Superposition of electrical properties in temperature-sensing wire composed of thermosensitive polyamide–phenol compounds at various temperatures and humidities

The relationship between the DC conductance (G) and the capacitance (C) in temperaturesensing wire composed of thermosensitive polyamide–phenol compounds has been studied. The G–C characteristics at various temperatures and humidities are approximately plotted on a same line, and the log G–log C plots draw a straight line with time. This implies that when the temperature-sensing wire is in equilibrium under the constant temperature and humidity, if either one of them has been known, the other value is determined from the characteristics. These characteristics will be available properties, e.g., for the temperature and humidity sensing material. These also show that the electrical behaviors due to an absorbed water cannot be distinguished from that due to the amide and phenol groups. This is because that both of them constitute the similar dielectric segments composed of hydrogen bonds, and proton carriers for conduction also generate from them. It also shows that the behaviors of protons from amide, phenol group, and absorbed water cannot be electrically distinguished from one another. It is deduced that the absorbed water mainly contributes to the number of proton carriers and the increase in moisture content contributes more to the DC conductance instead of less than the increase of mobility due to thermal activation of the proton carriers generating from amide, phenol, and absorbed water.     

Synthesis of copolyamide–esters and some aspects involved in their hydrolysis by lipase

Copolyamide–esters (CPAEs) were synthesized by the amide–ester interchange reaction. The change of intrinsic viscosity during CPAE synthesis was negligible. Polyamide blocks were shortened with increasing reaction time and polyester content. The polymerization degree of nylon 12 blocks on CPAE was smaller than that of nylon 6 blocks. CPAEs were hydrolyzed by Rhizopus delemar lipase. The biodegradability decreased with the shortening of the polyamide blocks and with increasing polyamide content. It was concluded that the amount and distribution of the hydrogen bonds, based on the amide group, in the CPAE chains strongly influenced their biodegradation by this lipase.     

The stress cracking of polyamides by metal salts. Part II. Mechanism of cracking

The action of metal halides on polyamide (nylon 6) and secondary amide model compounds has been investigated, using infrared and NMR techniques. Metal halides, which are active stress cracking agents for polyamides, induce characteristic changes in the spectra of both nylon 6 and the model compounds. Two types of changes were observed, depending on the metal halide involved, and on this basis the metal halides have been classified as Type I or Type II. The spectral changes appear to be due to the formation of complexes between the amide group and the metal halide, and structures for these complexes are proposed. Type I metal halides, such as zinc, cobalt_II, copper_II and manganese_II chlorides, form complexes in which the metal atom is coordinately bonded to the carbonyl oxygen atom of the amide group. These agents cause stress cracking by interference with the hydrogen bonding in the polyamide. Type II metal halides, such as lithium, calcium and magnesium chlorides and lithium bromide in solution form proton donating, solvated, species which act as direct solvents for nylon 6 in a manner similar to phenols and formic acid. Type II agents appear to cause simple solvent cracking.     

“Binary salt” of hexane‐1,6‐diaminium adipate and “carbon nanotubate” as a synthetic precursor of carbon nanotube/Nylon‐6,6 hybrid materials

A novel chemical approach was established to produce carbon nanotube/Nylon‐6,6 hybrid materials from readily available substrates, that is, Nylon‐6,6 salt and oxidized multiwall carbon nanotubes (O‐MWCNTs). The key synthetic precursor hexane‐1,6‐diaminium adipate and “carbon nanotubate”—“Binary nanotube salt”—was obtained and isolated as stable and easy‐to‐handle solid in over 80% yield and with no nanotube losses. The final hybrid materials of various nanotube loadings were synthesized at 270°C and were easily purified from the homopolymer. Purified hybrids were comprehensively analyzed (yields and grafting ratios, SEM, TEM, FT‐IR) revealing a two‐phase characteristics—individually grafted nanotubes and cross‐linked nanotube material. Isothermal TGA kinetic studies showed that in the “binary salts” diamine and diacid molecules were anchored to the nanotube outer shells and then held electrostatically enabling growth of polymer immobilized on O‐MWCNTs (“grafting‐from” mechanism). Depending on the density and type of nanotube functionalities and filler concentration in the “binary salt,” the O‐MWCNT/Nylon‐6,6 hybrids can be treated as hybrid material of a proportion of aliphatic polyamide and polyaramide properties. POLYM. COMPOS., 35:523–529, 2014. © 2013 Society of Plastics Engineers     

Infrared spectroscopic studies of a nematic liquid crystalline poly(ester amide) in the solid phase

Infrared spectroscopy has been used to study the hydrogen bonding conditions in a nematic liquid crystalline poly(ester amide). The results showed that the material formed interchain hydrogen bonding as a result of the inclusion of amide groups in the polymer chains. The hydrogen bonding was found to be stable in the temperature range studied (up to 150°C). However, the studies suggested that the hydrogen bond strength was weaker than in polyamide and did not appear to affect the mechanical properties of the material significantly.     

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture‐sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water‐vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (T_g's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the T_g of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen‐bond strength of the N H groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999     

Graft-copolyamide molecular composites

A novel family of graft-copolyamides was prepared in which several chains of high molecular weight polycaproamide (nylon 6) are grafted onto the backbone of each stiff aromatic polyamide chain. The unique feature of the present graft-copolyamides is that the side chains are connected through amide groups directly to the aromatic rings in the stiff chain, and not to the amide groups in the backbone of the stiff chain. Because they are miscible with linear nylon 6, blends of the graft-copolymers and nylon 6 are easily prepared. Electron microscopy, x-ray diffraction scans, DSC runs, and solid-state NMR relaxation and spin diffusion experiments all indicate that the aromatic stiff polyamide chains are molecularly dispersed in the graft-copolyamides and their blends with nylon 6. In an ungrafted blend of the stiff aromatic and flexible aliphatic nylon 6, the stiff chains tend to agglomerate into small hydrogen-bonded sheaf-like aggregates the size of which increases upon annealing above the melting point of the flexible polyamide. The NMR results point to a substantial flexibility of the stiff chains in the graft-copolyamides, helping to explain the levels of reinforcement reflected in the tensile properties of these materials. In the ungrafted blends, the aromatic-chain stiffness is greatly enhanced when these chains are phase separated in the minute sheaf-like particles. The tensile properties of the graft-copolymers and their mixtures with pure nylon 6 are far superior to those of the ungrafted blends. The reinforcement of the flexible matrix by the stiff polyamide chains is explained in terms of the Halpin—Tsai formulation. © 1994 John Wiley & Sons, Inc.     

PA6/CaCl2复合材料络合配位的红外研究

采用傅里叶变换红外光谱分析(FTIR)研究了尼龙6/氯化钙复合材料中胺基、酰胺Ⅰ带和酰胺Ⅱ带伸缩振动峰随氯化钙用量的变化情况。通过配位化合物中氧、氮原子参与配位的优先次序,以及酰胺基团的红外形成机理,提出两种络合机理假设,证实了钙离子通过与尼龙6分子链上的氮原子发生络合作用,插入尼龙6分子链,破坏尼龙6的氢键,降低其结晶度。     

Electro-mechanical deformation of amorphous and semi-crystalline polymeric films

In our previous study, electrically induced mechanical stress was produced on monolithic polycarbonate (PC) films under a DC voltage using a needle-plane electrode setup. This study investigated other materials with various structures and dielectric constants, in order to further understand the deformation mechanism. It was found that the elastic behavior occurred at electric fields intensities below that initiating measurable surface deformation. The amorphous materials, PS, and the semi-crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar observable deformation onset electric field at 200 MV/m. While PVDF, having a dielectric constant of 10.0–12.0, showed an onset at only 30 MV/m. The data was also compared to our previous study on PC. The depth and diameter of the deformation for all materials increased relative to the applied electric field up to film breakdown. Thermal annealing of the deformed films revealed a recoverable “delayed elastic” component and an irreversible “plastic” component. A three-stage electrically induced mechanical deformation mechanism was proposed for amorphous materials, while a two-stage mechanism was proposed for the semi-crystalline materials. The difference on the energy loss versus deformed volume for amorphous and semi-crystalline polymers was also determined and discussed.     

FT‐IR spectroscopic investigation on the interaction between nylon 66 and lithium salts

FT‐IR spectroscopy has been utilized to study nylon 66/lithium salt systems. The results show that coordination between nylon 66 and lithium ions brings about significant variation in the FT‐IR spectra: (1) a stronger hydrogen bond is formed in the systems; (2) the interaction induces obvious conformational changes of the nylon 66 chains. A coordination model has been proposed to rationalize the observed spectral phenomena. The interaction between amide groups and lithium ions is a feasible approach to modify the performance of nylon 66. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2869–2875, 2004     

Thermal conductivity of polymers by hot-wire method

The hot-wire standard technique, mostly used for ceramic materials, was adapted to determine the thermal conductivity of nylon 6,6, polypropylene, poly(vinyl chloride), and poly(methyl methacrylate). The results obtained showed that the hot-wire standard technique can be used with accuracy and reproducibility to measure the thermal conductivity of polymers. In the second stage, to verify the effect of the use of a lignin (a “macromonomer”) in the thermal conductivity of phenolic resins, this technique was applied to phenol-formaldehyde and phenol–lignin–formaldehyde resins. © 1996 John Wiley & Sons, Inc.     

Thermal decomposition of aliphatic nylons

An overview of the literature together with selected authors' data on thermal and thermo-oxidative decomposition of commercial aliphatic nylons (nylon 6, nylon 7, nylon 11, nylon 12, nylon 6.6, nylon 6.10, nylon 6.12) is presented. Despite the high level of research activity and the large number of publications in the field, there is no generally accepted mechanism for the thermal decomposition of aliphatic nylons. Polylactams (nylon 6, nylon 11 and nylon 12) tend to re-equilibrate to monomeric or oligomeric cyclic products. Diacid–diamine type nylons (nylon 6.6, nylon 6.10 and nylon 6.12) produce mostly linear or cyclic oligomeric fragments and monomeric units. Because of the tendency of adipic acid to fragment with elimination of CO and H₂O and to undergo cyclization, significant amounts of secondary products from nylon 6.6 are reported in some papers. Many authors have shown that the primary polyamide chain scission occurs either at the peptide C(O) NH or at adjacent bonds, most probably at the alkyl–amide NH CH₂ bond which is relatively the weakest in the aliphatic chain. Hydrolysis, homolytic scission, intramolecular C H transfer and cis-elimination (a particular case of C H transfer) are all suggested as possible primary chain-scission mechanisms. There are no convincing results reported which tend to generally support one of these mechanisms relative to the others; rather, it seems that the contribution of each mechanism depends on experimental conditions. This conclusion is also supported by the wide spread of kinetic parameters measured under the different experimental conditions. More uniform results are observed in the literature regarding the mechanism of thermo-oxidative decomposition of aliphatic nylons. Most authors agree that oxygen first attacks the N-vicinal methylene group, which is followed by the scission of alkyl–amide N C or vicinal C C bond. Alternatively, it is suggested that any methylene group which is β-positioned to the amide group methylene can be initially oxidized. There are few mechanisms in the literature which explain discoloration (yellowing) of nylons. UV/visible active chromophores are attributed either to pyrrole type structures, to conjugated acylamides or to conjugated azomethines. Some secondary reactions occurring during the thermal or thermo-oxidative decomposition lead to crosslinking of nylons. Nylon 6.6 crosslinks relatively easily, especially in the presence of air, whereas nylon 11 and nylon 12 crosslink very little. Strong mineral acids, strong bases, and some oxides or salts of transition metals catalyse the thermal decomposition of nylons, but minimize crosslinking. In contrast, many fire retardant additives promote secondary reactions, crosslinking and charring of aliphatic nylons. © 1999 Society of Chemical Industry     

Fixation characteristics of carboxylated dyes on polyamide fibres

Reactions of dyes, some of which contain a carboxylic acid group, on polyamide have been investigated using nine different dyes of differing chemical structures. Fixation characteristics and dye–fibre bond stability to alkaline washing were also studied. Light fastness and ability to cover barre effects on nylon were investigated. Studies were also made on the effect of carbodiimide on fixation and dye–fibre bond stability of these dyes on nylon fibres.     

Mesophase Structure‐Enabled Electrostrictive Property in Nylon‐12‐Based Poly(ether‐block‐amide) Copolymers

To search for alternative electrostrictive polymers and to understand the underlying mechanism, the structure‐ferroelectric/electrostrictive property relationship for nylon‐12‐based poly(ether‐b‐amide) multiblock copolymers (PEBAX) is investigated. Two PEBAX samples are studied, namely, P6333 and P7033 with 37 and 25 mol.% of soft poly(tetramethylene oxide) (PTMO) blocks, respectively. In both samples, poorly hydrogen‐bonded mesophase facilitates electric field‐induced ferroelectric switching. Meanwhile, the longitudinal electrostrictive strain (S₁)–electric field (E) loops are obtained at 2 Hz. Different from conventional poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)]‐based terpolymers, uniaxially stretched nylon‐12‐based PEBAX samples exhibit negative S₁, that is, shrinking rather than elongation in the longitudinal direction. This is attributed to the unique conformation transformation of nylon‐12 crystals during ferroelectric switching. Namely, at a zero electric field, crystalline nylon‐12 chains adopt a more or less antiparallel arrangement of amide groups. Upon high‐field poling, ferroelectric domains are enforced with more twisted chains adopting a parallel arrangement of amide groups. Meanwhile, extensional S₁ is observed for P6333 at electric fields above 150 MV m^?1. This is attributed to the elongation of the amorphous phases (i.e., amorphous nylon‐12 and PTMO). Therefore, competition between shrinking S₁ from mesomorphic nylon‐12 crystals (i.e., nanoactuation) and elongational S₁ from amorphous phases determines the ultimate electrostriction behavior in stretched PEBAX films.     

Unusual accelerated molecular relaxations of a tin fluorophosphate glass/polyamide 6 hybrid studied by broadband dielectric spectroscopy

Phosphate glass (Pglass)/polymer hybrids are a relatively new class of materials that combine the advantages of classical polymer blends and composites without their disadvantages. In the case of highly interacting Pglass/polymer (i.e., polyamide 6) hybrids, counter-intuitive properties that are difficult to explain are often observed. To shed light into the origins of the special behavior of the hybrids, we investigated the molecular relaxation processes in the hybrids using broadband dielectric spectroscopy. The dielectric loss spectra were fitted with the Havriliak-Negami equation and the characteristic relaxation times of the hybrid and the pure components were observed. The temperature dependence of the characteristic relaxation times was described using either the Vogel-Fulcher-Tammann, for the α-relaxations, or an Arrhenius type equation, for the β- and γ-relaxations. The addition of Pglass greatly accelerated both the α- and β-relaxations of the polyamide 6. However, the γ-relaxation was found to be independent of Pglass composition. This suggests partial miscibility in the solid state, which was confirmed via NMR spectroscopy. The unexpected dramatic change in the β-relaxation process in the 10 vol.% Pglass hybrid suggests that blending can change the local environment of polyamide 6 due to the nanoscale morphology of this system as confirmed by TEM and NMR. It is thought that the fraction of miscible Pglass disrupts the hydrogen bonding between polyamide 6 chains and thereby reduces coordinated, multiple chain motion. In turn, this produces a plasticization effect and possible modification of the polyamide 6's crystalline structure in the Pglass/polyamide 6 hybrids.     

In situ fourier‐transform infrared spectra analysis of hydrogen bond in polypropylene/chlorinated polypropylene/polyaniline composite

The previous studies suggest that hydrogen bond between chlorinated polypropylene (CPP) and polyaniline (PANI) plays a prominent role in the decision of polypropylene/CPP/PANI composites' electric property. In situ Fourier‐transform infrared spectra were employed to detect and identify the relationship between the hydrogen bond and the temperature. Two kinds of hydrogen bond were carefully studied in the nitrogen–hydrogen bond (N? H) stretching, sulfur–oxygen double bond (S?O) stretching, and carbon–chlorine bond (C? Cl) stretching regions, using an iterative least‐squares computer program to obtain the best fit of spectra. The ratio of absorptivity coefficients and the mole fraction of the “free” and two kinds of H‐bonded N? H were calculated. There exists an apparent turning point in the curves of the relationship between the fraction of two kinds of H‐bonded N? H and temperature. This phenomenon also exists in the S?O stretching region, and the turning point is at about 60°C. The mole fraction of H‐bonded C? Cl decreases, and that of “free” C? Cl increases with increasing temperature. The enthalpy gap between the H‐bonded N? H…O?S and the H‐bonded N? H…Cl?C dissociation was also obtained as 23.2 KJ/mol. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Synthesis,characterization, and applications of polyvinylpyrrolidone/SiO2 hybrid materials

This research discusses the properties of hybrid materials formed by polyvinylpyrrolidone (PVP) and tetraethoxysilane (TEOS) of different weight ratios, by the sol–gel process, to evaluate the feasibility of its application to process‐dyed nylon fabrics. After using equipment including FTIR, ¹³C‐NMR, and SEM, it was shown that PVP and SiO₂ are connected by hydrogen bonds, further showing the existence of special functional groups and the porous structure in hybrid materials. The pore size of the hybrid materials, specific volume of pores, and the specific surface area increased with increasing weight ratio of TEOS. In addition, the TGA testing results showed that the thermoresistance of hybrid materials can be improved. The color of the treated fabrics darkened if dyed nylon fabrics were treated by hybrid materials. When using metal complex acid dye for certain fabrics, when hybrid materials were used in finishing, there was significant improvement to the fabric's hygroscopicity and its colorfastness against chlorine. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1936–1942, 2005     

Change of chemical composition and hydrogen bonding behavior due to chlorination of crosslinked polyamide membranes

The effect of membrane exposure to hypochlorite oxidant on property changes (chemical composition and hydrogen bonding behavior) of four FilmTec© thin film composite crosslinked polyamide membranes has been investigated. Crosslinking densities of the membranes were about 25–35%, with about 3–4 chlorines bound to the repeating unit of the polyamide membranes. This was equivalent to ～ 39% of all nitrogens being chlorinated in the polyamide membranes assuming the amide nitrogen is the dominant reaction site with chlorine. FTIR spectra showed the amide I band (C?O stretching peak at 1663 cm^?1) of polyamide membranes shifted to higher wave‐numbers and the peak intensity of the amide II band (N? H bending peak at 1541 cm^?1) decreased after chlorination. The peak shift and decrease of peak intensity resulted from breakage of hydrogen bonds between C?O and N? H groups within the polymers. The XPS and FTIR analytical analysis showed that there is no difference in the chlorine attack of polyamide membranes of higher or lower crosslinking density, and that the chlorination breaks and weakens hydrogen bonding. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

“Orientation induced memory effect” in polyamides and the relationship to hydrogen bonding

The influence of molecular orientation on the “memory effect” of polyamides was investigated by differential scanning calorimetry. Melt crystallization of undrawn and drawn polyamide 6 (N6) and polyamide 66 (N66) fibers showed no difference either in the rate of crystallization or crystallization temperature. We demonstrated that hydrogen bonding does not play a major role in melt crystallization kinetics of polyamides (N6 and N66), and the “memory effect” is only retained for polymers, including N6 and N66, because of insufficient time spent above the melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 772–775, 2003     

Photophysical processes in poly(hexamethylene adipamide)–acid dye complexes: Energetics of nylon 66 phototendering

The mechanism of dye-sensitized photo-oxidative degradation of nylon 66 was investigated. A known phototendering dye, C.I. Acid Blue 40 (1-amino-4-(p-aminoacetanilide)-2-anthraquinone sodium sulfonate), was used for this study. Excitation and emission spectra of the dyed and undyed nylons indicated that a ground-state complex between the dye and the polyamide was formed upon dyeing. The energy level of the complex's electronic states favor triplet–triplet energy transfer from the nylon to the complex. Quenching studies show that the energy transfer occurs efficiently with a rate constant of 45.8 l. mole^?1 sec^?1. An additional energy transfer occurs between the excited free dye and the complex by either a singlet–triplet or a triplet–triplet mechanism. Kinetic analysis of the nylon-complex energy transfer suggests that the triplet energy of nylon migrates 24 to 33 Å along the amide chromophores in an exciton fashion until an energy trapping complex is reached. Energy is then transferred by an exchange mechanism. Photo-oxidative studies verify that the dye–nylon complex sensitizes the polyamide photo-oxidative degradation at its own expense without dye photobleaching.