POLYCAPROLACTAM MODIFIED BY POLYBENZIMIDAZOLE

Three polycaprolactam samples modified by 0.05—0.50% polybenzimidazole (PBI) by weight were prepared. Their structure and mechanical properties were characterized by means of FT-IR, SEM, DTA, density tensile, impact and viscoelastic method. PBI delayed the superimposed polymerization-crystallization process of the activated anionic polymerization of caprolactam. The monomer casting (MC) nylons modified by PBI had lower crystallinities, lower T_g and more nearly perfect spherulites than MC nylon itself, and showed a typical toughening effect.     

含喹噁啉环的化合物改性聚己内酰胺

合成了14种由三种含喹(哑心)啉环的芳香化合物改性的聚己内酰胺(MC尼龙),并对其形态、抗冲击强度、吸水性及熔融行为等进行了表征。聚苯基单醚喹(哑心)啉(PPQ)单模型化合物对MC尼龙结晶部分几乎没有影响。少量(0.005—5.0％)吩嗪的引入使MC尼龙的颜色、形态及性能等发生巨大变化,改性体系被认为是氢键相互作用,PPQ双模型化合物的改性作用介于二者之间。     

含喹噁啉环的化合物改性聚己内酰胺

 合成了14种由三种含喹(哑心)啉环的芳香化合物改性的聚己内酰胺(MC尼龙),并对其形态、抗冲击强度、吸水性及熔融行为等进行了表征。聚苯基单醚喹(哑心)啉(PPQ)单模型化合物对MC尼龙结晶部分几乎没有影响。少量(0.005—5.0％)吩嗪的引入使MC尼龙的颜色、形态及性能等发生巨大变化,改性体系被认为是氢键相互作用,PPQ双模型化合物的改性作用介于二者之间。     

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L₁₀₀ and L₀₁₀ of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003     

Study on the brill transition and melt crystallization of nylon 65: A polymer able to adopt a structure with two hydrogen-bonding directions

Real time temperature dependence of X-ray diffraction patterns and infrared spectra for nylon 65, a representative polymer of the even-odd nylon series, was studied. A particular structure based on the establishment of two hydrogen-bonding directions had previously been postulated for this polymer. Therefore, the determination of its temperature-induced transitions is a relevant topic. Results indicate that nylon 65 undergoes a reversible Brill transition at high temperature, leading to a pseudohexagonal chain axis projected unit cell. Furthermore, this polyamide shows a polymorphic transition around 100 °C which is not completely reversible on cooling.Crystallization of nylon 65 was also analyzed by simultaneous WAXD and SAXS synchrotron radiation experiments to determine the evolution of the degree of crystallinity and morphological parameters on cooling. Optical microscopy studies were also performed under isothermal and non-isothermal conditions to distinguish the different spherulitic morphologies. Results reveal that the optical properties of nylon 65 spherulites are different from those of conventional even-even nylon spherulites. Multiple melting peaks associated with lamellae of different thicknesses were observed in the calorimetric heating scan of melt-crystallized samples.     

A modification of the properties of isotactic polypropylene film by γ-radiation in the presence of butadiene

The physical and mechanical properties of annealed (PPA) and quenched (PPQ) forms of isotactic polypropylene film modified by γ-irradiation in the presence of gaseous 1,3-butadiene (BD) have been studied. BD was chemically bound to the film in amounts up to 16.3 mass %. Gel contents were considerably greater than after corresponding in vacuo irradiations. T_g was reduced by up to 14°C after 5 and 15 Mrad but increased after 50 Mrad. Melting and crystallization behaviour was similar to that of samples after corresponding in vacuo irradiations suggesting that BD was incorporated mainly in non-crystalline regions. However, residues from extractions in refluxing xylene also melted and crystallized showing that light cross-linking must have occurred in the crystalline regions, probably at the lamellar surfaces. Compared with in vacuo irradiations the initial modulus and the yield stress of PPA were reduced after 5 and 15 Mrad such that the samples could be drawn beyond both yield point and the necking process without rupture. After 50 Mrad this improvement was lost probably because the more extensive cross-linking had counteracted the increased flexibility due to the incorporated BD. The elastic nature of the incorporated BD resulted in a reduction in the extent of the necking process in all samples. After 50 Mrad both PPA and PPQ exhibited good elastic complex moduli above the melting point.     

Formation of spherulites in polyamide melts: Part III. Even-even polyamides

A preliminary study of the isothermal crystallization of “even-even” polyamides reveals striking similarities in spherulitic morphology. The observed variations in textural features of spherulites of nylon 210, nylon 66, nylon 610, and nylon 1010 show parallel changes during growth conditions and conform to a definite sequence of behavior. At least four different types of spherulites exist in each polymer. Optical and x-ray techniques were used to examine some of these spherulites. Crystalline platelets possessing single-crystal properties have been grown in thin films of these polymers near their respective melting points.     

The electron microscope characterization of the fine structure of nylon 6: II. On the rearrangement of the structure during cold-drawing

The transmission electron microscope (TEM) visualization of the supermolecular structure of cold-drawn, oriented nylon 6 bulk material (bristles) by stained ultra-thin sections is reported. For evaluating the electron micrographs optical diffraction (OD) has been applied in comparison with small angle X-ray scattering (SAXS). The deformation of the spherulites was followed by polarization microscopy. In addition, investigations were carried out on commercial nylon 6 fibres. As the main result a transverse structure was revealed within the drawn samples at draw ratios between =4 and 4.5, consisting of mosaic crystals which show some lateral alignment. The structure is described by a modified layer lattice model. While the long period may increase slightly during drawing, the crystallite thickness remains almost constant. Fibres with =3.4 show a similarly oriented structure though the lateral alignment of the crystals is not so pronounced.     

聚丙烯力学性能与等规度及形态的关系

在单轴拉伸的条件下,在聚丙烯的四种不同球晶尺寸及堆集状态中,研究了等规度对力学性能的影响,并用偏光显微镜研究了不同球晶的拉伸变形机构。 一般地讲,等规度对聚丙烯力学性能是有影响的,但不及球晶尺寸和堆集状态的影响那么重要。不同球晶的聚丙烯在力学性能上的差别与其在拉伸变形机构上的差别密切相关。     

聚苯基单醚喹噁啉薄膜的性能与物理老化

研究了物理老化对聚苯基单醚喹啉薄膜的结构与力学性能的影响 .用差示扫描量热计 (DSC)及正电子湮没寿命谱 (PALS)方法表征了两种不同物理老化条件试样的凝聚结构以及自由体积的差别 .结果表明 ,物理老化使聚苯基单醚喹啉薄膜玻璃化转变温度移向高温 ,在其末端出现热焓吸收峰 ,分子链堆砌紧密使自由体积减小 ,分子可动性降低 .用动态力学分析 (DMTA)以及静态拉伸性能测试等方法研究了两类试样的力学性能 ,结果表明 ,物理老化后 ,试样的动态储能模量稍有增加 ,力学损耗降低 .而静态拉伸实验的断裂应变降低 ,屈服应力增加 ,断裂能降低 ,试样在宏观上由韧性断裂变为明显的脆性断裂 .     

Small-angle light scattering by random assemblies of incomplete spherulites. II. Truncated spherulites

Previous theoretical calculations of the scattering from spherulites are for isolated complete spheres, whereas most spherulitic polymer samples contain truncated spherulites as a result of impingement by other spherulites. The effect of such truncations on the scattering patterns for two-dimensional spherulites is explored as a function of the size, number and location of the truncations. The scattering of severely truncated spherulites is modified, particularly with regard to the enhancement of the H_V scattering at small angles. However, reasonable amounts of truncation corresponding to experimentally observed structures do not produce appreciable modification of the pattern so that the neglect of truncation will not lead to appreciable error in the estimated spherulite size from light scattering.     

Thermomechanical behavior of a polyphenylquinoxaline

Crosslinking of linear poly[2,2′-(1,4-phenylene)-6,6′-bis(3-phenylquinoxaline)] (PPQ) by isothermal heat exposure in the temperature range between 425 and 490°C was investigated by means of torsional braid analysis. The change in glass transition temperature due to isothermal exposure was used as a kinetic parameter. In order to determine the effect of molecular weight and type of polymer chain ends, three PPQ samples were prepared that differed only in molecular weight and polymer chain endgroups. The apparent activation energy of isothermal crosslinking was independent of molecular weight and chain endings. Its value of 60 kcal/mole is the same as that for the thermal degradation of PPQ (determined by isothermal weight loss measurements). The rates of change of T_g at a particular temperature, however, are a function of both molecular weight (at least for these polymers that do not have a sufficiently high molecular weight) and the type of polymer chain ends. It was observed that isothermally crosslinked PPQ gave a higher break point in the TGA curve and also an increased char yield at 800°C than the linear precursor.     

SYNTHESIS AND CHARACTERIZATION OF ORGANOMONTMORILLONITE AND POLYAMIDE 66/MONTMORILLONITE NANOCOMPOSITES

The montmorillonites (MMTs), layered, smectite-type silicates, were premodified by two different methods priorto the polymer melt intercalation. In one case MMTs were modified with cetyltrimethylammonium bromide (CTAB), andtermed as organomontmorillonites (OMMTs); in the other case MMTs were modified by nylon, and the products were calledmodified montmorillonites (MMMTs). The effects of CTAB and nylon on the MMTs were investigated by using TG andWAXD. The results show that interlayer spacings of CTAN and nylon modified MMTs are larger than that of sodium MMTs.Then, polyamide 66 (PA 66)/MMT nanocomposites were obtained through the method of melt intercalation of polymers. Thenanocomposites were characterized by WAXD, TEM and Molau experiments. The results indicate that the MMTs dispersehomogeneously in the PA 66 matrix. The mechanical properties of nanocomposites, such as tensile properties and flexuralproperties, were also measured and show a tendency to increase with increase of MMT content and reach the maximumvalues at 5phr MMT content. The heat distortion temperature (HDT) of the nanocomposites (7 phr) is about 32 K higher thanthat of pure PA 66.     

Effect of annealing on thermal properties and crystalline structure of polyamides. Nylon 12 (polylaurolactam)

Summary Thermal and crystalline behaviour of nylon 12 annealed at low supercooling for 10–2500 hours were studied by DSC, SAXS, WAXS and electron microscopy. The melting temperature and the heat of melting increased on annealing time and temperature from 174 °C and 10 cal/g to 187 °C and 23 cal/g, and at the same time the long period was enhanced from 80 to 160 Å. Long time annealing caused a partial transformation of the-crystal structure to the-crystalline modification.Annealed nylon 12 consisted typical folded chain spherulites of increased latteral dimensions.The extrapolated heat of meltingH _m ^* of the crystalline phase of nylon 12 in the-form is 50 cal/g.With 9 figures     

Influence of the β‐crystalline phase on the mechanical properties of unfilled and calcium carbonate‐filled polypropylene: Ductile cracking and impact behavior

The β‐crystalline form of isotactic poly(propylene) (PP) has been long recognized to have a greater mechanical absorption capacity than the α‐crystalline form. This is of major importance for improving impact properties and crack resistance of injection‐molding parts. Unfilled PP samples together with calcium carbonate‐filled PP samples having various β/α‐phase ratios, with nearly constant morphological parameters, have been investigated from the standpoint of ductile crack propagation and impact behavior. The presence of the β‐crystalline phase turned out to improve both properties. The β spherulites are notably more prone to craze initiation than α spherulites that display a propensity for cracking. Subsequent crack propagation appears to be faster in the latter ones. The plastic zone ahead from the crack tip broadens, and the specific plastic energy increases with increasing β‐phase content. The lower elastic limit of the β phase is likely to promote the early crazing. However, the suspected higher density of tie molecules in β spherulites provides more numerous and stiffer microfibrils. The impact strength of PP is also improved by the presence of β crystals as a result of greater energy‐absorption capabilities. However, filled samples turned out insensitive to the β phase. A discussion is made about the origins of the β‐phase‐induced improvement of the mechanical properties. The possible role of the β → α transition is also explained. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 31–42, 2002     

Structure-property behavior of films containing disk spherulites: A model study

Thin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress-strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperature T_g. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was above T_g.     

Crystalline texture of injection-molded nylon 6

Injection-molded specimens of nylon 6 were examined by x-ray diffraction as a function of depth in three characteristic directions. A skin and a core were always found to be present which differed in the degree of crystalline perfection and crystal modification. While the core of pure nylon 6 was found to be not oriented, the core of specimens containing nucleating agents was found to contain a typical texture of the monoclinic modification of nylon 6 in which the distribution probability of the a^* and c^* axes resembles ellipsoids with three unequal axes. A model explaining this texture as due to degenerated (deformed) spherulites is proposed. With a transcrystalline nylon 6 specimen the direction of the fastest growth in the unit cell (which forms the radius of spherulites) is found to be close to the a axis.     

Development of PE/PCL Bilayer Films Modified with Casein and Aluminum Oxide

The studied samples were prepared from polyethylene (PE) polymer which was coated with modified polycaprolactone (PCL) film in order to obtain bilayer films. Thin PCL film was modified with casein/aluminum oxide compound to enhance vapor permeability as well as mechanical and thermal properties of PE/PCL films. Casein/aluminum oxide modifiers were used in order to achieve some functional properties of polymer film that can be used in various applications, e.g., reduction of water vapor permeability (WVTR) and good mechanical and thermal properties. Significant improvement was observed in mechanical properties, especially in tensile strength as well as in water vapor values. Samples prepared with aluminum oxide particles indicated significantly lower values up to 60%, and samples that were prepared with casein and 5% Al₂O₃ showed the lowest WVTR value.     

Effects of gamma and electron beam irradiation on the properties of calendered cord fabrics

The effects of gamma and e-beam irradiation on mechanical and structural properties of nylon 66 (Ny 66), nylon 6 (Ny 6) and poly(ethylene terephthalate) (PET) fabrics used in tyres were investigated. The untreated (greige), treated cords and calendered fabrics were irradiated at different doses. It is found that the effects of high energy irradiation on greige, treated cords and calendered fabrics are similar. No protective effect of compounds used in calendering was observed against radiation-induced oxidative degradation. The deterioration effect of gamma irradiation on mechanical properties is much higher than that of e-beam irradiation for all types of samples. Limiting viscosity numbers of both gamma and e-beam irradiated nylon 6 and nylon 66 cords were found to decrease with increasing dose. It is concluded that PET calendered fabric has higher resistance to ionizing radiation. Ny 6 and Ny 66 calendered fabrics are more sensitive even at low doses. Therefore, the effects of high energy irradiation on tyre cords have to be taken into consideration during tyre design reinforced with particularly Ny fabrics if pre-vulcanization with high energy radiation is to be applied.     

Effects of toughening propylene/ethylene graft copolymer on the crystallization behavior and mechanical properties of polypropylene random-copolymerized with a small amount of ethylene

Linear low-density polyethylene (LLDPE) was grafted onto the backbone chains of isotactic polypropylene (iPP) during reactive melt-extrusion to produce a novel toughening modifier, propylene/ethylene graft copolymer (PEGC), to improve the properties of iPP random(-copolymerized with a small amount of ethylene) (PPR). The crystallization behavior as well as the non-isothermal crystallization kinetics of the PEGC modified PPRs were investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The fractured surface topography was characterized using scanning electron microscopy (SEM), and the mechanical properties through notched impact and tensile testing as well as dynamic mechanical thermal analysis (DMTA). The results show that, at a PEGC content of 8 wt%, notched impact strength of the PEGC modified PPR increased by 30.6% at low temperature (−25 °C). As regards crystalline morphology, the PEGC, as an effective heterogeneous nucleating agent, fostered nucleation of the PPR to elevate its crystallization temperature as well as rate of crystallization, thus refining the PPR (iPP) spherulites and improving the interfacial structure between iPP spherulites. The Jeziorny approach was unsatisfactory for simulation of the non-isothermal crystallization process of the PEGC modified PPRs; however, the Mo method described consistently the crystallization kinetics over the entire isothermal process.