) copolymer (PP-g-MA) containing 0.6 wt% maleic anhydride content was added to all nanocomposites at three different concentrations, 1, 2.5 and 5 wt%, based on silica content. Mechanical properties such as tensile strength at break and Young’s modulus were found to increase and to be mainly affected by the content of silica nanoparticles as well as by the copolymer content. For the tensile strength at break as well as for yield point, a maximum was observed, corresponding to the samples containing 2.5-5 wt% SiO₂. At higher concentrations, large nanosilica agglomerates are formed that have as a result a decrease in tensile strength. Young’s modulus increases almost linearly on the addition of SiO₂, and takes values up to 60% higher than that of neat iPP. Higher concentrations of PP-g-MA resulted in a further enhancement of mechanical properties due to silica agglomerate reduction. This finding was verified from SEM and TEM micrographs. Evidently the surface silica hydroxyl groups of SiO₂ nanoparticles react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual SiO₂ nanoparticles in the iPP matrix. The enhanced adhesion in the interface of the two materials, as a result of the mentioned reaction, has been studied and proved by using several equations. The increased Vicat point of all nanocomposites, by increasing the PP-g-MA content, can also be mentioned as a positive effect.     

Selective separation of lambdacyhalothrin by porous/magnetic molecularly imprinted polymers prepared by Pickering emulsion polymerization

Porous/magnetic molecularly imprinted polymers (PM‐MIPs) were prepared by Pickering emulsion polymerization. The reaction was carried out in an oil/water emulsion using magnetic halloysite nanotubes as the stabilizer instead of a toxic surfactant. In the oil phase, the imprinting process was conducted by radical polymerization of functional and cross‐linked monomers, and porogen chloroform generated steam under the high reaction temperature, which resulted in some pores decorated with easily accessible molecular binding sites within the as‐made PM‐MIPs. The characterization demonstrated that the PM‐MIPs were porous and magnetic inorganic–polymer composite microparticles with magnetic sensitivity (M_s = 0.7448 emu/g), thermal stability (below 473 K) and magnetic stability (over the pH range of 2.0–8.0). The PM‐MIPs were used as a sorbent for the selective binding of lambdacyhalothrin (LC) and rapidly separated under an external magnetic field. The Freundlich isotherm model gave a good fit to the experimental data. The adsorption kinetics of the PM‐MIPs was well described by pseudo‐second‐order kinetics, indicating that the chemical process could be the rate‐limiting step in the adsorption of LC. The selective recognition experiments exhibited the outstanding selective adsorption effect of the PM‐MIPs for target LC. Moreover, the PM‐MIPs regeneration without significant loss in adsorption capacity was demonstrated by at least four repeated cycles.     

Polymorphs of 1,1-bis(4-hydroxyphenyl)cyclohexane and multiple Z' crystal structures by melt and sublimation crystallization

Close packing conflict in a metastable polymorph of the pure title host (Z' = 2, melt crystal m) is resolved in the stable form (Z' = 1, sublimed crystal s) as O-H...O hydrogen bond changes to O-H...pi interaction. Melt crystallization and sublimation show a greater percentage of high Z' structures in CSD statistics.     

The role of polymer/drug interactions on the sustained release from poly(dl-lactic acid) tablets

The release profiles of model drugs (propranolol HCl, diclofenac sodium, salicylic acid and sulfasalazine) from low molecular weight poly(d,l-lactic acid) [d,l-PLA] tablets immersed in buffer solutions were investigated in an attempt to explore the mechanism of the related phenomena. It was confirmed that drug release is controlled by diffusion through the polymer matrix and by the erosion of the polymer. The pH of the surrounding medium influences the drug solubility as well as swelling and degradation rate of the polymer and therefore the overall drug release process. Physicochemical interaction between d,l-PLA and drug is an additional factor which influences the degree of matrix swelling and therefore its porosity and diffusion release process. Propranolol HCl shows extended delivery time at both examined pH values (5.4 and 7.4) and especially at pH 7.4 where release was accomplished in 190 days, most probably due to its decreased solubility at higher pH values. The acidic drugs gave shorter delivery times especially at pH 7.4. A slower drug release rate and more extended delivery time at pH 7.4 in comparison with that at pH 5.4 was recorded for tablets loaded with diclofenac sodium and salicylic acid. The opposite effect was observed with samples loaded with propranolol HCl.     

Cyclodextrin/polyethylenimine-based supramolecular nanoparticles for loading and sustained release of ATP

A new supramolecular nanoparticle PEI/SCD was successfully constructed, showing the loading/sustained release abilities towards ATP.     

溶胶-凝胶法制备的罗丹明B/二氧化钛分子印迹聚合物的结构与吸附性能

以罗丹明B为模板分子,以钛酸丁酯为交联剂,采用溶胶-凝胶法在酸性条件下制备了罗丹明B二氧化钛溶胶-凝胶分子印迹聚合物;利用傅立叶变换红外光谱和透射电镜分析了分子印迹聚合物的结构,使用热重分析测定了其热稳定性,采用静态吸附和动态吸附方法考察了其吸附性能,并与非印迹聚合物进行了对比.结果表明,与非印迹聚合物相比,印迹聚合物具有网络状多孔隙凝胶微结构及对模板分子的特异性识别结合位点,因而对模板分子具有更好的吸附性能和特异选择性.其原因可能在于,模板分子上的羰基与钛酸丁酯水解产生的羟基产生氢键作用,使钛酸围绕于模板分子周围,并通过缩聚形成凝胶;当模板分子洗脱后,孔隙得到保留并形成网络状凝胶,从而能够吸附更多的模板分子.     

Tailoring of polymers by combination of ionic and radical controlled polymerizations

Poly(methyl methacrylate)s with terminal bromine atom, prepared by bromination of anionically polymerized MMA, were used as ATRP macroinitiators giving di- and triblock copolymers with MMA, styrene and butyl acrylate blocks. Multifunctional ATRP macroinitiators were synthesized by introducing bromomethyl or 2-bromoacyloxy groups onto the main chain of polystyrene or poly(4-methyl styrene) and used for ATRP grafting of tert-butyl acrylate leading to densely grafted copolymers with more or less uniform grafts.     

Chromatographic characteristics of cholesterol-imprinted polymers prepared by covalent and non-covalent imprinting methods

Cholesterol-imprinted polymers were prepared in bulk polymerization by the methods of covalent and non-covalent imprinting. The former involved the use of a template-containing monomer, cholesteryl (4-vinyl)phenyl carbonate, while the latter used the complexes of template and functional monomer, methacrylic acid or 4-vinylpyridine prior to polymerization. Columns packed with these molecularly imprinted polymers (MIPs) were all able to separate cholesterol from other steroids. For different combinations of cholesterol and beta-estradiol concentrations in a total of 1 g/l, the peak retention times for both compounds were nearly constant. The adsorption capacity for cholesterol onto the MIPs was found to significantly depend on the use of functional monomers, but the selectivity factors were only slightly different from each other at 2.9 to 3.2 since the separation was all based on the specific binding of cholesterol to recognition sites formed on the imprinted polymers. The capacity factors for cholesterol were determined to be 3.5, 4.0 and 3.1, respectively, for covalently imprinted, 4-vinylpyridine-based, and methacrylic acid-based non-covalently imprinted polymers. However, the covalently imprinted polymer was found to have a higher adsorption capacity for cholesterol and about fivefold higher chromatographic efficiency for cholesterol separation, in comparison with non-covalently imprinted polymers. The use of covalent imprinting significantly reduced the peak broadening and tailing. This advantage along with constant retention suggests that the covalently imprinted polymer has potential for quantitative analysis.