7 research outputs found
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Acoustic and Thermal Properties of Recycled Porous Media
This thesis is concerned with developing porous materials from tyre shred
residue and polyurethane binder for acoustic absorption and thermal insulation
applications. The resultant materials contains a high proportion of open,
interconnected cells that are able to absorb incident sound waves through
viscous friction, inertia effects and thermal energy exchanges. The materials
developed are also able to insulate against heat by suppressing the convection
of heat and reduced conductivity of the fluid locked in the large proportion of
close-cell pores. The acoustic absorption performance of a porous media is
controlled by the number of open cells and pore size distribution. Therefore, this
work also investigates the use of catalysts and surfactants to modify the pore
structure and studies the influence of the various components in the chemical
formulations used to produce these porous materials. An optimum type and
amounts of catalyst are selected to obtain a high chemical conversion and a
short expanding time for the bubble growth phase. The surfactant is used to
reduce the surface tension and achieve a homogenous mixing between the
solid particulates tyre shred residue, the water, the catalyst and the binder. It is
found that all of the components significantly affect the resultant materials
structure and its morphology. The results show that the catalyst has a
particularly strong effect on the pore structure and the ensuing thermal and
acoustical properties. In this research, the properties of the porous materials
developed are characterized using standard experimental techniques and the
acoustic and thermal insulation performance underpinned using theoretical
models.
The important observation from this research is that a new class of
recycled materials with pore stratification has been developed. It is shown that
the pore stratification can have a positive effect on the acoustic absorption in a
broadband frequency range. The control of reaction time in the foaming
process is a key function that leads to a gradual change in the pore size
distribution, porosity, flow resistivity and tortuosity which vary as a function of
sample depth. It is shown that the Pade approximation is a suitable model to
study the acoustic behaviour of these materials. A good agreement between the
measured data and the model was attained.Ministry of Science and Technology of Thailand; Naresuan
University, Phitsanulok, Thailand
The Physical and Mechanical Properties of Biocomposite Films Composed of Poly(Lactic Acid) with Spent Coffee Grounds
Green fabrication route of robust, biodegradable silk sericin and poly(vinyl alcohol) nanofibrous scaffolds
Silk sericin (SS) has been extensively used to fabricate scaffolds for tissue engineering. However, due to its inferior mechanical properties, it has been found to be a poor choice of material when being electrospun into nanofibrous scaffolds. Here, SS has been combined with poly(vinyl alcohol) (PVA) and electrospun to create scaffolds with enhanced physical properties. Crucially, these SS/PVA nanofibrous scaffolds were created using only distilled water as a solvent with no added crosslinker in an environmentally friendly process. Temperature has been shown to have a marked effect on the formation of the SS sol–gel transition and thus influence the final formation of fibers. Heating the spinning solutions to 70 °C delivered nanofibers with enhanced morphology, water stability and mechanical properties. This is due to the transition of SS from β-sheets into random coils that enables enhanced molecular interactions between SS and PVA. The most applicable SS/PVA weight ratios for the formation of nanofibers with the desired properties were found to be 7.5/1.5 and 10.0/1.5. The fibers had diameters ranging from 60 to 500 nm, where higher PVA and SS concentrations promoted larger diameters. The crystallinity within the fibers could be controlled by manipulation of the balance between PVA and SS loadings. In vitro degradation (in phosphate buffer solution, pH 7.4 at 37 °C) was 30–50% within 42 days and fibers were shown to be nontoxic to skin fibroblast cells. This work demonstrates a new green route for incorporating SS into nanofibrous fabrics, with potential use in biomedical applications
Development of Natural Active Agent-Containing Porous Hydrogel Sheets with High Water Content for Wound Dressings
This work was concerned with the fabrication of a porous hydrogel system suitable for medium to heavy-exudating wounds where traditional hydrogels cannot be used. The hydrogels were based on 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPs). In order to produce the porous structure, additional components were added (acid, blowing agent, foam stabilizer). Manuka honey (MH) was also incorporated at concentrations of 1 and 10% w/w. The hydrogel samples were characterized for morphology via scanning electron microscopy, mechanical rheology, swelling using a gravimetric method, surface absorption, and cell cytotoxicity. The results confirmed the formation of porous hydrogels (PH) with pore sizes ranging from ~50–110 µm. The swelling performance showed that the non-porous hydrogel (NPH) swelled to ~2000%, while PH weight increased ~5000%. Additionally, the use of a surface absorption technique showed that the PH absorbed 10 μL in <3000 ms, and NPH absorbed <1 μL over the same time. Incorporating MH the enhanced gel appearance and mechanical properties, including smaller pores and linear swelling. In summary, the PH produced in this study had excellent swelling performance with rapid absorption of surface liquid. Therefore, these materials have the potential to expand the applicability of hydrogels to a range of wound types, as they can both donate and absorb fluid
In Situ Compatibilized Blends of PLA/PCL/CAB Melt-Blown Films with High Elongation: Investigation of Miscibility, Morphology, Crystallinity and Modelling
Ternary-blended, melt-blown films of polylactide (PLA), polycaprolactone (PCL) and cellulose acetate butyrate (CAB) were prepared from preliminary miscibility data using a rapid screening method and optical ternary phase diagram (presented as clear, translucent, and opaque regions) as a guide for the composition selection. The compositions that provided optically clear regions were selected for melt blending. The ternary (PLA/PCL/CAB) blends were first melt-extruded and then melt-blown to form films and characterized for their tensile properties, tensile fractured-surface morphology, miscibility, crystallinity, molecular weight and chemical structure. The results showed that the tensile elongation at the break (%elongation) of the ternary-blended, melt-blown films (85/5/10, 75/10/15, 60/15/25 of PLA/PCL/CAB) was substantially higher (>350%) than pure PLA (ca. 20%). The range of compositions in which a significant increase in %elongation was observed at 55–85% w/w PLA, 5–20% w/w PCL and 10–25% w/w CAB. Films with high %elongation all showed good interfacial interactions between the dispersed phase (PCL and CAB) and matrix (PLA) in FE-SEM and showed improvements in miscibility (higher intermolecular interaction and mixing) and a decrease in the glass transition temperature, when compared to the low %elongation films. The decrease in Mw and Mn and the formation of the new NMR peaks (1H NMR at 3.68–3.73 ppm and 13C NMR at 58.54 ppm) were observed in only the high %elongation films. These are expected to be in situ compatibilizers that are generated during the melt processing, mostly by chain scission. In addition, mathematical modelling was used to study the optimal ratio and cost-effectiveness of blends with optimised mechanical properties. These ternary-blended, melt-blown films have the potential for use in both packaging and medical devices with excellent mechanical performance as well as inherent economic and environmental capabilities