Photooxidation of polypropylene/layered double hydroxide nanocomposites: Influence of intralamellar cations

The influence of layered double hydroxides (LDHs) on the photooxidation of polypropylene (PP)/LDH nanocomposites was studied under irradiation at long wavelengths (λ > 300 nm, 60 °C and in the presence of oxygen). The influence of hybrid LDHs containing different divalent cations (Mg, Zn or both Mg and Zn) on the photooxidation mechanism of PP and on the rates of oxidation of the matrix was characterised based on infrared analysis. The presence of LDHs modifies the photoproducts accumulating in the PP and the rates of oxidation of PP were changed depending on the divalent cations in the LDH layers. Whereas natural clays, such as montmorillonite (MMt), can lead to a faster degradation of the materials, LDHs (Zn₂-Al-DS, for example) appear to have no inductive effect on polymer oxidation.     

Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

聚丙烯/多壁碳纳米管复合材料的热性能和流变性能

用熔融共混法制备了聚丙烯多壁碳纳米管(PP MWNTs)复合材料,TGA研究表明在氮气气氛下碳纳米管显著增加了聚丙烯基体的热稳定性.3wt%MWNTs可使PP热分解起始温度提高44℃.非等温结晶研究表明MWNTs对PP基体的结晶行为没有明显的影响.流变测试结果表明PP MWNTs复合材料的储能模量G′和损耗模量G″随着MWNTs含量增加逐渐增大.1wt%MWNTs的PP聚合物的零剪切粘度最低,5wt%MWNTs的PP聚合物的零剪切粘度最高,PP和3wt%MWNTs的PP纳米聚合物的零剪切粘度居于二者之间,随着频率的增加,剪切稀化作用越来越明显,呈现出假塑性流体行为.含5wt%MWNTs的PP复合材料的体积和表面电阻率与纯PP相比分别下降了9个和4个数量级,表明少量的MWNTs可以显著改变PP的电学性能.     

Influence of functional nanoparticles on the photostability of polymer materials: Recent progress and further applications

The photochemical behaviour of polymer–nanoparticles/nanocomposites has been studied depending on the geometry of the nanofiller and an overview of the studies reported in the last decade is tentatively given. Depending on their functionality, nanoparticles can impact the durability of the nanocomposite materials under light irradiation. The behaviour to UV-light exposure in presence of oxygen of various types of nanocomposites with clays, LDH and carbon nanotubes has been investigated and recent progress on the influence of functional nanoparticles on the polymer photodegradation is reported. The influence of photocatalytic (ZnO and TiO₂) nanoparticles and phosphors on the photooxidation of the polymeric matrix and the durability of the material properties are characterized. From a general point of view, the stabilization strategy of polymer nanocomposites must be adapted depending on the nanofiller.     

Photochemical stabilization of linear low-density polyethylene/clay nanocomposites: Towards durable nanocomposites

This article reports a study of the chemical modifications of LLDPE/nanoblend nanocomposites exposed to UV light in conditions of artificially accelerated ageing and natural weathering. Analysis by infrared spectroscopy of the chemical modifications produced by photoageing shows that the presence of an organo-clay leads to the decrease of the oxidation induction time of the polymer (LLDPE), which results in lower durability of the nanocomposites. Protection against photooxidation was tested with different kinds of UV stabilizers and with a metal deactivator. It is shown that the metal deactivator is very efficient in stabilizing the nanocomposite since it totally cancels the prodegradant effect of the organo-clay. This confirms the role played by iron impurities in natural clays. The use of a metal deactivator offers a new insight into the stabilization strategy for nanocomposites.     

Isotactic polypropylene/carbon nanotube composites prepared by latex technology: Electrical conductivity study

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1] and [2], render this type of nanocomposites extremely attractive from a technological point of view.     

Multiwalled carbon nanotube promotes crystallisation while preserving co-continuous phase morphology of polycarbonate/polypropylene blend

The influence of multiwalled carbon nanotubes (MWCNTs) on phase morphology, lamellar structure, thermal stability, melting behaviour and isothermal crystallisation kinetics of polycarbonate/polypropylene (PC/PP) blend nanocomposites has been investigated. Both neat blends and PC/PP (60/40)/MWCNT nanocomposites were prepared by melt mixing method. Morphological analyses were performed by high-resolution X-ray micro-computed tomography and scanning electron microscopy. The co-continuous morphology of the blend was retained irrespective of MWCNT loading. In addition, a substantial refinement in the co-continuous structure was observed. Wide angle and small angle X-ray scattering studies were used to analyse the structural properties of the blend nanocomposites. The addition of MWCNT increases the long period of polypropylene. The influence of addition of MWCNT on the crystallisation temperature and equilibrium melting temperature (Tm°) of polypropylene was followed. The MWCNTs promote crystallisation rate of polypropylene in the blend nanocomposites.     

Effect of UV Irradiation on Gas Permeability in Heterophasic Ethylene-Propylene Copolymer Films

Abstract

The permeability variations of carbon dioxide, oxygen, and nitrogen through isotactic polypropylene, heterophasic ethylene-propylene (E-P) copolymers, and polyethylene films were measured during photo-oxidation using polychromatic light at 60°C in air. For polypropylenebased samples the permeability decreases with increasing photooxidation, whereas for polyethylene and an elastomeric fraction from a heterophasic E-P copolymer an increase in permeability with photooxidation is observed.     

Photooxidation of vulcanized EPDM/montmorillonite nanocomposites

The photooxidation of a vulcanized ethylene-propylene-diene monomer (EPDM)/montmorillonite nanocomposite as well as EPDM/nanocomposite with stabilizers was studied under accelerated UV-light irradiation (λ ≥ 300 nm, 60 °C) for different times. The development of functional groups during oxidation was monitored by infrared spectroscopy. Photodegradation of the neat polymer and composites took place and the increases of absorbance in hydroxyl and carbonyl groups with irradiation times and also the decreases of the EPDM unsaturations were measured. The data indicated that the photooxidation products were not changed in the presence of the nanofiller. However, the presence of MMt was observed to dramatically enhance the rate of photooxidation of EPDM with a shortening of the oxidation induction time, leading to a decrease of the durability of the nanocomposites. On the other hand, it was observed that addition of stabilizers, either Tinuvin P or 2-mercaptobenzimidazole, was efficient in inhibiting the degradative effect of MMt.     

Effect of manganese nanoparticles on the mechanical, thermal and fire properties of polypropylene multifilament yarn

Polypropylene filled with 10 wt% of inorganic nanoparticles has been prepared by melt blending. The fillers investigated were manganese oxides (MnO and Mn₂O₃) and manganese oxalate (MnC₂O₄). The morphology and thermal stability of these nanocomposites have been studied by transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The experimental results reveal that the addition of 10 wt% manganese oxides improves the thermal stability in air of polypropylene by about 70-80 °C. In a second step, these nanocomposites have been processed by melt spinning in order to produce multifilament yarn. The mechanical properties of these filaments have then been characterized. It is shown that just the addition of Mn₂O₃ improves the mechanical properties of polypropylene filaments. The flammability of these nanocomposites used as knitted fabrics has finally been evaluated with a mass loss calorimeter at 35 kW/m². This kind of experiment has not revealed a real improvement of fire properties.     

Influence of nanodispersed hydrotalcite on polypropylene photooxidation

Nanocomposites containing hydrotalcite and prepared by melt compounding with polypropylene were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies.The presence of hydrotalcite was shown to change the global rate of photooxidation of polypropylene by reducing the oxidation induction time and increasing the oxidation rate. The differences of the oxidation induction time disappeared after solvent extraction of the antioxidant. They were attributed to a quenching of the antioxidant activity resulting from a migration onto the filler surface induced by the preferential interaction with the polar hydrotalcite. Extracting the antioxidant did not change the oxidation rate at the permanent regime. The increase of the oxidation rate was attributed to transition metal ions, present as impurities in hydrotalcite, which can accelerate the oxidation of the polymer by various mechanisms including a catalysed decomposition of hydroperoxides.     

Influence of MWNT on Polypropylene and Polyethylene Photooxidation

Summary: Nanocomposites containing multiwall carbon nanotubes (MWNT) were prepared by melt compounding with polypropylene and polyethylene. The samples were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by FT-IR spectroscopy.The behaviour of nanocomposites containing MWNT depends from the type of polymer and presence or absence of antioxidant. The presence of MWNT affect photooxidation of the two polymers working as an UV-screener on the other hand the increase of thermal oxidation provoked by conversion of photon energy into thermal partially balance the decrease of positive effects on oxidation rate. The negative effects can be minimized by the presence of antioxidants that show interesting synergistic effects with MWNT.     

聚丙烯/累托石纳米复合材料的非等温结晶动力学研究

在双螺杆挤出机上熔融共混制备了聚丙烯 (PP) 有机累托石 (OREC)纳米复合材料 ,采用广角X 射线衍射 (WAXD)定性地分析了PP OREC纳米复合材料及纯PP的结晶形态 ,由半峰宽定性地判断了对应晶面法向的晶粒的大小 .结果表明有机累托石没有改变聚丙烯的结晶晶型 (纳米复合材料主要还是α晶型 ) ,但是细化了晶粒的尺寸 .采用差示扫描量热法 (DSC)定量地研究了复合材料的非等温熔融结晶动力学 ,对所得数据分别用Jeziorny法的Mo法进行了处理 ,表明非等温结晶动力学参数Zc 及Avrami指数n随冷却速率的增加而增加 ,复合材料的Avrami指数n大于纯PP的n ;对相同配比的纳米复合材料 ,随着结晶度的增加 ,单位结晶时间里达到一定结晶度所需要的降温速率F(T)增大 ,对同一个设定的结晶度 ,纳米复合材料的F(T)比纯PP的小 ,说明需要的降温速率减小 .所有这些均说明有机累托石可作为聚丙烯的结晶成核剂 .     

Polymer/carbon nanotube nanocomposites: Influence of carbon nanotubes on EVA photodegradation

The influence of carbon nanotubes on the photodegradation of EVA/carbon nanotube nanocomposites was studied by irradiation under photooxidative conditions (at λ > 300 nm, at 60 °C and in the presence of oxygen). The influence of the nanotubes on both the photooxidation mechanism of EVA and the rates of oxidation of the matrix was characterized on the basis of infrared analysis. On one hand, it was shown that the carbon nanotubes act as inner filters and antioxidants, which contribute to reduction in the rate of photooxidation of the polymeric matrix. On the other hand, it was shown that light absorption could provoke an increase in the local temperature and then induce the photooxidation of the polymer. The competition between these three effects determines the global rate of photooxidation of the polymeric matrix. Several factors are involved, the concentration of the carbon nanotubes, the morphology of the nanotubes and the functionalization of the nanotube surface.     

Sustainable nanocomposites based on halloysite nanotubes and pectin/polyethylene glycol blend

This study was focused on the preparation and characterization of biofilms based on pectin/polyethylene glycol 20000 (PEG) blend and halloysite nanotubes (HNTs). The obtained blends loaded with a natural nanoclay are proposed as sustainable alternative to the polymers produced from non-renewable resources such as fossil fuels. Properties of technological interest have been monitored and they were correlated to the structural features of the nanocomposites. It turned out that the wettability of the films can be tuned by changing the composition and the distribution of HNTs into the material as well as the surface roughness. The tensile properties of the blend are enhanced by the presence of the nanoclays. The PEG crystallinity is reduced by the nanoparticles and preserved if a certain amount of pectin is added.     

MEH-PPV/层状硅酸盐纳米复合物的光物理性质

用稳态和时间分辨荧光光谱技术,结合13C固体NMR研究了共轭高分子聚2-甲氧基-5-(2′-乙基-己氧基)-1,4-亚苯基亚乙烯基(MEH-PPV)在层状硅酸盐(montmorillonite,MMT)纳米片层受限空间中的聚集态结构、性质和对外场的响应特性.结果表明,MMT二维纳米受限空间对MEH-PPV自聚集的阻隔作用,减少了MEH-PPV链间近程相互作用较强的H-聚集,增加了J-聚集含量.结果激发态激子自淬灭的几率降低,稳态荧光量子产率提高和动态荧光寿命的延长;通过共轭碳原子的自旋-晶格弛豫时间的测定,观察了MMT对聚合物分子运动的影响,并由此探讨了MEH-PPV凝聚态与光物理性质的关系.     

Investigation of water absorption in clay-reinforced polypropylene nanocomposites

The behaviour of polypropylene nanocomposites containing different amounts of commercial nanoclay upon exposure to distilled water and sea water at different temperatures was investigated and compared with that of neat polypropylene. In the initial stages, the weight gain (moisture absorption) follows Fick's second law, but at longer times deviations are observed owing to physical degradation and in some cases a loss of mass. Distilled water diffuses more rapidly than sea water. As the nanoclay content increases, both the rate of moisture absorption and the maximum moisture content increase, owing to the hydrophilic nature of the nanoclay and the added compatibilizing agent. Although the moisture absorption decreases the flexural properties of both the nanocomposites and neat PP, because the unexposed (as-moulded) nanocomposites are significantly superior to the neat PP they remain so even after prolonged exposure.     

ACNT/C纳米复合材料导热性能及其机理的初步研究

以定向碳纳米管(ACNT)阵列为骨架, 利用化学气相渗(CVI)工艺制备了新型的定向碳纳米管/碳(ACNT/C)纳米复合材料. 导热性能测试结果表明, 密度为1.47 g/cm3的ACNT/C纳米复合材料的热扩散系数和热导率均比相同工艺条件下密度为1.50 g/cm3的传统C/C复合材料高4～6倍; 经过2 500 ℃热处理, ACNT/C的热导率接近140 W/(m·K), 而C/C仅为40 W/(m·K)左右. 这主要是由于CNT对热解炭结晶存在诱导作用, 同时特殊的准一维结构也减少了热扩散时“声子”的散射.     

Formation of polymer-bonded nitroxyl radicals in the UV stabilization of polypropylene by a bifunctional hindered amine light stabilizer

The formation of polymer-bonded stabilizer derivatives during photooxidation of isotactic polypropylene, which contains the hindered amine light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and the corresponding bisnitroxyl radical, was investigated. The photooxidized polypropylene films that contain these additives were studied by ESR, IR, and nitrogen analysis before and after exhaustive solvent extraction of the photooxidized films. ESR showed that under the conditions in use a maximum of 20% of the nitroxyl radicals formed from the hindered amine was bonded to the polymer chain. Regeneration of nitroxyl radicals from the polymer-bonded stabilizer derivatives under photooxidative conditions indicated that the stabilizer was bonded to the polymer chain by O-alkyl-substituted hydroxylamine linkages >N? O? PP.     

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.