基于超临界CO2间歇法制备超轻TPU颗粒的研究

采用超临界流体间歇式微发泡技术制备了超轻热塑性聚氨酯弹性体(TPU)颗粒,利用扫描电子显微镜等研究了发泡温度、饱和时间及饱和压力对制备超轻TPU颗粒密度和性能的影响。结果表明,发泡温度和饱和压力是影响颗粒泡孔结构分布和粒料性能的主要因素;当饱和压力为11 MPa、发泡温度为145 ℃时,所得的超轻TPU颗粒密度较小、粒径较大,其内部泡孔数量较多,泡孔结构分布均匀。     

Mesoporous silica particles grafted with polystyrene brushes as a nucleation agent for polystyrene supercritical carbon dioxide foaming

In this study, spherical ordered mesoporous silica (s‐OMS) was applied as a new type of nucleating agent in polystyrene (PS) foaming with supercritical CO₂ as a blowing agent. These s‐OMS particles were modified by the selective grafting of PS brushes on the outside surface, by which the mesoporous structure inside particles could be maintained. Transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller surface area analysis were used to characterize the structure of the original and modified particles; these indicated that the PS brushes were grafted on the outside surface and the inside porous structure were maintained. PS/s‐OMS–PS composites were prepared by a solution blending method, and the s‐OMS–PS particles could have been well dispersed in the PS matrix because of the surface modification. Subsequently, PS and composite microcellular foams were prepared by a batch foaming process, and the morphology characterization on these foams showed that the s‐OMS particles exhibited an excellent heterogeneous effect on PS foaming. The heterogeneous effect became more significant when the foaming temperature or saturation pressure was low. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4308–4317, 2013     

Foaming behavior of microcellular foam polypropylene/modified nano calcium carbonate composites

A new process was used to prepare microcellular foams with supercritical carbon dioxide as the physical foaming agent in a batch. The foaming temperature range of the new process was about five times broader than that of the conventional one. Characterization of the cellular structure of the original polypropylene (PP) and PP/nano‐CaCO₃ (nanocomposites) foams was conducted to reveal the effects of the blend composition and processing conditions. The results show that the cellular structure of the PP foams was more sensitive to the foaming temperature and saturation pressure variations than that of the nanocomposite foams. Uniform cells of PP foams are achieved only at a temperature of 154°C. Also, the low pressure of 20 MPa led to very small cells and a low cell density. The competition between the cell growth and cell nucleation played important role in the foam density and was directly related to the foaming temperature. Decreasing the infiltration temperature depressed the initial foaming temperature, and this resulted in significantly larger cells and a lower cell density. A short foaming time led to a skin–core structure; this indicated that a decrease in the cell size was found from skin to core, but the skin–core structure gradually disappeared with increasing foaming time. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Cell structure and impact properties of foamed polystyrene in constrained conditions using supercritical carbon dioxide

To obtain cellular with small cell diameter, to control cell structure and to improve impact strength of foaming materials, the quick-heating method was applied for foaming polystyrene (PS) using supercritical CO₂ (Sc-CO₂) as physical blowing agent. Then, changes of cell structure and impact strength in microcellular foamed PS materials under constrained conditions were studied. The effects of foaming processing parameters, such as foaming temperature, saturation pressure and foaming time on the cell structure and impact strength of foamed PS in the constrained conditions were studied. The results showed that the Sc-CO₂ solubility and nucleation density in the constrained conditions were not influenced compared with those under free foaming conditions. However, cells in constrained foaming process are mostly circular and independent with thick cell walls; the phenomenon of cell coalescence and collapse was effectively eliminated under constrained conditions. In addition, cell diameters in constrained foaming process decrease with increase in foaming temperature and increase with increase in the foaming time. Compared with that in free foaming conditions, the cell growth was restrained dramatically under constrained conditions which resulted in smaller cell diameter. Moreover, higher impact strength could be obtained for foamed PS as foaming time was prolonged, foaming temperature was increased or saturation pressure was enhanced.     

Foaming of polypropylene with supercritical carbon dioxide: An experimental and theoretical study on a new process

A new process was used to foam polypropylene (PP) with batch foaming technique with supercritical carbon dioxide (scCO₂) as the blowing agent. Comparing with the conventional process, the new one takes less time to foam and the foaming temperature range is much broader, which is about 2.5 h and 55°C, respectively. An activation model was established on the basis of mass equilibrium, this model was combined with classical nucleation theory and S‐L EOS model to explain foaming behaviors of PP and simulate the cell nucleation and cell diameter. A satisfactory agreement between calculated and experimental values was obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2877–2885, 2013     

聚醚酰亚胺均相成核发泡行为研究

以超临界CO₂为发泡剂,采用间歇式发泡技术制备了聚醚酰亚胺（PEI）微孔泡沫。通过改变发泡温度、发泡压力与样品浸泡时间等工艺条件,研究了PEI的均相成核发泡行为。实验还通过二次降压法制备了具有复合泡孔结构的PEI微孔泡沫材料。结果表明,复合泡孔结构提高了PEI微孔泡沫的发泡倍率,第一次压力降ΔP₁与第二次保压时间Δt₂是影响复合泡孔结构参数的重要影响因素。     

Effects of Process Variables on Microcellular Structure and Crystallization of Polypropylene Foams with Supercritical CO2 as the Foaming Agent—A Study of Microcellular Foaming of Polypropylene

The effects of process variables on the microcellular structure and crystallization of foamed polypropylene (PP) with supercritical CO₂ as the foaming agent were investigated in this article. The cell size increased and the cell density reduced with increased foaming temperature. Differently, both the cell diameter and cell density increased as saturation pressure increased. DSC curves showed that the melting peak was broadened when supercritical CO₂ foaming PP. Furthermore, the width at half-height of the melting peak increased, the melting peak moved to higher temperature, and the melting point and crystallinity enhanced as the foaming temperature lowered and the saturation pressure enhanced.     

Foaming behavior of high‐melt strength polypropylene/clay nanocomposites

The foaming behavior of high‐melt strength polypropylene (HMS‐PP) and HMS‐PP/Cloisite 20A nanocomposites (PPNC) was studied in a batch process. PPNCs with 2, 4, 8, and 10 wt% clay were prepared in a twin screw extruder. The morphology of the nanocomposites was studied using XRD and TEM. Subsequently, foaming experiments were conducted using supercritical CO₂ as the blowing agent in a batch process, and foams with cell sizes varying from the sub micrometer to the micro meter range were prepared. The effect of variation in saturation pressure and temperature, foaming temperature, foaming time, and quench temperature was determined experimentally. Dynamic rheological measurements were conducted to relate the influence of nanocomposites morphology with foam cell growth and nucleation. Extensional rheological measurements were also conducted to detect the presence of strain hardening effect at the foaming temperatures used in the experiment. It was found that the nucleation efficiency of clay reduces with increase in clay loading. Also, the optimum amount of filler for generation of fine celled foams was found to be around the percolation threshold of the polymer. The extended strain hardening effect shown by the polymer in presence of clay plays an important role in stabilizing foam cell sizes. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Characterization of the porous structure of biodegradable scaffolds obtained with supercritical CO<Subscript>2</Subscript> as foaming agent

Poly(ε-caprolactone) foams were prepared, via a batch process, by using supercritical CO₂ as foaming agent. Their porous structure was characterized through mercury porosimetry, helium and mercury pycnometry, scanning electron microscopy (SEM) and X-ray microtomography observations coupled with image analysis. The pore size distributions obtained by these two latter techniques show that the pore structure is more homogeneous when the foaming process is performed under a high CO₂ saturation pressure (higher than 250 bars).     

Generation of microcellular biodegradable polycaprolactone foams in supercritical carbon dioxide

Microcellular foaming of low‐T_g biodegradable and biocompatible polycaprolactone (PCL) in supercritical CO₂ has been studied. The purpose is to apply microcellular materials to drug containers and medical materials for artificial skin or bone. Effects of a series of variable factors on the foam structures, such as saturation temperature, saturation pressure, saturation time, and depressurization time were studied. The experimental results indicate that, while keeping other variables unchanged, higher saturation temperature leads to reduced bulk densities and different saturation pressures result in different nucleation processes. In addition, saturation time has a profound effect on the structure of the product. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 593–597, 2004     

Study of different effect on foaming process of biodegradable bionolle in supercritical carbon dioxide

Microcellular foaming of biodegradable Bionolle in supercritical CO₂ has been produced. The effects of a series of variable factors, such as saturation temperature, saturation pressure, and depressurization time and step on the foam structures and density, were studied through measurement of density and SEM observation. The experimental results show that higher saturation temperatures lead to an increase in bulk densities; and different depressurization time and step result in different product cell morphology. In addition, at some saturation temperature, the orientation of the cells can be found in the product morphology. XRD experimental results show that the foaming treatment with SC CO₂ increased the crystallinity of Bionolle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2901–2906, 2006     

Investigation of the effect of foaming process parameters on expanded thermoplastic polyurethane bead foams properties using response surface methodology

Expanded thermoplastic polyurethane (ETPU) bead foams were fabricated by batch foaming with supercritical CO₂ as blowing agent. On the basis of single factor investigation, the response surface methodology based on Box‐Behnken Design was used to investigate the influences of saturation pressure, temperature, and soaking time and their interactions on foaming behavior of ETPU. The results showed that saturation temperature was the most significant parameter affecting the expansion ratio, shrinkage ratio, and cell morphology of ETPU. Moreover, there was an interaction effect between saturation temperature and soaking time, wherein the expansion ratio of ETPU was more sensitive to change of soaking time at higher temperature. As the soaking time increased, the shrinkage of ETPU increased firstly and then leveled off, and the cell diameter decreased significantly. By applying the response surface methodology optimization, ETPU bead foams with final expansion ratio of 8.04, mean cell diameter of 74.2 μm, and average cell density of 1.46 × 10⁷cell/cm³ can be obtained while the optimum conditions at saturation pressure of 15 MPa, saturation temperature of 100 °C and soaking time for 60 min. In addition, the dual melting peak of ETPU characteristics demonstrated that it is suitable for steam‐chest molding technology. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46327.     

Preparation of carbon foams with supercritical toluene

Carbon foams with pore sizes of 10–50 μm were prepared with mesophase pitch and toluene as the carbonaceous precursor and supercritical agent, respectively. Results revealed that the light pitch components and dissolved toluene in pitch significantly affected the pore structures of resultant carbon foams. The amount of toluene dissolved in molten pitch is greatly dependent on the foaming conditions, such as the ratio of toluene to pitch, foaming temperature, foaming pressure and saturation time. Carbon foams with hierarchical porous structures are obtained by controlling the amount of light pitch components.     

PVC微孔塑料加工工艺与泡孔结构及耐热性关系研究

以超临界CO2为发泡剂,用动态发泡实验装置在不同的发泡温度、气体饱和压力及振动频率和振幅等加工工艺条件下制备了聚氯乙烯(PVC)微孔塑料。研究发现,发泡温度存在着一个最佳温度范围,使得泡孔密度最大、泡孔尺寸最小;气体饱和压力越大,泡孔结构越好;当剪切速率较低时,在发泡过程中施加强振动作用能显著提高泡孔密度,减小泡孔尺寸,当剪切速率较高时,施加较弱的振动作用即可改善泡孔形态,而施加较强的振动作用可能会产生较大的剪切热和脉动剪切应力,从而破坏泡孔结构;PVC微孔塑料的维卡软化温度与泡孔结构有着密切的关系,泡孔密度越大、泡孔尺寸越小,维卡软化温度就越高。     

Degradation of polystyrene in supercritical n-Hexane

Degradation of polystyrene was carried out in supercritical n-hexane under reaction temperature ranging from 330 °C to 390 °C, pressure ranging from 30 bar to 70 bar and reaction duration of 90 min. The conversion of polystyrene increased with rising temperature and pressure. The degradation performance was influenced by the temperature rather than applied pressure. Polystyrene rapidly degraded in 30 min after reaching a prescribed temperature ranging from 350 °C to 390 °C. At a prescribed temperature of 390 °C, the degree of degradation was higher than 90%. The degradation reaction was examined experimentally at a relatively low temperature of 330 °C. The degradation of polystyrene by using supercritical n-hexane has been found to be more effective compared to general pyrolysis (thermal degradation). Among the selectivity of liquid products, that of a single aromatic ring group like styrene at 390 °C increased up to 65% in 90 min. It was found from the analysis by a gel permeation Chromatograph (GPC), that high molecular-weight compounds decreased but oligomers increased with rising temperature.     

Open‐celled microcellular thermoplastic foam

A theoritical model of the production of open‐cell microcellular foam is presented. This model allows the prediction of the conditions necessary to produce these materials. Experiments verify the model quite well. The results of the batch processing experiments indicate the processing parameters that promote the development of open‐celled microcellular polystryene foam. A saturation pressure of 17.2 MPa (2500 psig) provides the nucleation density necessary to form an impinged structure with microcellular bubble density. A foaming temperature of 200°C promotes the formation of both internal and surface porosity. A scaled time between 1 and 2.7 seconds develops a foam structure that intrudes a large volume. Samples foamed at 200°C for 1 and 2 seconds possess pores less than 1 μm in diameter. These samples represent scaled times of 1 and 2 seconds. Therefore, to produce open‐celled microcellular polystyrene foam with batch processing, samples should be saturated at approximately 17.2 MPa (2500 psig) and foamed for a scaled time between 1 and 2 seconds.     

Production of microcellular foam plastics by supercritical carbon dioxide

The production of microcellular plastic was studied in the polymethyl metacrylate (PMMA)-supercritical carbon dioxide and polycarbonate (PC)-supercritical carbon dioxide systems. The test pieces of PMMA and PC were put into a saturation vessel of which temperature and pressure were kept constant. Supercritical carbon dioxide at temperature between 303K and 393K and pressure between 100 bar and 250 bar was used as a foaming agent. After saturation of carbon dioxide, the pressure was quickly released to atmospheric pressure. The samples were immediately taken out from the vessel and heated in an oil bath. The fractured part of the sample was used for microstructure analysis with SEM. The effect of the saturation temperature, pressure of sorption and the foaming time on the cell mean size and cell density of the foam was investigated by considering the solubility of carbon dioxide in PMMA and PC. The foam morphologies of the foamed plastics were affected by solubility of carbon dioxide, which was directly related to saturation temperature and pressure. The cell density increased and, consequently, the cell size decreased with the solubility of carbon dioxide. The foaming time can be used a controlling factor to obtain the desired foam structure and the volume expansion ratio.     

Novel poly(aryl ether nitrile ketone) foams and the influence of copolymer structure on the foaming result

Novel poly(aryl ether nitrile ketone) foams were prepared through the batch foaming method with supercritical CO₂ as the blowing agent. Both temperature‐induced and pressure‐induced foaming methods were conducted to examine the influence of nitrile groups on the foaming result. The results indicated that nitrile groups influenced the foaming result by affecting both the viscoelasticity and CO₂ absorption of the polymers. In addition, the CO₂ solubility of the polymers increased with increasing CN content presumably because of the Lewis acid–base nature of the interaction between the CO₂ molecules and the nitrile groups. The cell growth process was assessed by analyzing the influence of foaming temperature and foaming time on the cell morphology. Nanocellular foams with a minimum size of 30–50 nm were achieved by the temperature‐induced foaming method. Moreover, highly expanded foams with a maximum expansion ratio of 23.6 were obtained by the pressure‐induced foaming method. © 2018 Society of Chemical Industry     

Fabrication and cell morphology of a microcellular poly(ether imide)–carbon nanotube composite foam with a three-dimensional shape

The preparation of microcellular poly(ether imide) (PEI) based foams with three-dimensional geometry remains a great challenge worldwide. In this study, we fabricated microcellular PEI–carbon nanotube (CNT) bead foams with a batch rapid depressurization method in a self-designed mold with supercritical carbon dioxide (scCO₂) as a blowing agent. The effects of the saturation time, foaming temperature, foaming pressure, and depressurization rate on the microcellular structures of the PEI foam were analyzed by the Taguchi approach to determine the optimum foaming conditions, and the influence of the CNT content on the cell structure was analyzed. The results show that the depressurization rate and foaming temperature were the key factors influencing the cell size and cell density (N _f); that is, the high depressurization rate and low foaming temperature favored a small cell size and high N _f. The foaming temperature also influenced the foaming ratio (ϕ), and a high ϕ was obtained at a high foaming temperature. Under optimal foaming conditions, PEI with 2.0 wt % CNTs presented the best cell structure; N _f, cell size, and ϕ were 6.14 × 10¹⁰ cell/cm³, 2.43 μm, and 2.08, respectively. The mechanical properties of the final parts were related more to the foaming time and CNT concentration, and the maximum tensile and compression strength were reached at 3 h foaming time and 2.0 wt % CNT, that is, at 2.75 and 15.1 MPa (10% strain), respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47501.     

Foam processability of polypropylene/sisal fiber composites having near-critical fiber length for acoustic absorption properties

The current research aims to develop a sound-absorbing material from polypropylene (PP) and sisal fibers (SFs). The study explores the foam processability of PP/SF composites with near-critical fiber length, employing supercritical CO₂-assisted batch foaming technology. Optimized foam processing conditions were determined to be 145°C, 100 bar, and 15 min saturation time. These conditions resulted in foams with the lowest density, maximum volume expansion ratio and an overall microcellular structure. Notably, increasing the fiber concentration significantly enhanced the compressive properties, exhibiting a remarkable 3000% improvement with the addition of 40 wt% SFs. Dynamic mechanical analysis further revealed improved dampening properties of the composites after foaming. Moreover, the incorporation of SFs led to an increase in the noise reduction coefficient, while foaming additionally improved the sound absorption properties. This renders the material highly applicable for soundproofing purposes. Thus, produced PP/SF microcellular foams offer properties that can potentially be used to produce lightweight structural components for acoustic absorption applications.