Effect of gamma irradiation on ethylene–octene copolymers

Two ethylene–octene copolymers (POE) were irradiated with ⁶⁰Co gamma radiation and influence of irradiation atmosphere, absorbed dose and heat treatment of samples on the crosslinking were studied. Thermal properties and crystalline morphology of non-irradiated and irradiated POE were determined by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS), respectively. The Charlesby–Pinner equation was used to describe the relationship between absorbed dose and sol fraction. The gel fraction of irradiated POE was lower and decreased with the increase of octene content when irradiated in oxygen, compared to irradiation in nitrogen atmosphere. The gel fraction increased significantly with the increasing of absorbed dose for the two copolymers. Heat treatment of samples prohibited the crosslinking of irradiated POE. The DSC results indicated that a subtle change of thermal properties of POE was observed before and after gamma irradiation at low dose. No change was found from the WAXS spectra of non-irradiated and irradiated POE. For heat-treating samples, the Charlesby–Pinner equation can not fit perfectly with the relationship between the sol fraction and absorbed dose, but it fits well with the crosslinking reaction of POE pellets.     

EFFECT OF COMPATIBILITY ON PHASE MORPHOLOGY AND ORIENTATION OF ISOTACTIC POLYPROPYLENE （IPP） BLENDS OBTAINED BY DYNAMIC PACKING INJECTION MOLDING

The effect of compatibility on phase morphology and orientation of isotactic polypropylene （iPP） blends under shear stress was investigated via dynamic packing injection molding （DPIM）. The compatibility of iPP blended with other polymers, namely, atactic polypropylene （aPP）, octane-ethylene copolymer （POE）, ethylene-propylene-diene rubber （EPDM） and poly（ethylene-co-vinyl acetate） （EVA）, have first been studied using dynamic mechanical analysis （DMA）. These blends were subjected to DPIM, which relies on the application of shear stress fields to the melt/solid interfaces during the packing stage by means of hydraulically actuated pistons. The phase morphology, orientation and mechanical properties of the injection-molded samples were characterized by SEM, 2D WAXS and Instron. For incompatible iPP/EVA blends, a much elongated and deformed EVA particles and a higher degree of iPP chain orientation were observed under the effect of shear. However, for compatible iPP/aPP blends, a less deformed and elongated aPP particles and less oriented iPP chains were deduced. It can be concluded that the compatibility between the components decreases the deformation and orientation in the polymer blends. This is most likely due to the hindering effect, resulting from the molecular entanglement and interaction in the compatible system.     

Blends of polycarbonate and ethylene-1-octylene copolymer

The mechanical properties and morphology of polycarbonate/ethylene-1-octylene copolymer (PC/POE) binary blends and PC/POE/ionomer ternary blends were investigated. The tensile strength and elongation at break of the PC/POE blends decreased with increasing the POE content. The impact strength of the PC/POE blends showed less dependence on thickness than that of PC. And the low-temperature impact strength of PC was modified effectively by addition of POE. The morphology of the PC/POE blends was observed by scanning electron microscope. The PC/POE weight ratio had a great effect on the morphology of the PC/POE blends. For the PC/POE (80/20)/ionomer ternary blends, low content (0.25 and 0.5 phr) of ionomer could increase the tensile properties of PC/POE (80/20) blend and had little effect on the impact strength. And 0.5 phr ionomer made the dispersed domain distribute more uniformly and finely than the blend without it. But with high content of ionomer, the degradation of PC made the mechanical properties of the blends deteriorate. Blending PC and ionomer proved the degradation of PC, and the molecular weight decreased with increasing the ionomer content.     

The synergistic effects of β-nucleating agent and ethylene–octene copolymer on toughening isotactic polypropylene

The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.     

Study on mechanical properties and phase morphology of polypropylene/polyolefin elastomer/magnesium hydroxide ternary composites

In this work, elastomer‐toughened polypropylene (PP)/magnesium hydroxide (MH) composites with ethylene–octene copolymer (POE) were prepared in a twin‐screw extruder and then injection‐molded. The structure, mechanical properties, phase morphology, and rheological behaviors of PP/POE/MH ternary composites were studied. The mechanical properties and fracture behaviors of PP/POE/MH ternary composites are strongly influenced by the incorporation of POE copolymer. The addition of POE causes a significant improvement in the impact strength of the composites, from 3.6 kJ/m² in untoughened composites to 47.4 kJ/m² in PP composites containing 30 phr POE. This indicates that POE is very effective in converting brittle PP composites into tough composites. Conversely, the tensile strength and the Young's modulus of the composites decrease with respect to the PP composites, as the weight fraction of POE is increased to 40 phr. Scanning electron microscopy (SEM) study shows a two‐phase morphology where POE, as droplets, is dispersed finely and uniformly in the PP matrix. The rheological behaviors show that the interfacial interaction in the composites is enhanced with increase in POE content. Interparticle interactions give rise to the formation of interparticle network. Copyright © 2009 John Wiley & Sons, Ltd.     

FRACTIONATED CRYSTALLIZATION OF HDPE IN PS/POE/HDPE/SBS BLENDS

The fractionated crystallization behavior of the minor dispersed HDPE phase in PS/POE/HDPE/SBS quaternary blends was investigated by differential scanning calorimetry (DSC).Interestingly,we found that the fractionated crystallization behavior of HDPE was molecular weight dependent.At a fixed composition,HDPE with lower molecular weight showed more obvious fractionated crystallization behavior than HDPE with higher molecular weight.This was ascribed to a finer dispersion of HDPE with lower molecular weigh...     

Organic–inorganic polymeric nanocomposites involving novel titanium tetraisopropylate in polyethylene–octene elastomer

The new nanocomposites, by means of an in situ sol–gel process consisting of metallocene polyethylene–octene elastomer (POE) and titanium tetraisopropylate (TTIP), were investigated. In addition, the acrylic acid grafted POE (POE‐g‐AA) was studied as an alternative to POE. Fourier transform infrared (FTIR) spectroscopy, a dynamic mechanical analyzer (DMA) spectrometer, an X‐ray diffractometer (XRD), differential scanning calorimetry (DSC), a thermogravimetric analyzer (TGA), an Instron mechanical tester, and a scanning electron microscope (SEM) were used to characterize and examine the samples. The results indicate that the POE‐g‐AA/TiO₂ hybrid could have a positive effect on the properties of the POE/TiO₂ hybrid because the carboxylic acid groups of acrylic acid should act as coordination sites for the titania phase to form a Ti? O? C chemical bond. The strength of interfacial bonding between the polymer chains and the ceramic phase depended on the amount of TiO₂, as shown by the change in glass‐transition temperature (T_g) with TiO₂ content. The result of mechanical and thermal tests showed that both the tensile strength and the T_g increased to a maximum value and then decreased with an increasing of TiO₂ because excess particles (e.g., greater than 10 wt % TiO₂) might cause separation or segregation between the organic and inorganic phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4272–4280, 2004     

Superstructure in segmented polyether–urethanes

The morphology of several series of segmented polyether–urethanes was studied. The “hard” segments contained urethane and urea linkages formed by 4,4′-dicyclohexylmethane diisocyanate (Hylene W) and selected aliphatic and aromatic monomeric diamines (DA). The “soft” segments were composed of oligomeric poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), or both PEO and PPO. For studying the composition–morphology relationships, the molecular weight and relative content of PEO, and the relative content of PPO were varied systematically. Different diamines were used as chain extenders. The methods of wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), polarizing microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed in the investigation. The effects of PEO content on domain formation were very significant. Calculations based on a highly simplified model indicated that, for two adjacent molecules, if two hard segments are associated with each other, the probability for the association of the next two hard segments varies inversely with the third power of soft segment length. Copolymers composed of both POE and PPO displayed enhanced domain and anisotropic superstructure. The phenomenon was interpreted in terms of polymer incompatibility. The effects on morphology of different DA's as chain extenders were tentatively accounted for by the symmetry, hydrogen bonding, and rigidity of the hard segments as well as their incompatibility with the soft segments. The formation and deformation of superstructure were of particular interest. A model was proposed to account for the formation of the resultant anisotropic structure and mechanical properties.     

高强超韧高密度聚乙烯/聚丙烯共混物性能与微相分离结构的研究

在常规注射过程中 ,难以获得超高性能的共混体系注射制件 ,已有的研究表明 ,采用高剪切注射 ,可以抬高共混体系的最低临界相容温度曲线 (LCST)的位置 ,增加相容性 .当熔体进入模具后 ,冷却的同时相容性下降 ,开始相分离 ,相分离程度发展到某一程度即可获得高性能的制件 .对于高密度聚乙烯 (HDPE)、聚丙烯 (PP)两组分均为结晶型聚合物的共混体系 ,由于其相形态与结晶形态相互制约、竞争 ,微相分离程度难以控制 ,因此对其液 液相形态与结晶过程的控制是获得共混物最终形态与性能的关键 .采用振动保压注射成型技术不仅对HDPE、PP各自力学性能有明显的自增强作用 ,而且对HDPE/PP共混体系的力学性能也有十分明显的改善 .DSC、WAXD、SEM结果表明共混体系拉伸强度的提高主要取决于试样中串晶数量和大分子链的定向程度 ,而冲击强度则主要取决于两组分微观的相分离程度 .研究结果表明 ,HDPE/PP含量为 92 / 8的试样拉伸强度为 97 1MPa,80 / 2 0试样的缺口冲击强度为 4 5 5kJ/m2 ,较静态试样分别提高 4 3倍和 9 5倍 .采用振动填充注射技术针对某一组分可以获得高强度、高韧性的共混制件 .     

Study on the application of the narrow distribution and controlled molecular weight hindered amine lighter stabilizers in poly(butylene succinate)

A series of hindered amine light stabilizer (HALS) with controlled molecular weight and narrow distribution was synthesized by reversible addition-fragmentation chain transfer(RAFT) polymerization, and its application in poly (butylene succinate) (PBS) was studied through accelerated aging experiments. The effects of different molecular weight light stabilizers on the degradation of PBS were studied. The aging degree and mechanism of PBS were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and mechanical properties testing. The extraction experiment was also carried out to study the migration of light stabilizers in PBS. Finally, the biodegradability test was conducted to study the effect of light stabilizers on biodegradation capability. The results showed that the hindered amine light stabilizer with high molecular weight can protect the PBS material to a great extent and reduce the photodegradation degree compared with the one with low molecular weight.     

Bioartificial materials based on blends of dextran and poly(vinyl alcohol-co-acrylic acid)

Bioartificial polymeric materials based on blends of dextran and poly(vinyl alcohol-co-acrylic acid) P(VA-co-AA) were prepared in the form of films and characterised to evaluate the miscibility of the natural component with the synthetic one. The idea of this work was to compatibilise PVA and dextran by introducing carboxylic groups along the PVA chains.The copolymer was synthesised and characterised in our laboratories. The results evidenced that the copolymer had an appropriate molecular weight and the content of PAA in the copolymer was 45% (weight). Then, films with different composition ratios were prepared by solution casting and analysed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), chemical imaging analysis and mechanical tests. The results obtained indicated that the introduction of carboxylic groups along the PVA chains had a positive effect on the miscibility degree of the synthetic component with the biological one.     

Role of gas delay time on the hierarchical crystalline structure and mechanical property of HDPE molded by gas-assisted injection molding

The relationship among the processing parameters, crystalline morphology, and macroscopic properties in injected molded bar becomes very complicated due to existence of temperature gradient and shear gradient along the sample thickness. To enhance the shear strength, gas-assisted injection molding (GAIM) was utilized in producing the molded bars. The aim of our research was to explore the relationship between processing conditions and the spatial variation of the hierarchy structure as well as the mechanical properties of high-density polyethylene (HDPE) obtained via GAIM. In our previous work [Wang L, Yang B, Yang W et al (2011) Colloid Polym Sci 289:1661–1671], we found that the enhancement of the gas pressure can remarkably increase the degree of molecular orientation in the HDPE samples, which turns out to improve the mechanical performances of GAIM parts. In this work, the hierarchy structure, orientation behavior, and mechanical properties of molder bars under different gas delay time were investigated using a variety of characterization techniques including rheological experiments, scanning electron microscope, tensile testing, differential scanning calorimetry, and two-dimensional wide-angle X-ray scattering. Moreover, the temperature field during the short shot stage of GAIM process was simulated using an enthalpy transformation approach. Our results indicate that these properties were intimately related to each other, and with prolonged gas delay time, GAIM samples with higher degree of orientation and improved mechanical properties were obtained.     

原位缩聚法制备碳纳米管/尼龙11复合材料

用原位缩聚法制备了碳纳米管增强的尼龙11复合材料,用X射线衍射仪、红外(FTIR)、扫描电镜(SEM)、热重(TGA)、机械拉伸测试仪等对其结构、形貌、热性能及机械性能进行了表征测试.扫描电镜结果显示碳纳米管均一地分散在尼龙11/碳纳米管复合材料中.复合材料的拉伸模量比纯尼龙11有较大的提高.当复合材料中碳纳米管含量分别为1%,5%,10%时,材料的拉伸模量分别提高了34.5%,92.9%和113,7%.同时,复合材料的储能模量也有提高.热分析结果显示当复合材料中碳纳米管含量为1%时,其失重5%和10%的温度分别由纯尼龙11的404℃、424℃提高到414℃和437℃.示差扫描量热分析(DSC)显示复合材料的结晶温度随碳纳米管的加入而升高,而结晶度则降低.     

剪切作用下PA1010/PP共混物的形态与性能研究

通过动态保压注射成型方法制备了聚酰胺1010/聚丙烯(PA1010/PP)共混物,并研究了形态与性能的关系.力学性能测试结果表明在熔体冷却过程中施加剪切可以大大提高共混物的拉伸强度、拉伸模量和缺口冲击强度,当PP的质量分数为20%时,共混物的缺口冲击强度达到21.3kJ/m2,是静态样的3倍多,拉伸强度达到50.9MPa,是静态样的1.5倍.扫描电镜(SEM)结果表明在动态保压样的横断面可以观察到剪切诱导的形态,中间是芯层,围绕着芯层的是剪切层,最外面是皮层,相区尺寸显著减小、分散相分散更趋均匀,特别是PP的质量分数为20%时,相区尺寸从原来的约3.9μm降低到约1.4μm.动态保压样机械性能的提高归因于剪切作用下独特相形态的形成,分子链沿流动方向的取向是拉伸强度提高的主要原因,而剪切使分散相颗粒变小和剪切层中分子链的取向是冲击强度提高的主要原因.     

MORPHOLOGY AND MECHANICAL PROPERTIES OF POLYPROPYLENE WITH in situ FORMED POLYAMIDE-6 FIBRILS

in situ Fibril formation of polyamide-6(PA6)in isotropic polypropylene(iPP)was first fabricated using a slit die extrusion and hot stretching process.Then the prepared materials were subjected to injection molding in the temperature range higher than the melting temperature of iPP but lower than that of PA6.The obtained injection-molded samples were characterized via scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and two-dimensional wide- angle X-ray scattering(2D-WAXS).Mechanical properties were also investigated.The SEM result shows that the optimum fibril formation could be only achieved in the range of 20 wt% to 30 wt% of PA6 content for the studied system.The fibril morphology changes along the sample thickness in the injection-molded bars.The fibril morphology in the skin layer was better than that in the core layer.2D-WAXS results showed that the orientation of PP decreased with the increase of PA6 content,which indicated that the orientation of PP was confined by PA6 fibrils.Combined consideration of mechanical properties and morphology indicates that only PP/PA6 composites with 20 wt% of PA6 content show better properties because of the better fibril morphology and PP chain orientation.     

Crystallization kinetics of polypropylene/ethylene–octene copolymer blends

Blends of polypropylene and ethylene–octene copolymers (EOC) were investigated by transmission electron microscopy, optical microscopy and differential scanning calorimetry (DSC). The main focus was on phase morphology and crystallization for blends containing EOC with different octene content (28, 37 and 52 wt.%). Also, for a given octene content (37 wt.%), the effect of molecular weight (115, 180, 229k) of EOC on morphology was observed. The largest particles were found in the blend with EOC-28 and the smallest with EOC-52. This blend with the smallest particles exhibits the fastest crystallization kinetics by two independent methods, optical microscopy and DSC. This behavior was explained by a model. Crystallizing polypropylene lamellae have to travel a longer distance going around large particles, which slows down overall crystallization growth rate. In the case of smaller particles, the obstacles are smaller and the crystallization is faster.     

EFFECT OF MOLECULAR WEIGHT OF PDMS ON MORPHOLOGY AND MECHANICAL PROPERTIES OF PP/PDMS BLENDS

A series of polydimethylsiloxane (PDMS) with varied molecular weights (M_w=3×10~6,1×10~6 and 0.5×10~6) were melt blended with PP to investigate the effect of PDMS molecular weight (MW) on the morphology and mechanical properties of PP/PDMS blends.Scanning electron microscopic (SEM) examination showed that the size of PDMS domains was dependent on the MW of PDMS.It was found that the lower the value of PDMS MW,the better dispersion of the PDMS domains in the PP matrix.Tensile and Izod impact tests reveale...     

Effect of natural weather on the structure and properties of polylactide/Cloisite 30B nanocomposites

The degradation of polylactide (PLA)/Cloisite 30B nanocomposites under natural weathering was investigated as a function of clay loadings (1, 3 and 5 wt.%) for up to 130 days using Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), nanoindentation measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). For comparative purposes, the neat PLA was also considered. The FT-IR results showed that the photo-oxidation mechanism of PLA was not modified in the presence of Cloisite 30B, but only the degradation rates were accelerated. Moreover, the photo-oxidative degradation of PLA nanocomposite samples led to the formation of vinyl unsaturation, carbonyls, anhydrides and hydroperoxides groups as a result of the occurrence of several chemical mechanisms simultaneously. The decrease of the weight-average molecular weight, and the number-average molecular weight associated with an enhanced polydispersity of the nanocomposite samples indicated that chain scission was the most prominent phenomenon in natural weathering. The thermal degradation of the PLA was faster in the presence of clay. Modulus and hardness measured by nanoindentation increased slightly with exposure time for both neat PLA and PLA nanocomposite samples; the increase is also a function of the clay content. Finally, the weathering effect on the morphology of exposed samples observed by SEM revealed that the fractured surfaces exhibited many voids and cracks. These defects were much more pronounced for the PLA nanocomposites.     

Improving polyethylene–octene elastomer/chitosan by graftation of acrylic acid onto polyethylene–octene elastomer—mechanical properties and biodegradability examination and composites characterization

In this study, the properties of polyethylene–octene elastomer/chitosan (POE/chitosan) and acrylic acid (AA)‐grafted‐polyethylene–octene elastomer/chitosan (POE‐g‐AA/chitosan) were examined using various characterizing instruments. Mechanical and thermal properties of POE deteriorated noticeably when it was blended with chitosan, due to the unsatisfactory compatibility between the two phases. The greater compatibility of POE‐g‐AA with chitosan, due to the formation of ester carbonyl and imide groups, led to a much better dispersion and homogeneity of chitosan in the POE‐g‐AA matrix and consequently to noticeably better mechanical properties. Furthermore, with a lower melting point temperature, the POE‐g‐AA/chitosan blend was more easily processed than POE/chitosan. POE‐g‐AA/chitosan had a higher water resistance than POE/chitosan. Both blends suffered weight loss when buried in soil, especially at high levels of chitosan substitution, indicating that both were biodegradable. The mechanical properties of both blends, such as tensile strength and elongation at break, also deteriorated after being buried in soil. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3882–3891, 2003     

Fabrication of Single Wall Carbon Nanotubes-Based Poly(vinyl butyral) Nanocomposites with Enhanced Mechanical and Thermal Properties

In this research, poly(vinyl butyral) (PVB)/single wall carbon nanotubes (SWCNT) composites were prepared via solution blending method. Dispersion degree of SWCNT in the composites was characterized by Scanning Electron Microscopy (SEM) and mechanical properties were measured with tensile testing. Thermal degradation of composites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). SEM analysis confirmed good dispersion of the nanotubes in the PVB. The tensile tests showed significant increases in mechanical properties such as exceptional improvement in tensile strength, Young's modulus and flexibility for the composites compared to PVB at low SWCNT content.The TGA curves indicated that adding SWCNT improved the thermal stability of the PVB significantly and the degradation of the polymer matrix shifted to the higher temperatures. For the sample containing 0.6 wt%, an increase of 171% in modulus and a 258.4% enhancement of tensile strength were achieved. Also, elongation at break increased 28.7% at this loading. In fact, intrinsic properties of nanotubes caused enhancement of strength and flexibility simultaneously. Also, for this composite, T_onset and T_max enhanced remarkably and weight loss reduced greatly and residue at 600°C increased to high values. These results are promising for application of the PVB in industry.