Silane and silazane surface modification of recycled glass fibers for polypropylene composites

Glass fiber (GF) composites are one of the significant challenges in recycling thermoset materials. After pyrolysis, the glass fibers lack sufficient strength and show poor matrix compatibility. Here we have investigated a series of multifunctional silane and silazane agents for surface modification of recycled glass fibers that provide a combination of hydrophobic properties and residual reactive groups on the surface. This allowed testing of interfacial effects from the surface modification as well as a potential synergistic compatibilization using maleated PP (MAPP). The treated GFs were used to prepare new polypropylene (PP) composites by multiple extrusion steps, resulting in a series of composites where the dispersion efficiency was attributed mainly to the surface chemistry and compatibilization effects. The amino-silane modifications of the recycled fibers resulted in further improvements in the mechanical properties of the PP composites in comparison with the hydrophobized GFs. Moreover, synergistic effects from the addition of MAPP were observed with scanning electron microscopy. The results clearly demonstrate that the surface modifications were effective and good alternatives to currently used methods.     

Flame surface modification of polypropylene film

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of oxygen molecules. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O₂.     

MPP无卤阻燃聚丙烯纤维的辐照改性研究

采用自制季戊四醇螺环磷酸酯双蜜胺盐(MPP)无卤阻燃剂与聚丙烯(PP)进行共混纺丝,制备了无卤阻燃PP纤维,采用低能电子辐照对无卤阻燃PP纤维进行改性,并对MPP的结构、PP纤维的力学性能及阻燃性能进行了表征。结果表明:自制MPP为预期结构;随着MPP含量的增加,PP纤维的极限氧指数(LOI)增大,但其断裂强度有所下降;MPP质量分数为8%时,纤维断裂强度为6.02 cN/dtex,LOI为24.5%;随低能电子辐照量的增大,MPP质量分数8%的阻燃PP纤维的LOI大幅度增加;当电子辐照量为200 kGy时,阻燃PP纤维的LOI为33.8%,断裂强度为3.08 cN/dtex,起始分解温度和残炭率比纯PP纤维均有较大幅度增加,燃烧形成连续致密的炭层。     

微孔聚丙烯膜表面胺基化修饰

发展了一种氨基接枝密度和分布可控的微孔聚丙烯膜(MPPM)表面修饰方法。首先通过紫外光接枝聚合法,在MPPM上接枝聚丙烯酸甲酯(PMA);然后通过丙烯酸甲酯和乙二胺的酰胺化缩合和Michael加成交替反应,将氨基可控地引入到MPPM表面。采用FTIR、XPS和ESEM对氨基化膜表面的化学组成及物理形态进行了表征;考察了氨基化膜的表面亲水性及渗透性能。结果表明,氨基化膜表面亲水性显著改善,吸水量可达(1 311.29±97.56)μg/cm2,为未修饰MPPM的145倍;制得的氨基化膜具有良好的水通量和金属离子渗透性能。     

碱性电池隔膜用丙纶非织造布的等离子体改性

利用低温等离子体技术对碱性电池隔膜用丙纶非织造布进行表面改性处理,探讨了影响电池隔膜性能的因素,利用红外光谱、扫描电镜对材料表面性能进行了表征分析。结果表明,不同气体的等离子体对丙纶非织造布进行表面处理的最佳工作参数放电气体、放电功率、放电时间、工作压强分别为:氩气,70 W,3 min,15 Pa;氧气,120 W,3 min,30 Pa;空气,100 W,3 min,50 Pa。通过等离子体表面活化处理,在丙纶表面引入了亲水性基团,同时产生了刻蚀,丙纶非织造布的吸碱速率可提高至每10 min 8 cm左右,吸碱率提高至250%,面电阻大幅降低至8 Ω/cm2左右。     

Study on the surface grafting of polypropylene fibers

In this article, the surfaces of polypropylene (PP) fibers were grafted by three different grafting systems, of which the initiators belonged to three different types, namely, the water‐soluble initiator, the redox initiator, and the oil‐soluble initiator, respectively. The grafted products were characterized by FTIR, and the grafting degrees were determined by acid–base titration. In comparison, it was found that the oil‐soluble initiator might be more suitable for the surface grafting modification of PP fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 734–737, 2006     

高性能纤维表面改性研究进展

高性能纤维具有优异的性能,广泛用于宇航和军事领域,但是其与树脂基体之间的界面粘接性能较差,复合材料的层间剪切强度较低。针对这一复合材料体系,全面论述了提高其性能的几种方法以及各种方法的优缺点,其中包括纤维表面接枝、偶联、聚合物涂层、冷等离子体、γ射线辐射和超声波处理等,同时介绍了改性纤维的性能表征方法。     

Chemical modification of wool fibers with acid anhydrides

Wool fibers were chemically modified by reaction with succinic and glutaric anhydrides. The weight gain (and acyl content) increased with increasing the reaction temperature (65–80°C) and time (1–2 h), attaining 18.9% (158.9 mol/10⁵ g) and 23% (163.9 mol/10⁵ g) for succinylated and glutarylated wool, respectively. Changes in the amino acidic pattern of acylated wool, i.e., decrease of basic amino acid residues and formation of ornithine, were observed by acid hydrolysis. The X‐ray diffraction profiles of modified wool fibers remained essentially unchanged, suggesting that the crystalline structure was not affected by reaction with acid anhydrides. The degree of molecular orientation of acylated wool slightly decreased, especially at high weight gain. The viscoelastic response of wool modified with succinic and glutaric anhydrides was characterized by a shift to a lower temperature of both the drop of the storage modulus and the peak of the loss modulus. These features are indicative of a higher mobility of the keratin chians in the amorphous and crystalline domains. In fact, it is suggested that the chemical agent diffused into the accessible parts of α‐crystallites, reaching the available reactive sites. This did not cause changes in the crystalline pattern of wool, but resulted in a different thermal behavior of fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1573–1579, 1999     

Chemical grafting of metallocene‐catalyzed functional polypropylene copolymer on glass substrates through surface modification

This work deals with surface modification of soda‐lime glass slides which, by itself, does not have hydroxyl groups at the surface. So, a glass surface pretreatment is needed, to create hydroxyl groups onto it, before carrying out the polypropylene (PP) grafting reaction. Different acid/base pretreatments were performed to develop an adequate concentration of superficial hydroxyl groups. Subsequently, a metallocenic polymerization (propylene‐α olefin graft reaction, catalyzed by EtInd₂ZrCl₂/methylaluminoxane), was carried out to provide graft‐PP chains chemically linked to the glass surface. The surface so modified can be further functionalized and tailored for different applications, including polymer composites. The pretreatment conditions that best preserved homogeneity and caused less damage to the glass surface resulted from a step of contact with dilute HF/NH₄F buffer, a washing step with distilled water, and a final exposure to KOH. After the propylene copolymerization was performed, part of the graft copolymer formed remained chemically bonded to the glass slide surface. The presence of grafted PP at the surface was confirmed by SEM, FTIR, and EDAX characterization, even after the physically adsorbed polymer was excluded by a severe solvent extraction treatment. From these results, the copolymerization of a hydroxy α‐olefin, grafted on a MAO‐pretreated glass slide, is foreseen as a possible way to graft polymers onto inorganic solids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The preparation and performance analysis of chemical-treated maize straw fibers and Its high-performance polypropylene/chemical-treated maize straw fibers/maleic anhydride grafted polypropylene/silane coupling agent composites

In recent years, there has been an increasing industrial interest in maize straws. In this work, chemical-treated fibers (CTF) were fabricated based on wasted maize straws by chemical treatment combined with stirring. The experimental results suggest that a part of lignin in CTF was removed after chemical treatment, which resulted in the smooth surface morphology, better thermal stability, and even higher degree of crystallinity of CTF. Furthermore, the CTF were used to composite with polypropylene (PP). With the addition of PP-g-MAH and silane coupling agent (SCA), the compatibility between CTF and PP was improved and thus the mechanical performance of PP composites was also improved. At the same time, the tensile strength (54.9 ± 5.4 MPa), Young's modulus (1950 ± 246 MPa), specific strength (49.4 ± 3.9 MPa g⁻¹ cm³) and impact strength (3.6 ± 0.3 kJ/m²) of the PP/CTF/PP-g-MAH/SCA (50/50/6/0.95) composite was increased by about 51%, 177%, 20%, and 113% relative to pure PP, respectively. In conclusion, transforming the wasted maize straws into CTF is an effective way to reduce environmental pollution and meet the growing global demand for energy-saving materials.     

Surface modification of multiwalled carbon nanotubes via gliding arc plasma for the reinforcement of polypropylene

To increase the applicability of multiwalled carbon nanotubes (MWCNTs), functional groups were generated on the generally inert surface of MWCNTs using gliding arc (GA) plasma. MWCNTs were modified using plasma polymerization with styrene (St) as monomer. The surface compositional and structural changes that occur on MWCNTs were investigated using FT‐IR, Raman spectroscopy, BET surface area, and elemental analysis. Dispersion of the treated MWCNTs in different solvents was evaluated. Transmission electron microscopy images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated ones in nonpolar solvents. Subsequently, MWCNTs‐reinforced polypropylene (PP) composites were prepared by internal batch mixing with the addition of 1.0 wt % MWCNTs. The morphology of MWCNTs/PP nanocomposites was studied through scanning electron microscopy. Observations of SEM images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated MWCNTs either on the composite fracture surfaces or inside the PP matrix. Moreover, the mechanical tests showed that the tensile strength and elongation at break were improved with the addition of polystyrene‐grafted MWCNTs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

芳纶表面改性研究进展

简单回顾了芳纶的发展历史,阐述了表面涂层法、化学改性、物理改性等几种芳纶表面改性方法的研究现状,同时介绍了3种常用来表征纤维复合材料界面结合强度的方法,最后指出芳纶表面改性技术的发展方向。     

Studies on intumescent flame retardant polypropylene composites based on biodegradable wheat straw

Wheat straw (WS) has numerous advantages compared with traditional bioadditives such as starch and lignin. So in this work, based on WS and silica microencapsulated ammonium polyphosphate, flame retardant polypropylene/wheat straw (WSP) composites were prepared by melted blend method. Flame retardant and thermal properties of WSP composites have been investigated. The results of cone calorimeter show that peaks of heat release rate and total heat release of the flame retardant WSP composite decrease substantially compared with those of pure polypropylene. The peak of heat release rate value of the flame retardant WSP composite decreases from 1290.5 to 247.9 kW/m², and the total heat release value decreases from 119.4 to 46.3 MJ/m². Meanwhile, thermal degradation and gas products of the flame retardant WSP composite were monitored by thermogravimetric analysis and thermogravimetric analysis‐infrared spectrometry. The result of thermal analysis shows that the flame retardant WSP composite has a high thermal stability and has a 30.0 wt% residual char at 600°C. From this work, we hope to provide a method to prepare flame retardant polymer composites with a biodegradable natural material‐WS.     

Plasma‐induced surface modification and adhesion enhancement of polypropylene surface

Unoriented (UPP) and biaxially oriented (BOPP) polypropylene films were treated under radio frequency plasma of air, nitrogen, oxygen, and ammonia. Surface modification of polypropylene films was investigated by using surface energy measurement and attenuated total reflection (ATR)‐FTIR spectroscopy. Surface energy of air and nitrogen plasma‐treated polypropylene film increased for shorter treatment time and then decreased and attained an equilibrium value. Such changes in surface energy were not observed for oxygen and ammonia plasma‐treated polypropylene film, which increased to an equilibrium value. ATR‐FTIR studies revealed characteristic differences in the absorption spectra for short‐duration and long‐duration treatments. From the relative intensity change in the C—H stretching vibration, the mechanism of surface chemical reaction could be inferred. Studies regarding the durability of surface modification due to plasma treatment were evaluated by investigating surface energy of samples aged for 2 months. Treated films subjected to peel strength measurement showed improvement in bondability for UPP and BOPP film by hydrophilic surface modification accompanied by surface crosslinking. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 925–936, 2002     

Chemical modification of hemp fibers by silane coupling agents

Natural hemp fibers were chemically modified using silane coupling agents to reduce their hydrophilic character. The existence of a chemical bond between coupling agents and hemp fibers was confirmed by ATR‐FTIR spectroscopy, ²⁹Si Nuclear Magnetic Resonance (NMR), thermogravimetric analysis (TGA), energy dispersive spectroscopy (EDS), and BET surface area measurements. It was shown that the initial concentration and the chemical structure of the organosilane coupling agent have an effect on the grafted quantity on the hemp fiber surfaces. The grafted quantity increased proportionally to the initial concentration of silane molecules. The presence of polar amino end group (NH₂) in silane structure can cause an increase in the grafted quantity, compared with results obtained in the case of silane molecules containing methacryloxy groups. This effect is attributed to the formation of hydrogen bonds between NH₂ and unreacted hydroxyl groups of hemp fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Steam-exploded wheat straw fibers as reinforcing material for polypropylene-based composites. Characterization and properties

Composites of wheat straw fibers with polypropylene (iPP) and maleic anhydride modified polypropylene (iPPMA) were prepared. Before being mixed with polypropylene matrices, the wheat straw fibers were subjected to a steam explosion process that induces morphological and structural changes in lignocellulosic materials. Such changes are able to enhance the interactions with the thermoplastic matrix. Compared with iPP, the modified matrix (iPPMA) has shown higher mechanical performances (tensile and impact behavior) and a remarkable decrease of water absorption, that is one of the main drawbacks of natural fiber composites. Finally, the presence of covalent bonds between maleic anhydride and steam-exploded (STEX) fibers, by means of an esterification reaction, produced during the melt-mixing process, can explain the resulting good interfacial adhesion found in iPPMA-based composities.     

激光表面改性对聚丙烯非织造布性能的影响

采用激光技术对聚丙烯(PP)非织造布进行表面改性处理,探讨了激光功率和进布速度对PP非织造布的面密度、厚度、抗静电性、透气性、断裂强力和色泽度(K/S)的影响。结果表明:激光表面改性对PP非织造布的抗静电性、面密度和厚度影响不大;进布速度对PP非织造布的透气性、断裂强力和K/S的影响比激光功率显著,但是激光功率相比进布速度对接触角的影响更明显;随着进布速度的提高,PP非织造布的断裂强力先增加后减小,透气性、接触角和K/S呈下降趋势;随着激光功率的增大,PP非织造布的透气性先增加后趋于稳定,断裂强力和接触角显著降低,K/S增加;当激光功率为40 W,进布速度为9.0 m/min,激光表面改性处理后的PP非织造布的综合性能较好。     

芳纶表面化学改性技术研究现状

概述了芳纶表面化学改性的方法。从芳纶分子结构的特点出发,论述了芳纶表面化学刻蚀及化学接枝等化学改性技术的原理、特点和应用效果;详述了基于芳纶结构中苯环上的硝化还原反应、氯磺化反应和酰胺基上的水解反应、氢取代反应、金属化反应等的反应原理及应用效果。指出多种化学改性技术的交叉应用将成为芳纶表面化学改性的趋势。