Porous materials for sound absorption

Hybrid composite meta-porous structure for improving and broadening sound absorption

A phase change material encapsulated in a mechanically strong graphene aerogel with high thermal conductivity and excellent shape stability

Recent progresses in two-dimensional correlation spectroscopy (2D-COS)

To predict the mechanical behavior of 3D printed products, it is important to understand the composite material properties and the effect that parameters of 3D printing process have on the properties of these materials. The mechanical properties of PLA-based composite materials were studied in this work. The mechanical properties of the hot pressed samples were compared to those of the 3D printed samples. The elongation at break and the yield strength of the samples fabricated by 3D printing are decreased by 15–60% compared to those for the hot pressed samples. It has been found that the mechanical properties of 3D printed samples do not practically depending on the deposition scheme.

Mechanical properties of PLA-based composites for fused deposition modeling technology

A series of microporous open-cell poly(vinyl formal) (PVF) foams were obtained by cross-linking poly(vinyl alcohol) (PVA) with different contents of formaldehyde during the first acetalization process. In this reaction, water acted not only as the solvent of PVA but also as the pore-forming agent, which made this method more concise and environment-friendly. However, the PVF foam walls were not strong enough to maintain the initial pore shapes and sizes. The second acetalization process was used to increase the acetalization degree to enhance the strength of the foam walls. The poly(vinyl formal) foams obtained by the two-step acetalization method (TPVF) were able to keep the pretty microporous structures during the drying process. The materials with highly microporous structures exhibited a good ability to absorb normally incident sound. Therefore, the microporous open-cell TPVF foams have great potential in the application of sound absorption materials.

Sound Absorption Properties of Microporous Poly(vinyl formal) Foams Prepared by a Two-Step Acetalization Method

A series of multiporous open-cell poly(vinyl formal) (PVF) foams were obtained by crosslinking poly(vinyl alcohol) (PVA) with different contents of formaldehyde in aqueous solution. Water did not only act as the solvent of PVA, but also as the pore-forming agent during the acetalization process. With the increasing acetalization degree, the multiporous PVF foams gradually separated out from water. And the higher the acetalization degree reached, the bigger the volume shrinkage observed. PVF foams with different pore sizes were obtained by changing the formaldehyde dosage. According to the results of FTIR spectra, the intensity ratio of O–H and C–H stretching mode (νs(O–H)/νs(C–H)) could reveal the acetalization degrees of PVF foams. The thermal properties and morphologies were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). The PVF foams could be used as sound absorbing materials because of the open-cell multiporous structures. The sound absorption coefficient (α) of the PVF foam largely increased with the decreasing pore size, especially in the frequency range of 800–2500 Hz. And the highest α value of 0.98 was obtained at 2000 Hz for PVF-3.0.

Multiporous open-cell poly(vinyl formal) foams for sound absorption

In this work, highly electrically and thermally conductive biopolymer composites were prepared by low-temperature expandable graphite (EG) filling Poly(L-lactic acid) (PLLA) via an in situ exfoliation melt blending process. The electrical conductivity of the composites with various graphite contents was measured by a four-point probe resistivity determiner and a high value of 0.37 S/cm was obtained at 70 wt.% EG content. A hot-disk method was used to evaluate the thermal conductivity of the composites. At EG loading fraction of 70%, thermal conductivity of PLLA/EG composites reached to the highest 26.87 W/mK, which is 100 times higher than neat PLLA. The electrical percolation was observed in the vicinity of the thermal percolation threshold concentration. The expansion of EG was crucial to the overall conductivity of the blends, which was confirmed by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). Dynamic rheology analysis was applied to study the structural change by the interconnection of the exfoliated graphite flakes and the formation of the networks in the blends. Thermogravimetric analysis (TGA) was employed to determine the thermal properties of the investigated PLLA/EG composites.

Highly conductive Poly(L-lactic acid) composites obtained via in situ expansion of graphite

In this work, high electrically conductive Polymethylmethacrylate/graphite (PMMA/G) composites with a specific core-shell structure were synthesized via Pickering emulsion (solid-stabilized emulsion) route. The electrical conductivity of the core-shell composites was measured by a four-point probe resistivity determiner and a very high value of 9.8 × 10−3 S/cm (1013 times higher than virgin PMMA) was obtained at 30 wt% graphite. However, the electrical conductivity of the PMMA/G composites gained through traditional blend process was relatively lower and the value only reached 9.4 × 10−9 S/cm at same graphite loading fraction. Contact angle measurement was applied to determine the surface free energy of the modified graphite which was cladded by Al(OH)3. The morphology of the core-shell composites was observed by SEM and optical microscopy. Dynamic rheology analysis was employed to study the structural change by the interconnection of the graphite flakes and the formation of the networks in the composites. The interconnected networks of the core-shell composites were more easily constructed when compared with the composites obtained by the traditional blending process.

High electrical conductive polymethylmethacrylate/graphite composites obtained via a novel pickering emulsion route

Abstract In this paper, highly electrically conductive polymeric composites were obtained by low-temperature expandable graphite (LTEG) filling poly(L-lactic acid) (PLLA) in the presence of ascorbic acid via an in situ exfoliation and subsequent reduction process during the melt blending. The electrical conductivity of the PLLA/reduced and expanded graphite (R-EG) composites was determined by a four-point probe resistivity determiner and compared with that of the PLLA/expanded graphite (EG) composites. The percolation threshold of PLLA/R-EG blends decreased from 11.2 wt% to 7.1 wt%, which illustrated the superiority of R-EG to the electrically conducting ability of PLLA composites. At the graphite concentration near the percolation threshold, the electrical conductivity of PLLA/R-EG composites was much higher than that of PLLA/EG composites. The effective in situ expansion and reduction of LTEG were crucial to the overall electrical conductivity of the blends, which was confirmed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. Dynamic rheology analysis confirmed that the connected networks that were the major cause of the rapid increase in electrical conductivity were much more easily formed for PLLA/R-EG blends than those of PLLA/EG blends. Thermogravimetric analysis (TGA) was applied to determine the decomposition and thermal stability of the PLLA/R-EG composites.

Bai Xue

Papers

Sound Absorption Properties of Microporous Poly(vinyl formal) Foams Prepared by a Two-Step Acetalization Method

Multiporous open-cell poly(vinyl formal) foams for sound absorption

Highly conductive Poly(L-lactic acid) composites obtained via in situ expansion of graphite

High electrical conductive polymethylmethacrylate/graphite composites obtained via a novel pickering emulsion route

Highly electrically conducting poly(L-lactic acid)/graphite composites prepared via in situ expansion and subsequent reduction of graphite