Effect of alcohol pretreatment in conjunction with atmospheric pressure plasmas on hydrophobizing ramie fiber surfaces

To improve interfacial adhesion between hydrophilic cellulose fiber and hydrophobic polymer matrix, ramie fibers were pretreated with isopropanol and n-butanol and then plasma treated using an atmospheric pressure plasma apparatus. For the plasma-treated fibers, the scanning electron microscopy shows increased surface roughness and the X-ray photoelectron spectroscopy analysis shows a significant increase of C–C bond in isopropanol-pretreated group, whereas for n-butanol-pretreated group the raise of C=O bonds is most noticeable. For both alcohol-pretreated and plasma-treated groups, the water contact angles increase significantly. Microbond pull-out test shows interfacial shear strengths of fiber/polypropylene (PP) samples increase by 47 and 34%, respectively, for the two groups compared with the control. Therefore, it can be concluded that the reaction between both alcohols and cellulose induced by plasma can indeed create a fiber surface with increased roughness and decreased polarity, and thus is more compatible to PP.     

Aging of hydrophobized surfaces of ramie fibers induced by atmospheric pressure plasma treatment with ethanol pretreatment

In order to investigate hydrophilic recovery of hydrophobic treatment of cellulose fibers, ramie fibers are ethanol-pretreated followed by atmospheric pressure plasma jet (APPJ) treatment using helium as the treatment gas and age for up to 150?days in 20?°C and 65% relative humidity. Scanning electron microscopy shows the fiber surfaces of the ethanol-pretreated?+?APPJ-treated group of freshly prepared, aged for 30?days, and aged for 150?days are covered with polypropylene matrix after fiber pullout tests. X-ray photoelectron spectroscopy shows that the freshly prepared ethanol-pretreated?+?APPJ-treated group has a 31% reduction in atomic ratio of oxygen to carbon and maintains at a similar level even after 150?days of aging. Water contact angle measurement demonstrates that the wettability of fiber surface of the freshly prepared ethanol-pretreated?+?APPJ-treated group drastically decreases and remains at the same lever after aging. Interfacial shear strength test reveals that the interfacial adhesion between PP matrix and ramie fiber for the freshly prepared ethanol-pretreated?+?APPJ-treated group increases 26% and remains substantially higher than that of the control group over time. These results indicate that the ethanol pretreatment followed by APPJ treatment is a permanent surface treatment with negligible aging for at least five months.     

Treatment of ramie fiber with different techniques: the influence of diammonium phosphate on interfacial adhesion properties of ramie fiber-reinforced polylactic acid composite

Ramie fiber-reinforced polylactic acid (PLA) composites were successfully prepared by hot compression molding. Different treatment techniques were used to modify the surface of ramie fiber. The influence of diammonium phosphate (DAP) on the interfacial adhesion between ramie fiber and PLA composites was investigated by the contact angle measurements, FTIR and SEM analyses. The contact angle measurement results showed that alkali treatment combined with DAP was very efficient in decreasing the hydrophilicity of fibers. After treatment, the hydrophilicity of untreated ramie fiber from 5.9 ± 1.3 decreased to 2.0 ± 0.8 mJ/m². The wettability of alkali/silane/DAP-treated ramie fiber/PLA composite was higher (95.4° ± 1.3°) than that of pure ramie fiber/PLA composite (87.3° ± 1.9°). The FTIR results were consistent with the wetting measurements as the increment of hydrophilicity. Thermal analysis indicated that DAP-modified ramie fiber/PLA composites exhibited a lower thermal decomposition temperature, unique decomposition behavior and more residual char formation at decomposition temperature. The tensile, flexural and impact properties of DAP-modified ramie fiber composites were comparable to those of untreated ramie fiber composite. Moreover, proper alignment and uniform distribution of ramie fibers within the PLA matrix were found to be excellent. The morphological structures observed by SEM showed that well-modified ramie fibers enhanced the failure of the PLA composites in tensile, flexural and impact tests.     

Increasing hydrophobicity of poly(propylene) fibers by coating reduced graphene oxide and their application as depth filter media

The effect of increasing the hydrophobicity of poly(propylene) (PP) fibers, the most frequently used synthetic filter materials, on depth filtration performance was investigated. Reduced graphene oxide (RGO) was employed to fabricate highly hydrophobic surfaces by a dip-coating method. The anchoring of RGO on the surface of the PP fibers was confirmed by the appearance of signals corresponding to RGO in Raman and X-ray photoelectron spectra. In addition, scanning electron microscopy images revealed the presence of wrinkled and folded RGO sheets on the PP fibers. The water contact angle increased from 108° to 125° after the first RGO coating, and it was saturated at about 135°. Using kaolin as model hydrophilic particles, the depth filters with RGO-coated PP fibers showed a superior performance in terms of water flux and trans-filter pressure in comparison with those with the pristine and hydrophilic PP fibers prepared by coating functionalized GO. More importantly, particle detachment was enhanced by the hydrophobic coating during backwashing. This can be ascribed to the weakened attractive force between the RGO-coated fiber surfaces and kaolin particles due to the increase of hydrophobicity. This approach provides an effective means of enhancing the performance of synthetic fiber-based depth filters.     

A study of the effect of oxygen plasma treatment on the interfacial properties of carbon fiber/epoxy composites

In this work, effects of the interface modification on the carbon fiber‐reinforced epoxy composites were studied. For this purpose, the surface of carbon fibers were modified by oxygen plasma treatment. The surface characteristics of carbon fibers were studied by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), dynamic contact angle analysis (DCAA), and dynamic mechanical thermal analysis (DMTA), respectively. The interlaminar shear strength (ILSS) was also measured. XPS and AFM analyses indicated that the oxygen plasma treatment successfully increased some oxygen‐containing functional groups concentration on the carbon fiber surfaces, the surface roughness of carbon fibers was enhanced by plasma etching and oxidative reactions. DCAA and DMTA analyses show that the surface energy of carbon fibers increased 44.9% after plasma treatment for 3 min and the interfacial bonding intensities A and α also reached minimum and maximum value respectively. The composites exhibited the highest value of ILSS after oxgen plasma treated for 3 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of Compound Surface Treatment on the Performance of Poly(butylene succinate)/Chemithermomechanical Pulp Fiber Composites

Chemithermomechanical pulp fiber was pretreated by alkali solution to alter the surface characteristics of fibers. The untreated and treated fibers were used to prepare poly(butylene succinate)/chemithermomechanical pulp fiber composites with or without the incorporation of cellulose fatty acid ester (hydroxyethyl cellulose lauric acid ester). X-ray photoelectron spectrum analysis shows that the O/C ratio on the fiber surface increased after alkali treatment, indicating that part of lignin was removed during alkali treatment process. Scanning electron microcopy images indicate that the fiber surface was changed to rough after alkali treatment. The modification effect of hydroxyethyl cellulose lauric acid ester reflects as the improvement of fiber order in matrix, together with the enhancement of interfacial bonding, whereas, the modification effect of alkali treatment is mainly due to the enhancement of interfacial bonding. The integrated mechanical properties of composite prepared by alkali-treated fibers are superior to those of composite prepared by hydroxyethyl cellulose lauric acid ester-treated fibers. The combination of these two modification methods favors the enhancement of tensile and impact strengths of composite. However, in comparison with the composite prepared only by alkali treatment, the flexural strength and modulus would be despaired in a certain degree. When fibers were alkali treated, the shear viscosity of composite exhibited a larger increase, whereas the shear viscosity of composite prepared fibers with hydroxyethyl cellulose lauric acid ester treatment exhibits a slight decrease.     

Influence of oxygen plasma treatment parameters on the properties of carbon fiber

This study is focused on the impact of oxygen plasma treatment on properties of carbon fibers and interfacial adhesion behavior between the carbon fibers and epoxy resin. The influences of the main parameters of plasma treatment process, including duration, power, and flow rate of oxygen gas were studied in detail using interlaminar shear strength (ILSS) of carbon fiber composites. The ILSS of composites made of carbon fibers treated by oxygen plasma for 1 min, at power of 125 W, and oxygen flow rate of 100 sccm presented a maximum increase of 28% compared to composites made of untreated carbon fibers. Furthermore, carbon fibers were characterized by scanning electron microscopy (SEM), tensile strength test, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy analyses. It was found that the concentration of reactive functional groups on the fiber surface was increased after the plasma modification, as well the surface roughness, which finally improved the interfacial adhesion between carbon fibers and epoxy resin. However, high power and long exposure times could partly damage the surface of carbon fibers and decrease the tensile strength of filaments and ILSS of treated fiber composites.     

Chemical surface modification of wheat straw fibers for polypropylene reinforcement

The use of natural materials has grown in the last years in the plastics industry. Natural lignocellulose fibers derived from agricultural waste present potential to be used as a replacement for glass fibers for polymer reinforcement, leading to lower CO₂ footprint products. However, cellulose fibers are hydrophilic and polar and as a result of that, incompatible with hydrophobic polymers such as polypropylene. For this reason, a surface modification on the cellulose fiber is required. This work focuses on the modification of the cellulose fibers to improve the compatibility with polypropylene. Wheat straw fibers derived from agricultural waste were scoured with the purpose to remove lignin, hemicellulose and pectin to facilitate the defibrillation. The fibers were then esterified using acetic anhydride. Thermal gravimetric tests have shown an increase in the thermal stability of the scoured and esterified cellulose fibers, from 246°C for untreated fibers to 292°C and 316°C, respectively. From mechanical tests results it could be seen that the tensile modulus of the composites with esterified cellulose fibers increased 57% compared with the neat PP. Flexural strength increased by 31% and flexural modulus by 70%. The use of esterified fibers led to an improvement of 79% in the impact strength compared with the neat PP. A better compatibilization between fibers and matrix could be seen using maleic anhydride modified polypropylene copolymer as compatibilizer, even with esterified fibers, probably due to residual hydroxyl groups still available on modified cellulose. POLYM. COMPOS., 37:2133–2141, 2016. © 2015 Society of Plastics Engineers     

Toughening vinyl ester networks with polypropylene meso-fibers: Interface modification and composite properties

Polymer-polymer composites comprised of vinyl ester matrices (VE) and polypropylene (PP) fiber meshes were fabricated and tested in this investigation. Results indicated that PP fibers greatly enhanced fracture toughness; however, strength of the VE was significantly reduced as voids were observed at the interface of the PP and VE. A two-step surface modification, oxygen plasma treatment followed by grafting vinyltrimethoxysilane (VTMS), was conducted on PP fibers in an effort to improve interfacial strength. Interfacial discontinuities of composites were improved after surface modification of PP. The oxygen plasma treatment added hydrophilic functional groups but caused surface roughness. Surface treatment of PP slightly increased fracture toughness of the PP-VE composite by enhancing energy absorption capacity at the interface. However, mechanical strength and modulus did not significantly increase for the composite using VTMS grafted PP fibers due to the weak fiber material. Small PP fibers with higher strength may attain the expected improvement in mechanical properties after surface treatment.     

Effect of fiber surface morphology on the hydrophilicity modification of cold plasma‐treated polypropylene nonwoven fabrics

Cold oxygen plasma was employed to give hydrophilicity modification to polypropylene (PP) nonwoven fabric (NWF). It was found that, after plasma treatment, PP NWF made from fibers with smooth surfaces can only keep its hydrophilicity for a short time and then shows a quick hydrophobic recovery at room temperature. However, this hydrophilic property can last for a long time in the case of the PP NWF made from fibers with rough surfaces. To prove the contribution of the rough surface to the long‐term hydrophilicity, this PP NWF was treated in an organic solvent to smooth the fiber surface. The hydrophilic feature of this PP NWF no longer lasts for a long time after the same plasma treatment. This observation strongly supports our opinion that the fiber surface morphology of PP NWF is a critical factor for long‐term hydrophilicity improvement after plasma treatment, which gives a positive solution to overcoming the aging effect of hydrophilicity modification often found in this technique. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization of ramie fiber/soy protein concentrate (SPC) resin interface

Ramie fiber/soy protein concentrate (SPC) polymer (resin) interfacial shear strength (IFSS) was measured using the microbond technique. To characterize the effect of plasticization, SPC resin was mixed with glycerin. Fibers were also treated with ethylene plasma polymer to reduce fiber surface roughness and polar nature to control the IFSS. Fiber surfaces after ethylene plasma polymerization, and fracture surfaces of specimens before and after the microbond tests were characterized using a scanning electron microscope (SEM). Some specimens were also characterized using electron microprobe analyzer (EMPA) to map the residual resin on the fiber surface after the microbond test. Effects of glycerin concentration in SPC and ethylene plasma fiber surface treatment time on the IFSS were investigated. Preparation of SPC resin requires a large amount of water. As expected, during drying of SPC resin, the microdrops shrank significantly. The high IFSS values indicate strong interfacial interaction in the ramie fiber/SPC resin system. This strong interfacial interaction is a result of a highly polar nature of both the ramie fiber and the SPC resin and rough fiber surface. Ethylene plasma polymerization was used to control the IFSS. The plasma polymer imparted a polyethylene-like, non-polar polymer coating on the fiber surface. As a result, the fiber surface became smoother compared to the untreated fiber. Both fiber smoothness and non-polar nature of the coating reduced the ramie fiber/SPC resin IFSS. Plasticization of the SPC resin by glycerin also decreased the adhesion strength of the ramie fibers with the SPC resin. The load-displacement plots for IFSS tests obtained for different resin and fiber combinations indicate different interfacial failure modes.     

苎麻纤维增强聚丙烯复合材料的性能研究

用偶联剂对苎麻纤维进行改性处理,研究了偶联剂处理浓度及苎麻用量对聚丙烯/苎麻增强复合材料力学性能的影响。结果表明:随着苎麻纤维用量的增加,复合材料的拉伸强度和弯曲强度都随之提高,其中经偶联剂处理复合材料的力学性能提高幅度较大;偶联剂处理浓度为1%时,材料的拉伸强度最高。SEM观察发现:未经处理的苎麻纤维表面较光滑,而经偶联剂处理的苎麻纤维表面较粗糙,并黏附了聚丙烯基体,说明偶联剂的添加改善了复合体系的界面相容性,界面结合力提高。     

苎麻落麻的表面处理及其复合材料的性能研究

采用甲基丙烯酸甲酯、丙烯腈接枝,硅烷偶联剂(A-151)偶联,聚氯乙烯(PVC)包覆等方法对苎麻落麻纤维进行表面处理;测试了处理前后落麻纤维的吸水率、单丝强度及其与环氧树脂(EP)、酚醛树脂(PF)和不饱和聚酯(UP)等的接触角;观察了偶联和包覆后落麻纤维的表面状况;选取偶联和包覆后的落麻纤维制备了UP/落麻毡和PP/落麻纤维复合材料,测试了其拉伸和弯曲性能并观察了处理前后复合材料的拉伸断面形貌。结果表明,接枝、偶联和包覆不仅降低了落麻纤维的吸水速率。而且也降低了平衡吸水量;接枝对落麻纤维单丝强度影响最大,偶联次之,包覆最小;接枝、偶联和包覆均能大幅度改善落麻纤维与EP、PF和UP的浸润性;偶联和包覆后的落麻纤维表面都比处理前粗糙;偶联使UP/落麻毡复合材料的拉伸强度、拉伸弹性模量提高了21％,弯曲强度提高了34％,弯曲弹性模量提高了40％,包覆使PP/落麻纤维复合材料的拉伸、弯曲强度提高了20％左右。     

Influence of environmental moisture on atmospheric pressure plasma jet treatment of ultrahigh-modulus polyethylene fibers

One of the main differences between low-pressure and atmospheric-pressure plasma treatments is that there is little moisture involved in the low-pressure plasma treatment, although moisture could exist at the wall of the vacuum chamber or react with the substrate after plasma treatment, while in the atmospheric-pressure plasma treatment moisture exists not only in the environment but also in any hygroscopic substrate. In order to investigate the influence of environmental moisture on the effect of atmospheric pressure plasma treatment, ultra-high-modulus polyethylene (UHMPE) fibers were treated using an atmospheric-pressure plasma jet (APPJ) with 10 l/min helium gas-flow rate, treatment nozzle temperature of 100°C and 5 W output power. The plasma treatments were carried out at three different relative humidity levels, namely 5, 59 and 100%. After the plasma treatments, the surface roughness increased while the water-contact angle decreased with increasing relative humidity. The number of oxygen containing groups increased as the environmental moisture content increased. The interfacial shear strength of the UHMPE fiber/epoxy system was significantly increased after the plasma treatments, but the moisture level in the APPJ environment did not have a significant influence on the adhesion properties. In addition, no significant difference in single fiber tensile strength was observed after the plasma treatments at all moisture levels. Therefore, it was concluded that the environmental moisture did not significantly influence the effect of atmospheric-pressure plasma treatment in improving interfacial bonding between the fiber and epoxy. The improvement of the interfacial shear strength for the plasma-treated samples at all moisture levels was mainly due to the increased surface roughness and increased surface oxygen and nitrogen contents due to the plasma etching and surface modification effect.     

等离子体射流载气流量大小对玻璃纤维改性效果影响的研究

通过大气压等离子体射流在玻璃纤维（GF）表面沉积氧化硅（SiO_x）纳米颗粒的方法改善玻璃纤维增强聚丙烯（GFRP）复合材料的界面结合性能,利用扫描电子显微镜、原子力显微镜和X射线光电子能谱等表征分析了改性纤维的表面形貌、化学成分、润湿性能和复合材料的界面结合性能,并考察了等离子体射流载气流量大小对GF改性效果的影响。结果表明,当载气流量为40 mL/min时,GF的改性效果最好,且此时GF的表面能相比对照组提高了43.18 %,GFRP复合材料的层间剪切强度提高了30.79 %;经过等离子体处理后,GF的表面粗糙度增大,极性官能团增多,复合材料的界面结合性能提升。     

Pretreatments of natural fibers and their application as reinforcing material in polymer composites—A review

In recent years, natural fibers reinforced composites have received much attention because of their lightweight, nonabrasive, combustible, nontoxic, low cost and biodegradable properties. Among the various natural fibers; flax, bamboo, sisal, hemp, ramie, jute, and wood fibers are of particular interest. A lot of research work has been performed all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composites. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. Pretreatments of the natural fiber can clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. Among the various pretreatment techniques, graft copolymerization and plasma treatment are the best methods for surface modification of natural fibers. Graft copolymers of natural fibers with vinyl monomers provide better adhesion between matrix and fiber. In the present article, the use of pretreated natural fibers in polymer matrix‐based composites has been reviewed. Effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites has also been discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Surface modification of armos fibers with oxygen plasma treatment for improving interfacial adhesion with poly(phthalazinone ether sulfone ketone) resin

We introduce in this article oxygen plasma treatment as a convenient and effective method for the surface modification of Armos fibers. The effects of oxygen‐plasma‐treatment power on both the Armos fiber surface properties and Armos‐fiber‐reinforced poly(phthalazinone ether sulfone ketone) composite interfacial adhesion were investigated. The Armos fiber surface chemical composition, surface morphology and roughness, and surface wettability as a function of oxygen‐plasma‐treatment power were measured by X‐ray photoelectron spectroscopy, scanning electronic microscopy, atomic force microscopy, and dynamic contact angle analysis. The results show that oxygen plasma treatment introduced a lot of reactive functional groups onto the fiber surface, changed the surface morphology, increased the surface roughness, and enhanced the surface wettability. Additionally, the effect of the oxygen‐plasma‐treatment power on the composite interfacial adhesion was measured by interlaminar shear strength with a short‐beam bending test. Oxygen plasma treatment was an effective method for improving the composite interfacial properties by both chemical bonding and physical effects. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of plasma treatment on properties of ramie fiber and the reinforced composites

In this research, 9 series of ramie fibers were treated under low-temperature plasma with diverse output powers and treatment times. By analysis of the surface energy and adhesion power with epoxy resin, 3 groups as well as control group were chosen as reinforced fibers of composites. The influences of these parameters on the ramie fiber and its composites such as topography and mechanical properties were tested by scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile property and fragmentation test of single-fiber composites. Contact angle and surface free energy results indicated that with the increased treatment times and output powers, surface energy and adhesion work with epoxy resin improved. Compared with the untreated fibers, surface energy and adhesion work with epoxy resin grew 124.5 and 59.1% after 3 min-200 w treatment. SEM and AFM showed low temperature plasma treatment etched the surface of ramie fiber to enhance the coherence between fiber and resin, consequently fiber was not easy to pull-out. After 3 min-200 w treatment, tensile strength of ramie fiber was 253.8 MPa, it had about 30.5% more than that of untreated fiber reinforced composite. Interface shear stress was complicated which was affected by properties of fiber, resin and interface. Fragmentation test showed biggest interface shear stress achieved 17.2 MPa, which represented a 54.0% increase over untreated fiber reinforced composites.     

The Effect of Silane Surface Treatment of Carbon Fiber on the Tribological Properties of Bismaleimide(BMI) Composite

Silane surface modification method was used for the surface treatment of carbon fiber to improve the interfacial adhesion of the carbon fiber reinforced bismaleimide(BMI) composite. The surface characteristics of untreated and treated carbon fiber were characterized by Fourier transform infrared (FT-IR) spectroscope. The friction and wear properties of the BMI composites filled with differently surface treated carbon fibers(20 vol%), were investigated on a ring-on-block tribometer. Experimental results revealed that silane treatment largely reduced the friction and wear of CF/BMI composites. Scanning electron microscope (SEM) of worn surfaces of BMI composites showed that surface treated CF/BMI composite had the strongest interfacial adhesion.     

Characterization of EPDM Vulcanizates Modified with Gamma Irradiation and Trichloroisocyanuric Acid and Their Adhesion Behavior with Natural Rubber

The adhesion strength between surface-modified vulcanized ethylene propylene diene methylene (EPDM) rubber and unmodified natural rubber (NR) was investigated by a 180° peel test. Surface modification of EPDM vulcanizate was carried out by two different techniques: (a) irradiation of the surface by gamma radiation in the presence and absence of trimethylol propane triacrylate (TMPTA) as a sensitizer and (b) chemical treatment of the surface with trichloroisocyanuric acid (TCICA). The modified EPDM surface was thoroughly characterized by attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray sulfur mapping (EDX), surface energy measurements, and free sulfur and gel content analysis. The joint between the modified vulcanized EPDM and the unmodified unvulcanized NR was prepared by a co-curing method. The adhesion strength between these two surfaces was found to depend on the nature of oxidation, roughness of the joining surfaces, and extent of blooming of sulfur on the modified surface. Surface modification of EPDM sample with 1 kGy of gamma irradiation in the presence of 10 wt% TMPTA resulted in a good increase in the adhesion strength between EPDM and NR (～76% improvement over the untreated sample). On the other hand, for the trichloroisocyanuric acid modified sample, maximum improvement of adhesion strength was observed at 0.5 wt% of TCICA (～29% improvement in comparison with the untreated sample).