Self-Associated Polyamide Alloys with Tailored Polymorphism Transition and Lamellar Thickening for Advanced Mechanical Application

Abstract

Long chain polyamides with various number of methylene units in recurring amide groups, PA1012 and PA612, were blended to combine their unique advantages. The Brill transition and accompanied lamellar thickening were investigated by in situ wide angle X-ray scattering (WAXS) and small angle X-ray scattering. From WAXS patterns, the transformation from the α- to γ-crystalline phase, known as "Brill transition", can be independently observed in the constituent phases of the long chain polyamide alloys (LCPAs) during heating. A constant T (ca., 100 °C) irrespective of the blend composition and proportional variations of the phase content was obtained. Additionally, with elevated temperature, a gradual increase in both the crystalline layer (L) and amorphous layer (L) was detected in constituent polyamides. The compositional independence of the Brill transition in LCPAs and similar lamellar thickening originate from the complete immiscibility of both polyamides, which share stronger intramolecular rather than intermolecular hydrogen-bonding interaction and hence exhibit self-association. Contributed by the γ phase, with less extended structure and increased lamellar thickness with compact stacking, LCPAs with controlled strength and flexible features can be achieved, which can be utilized in advanced mechanical applications, particularly for hoses of automobiles. The unusually linear compositional dependence of mechanical parameters makes it possible to tailor the polymorphic and tensile properties.

The origin of memory effects in the crystallization of polyamides: Role of hydrogen bonding

“…However, the mechanism of the memory effect is still under debate. Lorenzo et al [12], proposed that self-nuclei originated in the high temperature region within Domain II (where no trace of crystal fragments remains) are constituted by regions in the melt with the residual orientation that the chains had in the crystalline state [13]. Luo et al [24] have postulated that memory effect comes from heterogeneities in the topological constraints and melt entanglements distribution.…”

Composition dependent miscibility in the crystalline state of polyamide 6 /polyamide 4,10 blends: From single to double crystalline blends

“…Polyamides are extensively used engineering thermoplastics, which represent a success in the polymer composites industry due to their excellent thermo-mechanical properties, and nowadays many different polyamide grades are commercially available, including various filler-reinforced materials. The replacement of traditional petrochemical polyamides with others obtained from renewable resources would result in the development of a range of environmentally more sustainable materials, which seems to be the trend in the near future [4][5][6][7] . In this sense, PA blends of traditional and frequently used PAs, such as PA6 or PA66, with newly commercially available bio-PAs, either totally or partially derived from renewable resources, arise as a halfway solution and, therefore, the study of these blends is imperative.…”

“…Literature concerning polyamide blends focuses largely on PA6 blended with PP [9][10][11] , ABS [12][13][14] , PE [15][16][17] , PA66 18 , PET 19 , long chain polyamides (LCPAs) 20 and different rubbers [21][22] , the majority of which are immiscible systems. Polyamide-polyamide blend literature consists primarily of studies on aliphatic/aromatic polyamide blends [23][24][25][26][27][28][29] , whereas little work has been reported on aliphatic/aliphatic blends 2,[6][7][30][31][32] . In addition, few works have been reported on bio-based polymer blends for durable high-performance applications [33][34][35][36][37] , while studies concerning biodegradable polymer blends for either biomedical or packaging applications are numerous 33,[38][39][40][41][42][43][44][45][46] .…”

“…Therefore, most polymers stay phase-separated when physically mixed. Most of the self-associated polyamide blends are immiscible 6,7 . At the same time, transamidation happens at high temperature 20 , which can improve miscibility, due to the formation of a copolymer at the interphase.…”

Aliphatic polyamides (nylons): Interplay between hydrogen bonds and crystalline structures, polymorphic transitions and crystallization

“…Thus, nearly 10% of plastics used in modern vehicles correspond to different polyamides. For example, polyamides with more than 10 CH 2 groups between adjacent amide groups have excellent properties like toughness, low water absorption, and good dimensional stability to be employed as automobile hoses 2 . In general, nylons can be considered as fossil‐based plastics, although nowadays great efforts have been focused on the production of bio‐based polyamides as those based on castor oil as a natural source (e.g., nylon 11, Rilsan®), and those derived from cadaverine (e.g., nylons 54, 56 and 510), a natural diamine that can also be produced at large scale by biotransformation of lysine using recombinant Escherichia coli 3–5 …”