超临界CO2制备NaCl/PS微孔泡沫复合材料

利用超临界流体发泡技术制备了氯化钠(NaCl)颗粒填充聚苯乙烯(PS)的微孔泡沫复合材料。通过扫描电子显微镜(SEM)观察了材料的断面形态,并分析了氯化钠的粒径、含量及超临界CO2的饱和温度对微孔泡沫复合材料的泡孔形态的影响。结果表明:含有NaCl颗粒的微孔PS泡沫与纯PS泡沫在泡孔的形状和泡孔的尺寸等方面有所不同,纯PS微孔泡沫材料的泡孔分布较均匀、形状呈椭圆形,而添加了NaCl的PS微孔泡沫出现了大、小泡孔并存的泡孔结构。     

Open Cell Microcellular Foams of Polylactic Acid (PLA)‐based Blends with Semi‐Interpenetrating Polymer Networks

Microcellular biodegradable polymer foam with an open porous structure was prepared from amorphous poly‐L,D ‐lactic acid (P_{L ,D} LA) blended with polystyrene (PS), or polymethyl methacrylate (PMMA). The blends were prepared by polymerizing either styrene or methyl methacrylate (MMA) in a P_{L ,D} LA matrix. The styrene and MMA monomers are good cell‐opening agents and constituents for an IPN. Pressure‐quench batch foaming was conducted using carbon dioxide as a foaming agent at 80 °C under 10 MPa. The effects of monomers and a cross‐linking agent on the foamability and OCC were investigated. Manipulation of the monomer and the cross‐linking agent concentrations was able to change the viscoelasticity and partial miscibility of the blend and control the cell size at the micron scale as well as open pore content in the range of 20–90%.

     

Thermal‐Insulation,Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

Foaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO₂. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.     

发泡工艺对超临界CO_2/PLA微孔发泡泡孔形态的影响

研究了超临界CO2/PLA微孔发泡过程中,发泡温度、饱和压力、剪切速率对聚合物PLA泡孔形态的影响。结果表明,发泡温度对泡孔形态影响很大,温度降低,熔体强度增加,泡孔塌陷和合并减少,发泡材料的泡孔密度增大,泡孔尺寸减小,但温度太低时,熔体黏度和表面张力增加,发泡样品泡孔密度较低,泡孔壁较厚;压力对发泡形态的影响也是很显著的,压力太低,CO2的溶解度小,泡孔壁厚,泡孔分布不均匀。随着压力升高,CO2的溶解度增加,发泡样品的泡孔密度增加,泡孔更加均匀;随着转子转速增加,泡孔尺寸减小,气泡成核密度增大。但是转子转速过快,泡孔沿剪切的方向被拉长,泡孔取向严重,泡体质量变差。     

CO2‐Induced Mechanical Reinforcement of Polyolefin‐Based Nanocellular Foams

The effect of CO₂‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO₂ at temperatures below T_m. CO₂ sorption thickens the crystalline lamellae and consequently increases T_m from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO₂‐induced crystallization. Including CO₂‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively.

     

Mechanical Properties of Silicone Rubber Enhanced Microcellular EPDM Foams Based on Supercritical CO2 Foaming Technology

Microcellular ethylene-propylene-diene monomer (EPDM) foams derived from miniaturizing the cellular structure can improve mechanical properties of traditional EPDM foams. It is a current challenge that microcellular EPDM foams prepared by supercritical CO₂ foaming technology cannot undergo the post-crosslinking process due to the disappearance of cellular structure, which strongly restricts the development of the mechanical properties of EPDM foams. Hence, a scalable and blending route by selecting the silicone rubber (SR) with different crosslinking temperature compared to EPDM is developed to improve mechanical properties of EPDM foams. During the pre-crosslinking process of EPDM, SR forms a complete crosslinking network, which can make up for the strength of EPDM without the post-crosslinking. Meanwhile, the silica can reduce the domain size of SR and enhance the compatibility between EPDM and SR. As expected, the addition of SR improves the storage modulus, viscosity and matrix strength of EPDM, which shows enhanced mechanical properties of EPDM foams. When the foam density is basically the same, the tensile strength and compressive strength of SR/EPDM foam are increased by 461% and 283% respectively compared with that of EPDM foam. Finally, the maximum tensile strength and compressive strength (40% strain) of SR/EPDM foam achieves 3.58 MPa and 0.59 MPa, respectively.     

Supercritical CO2 deposition and foaming process for fabrication of biopolyester–ZnO bone scaffolds

Subsequent supercritical CO₂‐assisted deposition and foaming process followed by in situ synthesis was used to fabricate functional polylactide (PLA) and polylactide–poly(?‐caprolactone) (PLA–PCL) bone scaffolds. Deposition of zinc bis(2‐thenoyltrifluoroacetonate) as a ZnO precursor onto biopolyester substrates (30 MPa; 110 °C) was followed by fast depressurization to create cellular structure. Contact time was optimized regarding the deposition yield (2 h), while PCL content in PLA was varied (1–10 wt %). Scaffolds impregnated with the precursor were treated with hydrazine alcoholic solution to obtain biopolyester–ZnO composites. Precursor synthesis and deposition onto the scaffolds was confirmed by Fourier‐transform infrared. Processed scaffolds had micron‐sized pores (d₅₀ ～ 20 μm). High open porosity (69–77%) and compressive strength values (2.8–8.3 MPa) corresponded to those reported for trabecular bone. PLA blending with PCL positively affected precursor deposition, crystallization rate, and compressive strength of the scaffolds. It also improved PLA surface roughness and wettability which are relevant for cell adhesion. ZnO improved compressive strength of the PLA scaffolds without significant effect on thermal stability. Analysis of structural, thermal, and mechanical properties of biopolyester–ZnO scaffolds testified a great potential of the obtained platforms as bone scaffolds. Proposed processing route is straightforward and ecofriendly, fast, easy to control, and suitable for processing of thermosensitive polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45824.     

Formulation of silver chloride/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (AgCl/PHBV) films for potential use in bone tissue engineering

Orthopedic implant failure due to bacterial infection has been a concern in bone tissue engineering. Here, we have formulated a composite made of biodegradable polymer, i.e., poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and silver chloride. Ag⁺ ions released from the AgCl/PHBV film can promote an aseptic environment by promoting inhibition of bacterial growth while maintaining bone cell growth, depending on AgCl loading. The objective of this study is to formulate AgCl/PHBV film(s) of varying composition so as to evaluate the dependence of AgCl loading in the film on antimicrobial activity and cytotoxicity. The release kinetics of silver ions from AgCl/PHBV film in aqueous and Dulbecco's Modified Eagle Medium showed similarity in the initial burst of ions during the first day of desorption followed by a gradual release of ions over extended time period. The antibacterial efficacy of AgCl/PHBV film against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa was evaluated by microbiological assay, while cytotoxicity of the film toward MC3T3‐E1 cells was determined by MTT assay. For all compositions studied, a clear zone of inhibition around AgCl/PHBV film was noticed on a modified Kirby‐Bauer disk diffusion assay. We established that MC3T3‐E1 cell attachment on AgCl/PHBV film is strongly related to loading of AgCl in the film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45162.     

Poly(ε‐caprolactone) composite scaffolds loaded with gentamicin‐containing β‐tricalcium phosphate/gelatin microspheres for bone tissue engineering applications

In this study, novel poly(ε‐caprolactone) (PCL) composite scaffolds were prepared for bone tissue engineering applications, where gentamicin‐loaded β‐tricalcium phosphate (β‐TCP)/gelatin microspheres were added to PCL. The effects of the amount of β‐TCP/gelatin microspheres added to the PCL scaffold on various properties, such as the gentamicin release rate, biodegradability, morphology, mechanical strength, and pore size distribution, were investigated. A higher amount of filler caused a reduction in the mechanical properties and an increase in the pore size and led to a faster release of gentamicin. Human osteosarcoma cells (Saos‐2) were seeded on the prepared composite scaffolds, and the viability of cells having alkaline phosphatase (ALP) activity was observed for all of the scaffolds after 3 weeks of incubation. Cell proliferation and differentiation enhanced the mechanical strength of the scaffolds. Promising results were obtained for the development of bone cells on the prepared biocompatible, biodegradable, and antimicrobial composite scaffolds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40110.     

CA/RDX复合材料超临界CO2间歇法微孔发泡研究

以醋酸纤维素(CA)为黏结剂,黑索今(RDX)为含能组分,通过超临界二氧化碳(SC-CO2)间歇法发泡技术制备了微孔可燃复合材料CA/RDX.采用重量法研究了SC-CO2在该复合材料中的吸收与解吸收过程,同时利用Fickian扩散定律,研究了SC-CO2的扩散系数.采用扫描电子显微镜(SEM)研究了发泡温度和饱和压力对该材料内部形貌的影响规律.结果表明,CO2的吸收量与扩散系数随着饱和压力的提高而增加,在20 MPa,40℃饱和条件下达到最大饱和量11.16％.RDX和CA界面降低了微孔异相成核能垒,因此增加了微孔成核速率,微孔产生于RDX和CA界面间的微裂纹并逐步长大成为完整的气泡;在微孔成核后,微孔尺寸随饱和温度与发泡温度差(ΔT)的增加而增大;由于CO2解吸收过程中扩散系数随饱和压力的增加而增加,因此饱和压力对泡孔形貌的影响不明显.     

Ethylene–propylene‐diene terpolymer/halloysite nanocomposites: Thermal,mechanical properties,and foam processing

Ethylene–propylene‐diene terpolymer (EPDM)/halloysite nanotube (HNT) nanocomposites were prepared by melt mixing in an internal mixer using a commercially available maleated semicrystalline EPDM and HNT. Transmission electron microscopy analysis of the EPDM/HNT composites revealed that the HNTs are uniformly dispersed at a nanometer scale in the matrix. Differential scanning calorimeter studies indicated that the HNT caused an increase in the nonisothermal crystallization temperature of the EPDM. Tensile and dynamic mechanical analysis exhibited that a small amount of the HNTs effectively enhanced the stiffness of the EPDM without adversely affecting its elongation‐at‐break. The EPDM/HNT nanocomposites were used to produce foams by using a batch process in an autoclave, with supercritical carbon dioxide as a foaming agent. The nanocomposite foams showed a smaller cell size and higher cell density as compared to the neat EPDM foam, and the nanocomposite with 10 phr HNT produced a microcellular foam with average cell size as small as 7.8 μm and cell density as high as 1.5 × 10¹⁰ cell/cm³. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40307.     

Microcellular polymeric foams based on 1‐vinyl‐2‐pyrrolidone and butyl‐acrylate with tuned thermal conductivity

Microcellular polymers have been produced by ScCO₂ foaming, based on 1‐vinyl‐2‐pyrrolidone (VP) and butyl‐acrylate (BA). Three different copolymers were prepared, varying the compositions of VP and BA, following a simple radical polymerization process using an UV initiator. The samples a good foaming behavior and also excellent flexibility and handle ability, with expansion ratios between 1.53 and 1.72, and cell sizes in the microcellular range (below 5 µm). However, it was observed that the gas distribution and, consequently, the cellular structure inside the polymer foams was highly dependent on the VP and BA proportions, leading to very different thermal conductivity values, even for similar volume gas fraction values. These results were related to the copolymer nanostructuration, which seems to have an influence in the final pore structure, thus opening the possibility of designing microcellular foams with similar macroscopic characteristics but different thermal conductivity values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45872.     

Poly(acrylic acid‐co‐acrylamide‐co‐2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐grafted nanocellulose/poly(vinyl alcohol) composite for the in vitro gastrointestinal release of amoxicillin

Superabsorbent polymer composites (SAPCs) are very promising and versatile materials for biomedical applications. This study concentrates on the development of novel cellulose‐based SAPC, Poly(acrylic acid‐co‐acrylamide‐co?2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐grafted nanocellulose/poly(vinyl alcohol) composite, P(AA‐co‐AAm‐co‐AMPS)‐g‐NC/PVA, as a potential drug delivery vehicle. Amoxicillin was selected as a model drug, which is used for the treatment of Helicobacter pylori induced peptic and duodenal ulcers. P(AA‐co‐AAm‐co‐AMPS)‐g‐NC/PVA was synthesized by graft copolymerization reaction, and FTIR, XRD, SEM, and DLS analyses were performed for its characterization. Equilibrium swelling studies were conducted to evaluate the stimuli‐response behavior of the SAPC and found that equilibrium swelling was dependent on pH, contact time, temperature, ionic strength, concentration of crosslinker and PVA. Maximum drug encapsulation efficiency was found out by using different concentrations of amoxicillin. Drug release studies were carried out at simulated gastric and intestinal fluids and the release % was observed as maximum in intestinal fluids within 4 h. The drug release kinetics was investigated using Peppas' potential equation and follows non‐Fickian mechanism at pH 7.4. Thus, the drug release experiments indicate that P(AA‐co‐AAm‐co‐AMPS)‐g‐NC/PVA would be a fascinating vehicle for the in vitro administration of amoxicillin into the gastrointestinal tract. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40699.     

Surface‐modified pliable PDLLA/PCL/β‐TCP scaffolds as a promising delivery system for bone regeneration

Surface‐modified poly(d , l ‐lactide)/polycaprolactone/β‐tricalcium phosphate complex scaffold was fabricated in this study and we hypothesized that pliable and mechanical strong scaffold would be achieved by regulation of ternary compositions; while superficial modification strategy conduced to preserve and controlled‐release of bioactive growth factors. Properties of the composite scaffolds were systematically investigated, including mechanical properties, surface morphology, porosity, wettability, and releasing behavior. Moreover, the representative cytokine, recombinant human bone morphogenetic protein‐2 (rhBMP‐2), was loaded and implanted into muscular pouch of mouse to assess bone formation in vivo. Improved osteogenesis was achieved ascribed to both amplified β‐tricalcium phosphate (β‐TCP) content and retarded initial burst release. Particularly, scaffold doped with hydroxypropyl methylcellulose (HPMC) displayed optimal osteogenic capability. The results indicated that the PDLLA/PCL/β‐TCP complex scaffold along with HPMC‐coating and rhBMP‐2 loading was a promising candidate for bone regeneration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40951.     

发泡工艺对超临界CO2／PP微孔发泡泡孔形态的影响

研究了超临界CO2／PP微孔发泡过程中发泡温度和饱和压力对结晶性聚合物PP泡孔形态的影响。结果表明，温度对泡孔形态影响很大，温度升高，熔体黏度和表面张力降低，泡孔变大，泡孔密度减小。与发泡温度相比，CO2饱和压力对泡孔结构的影响较小。压力太低，CO2的溶解度小，泡孔壁太厚，泡孔分布不均匀。随着压力升高，CO2的溶解度增加，熔体黏度减小，所以泡孔直径和泡孔密度都增加，泡孔壁变薄。     

Micronization of Gefitinib Using Solution‐Enhanced Dispersion by Supercritical CO2

The antineoplastic gefitinib has a low aqueous solubility, leading to poor absorption rates. To overcome this problem, microparticles (MP) were prepared using solution‐enhanced dispersion by supercritical fluids (SEDS) with supercritical CO₂ and the cosolvents dichloromethane and ethanol. The results showed that the use of SEDS resulted in the formation of smaller particles and rendered the usually heterogeneous crystals of the crude drug pure and uniform. Furthermore, the reduction in the MP size increased the dissolution rate of gefitinib, and in vitro cytotoxicity assays indicated that the MP inhibited the proliferation of A549 cells to a larger extent than did the crude drug. Given the beneficial properties of the MP, SEDS could potentially be used to micronize drugs for therapeutic applications.     

Research on Perfusion Explosives from SF‐3 Double‐Base Propellants Using Supercritical CO2

Perfusion explosives were prepared using porous SF‐3 propellants, which were synthesized by a supercritical fluid foaming process. Scanning electron microscopy (SEM) was used to characterize the porous SF‐3 propellants. Massive holes were generated after the foaming process. The density of perfusion explosives using foamed SF‐3 propellants exceeds 1.3 g cm⁻³, and the detonation velocities exceed 6000 m s⁻¹. Underwater energy tests and high‐speed photography were carried out to investigate the detonation performance of perfusion explosives. The results showed that perfusion explosives using unfoamed SF‐3 propellants could not be detonated. However, perfusion explosives using their foamed analogs could be detonated herein.     

Stabilization of CO2‐in‐water emulsions with high internal phase volume using PVAc‐b‐PVP and PVP‐b‐PVAc‐b‐PVP as emulsifying agents

Two newly‐designed hydrocarbon surfactants, that is, poly(vinyl acetate)‐block‐poly(1‐vinyl‐2‐pyrrolidone) (PVAc‐b‐PVP) and PVP‐b‐PVAc‐b‐PVP, were synthesized using reversible addition–fragmentation chain transfer polymerization and used to form CO₂/water (C/W) emulsions with high internal phase volume and good stability against flocculation and coalescence up to 60 h. Their structures were precisely determined by nuclear magnetic resonance, gel permeation chromatography, thermal gravimetric analysis, and differential scanning calorimetry. Besides low temperature and high CO₂ pressure, the surfactant structures were the key factors affecting the formation and stability of high internal phase C/W emulsions, including the polymerization degrees of CO₂‐philic block (PVAc) and hydrophilic block (PVP), as well as the number of hydrophilic tail. The surface tension of the surfactant aqueous solution and the apparent viscosity of the C/W emulsions were also measured to characterize the surfactants efficiency and effectiveness. The surfactants with double hydrophilic tails showed stronger emulsifying ability than those with single hydrophilic tail. The great enhancement of the emulsions stability was due to decrease of the interface tension as well as increase of the steric hindrance in the water lamellae, preventing a frequent collision of CO₂ droplets and their fast coalescence. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46351.     

超临界CO_2/PS微孔塑料挤出成型中CO_2浓度对气泡成核影响的数值模拟

通过CFD软件对超临界CO_2/PS均相熔体在快速降压口模中流动状态的数值模拟,研究了CO_2浓度对CO_2/PS均相熔体气泡成核的影响。结果表明:当其他工艺条件不变时,在CO_2溶解度范围以内,增加CO_2浓度有利于提高成核率,从而产生更多的气泡,但不利于小尺寸泡孔的生成。