Effect of Graphene Surface Functional Groups on the Mechanical Property of PMMA Microcellular Composite Foams

The functional groups on graphene sheets surface affect their dispersion and interfacial adhesion in polymer matrix. We compared the mechanical property of polymethymethacrylate（PMMA） microcellular foams reinforced with graphene oxide（GO） and reduced graphene oxide（RGO） to investigate this influence of functional groups. RGO sheets were fabricated by solvent thermal reduction in DMF medium. UV-Vis, FT-IR and XPS analyses indicate the difference of oxygen-containing groups on GO and RGO sheets surface. The observation of SEM illustrates that the addition of a smaller number of GO or RGO sheets causes a fine cellular structure of PMMA foams with a higher cell density(about 1011 cells/cm3) and smaller cell sizes（about 1-2 μm） owing to their remarkable heterogeneous nucleation effect. Compared to GO reinforced foams, the RGO/PMMA foams own lower cell density and bigger cell size in their microstructure, and their compressive strength is lower even when the reinforcement contents are the same and the foam bulk density is higher. These results indicate that the oxygen-containing groups on GO sheets’ surface are beneficial to adhere CO2 to realize a larger nucleation rate, and their strong interaction with PMMA matrix improves the mechanical property of PMMA foams.

Electroless copper plating on microcellular polyurethane foam

In order to obtain substrates with good conductive foam for high porosity foam metal materials used in the metal electrodes,the technique of electroless copper plating on the microcellular polyurethane foam with pore size of 0.3 mm was investigated.The main factors affecting the deposition rate such as the solution composition,temperature,pH value and adding ultrasonic were explored.The results show that the optimum process conditions are CuSO4 16 g/L,HCHO 5 mL/L,NaKC4H4O6 30 g/L,Na2EDTA 20 g/L,K4Fe(CN)6 25 mg/L,pH value of 12.5-13.0 and temperature of 40-50℃.Under these technical conditions, the process has excellent bath stability.Adding ultrasonic on the process can elevate the deposition rate of copper by 20%-30%.The foam metal material with a porosity of 92.2%and a three-dimensional network structure,was fabricated by electro-deposition after the electroless copper plating.

Cell structure of microcellular combustible object foamed by supercritical carbon dioxide

In order to solve the issue that the combustible objects for cased telescoped ammunition (CTA) didn't burn completely during the combustion process, the microcellular combustible objects were foamed with numerous cells in the micron order to improve the combustion performance by the supercritical carbon dioxide (SCeCO2) foaming technology. As the cell structure determined the combustion properties of microcellular combustible objects, the solubility of SCeCO2 dissolved into the combustible objects was obtained from the gravimetric method, and scanning electron microscope (SEM) was applied to characterize the cell structure under various process conditions of solubility, foaming temperature and foaming time. SEM images indicate that the cell diameter of microcellular combustible objects is in the level of 1 mm and the cell density is about 1011 cell,cm^-3. The microcellular combustible objects fabricated by the SCeCO2 foaming technology are smooth and uniform, and the high specific surface area of cell structure can lead to the significant combustion performance of microcellular combustible object for CTA in the future.

Microcellular Foaming of Plasticized Thin PC Sheet I.Effects of Processing Conditions

Novel microcellular foams using thin plasticized PC sheet were prepared by compression molding. The measurement results showed that T of plasticized PC was decreased and the molecular chain mobility was increased. Decrease in T and increase in chains mobility were contributed to the widen of foaming temperature window. Effects of processing conditions on cell size, cell density and relative density were also investigated. The experimental results show that the temperature, tributyl citrate and foaming agent content have more effects on the structures and morphology of the plasticized PC microcellular foam. Effects of experimental conditions on cell size distribution have also been discussed.

Interface Engineered Microcellular Magnetic Conductive Polyurethane Nanocomposite Foams for Electromagnetic Interference Shielding

Lightweight microcellular polyurethane(TPU)/carbon nanotubes(CNTs)/nickel-coated CNTs(Ni@CNTs)/polymerizable ionic liquid copolymer(PIL)composite foams are prepared by non-solvent induced phase separation(NIPS).CNTs and Ni@CNTs modified by PIL provide more heterogeneous nucleation sites and inhibit the aggregation and combination of microcellular structure.Compared with TPU/CNTs,the TPU/CNTs/PIL and TPU/CNTs/Ni@CNTs/PIL composite foams with smaller microcellular structures have a high electromagnetic interference shielding effectiveness(EMI SE).The evaporate time regulates the microcellular structure,improves the conductive network of composite foams and reduces the microcellular size,which strengthens the multiple reflections of electromagnetic wave.The TPU/10CNTs/10Ni@CNTs/PIL foam exhibits slightly higher SE values(69.9 dB)compared with TPU/20CNTs/PIL foam(53.3 dB).The highest specific EMI SE of TPU/20CNTs/PIL and TPU/10CNTs/10Ni@CNTs/PIL reaches up to 187.2 and 211.5 dB/(g cm^(−3)),respectively.The polarization losses caused by interfacial polarization between TPU substrates and conductive fillers,conduction loss caused by conductive network of fillers and magnetic loss caused by Ni@CNT synergistically attenuate the microwave energy.

Relationship between Microcellular Foaming Injection Molding Process Parameters and Cell Size

In order to study the relationship between the main process parameters and the cell size, the mathematical model of cell growth of microcellular foaming injection process is built. Then numeric simulation is employed as experimental method, and the Taguchi method is used to analyze significance of effect of process parameters on the cell size. At last the process parameters are focused on melt temperature, injection time, mold temperature and pretidied volume. The significance order from big to small of the effect of each process parameters on cell size is melt temperature, pre-filled volume, injection time, and mold temperature. On the basis of above research, the effect of each process parameter on cell size is further researched. Appropriate reduction of the melt temperature and increase of the pre-filled volume can optimize the cell size effectively, while the effects of injection time and mold temperature on cell size are less significant.

Process of Microcellular Propellants with Adjustable Skin Thickness

Microcellular propellants show a vast applicable prospect due to their special shell-pore structure. The effects of saturation pressure and desorption time on skin thickness are studied. The skin thickness is observed and measured using scanning electron microscope (SEM). The results show that the skin thickness decreases when saturation pressure increases from 15 MPa to 30 MPa. In contrast, the skin thickness increases as the desorption time changes from 2 min to 20 min.Therefore, the microcellular propellants with adjustable skin thickness can be obtained under the variable process conditions such as saturation pressure and desorption time.

Burning characteristics of microcellular combustible objects

Microcellular combustible objects for application of combustible case,caseless ammunition or combustible detonator-holding tubes are fabricated through one-step foaming process,in which supercritical CO_2 is used as foaming agent.The formulations consist of inert polymer binder and ultra fine RDX.For the inner porous structures of microcellular combustible objects,the cell sizes present a unimodal or bimodal distribution by adjusting the foaming conditions.Closed bomb test is to investigate the influence of both porous structure style and RDX content on burning behavior.The sample with bimodal distribution of cell sizes burns faster than that with unimodal distribution,and the concentration of RDX can influence the burning characteristics in a positive manner.In addition,the translation of laminar burning to convective burning is determined by burning rate versus pressure curves of samples at two different loading densities,and the resulting transition pressure is 30 MPa.Moreover,the samples with bigger sample size present higher burning rate,resulting in providing deeper convective depth.Dynamic vivacity of samples is also studied.The results show that the vivacity increases with RDX content and varies with inner structure.

Performance Analysis of Slotted Multichannel ALOHA Systems with Capture in Microcellular Environments

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Lightweight,Strong and High Heat-Resistant Poly(lactide acid)Foams via Microcellular Injection Molding with Self-Assembly Nucleating Agent

Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength.In this study,a high-performance PLA foam with well-defined cell morphology,exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding(MIM)process.Differential scanning calorimetry(DSC)results revealed that the added hydrazine-based nucleating agent(HNA)significantly increased the crystallization temperature and accelerated the crystallization process of PLA.Remarkably,the addition of a 1.5 wt%of HNA led to a significant reduction in PLA’s cell size,from 43.5µm to 2.87µm,and a remarkable increase in cell density,from 1.08×10^(7)cells/cm^(3)to 2.15×10^(10)cells/cm^(3).This enhancement resulted in a final crystallinity of approximately 55.7%for the PLA blend foam,a marked improvement compared to the pure PLA foam.Furthermore,at 1.5 wt%HNA concentration,the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136%and 463%,respectively.Additionally,the Vicat softening temperature of PLA blend foam increased significantly to 134.8°C,whereas the pure PLA foam exhibited only about 59.7℃.These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance,which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.

Research on the Dynamic Compressibility of Polyurethane Microcellular Elastomer and its Application for Impact Resistance

The packaging materials with cushioning performance are used to prevent the internal contents from being damaged by the impact and vibration of external forces.The polyurethane microcellular elastomers(PUMEs)can absorb energy through cell collapse and molecular chain creep.In this study,PUMEs with different densities were investigated by scanning electron microscopy,dynamic mechanical analysis and dynamic compression tests.PUMEs exhibited significant im pact resistance and the maximum peak stress attenuation ratio reached 73.33%.The protective equipment was made by PUME with the optimal density of 600 kg/m^(3),and then the acceleration sensing device installed with the same protective equipment fell from a height of 3,5 and 10 m to evaluate the energy-absorbing property and reusability of PUMEs.The results showed that PUMEs equipment reduced the peak acceleration of the device by 93.84%,with a maximum deviation of 9%between actual test and simulation,and shortened the impact time of first landing by 57.39%.In addition,the equipment PUMEs equipment could effectively reduce the stress on the protected items.

Layered Structural PBAT Composite Foams for Efficient Electromagnetic Interference Shielding

The utilization of eco-friendly,lightweight,high-efficiency and high-absorbing electromagnetic interference(EMI)shielding composites is imperative in light of the worldwide promotion of sustainable manufacturing.In this work,magnetic poly(butyleneadipate-coterephthalate)(PBAT)microspheres were firstly synthesized via phase separation method,then PBAT composite foams with layered structure was constructed through the supercritical carbon dioxide foaming and scraping techniques.The merits of integrating ferroferric oxideloaded multi-walled carbon nanotubes(Fe3O4@MWCNTs)nanoparticles,a microcellular framework,and a highly conductive silver layer have been judiciously orchestrated within this distinctive layered configuration.Microwaves are consumed throughout the process of“absorption-reflection-reabsorption”as much as possible,which greatly declines the secondary radiation pollution.The biodegradable PBAT composite foams achieved an EMI shielding effectiveness of up to 68 dB and an absorptivity of 77%,and authenticated favorable stabilization after the tape adhesion experiment.

Lightweight Dual‑Functional Segregated Nanocomposite Foams for Integrated Infrared Stealth and Absorption‑Dominant Electromagnetic Interference Shielding

Lightweight infrared stealth and absorption-dominant electromagnetic interference(EMI)shielding materials are highly desirable in areas of aerospace,weapons,military and wearable electronics.Herein,lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO_(2)(SC-CO_(2))foaming combined with hydrogen bonding assembly and compression molding strategy.The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity,and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures.Particularly,the segregated nanocomposite foams present a large radiation temperature reduction of 70.2℃ at the object temperature of 100℃,and a significantly improved EM wave absorptivity/reflectivity(A/R)ratio of 2.15 at an ultralow Ti_(3)C_(2)T_(x) content of 1.7 vol%.Moreover,the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles.The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace,weapons,military and wearable electronics.

注塑发泡工艺对PEEK制品性能影响

聚醚醚酮(PEEK)作为最具代表性的特种工程塑料,由于其具有较好的力学性能已被广泛应用于航天和军事领域。采用超临界流体注塑发泡的方式制备了发泡聚醚醚酮,发泡制品的质量降低了21%(比强度为59.8),最低介电常数为2.47。泡孔结构的介入降低了制品的力学性能,但是,较好的减重效果使发泡制品仍然具有较好的比强度。探究了泡孔结构对发泡PEEK制品的介电性能的影响规律,结果表明,更宽的发泡层使样品中的气体含量更高,可以有效降低制品的介电常数。由于分子链的极化作用,PEEK试样在X波段存在明显的介电常数波动现象。结晶可以抑制分子链的极化,因此,较高的结晶度可以降低制品的介电常数。研究表明,定向调控PEEK发泡制品的介电性能提供了指导方向。

原位成纤PTFE对PP/CNT微孔注塑发泡材料电磁屏蔽性能的影响

采用聚丙烯(PP)为基体、以多壁碳纳米管(CNT)为碳纳米填料,制备二元复合泡孔材料PP/CNT,并且,当CNT含量为1%时,复合微孔材料泡孔质量及电磁屏蔽性能均较好。以聚四氟乙烯(PTFE)为原位成纤增强相,进行微孔注塑发泡成型,探究PP/CNT/PTFE三元复合微孔材料的电磁屏蔽性能,制备了力学性能较好、对电磁辐射吸收率较高的微发泡电磁屏蔽复合材料;研究了PTFE微纤含量对PP/CNT/PTFE三元复合微孔材料注塑发泡泡孔形貌及电磁屏蔽性能的影响规律;得到了该实验条件下PTFE的最佳添加量。结果表明,当PTFE含量为1%时,原位成纤效果较好,三元复合微孔材料的泡孔直径显著减小,电磁屏蔽性能从未添加PTFE时的12.6 dB提高至24.8 dB。

无机粒子对热塑性聚酰胺弹性体发泡及抗收缩行为的影响:开孔机制揭示

以超临界CO_(2)为发泡剂,制备了低收缩高倍率的热塑性聚酰胺弹性体(TPAE)/无机粒子微孔泡沫。基于扫描电子显微镜、接触角仪、真密度仪等仪器,并结合间歇发泡实验研究了无机粒子对TPAE发泡及抗收缩行为的影响。结果表明,相比较于滑石粉(Talc),硅酸钙(CaSiO_(3))、碳酸钙(CaCO_(3))以及硅灰石(WI)这3种无机粒子都分别与TPAE间的界面张力更高,表现出明显的热力学不相容行为。通过对泡沫开孔结构形成机制的分析,发现复合物泡沫的开孔率随无机粒子与TPAE基体间界面张力、无机粒子直径以及分布密度的增加而提高。而开孔结构的形成可加快CO_(2)与空气的置换速率,降低TPAE泡沫的收缩。故无机粒子的引入改善了TPAE泡沫的泡孔密度和泡孔结构的均匀性和尺寸稳定性,进而制备出开孔率超过90%、发泡倍率达到20倍、收缩率低于5%的TPAE泡沫,并显著增强了TPAE泡沫的尺寸稳定性。

微孔发泡材料成型装置及其可视化研究进展

微孔发泡材料成型装置对微孔发泡材料的制备及基础研究至关重要。微孔发泡材料成型装置的设计与创新直接关系到发泡制品质量的改善、生产效率的提高以及微孔发泡相关基础研究。根据成型方式的不同,微孔发泡材料成型装置主要分为四类,即间歇发泡成型、连续挤出发泡成型、注塑发泡成型、模压发泡成型装置,分别阐述了各类装置设计原理和结构特点,并总结了几种发泡装置的优点和不足;同时总结了各种可视化装置设计方案,与挤出、注塑发泡成型方式下的可视化装置相比,自由发泡可视化装置结构较简单、成本较低廉、操作较简便,目前研究和应用居多;但是,存在与发泡环境相差很大的问题,很难用于实际生产。最后展望了当前微孔发泡材料成型装置设计中亟需解决的问题,并提出了今后微孔发泡材料成型装置的设计思路及研究前景。

含气材料的可压缩性在注塑微发泡中的研究与应用

利用改进的常规微发泡注射成型机可对预塑含气聚合物熔体产生高压而实现了注射成型的压力-体积-温度(PVT)的在线测量。通过对聚苯乙烯和聚丙烯的含气或不含气熔体在一定温度下的压力-体积(PV)行为进行研究,发现含气聚合物熔体的可压缩性远大于不含气聚合物熔体。在实际应用中,含气聚合物熔体的较大的可压缩性可用于辅助注射和加快气体融入熔体过程从而提高发泡质量。另一方面,根据含气聚合物熔体的可压缩性大而存在的安全隐患所做的压力释放试验,首次在国内提出了新的含气材料注射成型的安全操作指导。