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In single-polymer or self-reinforced composite SPCs both the reinforcing and matrix phases are given by the same polymer one constituent , or by polymers belonging to the same family two constituents.
SPCs are lightweight the density of polymers is usually below that of traditional reinforcement composites with ultimate recyclability via remelting. In respect of LCM the AROP of lactams features two major benefits: i the melt viscosity of the polymerizable lactam is very low, and ii the polymerization can be performed below the T m of the resulting PA. Low viscosity is helpful to wet-out and impregnate the reinforcing structures.
This large temperature difference is of great importance because the reinforcement otherwise loses its stiffness and strength with increasing temperature and dwelling time the closer the polymerization temperature is to the melting of the reinforcement. Last but not least, the fact that polymerization below T m is accompanied by crystallization, allowing a faster demolding, is the guarantee for high productivity.
Gong et al. This was attributed to the following effects: i impeded movement of CL toward the growth center within the reinforcing textile, and ii presence of H 2 O and —COOH groups on the PA-6 reinforcement surface which consumes —NCO groups of the activator used. Dencheva et al. To study the effect of sizing, they were removed by washing with acetone. Based on detailed WAXS studies the authors confirmed the appearance of a transcrystalline layer interphase between the matrix and reinforcement. Transcrystallinity is caused by laterally impeded spherulitic growth on closely spaced nuclei on a heterogeneous substrate here the PA-6 or PA-6,6 reinforcements.
Generally, the presence of a transcrystalline layer is considered to be a controlling factor of the stress transfer from the matrix to the reinforcement [ , ]. Interestingly, the thickness of this layer became smaller when the sizing was removed.
The ultimate tensile strength and strain were enhanced with increasing reinforcement content, while only small changes were found for the stiffness. This was expected due to the low amount of the reinforcement and to the rather long dwelling time at the polymerization temperature. The E -modulus stiffness and strength of the reinforcing PA-6 and PA-6,6 diminished with increasing temperature and holding time.
This is often accompanied by considerable shrinkage that can be limited by processing under pressure when applicable see below. In the recent paper Dencheva et al. Note that the compression molding temperature was below the T m of the PA-6,6 reinforcement. The beauty of this technique is that the MMT particles are well and uniformly dispersed.
By contrast, direct impregnation of the reinforcement with a polymerizable CL melt containing MMT may result in a filtering-off of the particles owing to the dense mesh structure of the fabric layers. In this way an MMT-rich surface layer may appear which is undesirable. At higher PA-6,6 fabric content the tensile mechanical properties dropped owing to poor impregnation. Unexpectedly, this had only a marginal effect on the toughness. Solvent-borne, liquid initiators and activators may likely be preferred. The copolymerization strategy will further focus on the toughness improvement of the related PAbased block copolymers.
Besides the traditional block segments polyether- and polyester-based diols others, like polycaprolactone, polylactic acid etc. The in situ blending via AROP will hardly achieve industrial breakthrough. This development will target the production of new tribological compounds, containing novel carbonaceous nanofillers, which will be most likely produced still by casting. The toughness of such nanocomposites will be a key factor and thus the related works will be supported by extensive modeling [ ].
According to our view, novel and adapted manufacturing methods will be the real future drivers of the development of thermoplastic composites with AROP-produced matrix. Additive manufacturing via ink jetting should be mentioned among the emerging novel techniques. This claim is based not only on the straightforward recyclability of the related composite parts, but also on other beneficial design- and post-processing-related features, such as part integration, overmolding with and without additional reinforcements , surface coating and finishing, and welding.
The related research and developments works will run parallel with extensive modeling especially via finite element codes studies. The potential of PAbased single-polymer self-reinforced composites has been strongly underestimated, therefore in this field interesting developments may be expected. National Center for Biotechnology Information , U. Journal List Polymers Basel v. Polymers Basel. Published online Mar Author information Article notes Copyright and License information Disclaimer. Received Feb 26; Accepted Mar Abstract This paper presents a comprehensive overview of polymers and related nano composites produced via anionic ring opening polymerization AROP of lactams.
Introduction Polyamides PAs belong to the engineering thermoplastics with a broad range of applications. Homopolymers 2. Chemistry The polymerization capability of cyclic monomers depends on both thermodynamic relative stability of the monomer and the resulting linear polymer and kinetic initiation, propagation, termination reactions factors. Open in a separate window. Figure 1. Figure 2. Properties The anionic polymerization of lactams can be performed in two temperature ranges: below or above the melting temperature T m of the resulting polylactams.
Figure 3. Manufacturing PA-6 and PA homopolymer products in forms of plaques, pipes, rods, and various half-fabricates for further machining, are produced by casting see the related scheme in Section 6. Figure 4. Table 1 Processing and material parameters of specimens produced by classical and reactive rotational molding [ 46 ]. Copolymers Extensive research was dedicated to the modification of anionically polymerized PA-6 and PA through various copolymerization strategies.
Chemical and Structural Aspects 3. Block Copolymers The preparation of copolymers di-, triblock with blocks composed of lactam or non-lactam chains requires the incorporation of suitable prepolymers in the molten, anionically polymerizable lactam. Figure 5. Graft Copolymers Copolymers are rarely formed by interfacial reactions. Manufacturing The preparation method of the copolymers is identical—both in laboratory and industrial scales—with those repeated for PA homopolymers.
Blends Blending of immiscible polymers envisages creation of blends with superior properties to those of the blend components. Nanocomposites Different definitions exist for polymer nanocomposites which are also referred to as nanostructured and organic-inorganic hybrid composites. Figure 6. Figure 7. PA-6 nanocomposites exhibited enhanced E -modulus and tensile strength. No electric percolation observed. Potential for energy storage deduced. Nucleation and crystallization affected by the silica presence.askyounow.com/images/dropped/buso-rande-naslepo.php
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The latter surface treatment improved the strength. Mechanical and dielectrical properties tailored upon amount, type and combination of the additives. At high macroactivator content polymerization rate and yield are influenced by the filler B 4 C and graphite. AROP performed better than the hydrolytic route.
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Capsules filtered and dried prior to compression molding Optical microscopy, viscosimetry M v DSC, TGA, synchrotron WAXS electrical, dielectrical behavior All fillers enhanced the stiffness and reduced the deformation at break with increasing content. The volume resistivity above 0. Volume resistivity decreased with 6 order of magnitudes at a fullerene content of 0. The coefficient of friction was halved in presence of fullerenes. Crystallinity slightly reduced. Effect of the dose of electron beam irradiation was moderate for nanoscaled CB.
Graphite worked as heterogeneous nucleant during crystallization. Notched Charpy IS improved only at 0. Polyether-urethane as macroactivator yielded high MW with crosslinking.
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All nanocomposites showed increased tensile modulus and strength compared to neat PA Fibers produced at different stretching ratios. MWCNT worked as nucleating agent and also improved the thermal stability. Tensile modulus and strength were markedly improved at cost of the elongation at break. DOC was simulated. M v values between 10 and 41 kDa along with polydispersity in the range of 1.
MWCNT delayed the polymerization.
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M v data scattered between 54 and 59 kDa. Initiator added in N 2 atmosphere. The zero shear viscosity was prominently higher in CNC presence compared to the neat PA-6, suggesting the onset of a percolated structure that was prone for breaking upon shear. Samples produced by extrusion. For comparison purpose classical melt blending served. Tensile stiffness and strength strongly improved at cost of elongation at break.
Melt elasticity and strength enhanced by CNC reinforcement. OMMT introduced directly or in acetone—assisted dispersion. M n and M w values were at about 20 and 50 kDa respectively. Above this intercalation took place. The thermal stability was prominently improved by NaMMT. Clay added differently. The intercalation was reduced with increasing LL content.