Boron/nitrogen flame retardant additives cross‐linked cellulose nanofibril/montmorillonite aerogels toward super‐low flammability and improved mechanical properties

Low‐flammability freeze‐dried cellulose nanofibril (CNF)/sodium montmorillonite (MMT) aerogels with improved mechanical properties were fabricated via a facile cross‐linking of boric acid (BA) and melamine‐formaldehyde (MF) resins. Scanning electron microscopy analysis showed that BA cross‐linking reduced the interspacing of layered CNF/MMT aerogels whereas introduction of MF formed polymeric fibrils that connected the layers. These changes on microstructures resulted in the improvement on compressive mechanical properties of the cross‐linked aerogels. Moreover, the boron (B)/nitrogen (N) containing flame retardant cross‐linkers greatly increased the limiting oxygen index values that could reach 85% and leveled the UL‐94 rating from no rating to V‐0. Cone calorimetric results suggested that BA and MF induced a synergistic effect on the flame retardant properties of the CNF/MMT aerogels. However, the thermal conductivity was little affected because pore structure and size was not substantially modified. This simple approach fabricated highly flame‐resistant and mechanically strong CNF‐based aerogels that could be used in various engineering fields.     

Supercritical CO<Subscript>2</Subscript> assisted preparation of open-cell foams of linear low-density polyethylene and linear low-density polyethylene/carbon nanotube composites

The open-cell structure foams of linear low-density polyethylene (LLDPE) and linear low-density polyethylene (LLDPE)/multi-wall carbon nanotubes (MWCNTs) composites are prepared by using supercritical carbon dioxide (sc-CO₂) as a foaming agent. The effects of processing parameters (foaming temperature, saturation pressure, and depressurization rate) and the addition of MWCNTs on the evolution of cell opening are studied systematically. For LLDPE foaming, the foaming temperature and saturation pressure are two key factors for preparing open-cell foams. An increase in temperature and pressure promotes both the cell wall thinning and cell rupture, because a high temperature results in a decrease in the viscosity of the polymer, and a high pressure leads to a larger amount of cell nucleation. Moreover, for the given temperature and pressure, the high pressurization rate results in a high pressure gradient, favoring cell rupture. For LLDPE/MWCNTs foaming, the addition of MWCNTs not only promotes the cell heterogeneous nucleation, but also prevents the cell collapse during cell opening, which is critical to achieve the open-cell structures with small cell size and high cell density.     

Rigid polyurethane foams reinforced with disilanolisobutyl POSS: Synthesis and properties

This work reports the synthesis of rigid polyurethane (PU) foams modified by disilanolisobutyl polyhedral oligomeric silsesquioxane (DSIPOSS). This open‐cage nanostructure silsesquioxane has 2 hydroxyl groups and therefore can be chemically built directly in the PU backbone to form hybrid polyurethane‐POSS foam. Synthesis procedure using polymeric 4,4′‐diphenylmethane diisocyanate, polyetherol, and DSIPOSS has been elaborated, and the influence of POSS on the cell structure, closed cell content, apparent density, thermal conductivity, and compression strength of the rigid polyurethane composites has been evaluated. The hybrid composite foams containing 1.5 and 2.0 wt% DSIPOSS showed a reduced number of cells and an increased average area of foam cells in comparison with the unmodified PU, while the addition of 0.5wt% of DSIPOSS causes an increase in the number of cells of the foam as compared with the reference and thus a reduction in the average area of cells. X‐ray microtomography provided data on the porous structure of polyurethane hybrid materials, including reduction of the pore surface area. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy analysis revealed a good homogenization of DSIPOSS in polyurethane matrix. Thermogravimetric analysis results have shown that incorporation of POSS nanoparticles into PU foam does not significantly change the degradation process. The compressive strength of PUF‐POSS hybrids in the direction parallel and perpendicular to the direction of foam rise is greater than the strength of the reference foam already for the lowest DSIPOSS content.     

毛竹屑与玉米淀粉共液化产物制备聚氨酯泡沫研究

采用单因素试验设计,研究了液化剂组成、液比以及毛竹屑与淀粉的比例对液化产物理化性质、及所制备的聚氨酯泡沫材料的物理力学指标影响.结果显示当以50%乙二醇+50%碳酸亚乙酯混合物作为液化剂、添加相当于液化剂质量3%的浓硫酸为催化剂、在(150±5)℃(油浴)和常压条件下,液化150min,搅拌速度30r/min,取得本试验条件下最好的竹屑液化效果,液化产物中竹屑含量25%,残渣率3.96%,但该液化产物中天然聚合物碎片含量少,所制备的聚氨酯泡沫材料塌陷;竹屑与玉米淀粉共液化有效提高了液化产物中生物质的含量,但占液化剂质量25%竹屑+占液化剂质量125%玉米淀粉共液化产物粘度太高(8.85Pa.s);而20%竹屑+130%玉米淀粉的共液化产物与4,4′-二苯基甲烷二异氰酸酯以及各种助剂按异氰酸酯基/羟基摩尔比为1.1配合时,所制备的聚氨酯泡沫材料表观密度为33.6kg/m3、压缩强度118kPa、弹性模量6.91MPa,在周年生物降解试验中,该生物质基聚氨酯硬质泡沫失重率为12.63%.     

Acid character control of bioactive glass/polyvinyl alcohol hybrid foams produced by sol–gel

Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of bioceramics with the flexibility of polymers. In previous work hybrid foams with 80% bioactive glass and 20% polyvinyl alcohol were prepared by the sol–gel method. The produced hybrids presented a high acidic character due to the catalysts added. In this work different methods to control the acidity and toxicity of the hybrids were also evaluated, through changes in the synthesis pH and use of different neutralization solutions. The hybrids were prepared with inorganic phase composition of 70%SiO₂–30%CaO and PVA fractions of 20–60% by the sol–gel method. The characterization of the obtained foams was done by FTIR, SEM, Raman Spectroscopy, Helium Picnometry and TGA. The immersion of hybrids in a calcium acetate solution was the most adequate neutralization method. The foams presented porosity of 60–85% and pore diameters of 100–500 μm with interconnected structure.     

Foams in contact with solid boundaries: Equilibrium conditions and conformal invariance

A liquid foam in contact with a solid surface forms a two-dimensional foam on the surface. We derive the equilibrium equations for this 2D foam when the solid surface is curved and smooth, generalising the standard case of flat Hele-Shaw cells. The equilibrium conditions at the vertices in 2D, at the edges in 3D, are invariant by conformal transformations. Regarding the films, conformal invariance only holds with restrictions, which we explicit for 3D and flat 2D foams. Considering foams confined in thin interstices between two non-parallel plates, normal incidence and Laplace’s law lead to an approximate equation relating the plate profile to the conformal map. Solutions are given for the logarithm and power laws in the case of constant pressure. The paper concludes on a comparison with available experimental data.     

Synthesis and combined properties of novel fluorinated cationic surfactants derived from hexafluoropropylene dimer

Three novel fluorinated surfactants with branched short fluorinated tails as hydrophobic groups, ammonium oxide as polar groups are prepared. Surface tension measurement shows that these fluorinated surfactants are ideal compounds to design new formulations in fire-fighting field.     

耐高温聚酰亚胺泡沫材料

聚酰亚胺泡沫具有低介电、隔热、吸声、高比强度以及高经济效益等诸多优点,因而近些年来在航空、航天、船舶航舰、能源与环境保护等领域有着广泛的应用。聚酰亚胺泡沫按照泡孔结构分为软质开孔泡沫和硬质闭孔泡沫两大类,其通常是由芳香族二酐与芳香族二胺通过缩聚反应制备得到分子量可控的聚酯铵盐,再将其作为前驱体经过热发泡制备得到最终的聚酰亚胺泡沫。前驱体的化学结构对最终的聚酰亚胺泡沫的机械性能和热性能都有非常显著的影响,同时前驱体的分子量也会对泡沫的密度、机械性能和热性能有非常显著的影响。聚酰亚胺泡沫的研究进展,特别是其化学结构、性能和应用都会在本文中逐一阐述。