RECYCLED POLYAMIDES, A LITERATURE REVIEW AND RESEARCH OPPORTUNITIES.

Polymers, 2023

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Nylon/Polyamide is widely used in many applications. There is a vast amount of recycled polyamides coming from the carpet and textile and other industries. Due to degradation and loss of viscosity as well as contamination with other materials, this recycled polyamide has reduced performance and limited its use widely. The unique chemistry of alternating copolymers of ethylene and maleic anhydride provide several advantages for upgrading recycled polyamide. This paper discusses the results obtained with compounding recycled nylon grades from many different sources with the addition of small quantities of this copolymer and specific property improvements for applications in injection molded compounds. The resulting compounds have performance that can come close to matching or exceeding prime virgin nylon at 30-50% cost savings.

Journal of Applied Polymer Science, 2002

Recycling of polycondensation polymers can give rise to secondary materials with good mechanical properties only if a careful drying is carried out before the melt reprocessing operations. The presence of humidity provokes the hydrolytic chain scission of the macromolecules and the consequent decrease of molecular weight and properties. In this work, the drying step was substituted by the addition of an antioxidant that is able to protect the macromolecules because it is the autioxidant is more prone to hydrolysis, thus removing the water from the melt. The mechanical properties of polyamide 6 reprocessed more times in wet conditions and in the presence of this stabilizer are even better than those obtained reprocessing the dry polyamide.

Polymer Testing, 2002

Polyamides are intrinsically hygroscopic because of the polar nature of their chains, which make them moisture sensitive materials, and hence chemically unstable towards hydrolytic conditions. Prior to processing steps, polyamide composites need to be dried in order to attain their good mechanical properties afterwards. Nevertheless, polyamide based materials may undergo discoloration and some deterioration after long drying periods. Industrial wastes consisting of glass fiber reinforced polyamide 6 (PA 6) composite were dried for 3, 6 and 9 h before reprocessing. The reprocessing of this type of composite was shown to be quite viable, because satisfactory physical-mechanical properties are attained thereafter, which make them suitable for several applications where these properties are desirable. 

Composite Structures

Previous studies have highlighted the potential application of Polyamide 6 (PA6) as excellent recyclable polymeric material, which is well suited to form carbon-fiber-reinforced, graphene-nanoplatelets-reinforced or metal-porouspolymer composite structures. The conventional screw extrusion process is one of the established melt processing techniques, having potential of enhancing mechanical, thermal and morphological properties of polymeric materials. PA6 is an important engineering material which exhibits excellent mechanical properties, chemical resistance, wear resistance, dimensional stability, and low coefficient of friction. In the present study attempts have been made to explore the behavior and characteristics of the recycled PA6 polymer through twin screw extrusion process towards increase in recyclability (as primary recycling process). The mechanical properties (tensile strength, Young's modulus, peak load), metallurgical properties (porosity, wear and material loss) supported with optical microscopy were investigated to ensure the recyclability of PA6 as a properties enhancing extrusion process. It has been observed in the present study that, melt processing by screw extrusion at best settings of input process parameters enhances the material properties for applications in sustainable civil engineering.

Journal of Applied Polymer Science, 2019

The objective of this work is to analyze the possibility of thermomechanical recycling of polyamide 6 (PA6) from fishing nets waste. The effect of thermomechanical processing on PA yarns obtained from fishing nets waste was investigated by means of physicochemical, rheological, and thermal characterization. Infrared analysis indicated that the chemical composition of samples before and after thermomechanical recycling process was maintained, also confirmed by the thermal transitions detected by calorimetry and the presence of main peaks related to γ and α crystal phases of polyamides at X-ray diffraction spectra. As rheological and mechanical behavior showed by all recycled samples after processing is similar to those for virgin one, PA obtained from fishing nets waste seems to be valid for recycling, as they can be processed for different potential industrial applications without any remarkable loss of main properties.

Polymer Composites, 1996

The fiber length distribution was found to control the overall short term performance of reprocessed heat-stabilized short fiberglass reinforced polyamide 66. Length changes, and matrix and interface degradation were studied. Fiber shortening dominates during compounding and during the first injection molding cycle. Further regrinding and remolding has a lesser effect. The short term mechanical strength decreased for reprocessed samples. Using a modified Kelly-Tyson model, the lower tensile strength of reprocessed samples, compared with virgin samples, can be explained by fiber shortening. Reprocessing had a negligible effect on the strength for both the fiber matrix interface and the matrix of this system. Studies on unreinforced samples confirmed that thermal degradation of the matrix during reprocessing had a negligible effect on short term mechanical performance. POLYMER COMPOSITES, DECEMBER 1-Yo/. 17, No. 6 a23 P.-A. Eriksson et al. T. M. Roder, in Nylon Plastics Handbook, p. 171, M. I.

Composites Part B-engineering, 2019

The effects of a closed-loop recycling methodology are evaluated for degradation using a discontinuous carbon fibre polyamide 6 (CFPA6) composite material. The process comprises two fundamental steps: reclamation and remanufacture. The material properties are analysed over two recycling loops, and CFPA6 specimens show a total decrease of 39.7 % (± 3.5) in tensile stiffness and 40.4 % (± 6.1) in tensile strength. The results of polymer characterisation and fibre analysis suggested that the stiffness reduction was likely due to fibre misalignments primarily caused by fibre agglomerations, as a result of incomplete fibre separation, and by fibre breakages from high compaction pressures. The ultimate tensile strain was statistically invariable as a function of recycling loop which indicated minimal variation in polymer structure as a function of recycling loop. To the authors' best knowledge, the mechanical performance of the virgin CFPA6 is the highest observed for any aligned discontinuous carbon fibre thermoplastic composites in the literature. This is also true for recycled specimens, which are the highest observed for any recycled thermoplastic composite, and, for any recycled discontinuous carbon fibre composite with either thermosetting or thermoplastic matrices.

International Journal of Plastics Technology, 2013

The objective of this study is to develop a green composites based on recycled polypropylene (rPP)/recycled polyamide 6 (rPA6) reinforced with kenaf. The investigations were carried out by collecting rPP from the nearest landfill and rPA6 was prepared by re-extrusion and composites preparations were obtained using a twin screw extruder and injection moulding. The rPP/rPA6 composition was selected in a ratio of 70/30 with compositions of kenaf from 10-30 wt.%. Tensile, flexural and impact tests were conducted to investigate the mechanical properties. The composites thermal properties, processing behaviour and morphological study were also investigated. Beside the decrement in impact properties other mechanical properties of the composites were improved upon as the compositions of kenaf were increased. A difficulty resulted in processing the composites using injection moulding machine as the melt flow index values increased. Scanning Electron Microscopy (SEM) micrographs showed an improvement in the dispersion of kenaf in the matrix when kenaf compositions were increased. The overall results showed the best composition of kenaf was at 30 wt. %.

Polyester polymer has for many years maintained its number one position as the polymer of choice for multiple applications. Recently the recycling of polyester has become very popular and even though recycling polyester is not a new technology subject being able to successfully recycle bottles into fiber and get attention from consumers to support the idea by buying it in large scale quantities is unheard of until now. Given the current reality this article attempts to introduce recycling giving an idea of the magnitude of the business worldwide, short description on methods available, followed by focusing on the mechanical recycled process (re-melting through extrusion), main testing procedures and its implications, discussing state of the art mechanical recycling technology, its different stand point from field researchers, when appropriate some criticism is listed, and finally point out some need for further research or improvements.