Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by γ irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was γ irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2°‐PTFE) and grafted with styrene (St), vinyl acetate (VAc), and 4‐vinylpyridine (4‐VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2°‐PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2°‐PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4‐VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2°‐PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2°‐PTFEs into LDPE showed low film quality and poor mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 816–826, 2001     

高性能氢化丁腈橡胶的配方与性能

在加氢度为96％、结合丙烯腈质量分数为34％的氢化丁腈橡胶(HNBR)中,以2,5-二甲基-2,5-双(叔丁基过氧基)己烷为硫化剂,三烯丙基异氰脲酸酯(TAIC)为助硫化剂,分别加入不同牌号的炭黑[N330,N539,N550,半补强炭黑(SRF)或喷雾炭黑],于180℃下硫化15min,制备了具有低压缩永久变形、优异力学性能的HNBR硫化胶。结果表明,增加硫化剂用量,以及在其较小用量下添加TAIC时,可降低HNBR硫化胶的压缩永久变形。对不同牌号炭黑增强硫化胶综合性能的分析可知,在硫化剂用量为6．25份(质量,下同),TAIC用量为1．25份时,炭黑对HNBR硫化胶增强效果由大到小为：N330,N539,N550,SRF,喷雾炭黑。     

Synthesis of poly(tetrafluoroethylene)/poly(butadiene) core-shell particles and their graft copolymerization

This article describes how to convert the unreactive surface of poly(tetrafluoroethylene) (PTFE) into poly(styrene-co-acrylonitrile) (SAN). Composite particles with a crosslinked poly(butadiene) (PB) shell covered over a PTFE core were prepared by an emulsifier-free seeded emulsion polymerization of butadiene in the presence of PTFE latex. It was found that the increase in the PB crosslink density resulted in depressing the formation of PB secondary particles. Then, styrene and acrylonitrile were able to graft onto PB shell in high efficiency of 70%. SAN-modified PTFE/PB core-shell particles could eventually be dispersed homogeneously in a SAN matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:185–190, 1998     

Ageing of plasma-treated poly(tetrafluoroethylene) surfaces

Highly hydrophobic poly(tetrafluoroethylene) (PTFE) surfaces were modified with an air glow discharge plasma to improve their wettability. However, the hydrophilic character obtained diminishes with time, due to molecular movement in the polymer. We have determined that the ageing process is strongly affected by the environment and temperature in which the surfaces are stored. A hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures. Nonetheless, a hydrophilic environment, even at high temperatures, prevents the surface from losing the polar character obtained from the plasma treatment, stopping the ageing process. Moreover, this process is reversible since the character of the treated surface changes when the environment changes (i.e. from water to air). The hydrophilicity of the surfaces was evaluated by contact angle measurements of a droplet of water.     

Mechanical and tribological properties of nitrile rubber filled with modified molybdenum disulphide

In this work, cetyl trimethyl ammonium bromide (CTAB), silane coupling agent (KH570) and polyethylene glycol (PEG) were used to modify the surface property of molybdenum disulphide (MoS₂). MoS₂/nitrile rubber (NBR) composites were directly prepared by mechanical blending. Meanwhile, the effects of loading content of MoS₂, the kinds of modifiers on the mechanical and tribological properties of the composites were evaluated. The dispersion of fillers in rubber matrix and the worn surface of the composites were analysed by SEM. Results showed that the properties of MoS₂/NBR composites prepared by CTAB modified MoS₂ were superior to that of KH570 or PEG modified MoS₂ and unmodified MoS₂ because of strong opposite charges attraction between cetyl trimethyl ammonium cation and MoS₂ surface. When adding 10?phr CTAB modified MoS₂ in rubber matrix, the dispersion of filler was optimum, and the coefficient of friction of composite was the lowest in the prepared composites.     

Argon plasma treatment-induced grafting of acrylic acid onto expanded poly(tetrafluoroethylene) membranes

Expanded poly(tetrafluoroethylene) (ePTFE) is used in facial reconstruction surgery. For some specific applications ePTFE is required to interface with the underlying bone. However, ePTFE is classified as bioinert thus limiting integration at the bone-tissue interface. The incorporation of functional groups onto the ePTFE surface was carried out in the current study using argon plasma treatment-induced grafting of acrylic acid (AA) to improve integration. High surface coverage (grafting extent from XPS of up to 90%) was achieved and resulted in high hydrophilicity and high water uptake (up to 470% of the grafted PAA mass). The contribution of species present in the plasma to the incorporation of functional groups onto the ePTFE surface was evaluated with charged species observed to play an equally important role to neutral species in this study. The effects of sample position in the plasma chamber as well as the effect of grafting parameters (plasma power, monomer concentration, and reaction time) on the grafting outcome were evaluated. The mechanical properties of the AA grafted membranes under tensile, compression and nanoindentation were evaluated.     

稀土掺杂炭黑填充型非硫调节型粉末氯丁橡胶的性能与结构

利用镧系稀土（Ln）对炭黑表面有特殊的活化作用,采用化学沉积法制备了稀土掺杂炭黑（HAF—Ln）,并将HAF—Ln与非硫调节型氯丁胶乳（CR232胶乳）进行共混,采用凝聚共沉法制备了稀土掺杂炭黑填充型非硫调节型粉末氟丁橡胶[P（CR232／HAF—Ln）]。研究了稀土类型及用量对P（CR232／HAF—Ln）硫化胶力学性能的影响,发现采用稀土La、Sm和Tm掺杂的P（CR232／HAF—Ln）具有较好的力学性能。通过P（CR232／HAF—Ln）硫化胶拉伸断面的SEM分析,发现稀土La、Sm和Tm可有效改善炭黑在橡胶基体中的分散。     

Plasma‐induced solid‐state polymerization modified poly(tetrafluoroethylene) membrane for pervaporation separation of aqueous alcohol mixtures

Acrylamide (AAm) solid state polymerization was induced using argon plasma to improve the pervaporation performance of poly(tetrafluoroethylene) (PTFE) membranes (PTFE‐g‐PAAm) in aqueous alcohol mixtures. The surface morphology, chemical composition, and hydrophilicity changes in the PTFE and PTFE‐g‐PAAm membranes were investigated using ATR‐FTIR, SEM, AFM, X‐ray photoelectron spectroscopy, and water contact angle measurements. The surface hydrophilicity rapidly increased with increasing Ar exposure time, but decreased after longer Ar exposure time because of the degradation in the PTFE‐g‐PAAm membrane grafted layer. Compared with the hydrophilicity of the pristine PTFE membrane (water contact angle = 120°), the argon plasma induced acrylamide (AAm) solid‐state polymerization onto the PTFE surface (water contact angle = 43.3°) and effectively improved the hydrophilicity of the PTFE membrane. This value increases slowly with increasing aging time and then reaches a plateau value of about 50° after 10 days of storage under air. The pervaporation separation performances of the PTFE‐g‐PAAm membranes were higher than that of the pristine PTFE membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:909–919, 2006     

聚四氟乙烯胶乳与碳黑粒子共凝聚行为的研究

提出了用共凝聚的方法制备填充聚四氟乙烯(PTFE)的思想,以Al(NO3)3、CaCl2、KCI为凝聚剂进行PTFE分散乳液与碳黑粒子的共凝聚。考察了胶乳种类、凝聚温度、搅拌转速等对共凝聚过程的影响规律,初步探讨了共凝聚粒子的成粒机理。结果表明共凝聚粒子是疏水性的,粒子内碳黑分散均匀。     

Effects of hygrothermally decomposed polyurethane on the curing and mechanical properties of carbon black‐filled epoxidized natural rubber vulcanizates

Hygrothermally decomposed polyurethane (HD‐PUR) was mixed up to 20 phr in epoxidized natural rubber (with 50 mol % epoxidation; ENR50) recipes, and the curing and mechanical behaviors were studied. Mechanical testing of the ENR50/HD‐PUR vulcanizates determined the tensile, tear, compression‐set, hardness, abrasion, hysteresis, and resilience properties. No significant changes were observed in the tensile properties with the incorporation of HD‐PUR. The ENR50 compounds showed an increase in compression set with increasing HD‐PUR content. Rubbers cured by a semi‐efficient vulcanization system gave the best overall performance. A further improvement in curing and mechanical properties was achieved by the carbon black grade N330 being replaced with a more active grade (N375). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2265–2276, 2002     

Study on nitrile-butadiene rubber/poly(propylene carbonate) elastomer as coupling agent of poly (vinyl chloride)/poly (propylene carbonate) blends. I. Effect on mechanical properties of blends

Nitrile-butadiene rubber/poly(propylene carbonate) (NBR-PPC) elastomer was studied as a coupling agent of the blends of poly(vinyl chloride) (PVC) with poly(propylene carbonate) (PPC). It greatly improved the PVC/PPC system mechanical properties that were dependent on the amount and composition of the coupling agent. When the coupling agent consisted of a 70/30 ratio of NBR/PPC (in which NBR had 34% nitrile content) and 2.5 phr of benzoyl peroxide (BPO) initiator and underwent a prevulcanization, the blends of PVC/PPC displayed excellent mechanical properties by adding 8 phr of the coupling agent. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1107–1111, 1997     

Lamination of conductive polypyrrole films to poly(tetrafluoroethylene) films via interfacial graft copolymerization

A simple technique for the lamination of a conductive polymer film to an inert dielectric polymer film was demonstrated. The electrochemically synthesized and p‐toluenesulfonic acid‐doped polypyrrole (PPY) film was laminated simultaneously to the argon plasma‐pretreated PTFE film during the thermally induced graft copolymerization of the PTFE surface with a functional monomer. The graft copolymerization was carried out using glycidyl methacrylate (GMA) monomer containing 20% v/v hexamethyldiamine (HMDA) and in the absence of any polymerization initiator. Thermally induced graft copolymerization of the GMA monomer on the PPY surface was minimal. The lap shear and T‐peel adhesion strengths of the laminates were found to be dependent on the GMA graft concentration on the PTFE surface, which, in turn, was affected by the plasma pretreatment time of the film. To increase the GMA graft concentration for the enhancement of adhesion strength, the plasma‐pretreated PTFE surfaces were premodified via UV‐induced graft copolymerization with GMA prior to the simultaneous thermal graft copolymerization and lamination process. The modified surfaces and interfaces were characterized by X‐ray photoelectron spectroscopy (XPS). Through XPS measurements of the delaminated surfaces, it was found that the PPY/PTFE laminates failed predominantly by cohesive failure inside the PTFE substrate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 716–727, 2001     

Carbon black distribution driven by its concentration and its effect on physico-mechanical properties of styrene butadiene rubber and butadiene rubber miscible rubber blends

This paper discusses the influence of partitioning of carbon black (CB) with its increasing concentration (i.e., 10, 20, 30, 40, and 50 phr) on physical and static mechanical properties of Styrene Butadiene Rubber (SBR)/Butadiene Rubber (BR) rubber–rubber blends (RRB's) in 70SBR:30BR blend ratio. Partitioning of CB towards BR in CB-filled SBR/BR RRB's is quantitatively determined via dynamic mechanical analysis (DMA). DMA confirmed increased partitioning of CB towards BR phase with increasing CB. DMA data on the partitioning of CB towards BR were in good agreement with nuclear magnetic spectra obtained by solid-state nuclear magnetic resonance spectroscopy (SS-NMR spectroscopy). Curing properties, relative density, hardness, tensile test, tear test, and transmission electron microscopy (TEM) on CB filled SBR/BR RRB's were carried out to determine the effect of increasing concentration of CB on physical, mechanical, and dispersion characteristics in comparison to neat SBR/BR RRB's.     

Surface modification of poly(tetrafluoroethylene) with pulsed hydrogen plasma

Surface modification of polymers by pulsed plasma has been investigated to minimize degradation reactions occurring at the same time as the surface modification reactions. The hydrogen radical, ion, and electron concentrations in the hydrogen plasma were simulated as a function of the elapsed time after turning off the discharge. The contact angle measurement showed that hydrogen plasma treatment, regardless of pulsed or continuous plasma, led to degradation reactions as well as defluorination and oxidation on PTFE surfaces. The degradation reactions of PTFE chains initiated by the pulsed hydrogen plasma were not as vigorous as those by the continuous hydrogen plasma. A combination of the on‐time/off‐time of 30/270μs in the pulsed hydrogen plasma was efficacious in modifying PTFE surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 340–348, 2002     

Adsorption and desorption properties of expanded poly(tetrafluoroethylene) films grafted with DMAEMA and their regeneration

An investigation was undertaken on the adsorption and desorption properties of the expanded poly (tetrafluoroethylene) (ePTFE) films grafted with 2‐(dimethylamino)ethyl methacrylate (DMAEMA) to anionic dye anions with one to three sulfonic groups in response to temperature changes. The amount of adsorbed metanil yellow (MY) anions increased with the grafted amount and most of the dimethylamino groups appended to the grafted PDMAEMA chains worked as an adsorption site to MY anions for the DMAEMA‐grafted ePTFE (ePTFE‐g‐PDMAEMA) films with the grafted amounts of higher than 1.1 mmol/g. When the dye‐anion‐adsorbed ePTFE‐g‐PDMAEMA films were alternately immersed in water at two different temperatures, dye anions were desorbed from the ePTFE‐g‐PDMAEMA films at higher temperatures without any chemical agents. The amount of desorbed dye anions increased with an increase in the temperature of water from 40 to 80°C. Desorption of dye anions is caused by either deprotonation of dimethylamino groups appended to the grafted PDMAEMA chains or thermosensitive contraction of the grafted PDMAEMA chains. These results indicate that the ePTFE‐g‐PDMAEMA films can be applied as a regenerative ion‐exchange membrane for adsorption and desorption processes of anionic compounds in response to the temperature change. The thermally regenerative ion‐exchange properties of the ePTFE‐g‐PDMAEMA films was superior to that of the PE‐g‐PDMAEMA films reported in our previous article in the fact that the total degree of desorption was higher for the ePTFE‐g‐PDMAEMA films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

X-ray diffraction study of crystal transformation and molecular disorder in poly(tetrafluoroethylene)

The intermolecular and intramolecular disorders, and the crystalline phase transition in poly(tetrafluoroethylene) are examined by X-ray diffraction between 20° and 250°C. A presence of the crystalline phase transition around T_t = 150°C is confirmed by the rapid decrease in the intensity of the Bragg reflection 1015. This phase transition is ascribed to the abrupt increase of the intermolecular translational disorder along the chain. From the quantitative analysis of the profile of the 0015 reflection, it is found that the increase in the translational disorder described above is accompanied by the excitation of the intramolecular disorder in conformation. The intramolecular disorder in conformation below T_t is found to be due mainly to the thermal excitation of trans conformation in the usual 15-7 helix. Further increase in disorder in conformation is found above T_t, which is due to the excitation of gauche conformation. The fraction of trans conformation increases up to 40% with the increase of temperature, in good agreement with the theoretical calculation. The fraction of gauche conformation above T_t is also estimated to give, for example, 7.5 × 10^?3 at T = 214°C.     

Tribological action of metallic fillers in poly(tetrafluoroethylene) composites

The tribological behavior of poly(tetrafluoroethylene) composites filled with various metallic particles was investigated under the extreme friction conditions of a heavy load and reciprocation with a small amplitude. Two obviously distinct friction stages corresponding to the contact conditions were found. The phenomena of the accumulation of fillers on the contact surface and extrusion wear of the poly(tetrafluoroethylene) matrix were also observed. Based on the experimental results, the actions of metallic fillers on the transfer film formation were analyzed. It was noted that the transfer and accumulation of fillers could actually be considered to be an assimilating process of the friction pairs. Accordingly, the physical model of the transfer film formation process was described and some suggestions on the mechanism of load‐supporting actions of hard fillers were also proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1832–1840, 2002     

Radiation‐initiated graft polymerization of methylmethacrylate onto poly(tetrafluoroethylene): Characterization by 1H‐NMR

A broad‐line ¹H‐NMR study was carried out to examine the local structure of poly(methylmethacrylate) (PMMA) grafted onto Poly(tetrafluoroethylene) (PTFE). The NMR spectra were observed for three different samples with 1.0, 5.4, and 7.0 wt % PMMA over the temperature range from 150 to 380 K. With the help of selectively deuterated PMMA (PMMA‐d₅ and PMMA‐d₈)‐grafted samples, the NMR spectra were analyzed in terms of two components—a Gaussian (G) component, and a Lorentzian (L) component. Based on the second moments (〈ΔH²〉) analysis, the L and G components were attributed to the ¹H–¹H dipolar interactions within one CH₃ group and the interactions of CH₃ groups that are closely located in aggregated PMMA chains. Combining the results with the temperature dependence of 〈ΔH²〉 and the angular resolved XPS, the location and rotational motion of PMMA grafted onto PTFE are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1386–1394, 1999     

Rare earth compounds modified carbon black filled powdered natural rubber: Preparation,morphology and properties

Ten types of rare earth (RE) compounds modified carbon black (HAF‐RE) were prepared using chemical‐deposit method, then HAF‐RE were mixed with natural rubber latex to prepare HAF‐RE filled powdered natural rubber [P(NR/HAF‐RE)] by a carbon black/rubber latex coagulation method. It is found that most of the P(NR/HAF‐RE) vulcanizates showed better mechanical properties, especially higher tensile modulus, and tensile strength, compared with none‐rare earth modified carbon black filled powdered natural rubber [P(NR/HAF)]. Dysprosium (Dy) modified carbon black (HAF‐Dy) filled powdered natural rubber [P(NR/HAF‐Dy)] was chosen for intensive investigation because of its better comprehensive mechanical properties. It is found that the adding of Dy compounds could help to get smaller particles with narrower particle size distribution, and results from the SEM analysis show that carbon black has been dispersed in rubber matrix uniformly with diameter of 50–150 nm. The TEM analysis showed that Dy compounds could obviously reduce the aggregation of primary particles of carbon black, and promote the dispersion of carbon black in P(NR/HAF‐Dy) particles. © 2008 Wiley Periodicals, Inc. JAppl Polym Sci 2008     

Effects of surface modification by remote hydrogen plasma on adhesion in poly(tetrafluoroethylene)/copper composites

Poly(tetrafluoroethylene) (PTFE) sheet was modified with the remote hydrogen plasma, and the effect of the modification on adhesion between the PTFE sheet and copper metal was investigated. The remote hydrogen plasma was able to make PTFE surfaces hydrophilic without etching. In the modification process, defluorination and oxidation occurred on the PTFE surface. Reactivity of defluorination was 25% (estimated from the concentration of CF₂ component) −39% (estimated from the F/C atom ratio). Surface modification of PTFE surface by remote hydrogen plasma contributed to the adhesion between PTFE and copper metal. Peel strength was improved from 7.5 to 92 mN/5 mm by surface modification by a factor of 12. Failure of the PTFE/copper adhesive joint occurred at the interface between the PTFE and copper metal layers, rather than in the inner layer of the PTFE polymer or copper metal layers. Remote hydrogen plasma treatment is a preferable pretreatment of PTFE surface for the fabrication of PTFE and copper metal composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2191–2200, 1999