Current Applied Polymer Science - Volume 5, Issue 2, 2022

This paper signifies using coir pith lignin as a cheap and reliable carbon source for preparing bio-based carbonaceous material.

The coir pith is selected as it is abundantly available and has a very high lignin content of 38-59.5%. The soda extraction process does the extraction of lignin from coir pith with a yield of 45%.

This extracted lignin is then subjected to a different procedure to transform it into carbon nanofibers with an ID/IG ratio of 0.35 and carbon fillers with a high surface area of 1089.1 m²/g without the presence of an activating agent.

Thus prepared carbonaceous fillers are potential reinforcements for polymer matrices as these fillers may provide sufficient mechanical and thermal stability to the composites.

Furthermore, due to their excellent electrical conductivity, 0.221 S/cm, the carbonaceous nanomaterials are suitable for multifunctional composite applications. This is the first work based on coir pith lignin as a carbon precursor to the best of our knowledge.

Bio-based nanomaterials such as cellulose nanocrystals (CNCs) have been increasingly explored in nanotechnology owing to their chemophysical properties, self-assembly, and low toxicity.

CNCs can be isolated from various cellulosic biomass sources. Textiles which are mostly made of cotton, are under-utilized biomass that after their lifetime is either burned or dumped into landfills.

In this study, cotton-based textiles are studied as a source of CNCs. CNCs were extracted from textiles with and without bleaching before the acid hydrolysis step, and further comparing them with the properties of industrial microcrystalline cellulose-derived CNCs. Nanocrystals were synthesized from the three different sources and their morphology, thermal properties, and colloidal stability were compared.

The result show similar thermal properties and morphological characteristics for the three synthesized CNCs, and similar colloidal stability between the two textile-based CNC dispersions, suggesting that the dyes on CNCs do not impact the quality of the product. Removing the bleaching pre-treatment -a water-demanding and toxically harmful step- before CNC extraction provides cost and environmental benefits without compromising on the CNC quality.

This project seeks to streamline the CNC synthesis process with the long-term goal of eventually facilitating the textile recycling industry.

Thermoplastic expandable microspheres (TEMs) are spherical particles that consist of polymer shell encapsulating a low boiling point liquid hydrocarbon that acts as the blowing agent. When TEMs are heated at 80-190 °C, the polymer shell softens, and the hydrocarbon gasifies, causing the microspheres to expand, leading to an increase in volume and decrease in density. TEMs are used in food packaging, elastomeric cool roof coatings, shoe soles, fiber and paper board, and various applications in the automotive industry. It is noted that TEMs are known by their brand name ‘Expancel’, which is also used to refer TEMs in this paper.

The objective of this work was to develop and characterize forms prepared from TEMs with/without carbon nanofibers (CNFs) coatings to study the effect of CNFs on structural, thermal, and mechanical properties.

Sonochemical method was used to coat TEMs with various weight percentages (1, 2, and 3%) of CNF. Neat foam (without CNF) and composite foams (TEMs coated with various wt.% of CNF) were prepared by compression molding the TEMs and TEMs-CNF composites powders. Thermal and mechanical properties of the neat and composite foams were investigated.

The mechanical properties of the composite foam were notably improved, which is exhibited by a 54% increase in flexural modulus and a 6% decrease in failure strain with the TEMs-(2 wt.% CNF) composite foam as compared to the neat foam. Improvement in thermal properties of composite foam was demonstrated by a 38% increase in thermal stability at 800ºC with the TEMs-(1 wt.% CNF) composite foam as compared to the neat foam. However, no change in the glass transition of TEMs was observed with the CNF coating. SEM-based analysis revealed that CNFs were well dispersed throughout the volume of the TEMs matrix, forming a strong interface.

Straightforward sonochemical method successfully triggered efficient coating of TEMs with CNFs, resulting in a strong adhesion interface. The mechanical properties of composite foams increased up to 2% of CNFs coating and then decreased with the higher coating, presumably due to interwoven bundles and aggregation of CNFs, which might have acted as critical flaws to initiate and propagate cracking. Thermal properties of foams increased with the CNFs coating while no change in glass transition temperature was observed due to coating.

Brazil is the world’s largest producer of short fiber cellulose, generating large amounts of eucalyptus bark residue (EBR). Aiming to obtain composites known as wood plastic composites (WPC), the effect of ground EBR addition to a poly(vinyl chloride) (PVC) matrix was studied, considering different granulometries and matrix/load proportions. The influence of fiber content addition and particle size range was analyzed in terms of mechanical and thermal properties of the PVC-EBR fiber composites obtained. Finally, by comparing these properties with those reported in the literature, the viability of EBR application as filler/reinforcement in a WPC with PVC matrix was verified.

The main objective of the present study was to evaluate the influence of EBR fiber size and content in the WPC with PVC matrix, aiming to reduce the costs and improve its mechanical and physical properties.

The processing method for preparing the composites was two-roll milling and subsequent hot pressing. The residue was characterized via chemical and thermogravimetric analyses, scanning electron microscopy (SEM), and aspect ratio determination. Composite evaluation involved density, tensile and flexural tests, impact resistance, heat deflection temperature (HDT), moisture absorption, and SEM of tensile fractured specimens.

Tensile and flexural moduli were improved with fiber addition attaining 46% and 58% increases, respectively, with better results for smaller particle size fibers; impact resistance and elongation at break, however, were reduced, attaining 48% and 5% of the control sample’s properties. SEM images reveal fiber detachment and pull-out due to their low matrix adhesion. EBR fibers cause more void formation due to low interface adhesion, which results in poor stress transference from the matrix to the fiber, in addition to EBR acting as stress concentrators in the PVC matrix; therefore, impact fracture occurs with lower energy levels.

Regions with fiber detachment and pull-out from the matrix are visible, clearly demonstrating the low adhesion properties of the phases and also in accordance with the observed decrease in mechanical properties for both fibers. SEM images indicate that fibers can be considered foreign particles inside the PVC matrix, acting as stress concentrators. Also, since fibers have diameters larger than the voids caused by crazing, planar density is reduced in the direction perpendicular to chain stretching leading to low strain at break values. Composites of fiber with finer particles showed fewer voids, possibly indicating a more efficient adhesion for fibers. This could be due to higher penetration of polymeric chains in the rugosity of finer fibers, leading to higher values of tensile strength.

The addition of EBR content increased, especially flexural and tensile moduli whilst elongation at break and impact resistance are reduced. The reduction in tensile strength due to poor fiber-matrix interfacial adhesion, though significant, allowed the use of composites with higher fiber additions. The use of EBR is coherent with the concept of circular economy. Thus, higher fiber additions relate directly to money savings since this residue costs less than PVC, and also, this is an environmentally correct destination for this residue since WPC is long-term usable, allowing for recycling.