Semicrystalline Polyamide Research Articles

An Investigation of Polyamides Based on Isoidide-2,5-dimethyleneamine as a Green Rigid Building Block with Enhanced Reactivity

Novel, semicrystalline polyamides and copolyamides were synthesized from a new carbohydrate-based diamine, namely isoidide-2,5-dimethyleneamine (IIDMA). In combination with 1,6-hexamethylene diamine (1,6-HDA) as well as the biobased sebacic acid (SA) or brassylic acid (BrA), the desired copolyamides were obtained via melt polymerization of the nylon salts followed by a solid-state polycondensation (SSPC) process. Depending on the chemical compositions, the number average molecular weights (Mn) of the polyamides were in the range of 4000–49000 g/mol. With increasing IIDMA content in the synthesized copolyamides, their corresponding glass transition temperatures (Tg) increased from 50 °C to approximately 60–67 °C while the melting temperatures (Tm) decreased from 220 to 160 °C. The chemical structures of the polyamides were analyzed by NMR and FT-IR spectroscopy. Both differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses revealed the semicrystalline character of these nove...

Morphology evolution of miscible blends between crystalline PA6 and amorphous PA6IcoT

The morphology evolution of miscible blends of a semicrystalline polyamide 6 (PA6) and an amorphous polyamide 6Ico6T (PA6IcoT) was investigated using an internal Brabender mixer at a temperature range 220–260°C. Morphology of the blends was characterized by scanning electron microscopy (SEM) and laser particle analysis. Temperature rising dissolution was used to separate the different phases of the blends and the phase compositions were determined by Fourier transform infrared (FTIR) spectroscopy. The particle size evolution of the dispersed phase (PA6) was calculated and agreed well with experimental observation. It was found that the particle size was quickly reduced to nanometer scale after several minutes of processing. A convection-diffusion model was adopted to study the phase evolution during melt–melt mixing stage and compute the dimension of each phase. The results strongly support the notion of existence of distinct phases during blending, whose development can be well described by the model. The dispersed phase is reduced mainly by stretching of flow, while the broadening of the blending phase can be primarily attributed to molecular diffusion. The study also suggests the possibility to prepare novel polymer blends with nanometer sized domain of high uniformity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Structure, thermal stability, and mechanical properties of nanocomposites based on an amorphous polyamide

AbstractPolymer nanocomposites based on an amorphous polyamide (aPA) modified with three organoclays were obtained in the melt state. The observed Tg decreases indicated that some organic modifier of the OMMT (surfactant) migrated to the matrix during mixing. The decrease in the thermal stability of the aPA in nitrogen atmosphere on organoclay addition was attributed to the instability of the organoclays. The smaller decrease in the thermal stability of the nanocomposites in air atmosphere was attributed to a barrier effect. The largest dispersion (an average of only 1.2 layers per particle) occurred using the octadecylamine‐modified organoclay (I30) that has the maximum uncovered surface; this indicates the basic importance of this parameter on exfoliation. Despite the bulky nature of the aPA that hinders the matrix/inorganic surface interactions, this dispersion level is comparable to that of semicrystalline polyamides with similar polarity. This indicates that the relation between high polarity of the matrix and high dispersion level also works in bulky aPAs, as that of this study. The significant modulus increases (56% for the nanocomposite with 5% I30) are consistent with the measured high dispersion level. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Novel, Fully Biobased Semicrystalline Polyamides

Novel, semicrystalline polyamides and co(polyamides) were synthesized from biobased sebacic acid (SA), 2,5-diamino-2,5-dideoxy-1,4;3,6-dianhydroiditol (diaminoisoidide, DAII) as well as from 1,4-diaminobutane (DAB), also known as putrescine in nature. Low molecular weight polyamides were obtained by melt polycondensation of the salts based on these monomers or by interfacial polycondensation. In order to increase their molecular weights the polyamide prepolymers were submitted to a solid state polymerization (SSP) process. The chemical structure of the polymers was confirmed by 2D NMR correlation spectra (COSY), heteronuclear multiple-bond correlation spectra (HMBC) and by FT-IR spectroscopy. In the present work, FT-IR and X-ray techniques were used as a tool for the investigation of the crystal structure of the polymers after SSP. The X-ray diffractograms of the polyamides point to crystals containing both 4.10- and DAII.10-based repeat units. Because of the presence of diaminoisoidide residues the synthesized fully renewable products exhibit tunable polarities and melting points. Since most commercial polyamides have a much higher melting point than their end application requires, especially for fiber applications, this simple adaption can result in a significant reduction of energy consumption during processing.

Damage of semicrystalline polyamide 6 assessed by 3D X‐ray tomography: From microstructural evolution to constitutive modeling

AbstractIn this study an attempt is made to link the damage and microstructural evolution of semicrystalline polymers, in particular polyamide 6, to the macroscopic material behavior during tensile and creep tests. Tensile specimens, removed before failure were seen to have undergone striction. They were examined using synchrotron radiation tomography. These samples showed elongated axisymmetric columns of voids separated by thin ligaments of material. These observations were confirmed and refined through a cryofractography experiment of a different tensile sample, stopped before failure. An attempt was made to obtain quantitative data about void volume fraction and morphology through image analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1516–1525, 2010

Micro-mechanical modelling of Young’s modulus of semi-crystalline polyamide 6 (PA 6) and elastomer particle-modified-PA 6

In this study semi-crystalline polyamide 6 (PA 6) and its composites consisting of a semi-crystalline PA 6 matrix filled with up to 32.9vol.% submicron elastomeric copolymer particles are investigated. The aim of this paper is to show how micro-mechanical modelling can predict the elastic behaviour of these composites from the experimentally observed morphology and determined parameters.Semi-crystalline PA 6 possesses a spherulitic morphology, consisting of a radial assembly of amorphous layers and nano-sized crystalline lamellae. In the continuum mechanical representation of semi-crystalline PA 6, nano-sized crystallite lamellae are considered as a phase which is additionally embedded into the amorphous matrix. The 2D self-consistent embedded cell model was chosen to predict the Young’s modulus of the semi-crystalline PA 6 material. In this model a rectangular lamella is surrounded by an amorphous matrix, which is again embedded in the semi-crystalline PA 6 material with the mechanical behaviour to be determined iteratively in a self-consistent manner. The Young’s modulus of PA 6 has been calculated by an appropriate integration of results of all orientations of the crystalline lamellae. The Young’s modulus of PA 6/elastomer composite is also predicted by a 3D self-consistent embedded cell model. In this model a circular inclusion is surrounded by the PA 6 polymer matrix, which is again embedded in the PA 6/elastomer composite. Good agreement is obtained between experiments and the prediction with the self-consistent embedded cell models.

The Role of Superheated Water on the Crystallization of N,N′-1,2-Ethanediyl-bis(6-hydroxy-hexanamide): Implications on Crystallography and Phase Transitions

A symmetrical, hydrogen bonded low molecular weight molecule N,N′-1,2-ethanediyl-bis(6-hydroxy-hexanamide), crystallized from melt or from the superheated state of water, is examined. Thermodynamic and structural changes during phase transitions are followed by DSC, time-resolved X-ray techniques and polarized optical microscopy. Considering the hydrogen bonding motifs present in this bisamide-diol, it is selected as a model compound for crystalline domains present in semicrystalline polyamides. By studying this model compound it was moreover aimed to elucidate the specific role of water molecules that are likely to reside in the crystals obtained from the superheated state of water. On heating the melt crystallized sample, the observed crystalline transitions are not the same as observed in polyamides. However, similar to polyamides the origin of the transition is due to the electron exchange between the hydrogen bonding moieties and conformational changes in the aliphatic sequences. At low temperatures ...

Incidence of nanoscale heterogeneity on the nanoindentation of a semicrystalline polymer: Experiments and modeling

The nanoindentation of semicrystalline polyamide 6 (PA6) specimens was evaluated by atomic force microscopy with an extremely sharp diamond tip whose apex was nominally less than 10 nm in radius. Nanoindentation was performed under dry and wet conditions on PA6 samples injection-molded at different melt temperatures. The bulk Young’s modulus of dry PA6 was found to be in good agreement with the literature, thereby confirming the experimental approach developed in this study. A major finding is the observation of sudden increases in force during the loading portion of the experimental load–displacement curves, which occurred regardless of water absorption. We also found some irregularity in the pile-up morphology around the indents, linked to the heterogeneous nature of the deformation in PA6. Finite element analysis was used to elucidate the phenomenon of force discontinuity by independently considering the variations in elasticity, yield stress and friction coefficient of the crystalline lamellar aggregates in PA6. It is shown that force discontinuities in nanoindented PA6 result from local differences in yield phenomena at the lamellar level. The present investigation sheds some light on the importance of mechanical heterogeneity emerging from contact interactions between an extremely sharp tip and the nanoscale morphology of semicrystalline polymers.

Dynamic mechanical properties of a biomimetic hydroxyapatite/polyamide 6,9 nanocomposite

A biomimetic composite of nanohydroxyapatite (nHap) and semicrystalline polyamide 6,9 (PA 6,9) was synthesized by thermally induced phase separation. The nHap powder was dispersed in a polymer matrix with a low ratio ranging 1-10 wt %. The mean size of the nHap, determined by scanning electron microscopy (SEM) was approximately 100-200 nm (length), 40-60 nm (width). Physicochemical analyses were performed in order to characterize the PA 6,9 and nHap separately on the one hand, and the PA 6,9/nHap composites on the other hand. Differential scanning calorimetry (DSC) and dynamic mechanical analyses (DMA) have pointed out an optimization of the composite physical properties as a function of nHap content till a limit value of 5 wt %. Above this value, the mechanical properties decreased. Four main parameters have been found to influence the composite physical properties improvement: the fillers content, the physical structure of the polymeric matrix, the particles dispersion and the physical interaction strength between organic and inorganic phases. The dynamic mechanical properties of this biomimetic nanocomposite were compared with human cortical bone.

Effect of substrate crystalline morphology on the adhesion of plasma enhanced chemical vapor deposited thin silicon oxide coatings on polyamide

The influence of the surface morphology of semicrystalline polyamide 12 (PA12) on the adhesion of thin silicon oxide coatings is analyzed by means of uniaxial fragmentation tests and scanning local-acceleration microscopy (SLAM). Two types of PA12 substrates are investigated, namely, as-received PA12, which contains large spherulites, and quenched PA12, which has a relatively smooth, homogeneous surface structure. The adhesion of the coating is found to be identical for the two types of PA12. This indicates that plasma deposition of the oxide leads to an equivalent functionalization of the two types of surfaces. Nonetheless, localized delamination is observed at spherulite boundaries, and is argued to result from strain concentrations in the corresponding soft zones, revealed by SLAM measurements.

Shear banding in strained semicrystalline polyamide 6 films as revealed by atomic force microscopy: Role of the amorphous phase

AbstractAtomic force microscopy (AFM) has been used to visualize the plastic deformation mechanisms that are responsible for the yielding of semicrystalline polymers of low degree of crystallinity (<50%). Indeed, AFM, if operated in suitable conditions, is able to image both the amorphous and the crystalline phases. Polyamide 6 films have been drawn at temperatures T < 160 °C. Postmortem AFM observations show that, at yield, shear bands nucleate and propagate in the amorphous phase. They cross the crystalline lamellae and run over the whole surface of the sample. By crossing the lamellae, they form nanoblocks of uniform size. Neither the size of the nanoblocks nor the angle between the tensile axis and the shear bands can be explained in terms of crystal plasticity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 687–701, 2004

Influence of moisture on the viscoelastic relaxations in long aliphatic chain contained semiaromatic polyamide, (PA9-T) fiber

The effect of moisture on the mechanical relaxation processes of semiaromatic semicrystalline polyamides synthesized by a long-chain aliphatic diamine and terephthalic acid was investigated by dynamic viscoelastic analysis (DVA) and differential scanning calorimetry (DSC). Moreover, the implication of moisture with the amorphous and crystalline domains was also examined by temperature-dependent wide-angle X-ray diffraction and Fourier transform infrared spectra. The characteristics of the relaxations such as α, β, γ, and the pronounced peak shoulder appeared at 25–100 °C in DVA tan δ curves were found to be strongly susceptible to the presence of moisture. With moisture evaporation, the peak shoulder of 25–100 °C and the β-relaxation disappeared. The former is anticipated to originate from to the side group motion of hydrogen-bonded water, whereas the later one is from the motions of the amide–water complex units. With the disappearance of the β-relaxation, the γ-relaxation appeared simultaneously in much lower temperatures and ultimately coupled with the δ-relaxation. The γ-relaxation is attributed to be associated with the molecular motion of the amide group and δ-relaxation with for the motion of the methylene units. The existence of two types of water was identified in the polymer, namely, tightly bound and loosely bound. The tightly bound water is believed to be directly connected by hydrogen bonding with the strong polar groups and the loosely bound water weakly links with those connected water making hydrogen bridges. The moisture acts as a plasticizer in the polymer matrix, which causes quite a large depression in its glass transition temperature (Tg). WAXD and FTIR studies corroborated the existence of water solely in amorphous regions, i.e., no rapport of water with the crystalline parts. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2878–2891, 2003

Synthesis and crystallization behavior of nylon 12,14. I. Preparation and melting behavior

AbstractA long‐alkane‐segment semicrystalline polyamide based on 1,12‐diaminododecane and 1,12‐dodecanedicarboxylic acid was synthesized and characterized. The polymer was prepared by melt polycondensation. The molecular weight of the material ranged from 20,000 to 40,000 g/mol, depending on the polymerization conditions. The resulting product was characterized by means of elemental analysis, infrared spectrometry, 1H‐ and 13C‐NMR, intrinsic viscosity, differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical analysis, and wide‐angle X‐ray diffraction (WAXD). Some mechanical properties were measured. In addition, the thermal behavior of nylon 12,14 was systematically investigated with DSC and variable‐temperature WAXD. Double endotherms were observed during the melting of the polymer, which might have originated from the melt and recrystallization processes of nylon 12,14 on heating. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1581–1589, 2003

Precipitation of Nylon 6 membranes using compressed carbon dioxide

Membrane formation using a compressed antisolvent is analogous to conventional immersion precipitation using liquid nonsolvents and introduces pressure as an additional variable for tailoring the membrane microstructure. Thin films of a semicrystalline polyamide, Nylon 6, were precipitated from 2,2,2-trifluoroethanol by exposing the incipient membrane to compressed CO2 antisolvent at 35°C and variable pressures up to 173.4bar. Membrane structures dominated by liquid–liquid (L–L) and solid–liquid (S–L) demixing processes were observed as a function of precipitation conditions. Interpretation of the resulting membrane morphologies was based on structural features observed for traditional phase inversion processes and reflected the relative rates of L–L and S–L demixing as a function of the pressure-dependent strengths of the solvent and antisolvent. The ability to tailor the morphology of a semicrystalline membrane using compressed antisolvent suggests an alternative to current CO2-based polymer impregnation techniques, which require solute solubility in CO2, for the generation of composite thin films and membranes.

New polyamides with long alkane segments: nylon 6.24 and 6.34

A series of new amphiphilic, semi-crystalline polyamides based on hexamethylenediamine and long alkane carboxylic diacids has been synthesized and characterized, here exemplified by polyamide 6.24 (PA-6.24) and polyamide 6.34 (PA-6.34). The polymers were produced by melt polycondensation, which yielded materials of weight-average molecular weights in the range of 30,000–35,000 g/mol. The thermal properties of the polyamides were investigated by various thermo-analytical methods. PA-6.24 and PA-6.34 exhibit relatively high melting temperatures of 189 and 177°C, respectively. Both materials display rather poor solubility in solvents that are used for common polyamides, but by contrast, dissolve in, e.g. ethanesulfonic acid. PA-6.34 was found to aggregate in dilute methanesulfonic acid solutions and form thermo-reversible gels in H 2SO 4, which we attribute to its amphiphilic character. The latter enabled the use of PA-6.34 as a “compatibilizer” for blends of polyolefins and polyamides. Finally, the Young's moduli of isotropic films of PA-6.24 and PA-6.34 were determined to be 1.3 and 0.7 GPa, respectively, representing a stiffness that is intermediate between that of common polyamides and polyethylene.

Influence of interchange reactions on the crystallization and melting behavior of nylon 6,6 blended with other nylons

AbstractThe thermal behavior of blends of nylon 6,6, with an amorphous polyamide, Trogamid‐T, and a semicrystalline polyamide, nylon 6,12, was studied. The blends were prepared both by solution blending and by melt blending, using a Maxwell extruder and a twin screw extruder. The concentration of the blends ranged from 75% to 95% by weight of nylon 6,6. Annealing the blend samples in the molten state in a differential scanning calorimeter (DSC) produced changes in the melting and crystallization behavior. This was attributed to transamidation reactions occurring between the blend components, leading to the formation of in‐situ block copolymers. The length of the blocks decreased with annealing time, as suggested by reduced melting (Tm) and crystallization temperatures (Tc) and heat of fusion values. The changes in thermal behavior were dependent on the blending method, additive concentration, presence or absence of a catalyst, melt annealing time, and the extent of melt mixing. The extent of reaction, measured by the depression in equilibrium melting temperature, was linear with respect to the annealing time. The Trogamid‐T containing blends appeared to be “nearly miscible” while those with nylon 6,12 were initially immiscible. The glass transition temperature (Tg) vs. the composition curve of the nylon 6,6/Trogamid‐T blends showed a positive deviation from linear additivity, with the single Tg decreasing as a function of annealing time in the melt.

Synthesis and characterization of poly(4-alkyl-4-methyl-2-azetidinone)s

Poly-β-amides (nylons 3) were synthesized via the anionic polymerization of a series of 4-alkyl-4-methyl-2-azetidinones where the alkyl group is a methyl, ethyl, propyl, butyl, or pentyl. The “non-assisted” polymerization was conducted under vacuum, in the bulk, at 160°C, using potassium 2-pyrrolidonate as catalyst, whereas the “assisted” polymerization was carried in dimethylsulfoxide, at room temperature, using N-acetylpyrrolidinone-2 as activator but it gave no polymer with a propyl or bulkier side group. Side reactions occur in all cases. X-ray spectra showed that poly(4-alkyl-4-methyl-2-azetidinone)s are amorphous with propyl, butyl, and pentyl groups, and semi-crystalline with methyl or ethyl substituents. Both semi-crystalline polyamides exhibit an extended planar zigzag conformation, with a fiber identity period along the c axis of 4.9 Å. Glass transition temperatures, melting temperatures, and/or decomposition temperatures are also reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 761–769, 1999

Synthesis and characterization of poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s

Poly-β-amides (nylons 3) were synthesized via the anionic polymerization of a series of 4-alkyl-4-methyl-2-azetidinones where the alkyl group is a methyl, ethyl, propyl, butyl, or pentyl. The “non-assisted” polymerization was conducted under vacuum, in the bulk, at 160°C, using potassium 2-pyrrolidonate as catalyst, whereas the “assisted” polymerization was carried in dimethylsulfoxide, at room temperature, using N-acetylpyrrolidinone-2 as activator but it gave no polymer with a propyl or bulkier side group. Side reactions occur in all cases. X-ray spectra showed that poly(4-alkyl-4-methyl-2-azetidinone)s are amorphous with propyl, butyl, and pentyl groups, and semi-crystalline with methyl or ethyl substituents. Both semi-crystalline polyamides exhibit an extended planar zigzag conformation, with a fiber identity period along the c axis of 4.9 Å. Glass transition temperatures, melting temperatures, and/or decomposition temperatures are also reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 761–769, 1999

Nylon 66/poly(vinyl pyrrolidone) reinforced composites:

Abstract Nylon 66, an aliphatic semicrystalline polyamide, was reinforced with E-glass fibers or high-modulus (AS4) carbon fibers. As in many reinforced semicrystalline thermoplastics, an interphase composed of transcrystallinity developed owing to the high nucleation density of the polymer on the fiber surface. The influence of this region on the fiber–matrix adhesion was studied with a modified microdebond test. E-glass fibers were freshly prepared in our laboratory by traditional glass-forming techniques and embedded in a film of Nylon 66 or a Nylon 66/poly(vinyl pyrrolidone) (PVP) blend. Previous work has shown that PVP, an amorphous polar polyamide, has a dramatic influence on the morphology of Nylon 66. This phenomenon was utilized to manipulate the interphase formation in the Nylon 66 composite from one having a complete transcrystalline interphase to a composite with the absence of an interphase. PVP was introduced to the matrix by solution blending with Nylon 66 and/or to the fibers as a sizing prior to embedment. The resulting morphologies were studied by polarized hot-stage optical microscopy. From the microdebond and morphology results, it was shown that the fiber–matrix adhesion in this composite system is dependent upon interphase microstructure. Composites containing transcrystallinity have higher interfacial shear strength values than those that do not contain this interphase. This has profound implications for the bulk mechanical properties of the composite, which are addressed in Part 2 of this paper.

Water Accessibility in Aliphatic Polyamides by NIR and FT-IR Spectroscopies

The capabilities of FT-IR and NIR spectroscopies to analyse water absorption mechanisms in aliphatic semi-crystalline polyamides (PA) are presented. This work was carried out on PA6, PA11 and PA12 and was divided into three parts: (1) assignment of the NIR absorption bands of PA11; (2) comparison of FT-IR and NIR results on water accessibility; (3) comparison of solubility values given by gravimetric and spectroscopic methods. Primarily, the water accessibility for the polyamides tested can be estimated by FT-IR as well as by NIR. The NIR technique is more appropriate for melt processed samples, as film casting (for FT-IR) can induce structural modifications. The scheme of water incorporation in polyamides is confirmed. The complete hydration of some regions of the polymer is proved by correlation between gravimetric and NIR data. Finally, a concept for intrinsic solubility is suggested to take into account spatial and structural distributions of water molecules in the amorphous phase of polyamides. This parameter remains constant with temperature.