Development of hot-melt pressure–sensitive adhesives for transdermal drug delivery

Styrene–isoprene–styrene (SIS) copolymer was epoxidized by in situ epoxidation to prepare a series of epoxidized SIS resins (ESIS). Their epoxidation degrees, phase structures, and compatibility with hydrocarbon resin were characterized with ¹H nuclear magnetic resonance spectroscopy, atomic force microscopy, and differential scanning calorimetry, respectively. These ESIS resins were melt-mixed with synthetic hydrocarbon resin, mineral oil, and antioxidants to fabricate a series of ESIS-based hot-melt pressure–sensitive adhesives (HMPSAs), which were used as carriers of transdermal drug delivery system. Their adhesive performances were measured, including holding power and 180^o peel strength. Geniposide and oleanic acid were representatively chosen as hydrophilic and lipophilic drug, respectively. Their in vitro release behaviors in ESIS-based HMPSAs were investigated using a modified Franz-type horizontal diffusion cells. Although the introduction of epoxide groups could alter the compatibility and phase structures between SIS resins and additives, the adhesive performances were slightly affected, as SIS resins had lower epoxidation degree (<15%). It is even more important that the cumulative release rate of both hydrophilic and lipophilic drugs is markedly enhanced with the increase of epoxidation degree in these ESIS-based HMPSAs. Therefore, this kind of HMPSAs has a promising future as a carrier of transdermal drug delivery system as their SIS resins are appropriately epoxidized.     

In situ synthesis,physical and mechanical properties of ZrB2–ZrC–WB composites

In this study, two composition ZrB₂–ZrC–WB composites were synthesized by reactive hot-pressing of Zr + B₄C + WC powder mixtures at 1900 °C. The microstructure of the resulting composites was characterized by a combination of scanning electron microscopy and X-ray diffraction. It is seen that highly-dense ZrB₂–ZrC–WB composites with a homogenous fine-microstructure were obtained after the sintering. The mechanical behavior of the composites was evaluated using by testing under four-point bend testing at room and high temperatures. The results show that the high-temperature strength of the ZrB₂–ZrC–WB composites was substantially improved, compared to ZrB₂–ZrC-based composites without WB. In addition, the elastic properties, electrical conductivity, hardness and fracture toughness of the composites were measured at room temperature. The results reveal that these properties were comparable to those of ZrB₂–ZrC-based composites without WB.     

Microsphere pressure sensitive adhesives—acrylic polymer/montmorillonite clay nanocomposite materials

In this study, the synthesis and characterization of acrylic polymer/montmorillonite (MMT) clay nanocomposite pressure sensitive adhesives (PSA) are presented. Different types and amounts of modified and unmodified montmorillonite clays were dispersed in ethyl acrylate (EA)/2-ethylhexyl acrylate (2-EHA) monomer mixture, which was then polymerized using a suspension polymerization technique. Polymerization was monitored in-line using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The adhesion properties of the synthesized nanocomposite materials were determined using standard measurements of tack, peel and shear strength. Viscoelastic properties of dried adhesive films were analyzed using dynamic mechanical analysis (DMA). The results showed that the kinetics of suspension polymerization was independent of the addition of MMT clays. On the other hand, adhesive properties were strongly influenced by the type and the amount of MMT clay added. While peel strength and tack gradually decreased with higher amount of modified MMT clay, a substantial increase in shear strength was determined with a maximal value at 1 wt% of added MMT clay. Moderate influence on tack, peel and shear strength was observed when the unmodified type of MMT clay was used. DMA analysis showed an increase in storage modulus (G′) for adhesives synthesized with MMT clay addition, but no significant differences were determined between particular types of MMT clays. A decrease in tan δ value for adhesives with 1 wt% of added MMT clay was observed, which also concurs with higher shear strength and implies to the improved cohesion of adhesive.     

In situ synthesis of PcBN composites from Sialon–TiN–TiB2 binder and cBN under high temperature and pressure

Polycrystalline cubic boron nitride (PcBN) composites were synthesized in situ with TiB₂, TiN, and Sialon as binders under ultrahigh temperature (1550°C) and high pressure (5.5 GPa). X-ray diffractometry, universal testing machine, field emission scanning electron microscopy, and transmission electron microscopy were used to study the effect of Sialon content (0%, 20%, 40%, 60%, and 80% by mass of binder) on the phase composition, microstructure, and mechanical properties of PcBN composites. The results show that the main phases in the system are lamellar TiN, needle-rodlike TiB₂, and irregular long-rodlike Sialon. Some TiB₂ grows along the (1 0 −1 0) face, and Sialon grows along the (0 0 0 1) face. The density and mechanical properties of the sintered product are significantly improved due to the formation of Sialon. When the content of Sialon is 60%, the binder is uniformly distributed, the cBN interface is well bonded, and the density is the highest. At this time, the strength reaches the maximum 34.57 GPa, the fracture toughness is 6.82 MPa m^1/2, and the flexural strength reaches the maximum 870.79 MPa. On the whole, cBN composites have excellent prospects for future applications in cutting inserts due to their excellent mechanical properties.     

Synthesis and dynamic mechanical study of core–shell structure epoxy/polyacrylate composite particle

A material with high damping property and based on epoxy/polyacrylate (EP/PA) composite particles was synthesized by two-stage emulsion polymerization. Transmission electron microscopy (TEM) showed that the composite particles have a spherical morphology, a core–shell structure and a diameter of 100 nm–130 nm. Fourier transform infrared spectra (FTIR) indicated the cross-linking between EP groups in the core layer and carboxyl groups in the shell layer of the composite particles during film formation. The cross-linking reaction improved the dynamic mechanical property by the interaction of core and shell polymers. The effects of the cross-linking agent and ratio of the two polymers on the damping capacity were studied by dynamic mechanical analysis (DMA). DMA results revealed that a certain amount of acrylic acid could markedly enhance the loss factor (tan δ) and slightly widen the damping temperature range. When the EP/PA ratio was 1:7, peak values for tan δ of the composite materials could reach 2.10, exceeding the value for most damping materials. The result implies that the EP/PA composites have great potential application in damping steel surface coatings.     

In situ synthesis of ZrB2–MoSi2 platelet composites: Reactive hot pressing process,microstructure and mechanical properties

Using elemental Zr, B, Mo and Si as raw materials, partially textured ZrB₂–MoSi₂ composites with in situ platelet ZrB₂ grains were fabricated by reactive hot pressing. Synthesized by a combustion reaction, the in situ formed ZrB₂ phase had unique characteristics to grow up to platelet grains, on the surroundings of Mo–Si–B ternary liquid phase at high temperature. Mechanical properties were dependent on grain size and aspect ratio of the ZrB₂ platelets. The rotation and realignment of the platelet ZrB₂ grains under hot pressing led to a partially textured microstructure, which showed anisotropic mechanical properties on different directions of the as-sintered samples. A roadmap of the reaction process, microstructure evolution and texture formation was given to describe the preparation of partially textured ZrB₂–MoSi₂ composites by reactive hot pressing.     

In situ synthesis and characterization of Ca-Mg-Al hydrotalcite on ceramic membrane for biodiesel production☆

In situ surface synthesis of Ca–Mg–Al hydrotalcite (HT) on inorganic ceramic membrane (CM) was investigated with urea as precipitator. The effects of molar ratio of raw materials, crystallization time, and temperature on surface synthesis of HT were examined. The as-prepared HT/CM samples were characterized by XRD and SEM and an in sit growth mechanismof HT on CMwas proposed. KF/HT/CMobtained by loading potassium fluoride (KF) on the HT layer by impregnation and calcination method was used as catalyst for transesterification between palm oil and methanol. The comparison of KF/HT/CMand pure KF/HT powder under identical reaction conditions shows that the production of fatty acid methyl ester is equivalent, which means that the use of inorganic catalytic membrane in the transesterification is a viable alternative.     

Preparation of carbon nanotubes/hydrogenated nitrile rubber composite by ultrasonic technique

将低相对分子质量的液体氢化丁腈橡胶(HNBR)溶于丙酮溶剂中,加入碳纳米管,用超声波技术制备了液体HNBR与碳纳米管的复合母料,然后再与HNBR混炼、硫化,获得碳纳米管/HNBR复合材料.结果表明,碳纳米管在HNBR中分散性好,对HNBR有较好的增强性,但在后期机械加工中产生了断裂.     

In situ synthesis and interfacial bonding mechanism of SiC in MgO–SiC–C refractories

Adding SiC directly to MgO–C refractories possesses the disadvantages of low dispersion and interfacial bonding strength. Herein, the in situ synthesized SiC was introduced into the MgO–SiC–C refractories to maintain the original excellent performance of MgO–C refractories and reduce the carbon dissolution in molten steel. With the increase of Si and C content in raw materials, the morphology of SiC changed from whisker to network, whose growth mechanism was vapor–solid and vapor–liquid–solid. The network structure and uniform distribution of SiC improved the thermal shock resistance of MgO–SiC–C refractories. According to the analysis of molecular dynamics simulation by Materials Studio software, SiC strengthened the relationship between periclase and graphite to enhance the structure of the compound.     

Effects of in situ synthesis of CNTs/SiCw on microstructure and properties of Al2O3–SiC–C composites

Al₂O₃–SiC–C composites were prepared using tabular corundum, ball pitch and silicon carbide as the main raw materials. The carbon nanotubes (CNTs) and SiC whiskers (SiC_w) were in situ synthesized and their effects on the thermo–mechanical properties of Al₂O₃–SiC–C composites have been studied. The experimental results indicated that the high yield of SiC_w and CNTs with large aspect ratio could be obtained due to addition of Ni(NO₃)₂·6H₂O as catalyst in the composites. The cold modulus of rupture values were increased by 24% to 7.2 MPa, and the flexural modulus was increased from 19 GPa to 24 GPa. Additionally, the hot modulus of rupture reached a maximum value of 3.6 MPa, which presented a 71% increase over that of composites without catalyst. After three thermal shock cycles, the residual cold crush strength was improved from 57.1% to 76.9%. It is believed that the enhancement in the thermo-mechanical properties of Al₂O₃–SiC–C composites could be attributed to the reinforcement effect of SiC_w and CNTs.     

Preparation and characterisation of a lamellar hydroxyapatite/polylactic acid composite

ABSTRACT

In this study, laminated hydroxyapatite/polylactic acid (HAp/PLA) composites were synthesized through solution intercalation method. The phase composition and micro morphology of the prepared HAp/PLA composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The obtained data revealed that intercalated and exfoliated structures were obtained by different HAp contents. Computed tomography result showed that the HAp lamellae distributed well in the PLA matrix and no air-bubble existed in the interface of HAp and PLA. Differential scanning calorimetry and mechanical performance test revealed that the thermal stability and tensile strength were all improved by intercalating of HAp lamellae. Moreover, the degradation experiment confirmed that the 10HAp/PLA showed the slowest degradation rate attributing to the molecular barrier effect of HAp lamellae. Besides that, MTT assay suggested that HAp/PLA composite exhibit excellent biocompatibility, indicating that it may become a promising material for biomedical applications.     

Rheology and adhesive properties of filled PIB-based pressure-sensitive adhesives. II. Probe tack and 90° peel testing

Two nanosized fillers (fumed silica Rosil-175 and halloysite nanotubes) were used to eliminate the problem of the cold flow and to increase the adhesion strength for polyisobutylene-based formulations. Well-dispersed silica, having high specific area, allowed to obtain up to 2 orders of magnitude increase in PIB’s shear resistance at 20 wt% Rosil content. PIB–20 wt% Rosil formulations mostly demonstrated slightly increased tack characteristics – up to 20–50%. Adhesive peel of the PIB-Rosil systems was observed with the peel strength of the systems staying at the level of the pristine PIB matrices or slightly changing (depending on the film thickness and peeling rate). Transition to the mixed failure mode was observed for thin PIB-20 wt% Rosil films tested under increased peeling rate accompanied by up to 300% peel strength increase. Formation of the three-dimensional filler networks in PIB-halloysite formulations allowed notably lower increase in the shear resistance of the systems – only 4–5 times in the case of much higher filler content (40 wt%), which was connected with the low strength of the network. Incorporation of 40 wt% halloysite into the PIB matrix did not lead to notable changes in tack properties, except for the tack of 150-μm films – in this case, 30–60% decrease in the tack characteristics was obtained. Peel strength of PIB-halloysite systems stays at the level of the pristine PIB matrices or increases up to 300% when the failure mode shifts from adhesive for the thin films to cohesive for the thick films.     

Nonoxide–boron nitride composites: in situ synthesis,microstructure and properties

Hexagonal graphitic boron nitride (h-BN) composites show excellent corrosion and thermal shock resistance, good mechanical tolerance and machinability, especially Si₃N₄–BN and Sialon–BN composites; they have already been used as break rings for horizontal continuous casting of steel. However, the strength of the conventionally processed BN composites were remarkably degraded by the addition of BN due to the poor densification behavior and the existence of large BN flakes or agglomerates of BN flakes that acted as fracture flaws. This means that BN dispersoids with fine particle size and homogeneous distribution are the key factors to obtain high strength composites. By in situ process, such microstructural features can be realized. In this work, by using the proposed in situ reactions, synthesis, microstructures and properties of various in situ nonoxide-boron nitride (Nobn) composites including SiC–BN, Si₃N₄–BN, AlN–BN, Sialon–BN and Alon–BN composites were investigated. For some Nobn composite systems, due to the large volume expansion during the reaction processes, near-net shape sintering can be realized. For example, the sintering shrinkage of AlN-30 vol.% BN was 3.1% and that of Alon-21 vol.% BN was 4.2%. This will be an advantage for the fabrication of large and complicated products.     

A review on application of structural adhesives in concrete and steel–concrete composite and factors influencing the performance of composite connections

This paper chronicles the use of structural adhesives in civil engineering construction since its inception. The usage of structural adhesives as effective and popular strengthening agents has been discussed. The application of structural adhesives as connecting agents, especially in cases of steel–concrete composites has also been discussed in detail. Various factors influence the bond strength of interfaces, such as the physical, mechanical and chemical properties of structural adhesives and adherends, the shape of adherends, water immersion, adhesive layer thickness, bonded area geometry, relative humidity and temperature of the environment during curing and service life, the amount and type of fillers and surface finishing of adherends.     

Influence of Al content and post-annealing on synthesis and mechanical properties of plasma sprayed Cr–Al–C composite coatings

Due to ultra-high temperature and short reaction time, it was very challenging to produce high purity MAX phase by plasma spraying. In this study, Cr–Al-graphite agglomerated powders with different Al additions (x = 0.2–1.5) was used to prepare Cr–Al–C composite coatings by atmospheric plasma spraying followed with annealing. Results showed that the as-sprayed coatings displayed typical lamellar structure, mainly composed of Cr–C binary carbides (Cr₇C₃ and Cr₂₃C₆) and residual Al. After annealing at 700 °C, the newly formed Cr₂AlC phase increased significantly in the coatings. The higher addition of Al, the more Cr₂AlC phase formed after annealing. The enhanced atomic diffusion, sufficient Al source and existence of (Cr, Al)C_x contributed to the formation of Cr₂AlC under annealing. Annealing treatment improved the hardness of the coating, but with the increase of Cr₂AlC phase content, the hardness decreased slightly. The Al content and post-annealing had a synergistic effect on the formation of Cr₂AlC phase in the sprayed coatings. This provided an effective route to control the Cr₂AlC content in sprayed Cr–Al–C composite coatings.     

Molecular design and hygrothermal resistance of high-toughness polysiloxane–polyurethane block copolymer composite adhesives

With the development of new energy sources, the demand for aluminum composite films for power batteries is expanding; at the same time, higher requirements have been put forward for aluminum composite films and adhesives. Polyurethane, as the binder of aluminum composite films, strongly affects the performance of aluminum composite films when exposed to moisture and high temperature and can lead to delamination. This thesis prepares a polyurethane and silicone block copolymer composite adhesive by adjusting the ratio of hard and soft polyurethane segments to obtain polyurethane (PU) with excellent flexibility. On the basis of block copolymerization with bis-amino-terminated organosiloxane (ATPS), obtained excellent flexibility, high peel strength, moisture resistance, and heat resistance from a polysiloxane-based polyurethane composite adhesive (PUSR). The properties are also tested using tensile tests and peel strength tests. The test results show that by adjusting the ATPS content, the flexibility and hydrophobicity of the PUSR composite adhesive further improved, with a tensile strength of 36 MPa, an elongation at break of 757%, and bonding performance of 11 N/15 mm. Additionally, the damp heat resistance of 6 N/15 mm, exceeding the international standard of 3 N/15 mm, in the power battery soft package aluminum–plastic film has potential application prospects.     

Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

Polyimide/titania (PI/TiO₂) nanocomposite films have been successfully fabricated through the in situ formation of TiO₂ within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)₄] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO₂ hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO₂ nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.     

Polyaniline/polyacrylate core–shell composites: Preparation,morphology and anticorrosive properties

Polyaniline/partially phosphorylated poly(vinyl alcohol)/polyacrylate nanoparticles ((PAn/P-PVA)_x/PAc_y) were synthesized by encapsulation of varying amounts of PAn/P-PVA nanoparticles (x = 0.3, 0.5 or 0.7 g) with PAc (y = 4, 6 or 8 g acrylate monomers) via emulsifier-free emulsion polymerization. A monomer conversion level of 93.9% was achieved for the synthesis of the (PAn/P-PVA)_0.5/PAc₄ nanoparticles. X-ray diffraction analysis revealed that PAc was intercalated between the PAn/P-PVA layers, whilst transmission electron microscopy analysis of the different nanoparticles revealed they were spherical PAn/P-PVA agglomerates coated with PAc. Thermogravimetric analysis revealed that the thermal stability of the (PAn/P-PVA)/PAc nanoparticles decreased with increasing amounts of PAc. Cyclic voltammetry based analysis of the different (PAn/P-PVA)/PAc nanoparticles coated onto carbon fiber electrodes revealed that the PAn/P-PVA nanoparticles were encapsulated sufficiently by the non-conductive PAc and that the peak current decreased with increasing amounts of acrylate. With respect to the corrosion resistance in 1.0 M sulfuric acid, steel coated with the (PAn/P-PVA)_0.7/PAc₈ nanocomposite showed the best corrosion resistance (11.4%), but for the nanocomposites at each PAn/P-PVA loading level, the anticorrosive properties increased with increasing PAc levels, presumably due to the increasing tortuosity of the diffusion pathway through the coating for any corrosion agents.     

In situ preparation of Si3N4–TiN composite by pyrolysis of polytitanosilazane (PTSZ)

Si₃N₄–TiN composite powders were obtained by in situ pyrolysis of polytitanosilazane. Dense Si₃N₄–TiN composites were prepared by hot-pressing at 1800 °C under 20 MPa for 2 h without sintering additive. Crystallization of amorphous PTSZ powders occurred between 1400 and 1500 °C with major phases, α-Si₃N₄, β-Si₃N₄, and small amount of phase TiN. Mechanical properties and microstructure of Si₃N₄–TiN composites were characterized. The results showed that the mechanical strength was 620 MPa, the fracture toughness was 7.8 MPa m^1/2 and the Vickers hardness was 8.5 GPa. SEM analysis indicated that Si₃N₄–TiN composite possessed excellent fracture toughness because TiN grains produced by in situ pyrolysis were well dispersed in Si₃N₄ matrix.