Post-irradiation degradation of polypropylene

We present the mechanical changes (elongation at break, tensile strength, modulus of elasticity) and electrical changes (volume and surface resistivity, tg, , breakdown voltage) ofisotactic polypropylene (PP) due to -radiation. Ageing of PP was achieved in air by using a¹³⁷Cs -source with 400 Ci activity; the dose rate was of 8·10⁴ rad/h, and the integrated doses ranged from 2 to 160 Mrad. Severe deterioration of mechanical properties was observed. The changes of electrical properties were not as significant as those of mechanical characteristics. These variations are caused by the increase in density of crosslinking chain-scission and by oxidative processes. The rate of extent of degradations has been evaluated by the growth of the hyydroxy and carbonylbands in the IR spectrum By using FTIR mapping, we have also investigated the degradation of PP which had been irradiated in air 15 years ago. We determined the contour lines of FTIR absorption bands of carbonyl groups at different regions of the cross-section of an irradiated sample. Dust particles of irradiated brittle PP were also studied. The FTIR showed that the carbonyl band is broad, indicating a mixtures of many different functional groups (ester, acid, ketone, lactones). We determined also the gel content at different irradiation doses.     

Microhardness and thermal stability of compatibilized LDPE/PA6 blends

Microhardness tests, water absorption and thermogravimetric measurements have been performed on blends of low density polyethylene (LDPE) with different molar mass and polyamide 6 (PA6) compatibilized with 2 pph poly(ethylene-co-acrylic acid) (Escor 5001 by Exxon). The negative deviation of Vickers microhardness from the additivity has been interpreted by changes in the crystallinity of the blend components. The hardness values of the compatibilized blends that are lower than those of the corresponding uncompatibilized blends have been explained by the decrease of the degree of crystallinity of PA6 phase in the presence of Escor. The molar mass of LDPE almost does not influence on the hardness values. The lower water absorption of the compatibilized blends, caused by the formation of a copolymer between PA6 and the compatibilizer leads to microhardness values of the wet compatibilized blends higher than those of the corresponding uncompatibilized blends. The thermogravimetric measurements demonstrate that the thermal stability of blends increases in the presence of 2 pph Escor 5001. The results confirm the compatibilizing efficiency of Escor 5001 towards LDPE/PA6 blends in a wide composition range.     

Modeling Equilibrium Behavior of Nylon 6, Nylon 6,6 and Nylon 6/6,6 Copolymer

Nylon 6 and nylon 6,6 reaction equilibria depend in a complex way on water concentration and temperature. For example, data sets from six research groups reveal that the apparent equilibrium constant for polycondensation increases with water at low water concentrations, reaches a maximum, and then decreases as the water concentration rises further. In this article, semi‐empirical expressions are proposed to describe the experimentally observed equilibrium behavior for the five main reactions that occur during nylon 6 and nylon 6,6 polymerization. Nine side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends are used to develop expressions that account for the influence of both water and temperature on these equilibrium constants. Excellent fit to the data, over the entire range of the available nylon 6 and nylon 6,6 literature data, suggests that the proposed equations will be helpful for modeling reaction equilibria for nylon 6/6,6 copolymerization.     

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B^® and Nanofil 784^®, and a sodium MMT (Cloisite Na^®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis-gas-mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B^® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784^® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B^®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784^®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes -OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.     

Thermal-oxidative degradation of polyamide 6,6 containing metal salts

The thermal-oxidative stability of oven aged polyamide 6,6 (PA6,6) doped with Co, Cu, Ni and Zn chlorides combined with KI was examined. Aging caused a depression in melting temperature and an increase in enthalpy of fusion of PA6,6 films due to the formation of a strongly degraded crystalline fraction with a lower molecular weight. A build-up of carbonyl absorption in the range 1700-1780 cm⁻¹ due to primary and secondary photo-oxidation products was detected. The kinetics of carbonyl accumulation was affected by the morphology of the samples, and it was observed that at a later stage of aging the crystalline phase was also involved in the oxidation process. The above mentioned changes were greatest in the case of neat, Co and Ni doped polymer, suggesting that these metal salts acted as pro-oxidants. On the other hand, the use of Cu and Zn chlorides brought about a substantial increase in long-term polymer stabilization.Tensile tests revealed a large reduction in ductility as a result of aging for neat, Co and Ni doped polymer, whereas long-term retention of tensile properties was found for the polymer stabilized with Cu and Zn. The presence of the metal salts combined with KI led to increased stabilization for chlorides of Ni, and Co, owing to the participation of KI in non-radical decomposition of peroxides. No effect due to KI was observed for ZnCl₂.     

Thermal properties of PA 6 and PA 6 modified with copolyamides and layered silicates

This article focuses on the thermal properties of PA 6 and additives, i.e. ternary copolyamides, concentrates consisting of binary or ternary copolyamides + nanoadditive montmorillonite Bentonite 11958 or Cloisite 15A and PA 6 fibres modified with Bentonite, copolyamide and concentrate. The copolyamides are prepared from ε-caprolactam as a major comonomer and nylon salts AN2 from adipic acid + 1-(2-aminoethyl)piperazine and ADETA from adipic acid + diethylenetriamine. All copolyamides and concentrates exhibit lower melting temperatures T _m and lower melting enthalpies ΔH _m compared to neat PA 6. PA 6 fibres modified with 0.25–2.5 wt% MMT exhibit higher melting enthalpies in comparison with unmodified PA 6 fibres. PA 6 fibres modified with 10 wt% of ternary copolyamide containing 21.4 wt% of comonomers AN2 and ADETA have higher melting enthalpy as well. PA 6 fibres modified with 10 and 20 wt% of concentrate containing the same ternary copolyamide + 5 wt% of MMT have higher melting enthalpies and higher tensile strength in comparison with these characteristics of unmodified PA 6 fibres.     

Improved Kinetic Rate Constants for Nylon 6, Nylon 6,6, and Nylon 6/6,6 Copolymer

Nylon 6 and 6,6 literature data are collected over a wide range of water concentrations and temperatures (0 ≤ [W]₀ ≤ 40.8 wt%, 200 ≤ T ≤300 °C) and used to fit parameters in an updated batch reactor model. The resulting copolymerization model uses side reactions to account for the complex influence of water on kinetics and reaction equilibria. The proposed parameter estimates result in a significant improvement in the fit to the data, corresponding to a 73% reduction in the weighted‐least‐squares objective function compared to when the parameters of Arai et al. are used. Copolymerization simulations are conducted at industrially relevant conditions, shedding light on the complex influence of water and on the potential to include waste nylon 6 cyclic dimer in the feedstock. The model and parameter estimates will be helpful in future models of nylon 6/6,6 copolymerization in continuous reactor systems.     

Generation and trapping of 6,6-dimethyl-6-silafulvene

Flow pyrolysis of allylcyclopentadienyldimethylsilane and of 1-dimethylmethoxysilyl-1-trimethylsilylcyclopentadiene afforded 6, 6-dimethyl-6-silafulvene which was either trapped or allowed to dimerize.     

Ammonium sulfamate flame retarded polyamide 6: Morphology and thermal degradation

<正>The effect of ammonium sulfamate(AS) content on the flame retardancy of polyamide 6(PA6) was studied.It is found that the limiting oxygen index(LOI) of PA6 increases with the increase of AS content and the flame retardancy of PA6 is significantly improved.The morphology of the residues after combustion was examined by means of scanning electron microscopy(SEM).SEM results show that AS facilitates the formation of the intumescent char layer with honeycomb-like structure,which inhibits the transfer of heat and mass,and thus improves the flame retardancy of PA6.The thermal degradation of AS flame retarded PA6 was studied by thermogravimetric analysis(TGA).The Kissinger method was applied to estimate the activation energy(E_a) of the degradation.The activation energy of the thermal degradation of PA6 decreases by adding AS,indicating that AS can promote the degradation of PA6.     

Selective degradation of nylon 6,6. I. Description of the degradation technique and preliminary morphological characterization

A technique for the selective degradation of amorphous regions in nylon 6,6 is reported. Samples of unoriented film and single-crystal mats have been subjected to selective degradation by refluxing in hydrazine. Weight loss, viscosity-average molecular weight, density, and small-angle x-ray scattering of these samples were monitored as a function of time of degradation. In addition, selected samples have been investigated by gel permeation chromatography (GPC) and transmission electron microscopy. Based on the results of these investigations it is concluded that the reported degradation technique is unique in that the debris is not monodisperse in molecular weight distribution. The Weight loss, density, small-angle x-ray scattering, and microscopy data demonstrate that the unordered or noncrystalline regions of the material are removed upon treatement. However, the relatively high molecular weight and broad molecular weight distribution of the debris indicate that regular folds at lamellar surfaces are intact after degradation treatment.     

The effect of hBN on the flame retardancy and thermal stability of P-N flame retardant PA6

A novel thermally conductive Polyamide 6 (PA6) with good fire resistance was prepared by introducing a phosphorous-nitrogen flame retardant (FR) and platelet-shaped hexagonal boron nitride (hBN) into the matrix. With high thermal conductivity and good flame retardancy, the material is suitable for applications in electronic and electrical devices. The limiting oxygen index (LOI) changes for various loadings content of FR. However this formulation still does not show an ideal fire resistance, due to the appearance of melt dripping behavior during the UL 94 test. With the extra introduction of 3 vol% and 5 vol% hBN, the melt dripping behavior during the burning process completely disappeared. The hBN also increased the thermal conductivity. Furthermore PA6 compounded with FR and hBN showed a better thermal stability than neat PA6. The morphology of the char residues was investigated by scanning electron microscopy (SEM). The flaky hBN acted as the framework in the char structure and the rigid hBN could effectively break the bubble-shaped char on the surface of the residues which resulted in the enhancement of the strength and compactness of the char.     

阻燃玻纤增强尼龙66的制备及性能研究

研究了用环保型阻燃剂溴化聚苯乙烯(PBS)、三氧化二锑(Sb2O3)、玻璃纤维(GF)以及功能助剂通过双螺杆挤出机制备出27%(wt)玻纤含量的高性能环保型阻燃增强尼龙66(PA66)复合材料。DSC和TGA结果表明,玻纤和阻燃剂等填料阻碍PA66结晶过程中分子链段的运动,降低其结晶能力,同时降低了复合材料的热稳定性;SEM结果表明复合材料各组分之间的界面粘结力较强,填料在基体中的分散性较好;力学和阻燃性能测试结果表明,与PA66相比,复合材料的拉伸强度、弯曲强度和弯曲模量分别提高了100%、110%和250%,阻燃性能达到V-0级(0.8 mm)。     

Characterisation of filled and recycled PA6

Filled PA6 are important representatives of engineering plastics used in automotive components. Nowadays, the demand of plastic recycled grades is increasing in this branch of industry but polymer recycling can undergo thermomechanical degradation processes with the results of a poor secondary material, regarding its properties. In this paper an investigation of thermal, mechanical (tensile, flexural and impact tests) and rheological properties of a sample of recycled and filled PA6, is reported as a function of the number of reprocessing operations (3 times) and of the fraction of recycled material (15, 30 and 50%) added to the virgin material. Recycled PA6, used in this study, comes from fibre grade production waste. Material was filled with 20% glass beads and 10% glass fibre, according to the specifications of the application, mainly to obtain a lower shrinkage in the end product. This work also shows that the mineral fraction, not being degraded during the injection process, allows better recyclability to the filled material. The properties of the recycled material remain below the virgin, and the best combination of both appears to be the mixture with 30w.% recycled fraction, which shows a lost of properties similar to 3 reprocessing operations.     

PA66/PA12/clay based nanocomposites: structure and thermal properties

In a previous paper the structure and the physical properties of melt mixed polyamide 66 (PA66)/polyamide 12 (PA12) blends characterized by different compositions have been investigated by means of morphological and physical analyses. A low amount of organically‐modified layered silicate (OMLS, 4 wt%) was introduced in order to evaluate its effect on blends structure and components miscibility. This paper completes the characterization of these materials investigating their thermal properties by means of standard and modulated differential scanning calorimetry (DSC, MDSC), dynamic‐mechanical analysis (DMA), and thermogravimetric analysis (TGA). The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed by analyzing the glass transition temperature (T_g) dependence on composition as well as the existence of strong segmental interactions between polymer components. A compatibilizing action of OMLS has been observed because of a lowering of interfacial tension avoiding coalescence phenomena between particles during melt mixing process. Copyright © 2010 John Wiley & Sons, Ltd.     

尼龙1010／6及尼龙1010／66动态力学分析

通过动态力学参数温度谱,研究了尼龙１０１０／６、尼龙１０１０／６６两个共聚物系列的动态力学参数与组成的关系。研究表明尼龙１０１０／６、尼龙１０１０／６６在测试温度范围内出现三个明显的松驰转变：α、β、γ,其中各共聚物的β、γ松驰温度相差不大,而α松驰温度随组成改变有明显改变。一般均聚物的α松驰温度较高,共聚物的α松驰温度均低于均聚物,二个系列以尼龙１０１０／６（２９．８／７０．２）、尼龙１０１０／     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

Structure, morphology, thermal stability and carbonization mechanism studies of electrospun PA6/Fe-OMT nanocomposite fibers

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide 6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) nanocomposite fibers were prepared by a facile compounding and electrospinning. The catalyzing carbonization studies of the Fe-OMT based on PA6 nanocomposite fibers were performed. It was found from High-resolution electron microscopic (HREM) observations that the silicate clay layers were well dispersed within the nanocomposite fibers and was oriented along the fiber axis. The Scanning electron microscopic (SEM) images indicated that the nanofibers were randomly distributed to form the fibrous web and the Fe-OMT additives decreased the diameters of nanocomposite fibers. The Thermogravimetric analyses (TGA) revealed that the loading of the Fe-OMT led to the crosslinking of the PA6, promoted the charred residue yield and catalytic graphitization effect. The structure and morphology of the purified charred residue, characterized by XRD, HREM, Selected area electron diffraction (SAED) and Laser Raman spectroscopic (LR), approved further the presence of graphite sheets. The possible catalyzing carbonization mechanisms included: (1) catalyzing effect of the Fe³⁺, which promoted the crosslinking of polymer, (2) Hofmann degradation of the Fe-OMT, whose degraded products had also positive role in promoting crosslinking reactions, (3) gas barrier properties of the nano-dispersed silicate clay layers stopped or reduced the releases of the pyrolytic products, which was dehydrogenated and aromatized to form graphite.     

Selective degradation of nylon 6,6. II. Application of the degradation technique to commercially drawn fibers

Treatement with hydrazine was used to investigate the crystalline morophology of commercially drawn nylon 6,6 fibers. Electron microscopic investigation revealed a stacked lamellar structure for the debris of a highly oriented, rapidly drawn fiber. However, the high molecular weight range of the gel permeation chromatogram of this same oriented fiber indicated the presence of high molecular weight material. This is thought to be due to the production of rod-like, partially extended regions during drawing.     

Influence of SEBS-g-MA on morphology, mechanical, and thermal properties of PA6/PP/organoclay nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organically modified clay (organoclay) toughened with maleated styrene-ethylene-butylene-styrene (SEBS-g-MA) were prepared by melt compounding using co-rotating twin-screw extruder followed by injection molding. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize the structure of the nanocomposites. The mechanical properties of the nanocomposites were determined by tensile, flexural, and notched Izod impact tests. The single edge notch three point bending test was used to evaluate the fracture toughness of SEBS-g-MA toughened PA6/PP nanocomposites. Thermal properties were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). XRD and TEM results indicated the formation of the exfoliated structure for the PA6/PP/organoclay nanocomposites with and without SEBS-g-MA. With the exception of stiffness and strength, the addition of SEBS-g-MA into the PA6/PP/organoclay nanocomposites increased ductility, impact strength and fracture toughness. The elongation at break and fracture toughness of PA6/PP blends and nanocomposites were increased with increasing the testing speed, whereas tensile strength was decreased. The increase in ductility and fracture toughness at high testing speed could be attributed to the thermal blunting mechanism in front of crack tip. DSC results revealed that the presence of SEBS-g-MA had negligible effect on the melting and crystallization behavior of the PA6/PP/organoclay nanocomposites. TGA results showed that the incorporation of SEBS-g-MA increased the thermal stability of the nanocomposite.