Preparation of micron-sized PA6/12 copolymer microspheres via successive in-situ polymerization

Micron-sized polyamide 6/12 (PA6/12) copolymer microspheres were firstly synthesized via successive in-situ polymerization of styrene (free radical polymerization), equimolar Laurolactam (LL) and Caprolactam (CL) (anionic ring-opening polymerization). The resulting PA6/12 microspheres were regular sphericity, with diameter ranging from 9.2 to 138.0 microns and narrow size distribution (size distribution ranging from 1.2 to 3.3), as confirmed by scanning electron microscopy (SEM) and Laser diffraction size Analyzer. Furthermore, the study on the PA6/12 microspheres in PA6/12 and PS (PA6/12/PS) blends confirmed that the particle size distribution, diameter of PA6/12 microspheres were controllable, and closely related to the content of PS in the blends, which indicated that the formation of the PA6/12 microspheres in the PA6/12/PS blends can be elucidated via a phase inversion mechanism.     

PA6/磺化石墨烯功能微球的制备及性能研究

以己内酰胺(CL)、聚苯乙烯(PS)、磺化石墨烯(SG)为主要原料,通过阴离子聚合反应诱导相分离的方法,制备得到了一系列粒径可控的PA6/SG杂化微球。SG在PS的存在下,选择性分散在CL单体中,形成CL/PS/SG悬浮液;再通过CL原位阴离子聚合制备PA6/PS/SG合金,利用甲苯除去PS相后可以获得粒径分布在10~50μm的PA6/SG微球。扫描电镜及粒径测试结果表明,PS及SG含量可以影响PA6微球的形貌及尺寸。通过透射电镜可确定SG选择性分散在了PA6相中,同时SG的加入可有效地改善PA6的热稳定性、结晶性、熔融性能和烧结性能,并且适用于3D打印激光烧结领域。     

Effect of montmorillonite on the morphologies and properties of monomer casting polyamide 6/polystyrene blends via successive in situ polymerization

Monomer casting polyamide 6 (MCPA6)/polystyrene (PS)/montmorillonite (MMT) ternary composites were prepared via successive in situ polymerization. The effects of Na⁺-MMT and OMMT on morphologies of MCPA6/PS blends have been studied by scanning electron microscopy (SEM) and transmission electronic microscopy (TEM). Incorporation of certain amount of Na⁺-MMT results in the diameter of PA6 dispersed microspheres in PS matrix increased significantly from several to dozens of micrometers. It was interesting to find that all Na⁺-MMT was dispersed only in the MCPA6 microspheres. However, a different morphology was observed in MCPA6/PS blend with incorporation of OMMT, especially when the content of OMMT ≥1 wt%. That is, the morphologies of the ternary blends change from dispersed PA6 microspheres/PS matrix to dispersed PA6 network with inclusion of local PA6 microspheres/PS matrix. It was surprising that OMMT dispersed in PA6 microspheres at low OMMT loading (i.e., 0.5 wt%), while OMMT was dispersed in PA6 network phase, not in PA6 microspheres phase at high OMMT loading (i.e., ≥1 wt%). The incorporation of a various amount of MMT affected the crystallization behavior of PA6 phase in the MCPA6/PS blends by the results of XRD and DSC. The MMT layers leaded to the co-existence of α-crystalline form and γ-crystalline form of PA6. Furthermore, the more the MMT contents, the stronger the intensity of the γ-peak. Another interesting phenomenon was that there was a remarkable difference in molecular weight of PA6 microspheres phase and PA6 network phase in MCPA6/PS/OMMT (2 wt%) ternary composites from GPC results.     

Preparation and characterization of polystyrene/polycarbonate composite hollow microspheres by microencapsulation method

Polystyrene/polycarbonate (PS/PC) composite hollow microspheres were successfully prepared via microencapsulation method. Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry, and thermogravimetric analysis were used for the characterization of the obtained hollow microspheres. SEM images showed that there were a big cavity and some small cavities inside the composite hollow microspheres, and the hollow microspheres prepared at 42 °C presented better morphology and smaller size distribution compared with that prepared at higher temperature of solvent evaporation. The tap density of the composite hollow microspheres increased from 0.28 g cm⁻³ at PS/PC composite concentration of 5 wt% in oil phase to 0.42 g cm⁻³ at concentration of 11.7 wt%. The mean diameter of the composite hollow microspheres ranged from 13 to 528 μm. It increased with an increase in the concentration of composite in oil phase and decreased with increasing the second rotating speed. Thermal analysis showed that the composite hollow had thermal stability below 358 °C.     

中空TiO2微球的制备及其对聚丙烯酸酯薄膜保温性能的影响

以阳离子PS微球为模板, 钛酸四丁酯为钛源, 氨水为催化剂制备中空TiO₂微球, 通过物理共混法将中空TiO₂微球引入到聚丙烯酸酯薄膜中, 考察了中空TiO₂微球的空心粒径及用量对复合薄膜光反射性、导热系数及力学性能的影响。结果表明: 中空TiO₂微球的引入可显著提升聚丙烯酸酯薄膜的各项性能, 中空TiO₂微球的空心粒径和用量对复合薄膜的性能有不同程度的影响, 随着中空TiO₂微球空心粒径和用量的增加, 复合薄膜的性能基本呈现先提升后降低的趋势, 其中当中空TiO₂微球空心粒径为300 nm、用量为1%时, 所制备的复合薄膜保温性能和力学性能最优。     

Enhancement of thermal stability of poly(divinylbenzene) microspheres

In order to enhance the thermal stability and prepare a new kind of carbon microbeads from poly(divinylbenzene) microspheres (PDM), air oxidation treatment was introduced to modify the pristine PDM. The results showed that the spherical shape of PDM was preserved via the air oxidation and further carbonization at 700 °C. The changes of morphology, especially the surface functional groups and the thermal properties of PDM after air oxidation were investigated in detail by SEM, IR and TG/DSC measurements, respectively. The possible mechanism of oxidation treatment was elucidated.     

微波辐射乳液聚合制备磁性高分子微球

用化学共沉淀法制备了Fe3O4纳米粒子,并用油酸和十二烷基硫酸钠对Fe3O4纳米粒子进行表面修饰,得到了稳定的水分散性纳米Fe3O4磁流体。在Fe3O4磁流体存在下,以苯乙烯和丙烯酰胺为单体,采用微波辐射乳液聚合法制备了Fe3O4/聚(苯乙烯-丙烯酰胺)磁性高分子微球,表征了磁性高分子微球的形态与结构,研究了磁性高分子微球的粒径、热稳定性、磁含量与饱和磁化强度。研究发现,在选定合适的聚合条件下,通过微波辐射乳液聚合法可以制得粒径为70 nm~80 nm、磁含量为18.2%的磁性高分子微球。     

PLLA-PEG-PLLA/Fe_3O_4磁性微球的制备及性能

以聚乙二醇为引发剂,L-丙交酯为单体,开环聚合得到聚乳酸-聚乙二醇三嵌段共聚物(PLLA-PEG-PLLA),采用溶剂挥发法制备了PLLA-PEG-PLLA/Fe_3O_4磁性微球,并通过扫描电镜对其形态进行了表征。利用振动样品磁强计和Tg研究了微球的磁含量和磁性能,结果发现,相同粒径不同磁含量的磁性微球,磁含量越高,升温速率越快,当磁含量为70.57%时,升温速率最快,能达到磁热疗的有效温度42℃。对于磁含量相同,粒径不同的微粒,粒径越小,升温速率越快,粒径约为10μm时升温速率最快。     

Magnetic silica:epoxy composites with a nano- and micro-scale control

Multiscale composites with magnetic properties were prepared by incorporating Cu–Ni nanoferrites filled silica microparticles in an epoxy matrix. The size of the nanoferrites was controlled both by the structure of the silica template and the annealing temperature (700 and 900 °C) used during the synthesis procedure. The ferrite:silica particles prepared at 700 °C showed a narrow size distribution close to 8.3 nm with a superparamagnetic behaviour. A less symmetric size distribution was obtained when annealing was performed at 900 °C, with diameters ranging from 15 to 80 nm. The reinforcement incorporation increased up to 7 °C the glass transition temperature and 30 °C the decomposition temperatures of the composites. The proposed strategy permits the nanoscale control, by the trapping effect of the silica on the magnetic nanoparticles, as well as the control of the micro-scale distribution through a simple protocol. These composites could have potential applicability as EMI shielding materials, owing to their magnetic nature, lightweight and enhanced thermal stability.     

Structural properties of silver particulate films deposited on softened polymer blends of polystyrene/poly (2-vinyl pyridine)

Results of the structural studies of silver particulate films deposited at a rate of 0.4 nm/s on polymeric blends of polystyrene/poly (2-vinyl pyridine), PS/P2VP held at a temperature 457 K by evaporation in a vacuum of 8 × 10⁻⁶ Torr are reported here. The morphology of silver particulate films, characterized by their size, size distribution, shape and inter-particle separation, was observed to modify due to blending of PS with P2VP and amount of silver deposited. The red shift in the plasmon resonance indicates the effect of blending P2VP with PS. Scanning electron microscopy was used to study the change in morphology of the silver nanoparticles in correlation with the optical properties of silver particulate films on PS/P2VP blends. The silver nanoparticles on the thin layers of polymer blends exhibited much smaller, narrower dispersion and wide size distribution due to blending of PS with P2VP.     

Effect of polymer matrices on magnetic properties of plastic magnets

Plastic magnets were prepared using commercial polyamide (Nylon 12), polystyrene and ethylene-vinylacetate copolymer, and three kinds of ferrite magnetic powders with different concentration levels (20, 35 and 50 vol%). Their magnetic properties and thermal stability are discussed comparing viscoelasticity and thermal properties of the polymers and plastic magnets. Magnetic properties of the anisotropic plastic magnets were largely dependent on the concentration of the magnetic powder and its degree of orientation in the matrix. The degree of the orientation was mainly affected by the interaction between polymer matrix and magnetic powder, and viscoelastic property of the matrix polymer. It was also affected to some extent by the shape of the magnetic particles. The order of the interaction of the polymers to the magnetic powders was as follows: PA > EVA copolymer > PS, and PA-bonded magnets gave the highest magnetic properties among the matrices examined. The decrease in magnetic properties due to the change in the orientation of magnetic powder rarely occurred during thermal treatment.     

Fabrication and characterization of porous poly(lactic-<Emphasis Type="Italic">co</Emphasis>-glycolic acid) (PLGA) microspheres for use as a drug delivery system

In this work, Simvastatin (SIM) loaded porous poly(lactic-co-glycolic acid) (PLGA) microspheres were fabricated using the W/O/W1/W2 double emulsion and solvent evaporation method. The optimal conditions for fabricating porous PLGA microspheres were determined to be 20% distilled water (v/v), 10% PLGA (m/v), and a 4:1 ratio of internal polyvinyl alcohol (PVA) to dichloromethane (DCM). The pores size distribution of porous PLGA microspheres was varied from 0.01 to 40 μm, while their particle displayed a bimodal size distribution that had two diameter peaks at around 100 μm and 500 μm. The SIM encapsulation efficacy was found to be very high with a yield near 80% and the porous PLGA microspheres showed the excellent biocompatibility. In addition, the drug release profile was found to be significantly different from a temporal basis. Base on the combined results of this study, SIM loaded PLGA microspheres holds great promise for use in biomedical applications, especially in drug delivery system or tissue regeneration.     

Ni/PS核壳结构纳米复合微球的制备及磁性能

采用乳液聚合法制备了纳米级聚苯乙烯微球,利用化学沉积法在微球表面镀镍,制备出了具有磁性的金属/高分子(Ni/PS)纳米复合微球。利用透射电子显微镜(TEM)、X射线衍射仪(XRD)和能量色散谱仪(EDS)分别对镀镍前后纳米微球的形貌结构、相组成、化学成分进行表征分析,用振动样品磁强计(VSM)测试了不同制备工艺条件下复合微球的磁学性能。结果表明,活化工艺、还原剂浓度、镀液pH值和温度对镀后复合微球的磁性能有显著影响。根据磁性能结果,优化工艺参数,制备了具有规则球形、单分散性好、粒径约为100nm、镀层完整、均匀的磁性Ni/PS核壳结构纳米复合微球,并获得最大的饱和磁化强度Ms=8.8764emu/g。     

High temperature magnetic properties of Sm–Co and Sm–Co/polyamide-12 materials: effects of temperature, particle size, and silanization

There is an increasing demand for polymer-bonded magnets (PBM) in high temperature applications. While most research deals with high temperature properties of NdFeB–PBM, only a few studies consider Sm–Co PBM. Therefore, this study, on the thermal and magnetic properties of Sm–Co alloy powders and blends of these with polyamide-12 (PA12), was undertaken. Since the Sm–Co powders were the product of ball milling, they contained a variety of shapes and sizes. Studies on size fractions of these showed that the thermal stability and magnetic properties were improved as the particle size increased. It was suggested that higher residual strains and smaller crystallite sizes in the small particles were responsible for a decrease in the thermal stability and magnetic properties. In addition, energy dispersive X-ray spectroscopy revealed that the oxygen content increased with decreasing particle size (larger specific surface area) and higher oxygen content was possibly also responsible for a decrease in the magnetic properties. It was shown that, in general, the surface modification by silanization, using (3-aminopropyl)trimethoxsilane, increased the saturation magnetization and remanence of both the particles and the Sm–Co/PA12 composite. The silanization also improved the thermal stability of the particles.     

Toward multi-functional polymer composites through selectively distributing functional fillers

The distribution of functional filler is known to have significant influence on various functionalities, yet, not been systematically investigated. Herein, we use a blends system based on PA12/PA6 containing SiC and low-temperature expandable graphite (LTEG) to study it. The effect of filler distribution in such blends on various functionalities including: thermal conductivity, electrical conductivity, and electromagnetic interference (EMI) shielding ability, has been systematically studied. Further study on altering filler distribution with polished PA6-LTEG and PA6-LTEG in different sizes reveals that, polished particle surface results in reduced electrical and thermal conductivity; and smaller particle size leads to enhanced electrical conductivity, thermal conductivity and EMI shielding ability. Finally, theoretical approach on thermal conductivity demonstrates that the system illustrates very effective contribution in thermal conductivity from large PA6-LTEG “filler” comparing to much smaller traditional fillers. Such study could provide a guideline for the processing of functional polymer composites.     

Release of PLGA–encapsulated dexamethasone from microsphere loaded porous surfaces

The aim of the present study was to investigate the morphology and function of a drug eluting metallic porous surface produced by the immobilization of poly lactide-co-glycolide microspheres bearing dexamethasone onto plasma electrolytically oxidized Ti–6Al–7Nb medical alloy. Spheres of 20 μm diameter were produced by an oil-in-water emulsion/solvent evaporation method and thermally immobilized onto titanium discs. The scanning electron microscopy investigations revealed that the size distribution and morphology of the attached spheres had not changed significantly. The drug release profiles following degradation in phosphate buffered saline for 1000 h showed that, upon immobilisation, the spheres maintained a sustained release, with a triphasic profile similar to the non-attached system. The only significant change was an increased release rate during the first 100 h. This difference was attributed to the effect of thermal attachment of the spheres to the surface.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

新型磁性海藻酸钠复合微球的制备与表征

以碳包铁(Fe@C)纳米粉作为磁性内核,用海藻酸钠作表层高分子,以正庚烷为油相,AOT为表面活性剂,氯化钙、环氧氯丙烷作交联剂,通过反相微乳法制备出了碳包铁/海藻酸钠核壳微球,系统考察了海藻酸钠的浓度、交联剂用量等对所制复合纳米微球性质的影响,并对产物进行了初步的性能表征.结果表明,选择合适的海藻酸钠的浓度、交联剂用量和其它相关参数,可以制备出外观为球形、分散性好、平均粒径约为250nm、具有强磁响应性的复合微球.     

Convenient preparation and photoluminescence properties of polymer microspheres based on europium complex

The preparation and properties of luminescent polystyrene (PS) composite microspheres with rare earth (RE) organic complexes Eu(DBM)₃(Phen) (DBM = dibenzoylmethanate, Phen = 1,10-phenanthroline) entrapped in the microspheres are presented. The luminescent composite microspheres are readily obtained by the soaking pre-existing particles method. The morphologies of resulting composite microspheres are characterized by field emission scanning electron microscope. The photoluminescence properties of the composite microspheres are also investigated. The results show that the existence of the rigid PS matrix can improve the photostability of the RE complex under UV irradiation and elongate the fluorescence lifetime of the RE complex. The improvement of the properties, the convenient preparing method, and brilliant red emission make the composite microspheres promising candidates for in cellulo applications.     

Enhanced thermal-conductive and anti-dripping properties of polyamide composites by 3D graphene structures at low filler content

In this work, 3D graphene structures constructed by graphene foam (GF) were introduced into polyamide-6 (PA6) matrix for the purpose of enhancing the thermal-conductive and anti-dripping properties of PA6 composites. The GF were prepared by one-step hydrothermal method. The PA6 composites were synthesized by in-situ thermal polycondensation method to realize PA6 chains covalently grafted onto the graphene sheets. The 3D interconnected graphene structure favored the formation of the consecutive thermal conductive paths or networks even at relatively low graphene loadings. As a result, the thermal conductivity was improved by 300% to 0.847 W·m⁻¹·K⁻¹ of PA6 composites at 2.0 wt% graphene loading from 0.210 W·m⁻¹·K⁻¹ of pure PA6 matrix. The presence of self-supported 3D structure alone with the covalently-grafted PA6 chains endowed the PA6 composites good anti-dripping properties.