The Effect of Alkaline Treatment on Poly(Lactic Acid)/Date Palm Wood Green Composites for Thermal Insulation

[Study on NaOH improving the surface morphology of three-dimensional printed poly- L- lactic acid mesh scaffolds]

Objective

To explore the effect of NaOH on the surface morphology of three-dimensional (3D) printed poly- L-lactic acid (PLLA) mesh scaffolds.

Methods

The 3D printed PLLA mesh scaffolds were prepared by fused deposition molding technology, then the scaffold surfaces were etched with the NaOH solution. The concentrations of NaOH solution were 0.01, 0.1, 0.5, 1.0, and 3.0 mol/L, and the treatment time was 1, 3, 6, 9, and 12 hours, respectively. There were a total of 25 concentration and time combinations. After treatment, the microstructure, energy spectrum, roughness, hydrophilicity, compressive strength, as well as cell adhesion and proliferation of the scaffolds were observed. The untreated scaffolds were used as a normal control.

Results

3D printed PLLA mesh scaffolds were successfully prepared by using fused deposition molding technology. After NaOH etching treatment, a rough or micro porous structure was constructed on the surface of the scaffold, and with the increase of NaOH concentration and treatment time, the size and density of the pores increased. The characterization of the scaffolds by energy dispersive spectroscopy showed that the crystal contains two elements, Na and O. The surface roughness of NaOH treated scaffolds significantly increased ( P<0.05) and the contact angle significantly decreased ( P<0.05) compared to untreated scaffolds. There was no significant difference in compressive strength between the untreated scaffolds and treated scaffolds under conditions of 0.1 mol/L/12 h and 1.0 mol/L/3 h ( P>0.05), while the compression strength of the other treated scaffolds were significantly lower than that of the untreated scaffolds ( P<0.05). After co-culturing the cells with the scaffold, NaOH treatment resulted in an increase in the number of cells on the surface of the scaffold and the spreading area of individual cells, and more synapses extending from adherent cells.

Conclusion

NaOH treatment is beneficial for increasing the surface hydrophilicity and cell adhesion of 3D printed PLLA mesh scaffolds.

Effect of Alkaline Treatment on Mechanical and Thermal Properties of Miswak (Salvadora persica) Fiber-Reinforced Polylactic Acid

This study examines the effects of alkaline treatment on the mechanical and thermal properties of miswak fiber-reinforced polylactic acid. The treatment was performed with three distinct concentrations of sodium hydroxide (NaOH): 1 wt %, 2 wt %, and 3 wt %. The difficulties of interaction between the surface of the fiber and the matrix, which led to this treatment, is caused by miswak fiber's hydrophilic character, which impedes its ability to bind with hydrophobic polylactic acid. FTIR, tensile, TGA, and DMA measurements were used to characterize the composite samples. A scanning electron microscope (SEM) was used to examine the microstructures of many broken samples. The treatment is not yet especially effective in enhancing interfacial bonding, as seen by the uneven tensile strength data. The effect of the treated fiber surface significantly improves the tensile strength of miswak fiber-reinforced PLA composites. Tensile strength improves by 18.01%, 6.48%, and 14.50%, respectively, for 1 wt %, 2 wt %, and 3 wt %. Only 2 wt %-treated fiber exhibits an increase of 0.7% in tensile modulus. The modulus decreases by 4.15 % at 1 wt % and by 19.7% at 3 wt %, respectively. The TGA curve for alkali-treated fiber composites demonstrates a slight increase in thermal stability when compared to untreated fiber composites at high temperatures. For DMA, the composites with surface treatment have higher storage moduli than the composite with untreated miswak fiber, especially for the PLA reinforced with 2 wt % alkali miswak fiber, proving the effectiveness of the treatment.

Physical, Mechanical, and Thermal Properties and Characterization of Natural Fiber Composites Reinforced Poly(Lactic Acid): Miswak (Salvadora Persica L.) Fibers

7000 years ago, miswak fiber (MF) was used as a toothbrush for oral care. However, since the emergence of plastic materials, it monopolized the oral care industry. The increment of plastic products also promotes accumulation of plastic wastes after its disposal. Thus, many researchers have turn to biodegradable products to reduce this problem. The aim of this study is to investigate the chemical, physical, and mechanical properties of MF as reinforcement in composites that are suitable to replace the toothbrush materials. The MF was reinforced in PLA composite with different weight percentage (0%, 10%, 20%, and 30%) and undergoes several types of testing. The chemical results show that there were high presence of cellulose in the fiber which could act as medium to transfer stress load equally from fiber to matrix. However, the results show low cellulosic contents in MF that affects the poor interfacial bonding between fiber and matrix. Physical properties shows a positive indication to be used as a toothbrush handle. As the fiber content increases, the density also increased. SEM micrographic illustrated the presence of voids as the cause for reduction in mechanical properties of composites. The mechanical results show the proposed material is comparable to the materials used in commercial applications. As for the thermal result, the TGA test melting point of the proposed composite material was comparable to the pure PLA, which means the proposed material can use similar processing temperature as PLA. DSC shows that Tg of PLA/MF composite is found to be similar to Tg in loss modulus of composites. DMA finding found that PLA/MF30 have the highest storage modulus 2062 MPa and the lowest tan δ 0.6 among PLA/MF composites. This concludes that there is a possibility of using these materials as an alternative in composites and increase the fiber strength by using pretreatments and/or compatibilizer.

Date Palm Surface Fibers for Green Thermal Insulation

Some of the major challenges of the twenty-first century include the continued increase in energy consumption and environmental pollution. One approach to overcoming these challenges is to increase the use of waste materials and environmentally friendly manufacturing methods. The high energy consumption in the building sector contributes significantly to global climatic changes. Here, by using date palm surface fibers, a high-performance green insulation material was developed via a simple technique that did not rely on any toxic ingredients. Polyvinyl alcohol (PVA) was used as a binding agent. Four insulation samples were made, each with a different density within the range of 203 to 254 kg/m3. Thermal conductivity and thermal diffusivity values for these four green insulators were 0.038–0.051 W/m·K and 0.137–0.147 mm2/s, respectively. Thermal transmittance (U-value) of the four insulation composites was between 3.8–5.1 W/m2·K, which was in good comparison to other insulators of similar thickness. Thermogravimetric analysis (TGA) showed that insulating sample have excellent thermal stability, with an initial degradation temperature of 282 °C, at which just 6% of its original weight is lost. Activation energy (Ea) analysis revealed the fire-retardancy and weakened combustion characteristics for the prepared insulation composite. According to differential scanning calorimetry (DSC) measurements, the insulating sample has a melting point of 225 °C, which is extremely close to the melting point of the binder. The fiber-based insulating material’s composition was confirmed by using Fourier transform infrared spectroscopy (FTIR). The ultimate tensile range of the insulation material is 6.9–10 MPa, being a reasonable range. Our study’s findings suggest that developing insulation materials from date palm waste is a promising technique for developing green and low-cost alternatives to petroleum-based high-cost and toxic insulating materials. These insulation composites can be installed in building envelopes during construction.