Preparation and characterization of poly (ethylene glycol) grafted Ca-alginate fibers by γ-irradiation for biomedical applications

Radiation processing, being a physical process, is an environmentally friendly alternative to chemical modifications. It is economically viable, safe, and possesses several advantages over other conventional methods employed for modification and grafting. To improve the physico-mechanical properties of Ca-alginate fiber (CaAF), poly (ethylene glycol) (PEG) was grafted by applying γ-radiation of different intensities. The effect of γ-irradiation on the physico-mechanical, thermal, morphological, thermal and water aging, water, and simulated body fluid (SBF) uptake were evaluated. FT-IR results confirmed that PEG was successfully grafted onto Ca-alginate fibers by γ-irradiation. From the detailed experimental results, irradiation doses and PEG concentration were optimized for grafting processes. The results showed that 50% PEG and 2.5?kGy irradiation dose yielded the highest tensile strength. Differential scanning calorimetric (DSC) analysis showed that with increasing γ-intensity a decrease of dehydration temperature of the fibers had occurred. On the other hand, the glass transition temperature (T _g) increased with increasing irradiation dose. The tensile cracked surfaces of the grafted alginate fibers were analyzed by scanning electron microscope (SEM) in order to monitor their surface morphologies. The SEM images of the cracked surfaces demonstrated that spherical shape rods were present for irradiated fiber sample while no such rods were observed for non-irradiated fibers. The characteristic data obtained from SBF and water uptake, and water and thermal aging experiments indicated that CaAF grafted with 50% PEG by applying 2.5?kGy γ-irradiation can be potentially employed for biomedical purposes, such as surgical suture.     

Changes in the fine structure of silk fibroin fibers following gamma irradiation

The physicochemical changes of silk fibers irradiated with γ-rays was studied in relation to the amount of absorbed does in the range 0–21 Mrad. The yellowing index (b/L) suddenly increased at low dose for both raw and degummed silk fibers. An equilibrium value was attained from 10 Mrad upward. The tensile properties were significantly affected by exposure to γ-rays. Both strength and elongation at break decreased at almost the same rate and extent, attaining a final value that was one-half of the untreated control. The birefringence and isotropic refractive index of exposed silk fibers decreased, the effect being larger in the low dose range, suggesting a decrease of crystallinity and molecular orientation. X-ray diffraction curves, however, demonstrated that the crystalline structure remained unchanged even after exposure of the highest γ-ray dose. The thermal behavior evaluated by DSC and TMA measurements showed that the γ-irradiation induced a slight decrease of thermal stability in irradiated silk fibers, this effect being detectable only at 21 Mrad of the absorbed dose. The dynamic viscoelastic behavior suggested that the thermal movement of the fibroin molecules in the amorphous and crystalline regions increased with increasing absorbed dose, attributing to the physicochemical modifications induced by the ionizing radiations. © 1994 John Wiley & Sons, Inc.     

Structure–property relationships in glass reinforced polyamide,part 2: The effects of average fiber diameter and diameter distribution

We present the results of an extensive study of the influence of average fiber diameter and the width of the diameter distribution on the performance of injection‐molded glass‐fiber reinforced polyamide 6,6. In the average fiber diameter range from 9 to 18 μm, dry‐as‐molded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fiber diameter. The influence of broadening the fiber diameter distribution by blending glass fiber samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment, the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fiber diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fiber diameter was above 14 μm. Residual fiber length correlated significantly with fiber diameter with a lower average length for thinner fibers. The interfacial shear strength was found to be in the range of 26–34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fiber diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fiber diameter, which is more heavily weighted to the thicker fibers in the distribution. POLYM. COMPOS., 28:331–343, 2007. © 2007 Society of Plastics Engineers     

Maleated polypropylene film and wood fiber handsheet laminates

The grafting effect of maleic anhydride (MA) as an interfacial bonding agent and its influence on the tensile strength properties of thermomechanical pulp handsheet‐isotactic polypropylene (iPP) film laminates was studied. For the MA treated with benzoyl peroxide (BPO) as an initiator, tensile strength properties increased 76% with PP film over untreated laminates. The optimal strength properties were obtained with a MA and BPO ratio of 2:1. A strong correlation was observed between the number of fibers in the web and tensile strength properties for both handsheet drying conditions. The R² values were 0.95 for air‐dry conditions and 0.94 from oven‐dry conditions. Scanning electron microscopy images also showed the effectiveness of MA loading on the surface of thermomechanical pulp fibers due to increased fiber failure, which occurred without fiber being pulled out from the PP matrixes. Crystallinity and heat flow were determined using differential scanning calorimetry (DSC) and increased as expected as the ratio of MA and BPO increased from 0:0 to 2:1. These results were also in accordance with the morphological observations at the fracture surface, Fourier transform infrared spectra, and thermal analysis. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

γ-射线辐照对聚丙烯腈纤维结构和强度的影响

采用γ-射线辐照方法对在氮气介质中的聚丙烯腈纤维进行处理,探索辐照剂量对纤维单丝拉伸强度和复合材料界面性能的影响。研究结果表明：在辐照剂量10-1000kGy范围内,随着辐照剂量的增加纤维单丝拉伸强度逐渐降低,同时辐照使得复合材料的层间剪切强度降低。进而采用原子力显微镜（AFM）对纤维表面形貌进行观察,用红外光谱（FT-IR）表征纤维表面化学结构,用X射线衍射（XRD）分析结晶状态,用差示扫描量热仪（DSC）测定纤维的耐热性能。     

Electrical conductivity of γ-irradiated native and mercerized cotton celluloses

In the present study the electrical conductivity (σ) of ball-milled and NaOH-treated cotton fibers were measured in vacuum. The induced electrical conductivity and the activation energy ΔE of γ-irradiated samples were measured as a function of radiation doses and at various temperatures. It was found that γ-irradiation of cotton fibers either decreases or increases its electrical conductivity. Thus, it was found that γ-irradiation of cotton reduces the conductivity of the samples having particle sizes ranging from 0.07 to 0.11 mm and the magnitude of the reduction diminishes as the particle size increases. The results have also shown that, for any given concentration, γ-irradiation of NaOH-treated samples causes an increase of the measured electrical conductivity.     

Fatigue behavior and relation between fatigue resistance and tensile properties of poly(para-phenylene-co-3,4'-oxydiphenylene terephthalamide) fiber

The poly(para-phenylene-co-3,4′-oxydiphenylene terephthalamide) (PPODTA) fiber is one of the high strength organic fibers, and it has been reported that the PPODTA fiber has superior fatigue resistance. The high strength fibers are used in the applications to utilize their high mechanical properties in general. Therefore, the long-term durability of these fibers is also required. In this study, the fatigue tests were conducted for the PPODTA fibers. As a result, it was found that the PPODTA fibers were able to be fractured by the cyclic tensile stress, and the fatigue behavior was influenced by the stress conditions. In addition, the single fiber tensile tests were also conducted for the PPODTA fibers, and the relation between the tensile properties and the fatigue resistance of the PPODTA fiber was investigated. The fatigue resistance of the PPODTA fiber was increased with the decrease of the fiber diameter and the increase of the tensile modulus.     

Effects of gamma radiation on two aromatic polysulfones

Two aromatic polysulfones, poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylidene-1,4-phenylene) (I) and poly (oxy-1,4-phenylenesulfonyl-1,4-phenylene) (II), undergo crosslinking and chain scission at 30°C during γ-irradiation, the former being predominant in vacuum and the latter in air. Both processes occurred more readily in I, which contains isopropylidene linkages. Gel measurements gave G(crosslink) = 0.051, G(scission) = 0.012 for this polymer at 30°C in vacuum. Increased irradiation temperatures resulted in higher crosslinking and gas yields, especially above the glass transition temperature. The tensile strength, flexural strength, and modulus of I were unaffected by γ-irradiation up to about 50 Mrad in air, but the strength decreased markedly at higher doses. The elongation at break decreased progressively with dose. For both polymers, G(gas) = 0.04 at 30°C with the main products being SO₂, H₂, CO₂, CH₄, and H₂O.     

The in situ polymerization of vinyl monomers in polyester yarns

The effects of a pretreatment of polyester (PET) yarns with a strongly interacting solvent such as dimethylformamide (DMF) on vinyl monomer incorporation were investigated. When the DMF pretreatment is carried out at high temperatures (above 120°C), the swollen PET structure is stabilized by solvent-induced secondary crystallization. This substrate is highly suitable for the incorporation of vinyl monomers. In situ polymerization of vinyl monomers in DMF-treated PET was investigated using chemical and γ-irradiation polymerization techniques, both in the presence and in the absence of excess monomer outside the PET fibers. When polymerization was carried out in a system in which a constant supply of free radicals was available from the outside of the PET fibers, lower initiator concentrations and smaller γ-irradiation doses were necessary. These results are attributed to a low efficiency of the initiator inside the PET fiber due to mobility restrictions. Water uptake and moisture regain of PET yarns containing poly(hydroxyethyl methacrylate) and poly(acrylic acid) were also investigated. When most of the vinyl polymer was inside the PET fiber, water absorption was limited. The changes in mechanical properties of the PET yarns resulting from the DMF pretreatment were partially reversed by in situ polymerization of vinyl monomers.     

Influence of Processing Parameters on the Strength of Fluoride Glass Fibers

The different factors affecting the tensile strength of heavy-metal fluoride glasses are presented. Surface crystals were found to be responsible for the lower fiber strength. The tensile strength of fluoride glass fibers can be increased by controlling the preform surface and drawing in a dry atmosphere. Using lower draw temperature and dual polymeric coatings increases the strength. Finally, phosphate glass overclad on fluoride glass fiber can be used to prevent surface hydrolysis during the drawing process and increases the tensile strength of fibers due to formation of compressive stress on the outside of the glass fiber.     

Influence of interfacial interactions on the properties of PVC/cellulosic fiber composites

The surface properties at the interface between thermoplastic and cellulosic fibers strongly influence the mechanical properties of plastic/cellulosic fiber composites. This paper examines the role of surface acid-base properties of plasticized PVC and cellulosic fibers on the mechanical properties of the composites. The acid-base surface characteristics of cellulosic fibers were modified by treating the fibers with γ-aminopropyltriethoxysilane (A-1100), dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene. The empirical acid (K_A) and base (K_D) characteristics (i.e., electron donor/acceptor abilities) of untreated and treated fibers, as well as plasticized PVC, were determined using inverse gas chromatography (IGC) technique. These parameters were used to yield information on the acid-base pair interactions that were correlated with the tensile and notched Izod impact properties of the composites. Acid-base pair interactions have been found to be a valuable parameter in the design of surface modification strategies intended to optimize the tensile strength of the composites. By tailoring the acid-base characteristics of cellulosic fibers and plasticized PVC, a composite with equal tensile strength and greater modulus than unfilled PVC was developed. However, the acid-base factors did not correlate with tensile modulus, the elongation at break, and the notched Izod impact property of PVC/newsprint fiber composites. Aminosilane has been observed to be a suitable adhesion promoter for PVC/wood composites improving significantly the tensile strength of the composites. Other treatments (dichlorodiethylsilane, phtalic anhydride, and maleated polypropylene) were found to be ineffective, giving similar strength compared to the composites with untreated cellulosic fibers. FTIR spectroscopy results suggested that aminosilane was effective because treated cellulosic fibers can react with PVC to form chemical bonds. The resulting bond between PVC and cellulosic fibers accounts for the effectiveness of aminosilane, when compared with other coupling agents.     

The adhesion of elastomer-coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers

E-glass fibers were subjected to various surface treatments to study the interfacial adhesion with an epoxy matrix by means of the fragmentation test. The glass fibers considered were both untreated and treated with γ-aminopropyltriethoxysilane (γ-APS). In addition, glass fibers were coated with a thin layer of a crosslinkable elastomer including (or not) a silane coupling agent. To evaluate the effect of the coating process, the glass fibers were also passed through the pure solvent (washed fibers). The tensile strength of glass fibers at short length (near the critical length, l_c, for the fragmentation test) cannot be measured directly, thus, extrapolation techniques were used. The Weibull statistics technique was applied and accurately described the tensile strength data of the tensile strength at various fiber gauge lengths for the different surface treatments. Nevertheless, the Weibull parameter, m, changes with the gauge length, and therefore, the extrapolation value at l_c depends on the method. The tensile strength of the silane-treated glass fibers is higher than for the untreated fibers, in agreement with reported data. This effect could be attributed to the protection against water provided by the silane sizing. The coating process does not induce any damage of the glass fibers since the washed fibers display mechanical properties close to those obtained for the untreated fibers. An additional effect is observed for the elastomer-coated fibers which present the highest tensile strength. This effect could be attributed to an improved protection and/or elimination of the weakest filaments in the glass strand during the treatment.     

Biodegradable biocomposites from poly(butylene adipate‐co‐terephthalate) and miscanthus: Preparation,compatibilization, and performance evaluation

Miscanthus fibers reinforced biodegradable poly(butylene adipate‐co‐terephthalate) (PBAT) matrix‐based biocomposites were produced by melt processing. The performances of the produced PBAT/miscanthus composites were evaluated by means of mechanical, thermal, and morphological analysis. Compared to neat PBAT, the flexural strength, flexural modulus, storage modulus, and tensile modulus were increased after the addition of miscanthus fibers into the PBAT matrix. These improvements were attributed to the strong reinforcing effect of miscanthus fibers. The polarity difference between the PBAT matrix and the miscanthus fibers leads to weak interaction between the phases in the resulting composites. This weak interaction was evidenced in the impact strength and tensile strength of the uncompatibilized PBAT composites. Therefore, maleic anhydride (MAH)‐grafted PBAT was prepared as compatibilizer by melt free radical grafting reaction. The MAH grafting on the PBAT was confirmed by Fourier transform infrared spectroscopy. The interfacial bonding between the miscanthus fibers and PBAT was improved with the addition of 5 wt % of MAH‐grafted PBAT (MAH‐g‐PBAT) compatibilizer. The improved interaction between the PBAT and the miscanthus fiber was corroborated with mechanical and morphological properties. The compatibilized PBAT composite with 40 wt % miscanthus fibers exhibited an average heat deflection temperature of 81 °C, notched Izod impact strength of 184 J/m, tensile strength of 19.4 MPa, and flexural strength of 22 MPa. From the scanning electron microscopy analysis, better interaction between the components can be observed in the compatibilized composites, which contribute to enhanced mechanical properties. Overall, the addition of miscanthus fibers into a PBAT matrix showed a significant benefit in terms of economic competitiveness and functional performances. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45448.     

Development of waste tire modified concrete

In this study, waste tire modified concrete was investigated experimentally. Two types of waste tire configurations were evaluated. One was in the form of chips, or particles, and the other was in the form of fibers. For the waste tire chip modified concrete, surface treatment by saturated NaOH solution and physical anchorage by drilling a hole at the center of the chips were also investigated. For the waste tire fiber modified concrete, fibers with various aspect ratios were utilized. A hybrid fiber reinforcement using waste tire fiber and polypropylene (PP) fiber was also investigated. The effect of waste tire resources (car tires or truck tires) on the strength and stiffness was evaluated. A total of 10 batches of concrete, which yielded sixty φ152.4×304.8 mm cylinders, were prepared. Compressive strength, compressive modulus of elasticity, Poisson's ratio, and split tensile strength tests were conducted on the prepared samples. Ways to further recover the lost strength and stiffness of waste tire modified concrete were discussed based on the test results.     

Study of SiC fiber axial compressive behavior using tensile recoil measurement

SiC fibers have been widely investigated as reinforcements for advanced ceramic matrix composites owing to their excellent high-temperature properties. However, the axial compressive strength of SiC fibers has not been thoroughly studied. In this study, the compressive behavior of two SiC fiber types containing different compositions and thermal degradation were characterized by tensile recoil measurements. Results illustrated that the SiC fiber compressive strength was 30%–50% of its tensile strength, after heat treatment at 1200℃–1800℃ for 0.5 h in argon. The fiber compressive failure mechanism was studied, and a “shear-bending-cleavage” model was proposed for the recoil compression fracture of pristine SiC fibers. The average compressive and tensile strengths of the pristine SiC-II fiber were 1.37 and 3.08 GPa, respectively. After treatment at 1800℃ for 0.5 h in argon, the SiC-II fiber compressive strength decreased to 0.42 GPa, whereas the tensile strength reduced to 1.47 GPa. The mechanical properties of the fibers degraded after high-temperature treatment. This could be attributed to SiC grain coarsening and SiC_xO_y phase decomposition.     

Development of oriented morphology and tensile properties upon superdawing of solution-spun fibers of ultra-high molecular weight poly(acrylonitrile)

The uniaxial drawing of UHMW-PAN fibers spun from a dilute solution into methanol coagulation baths at different temperatures and the resultant structure and tensile properties of the drawn products were studied. Although the initial morphology of the fibers and the deformation mode in a lower draw ratio (DR_t) range were significantly dependent on the temperatures of the coagulation bath, the tensile properties at a given DR_t, as well as the maximum achieved ones, were comparable. Both the tensile modulus and strength increased steadily with the DR_t and reached 35 and 1.8 GPa, respectively, at the highest DR_t of ∼80. These tensile properties are among the highest ever reported for PAN fibers. The achievement of such high tensile properties for extremely drawn fibers is ascribed to the conformational changes of crystalline chains from the 3/1 helix to the planar-zigzag with increasing DR_t, the improvement in the uniformity of the fiber diameter along the fiber axis, and the decrease in fiber diameter. Indeed, the tensile strength of fibers prepared from a dilute solution and having comparable moduli increased with a decrease in the fiber diameters. The reciprocal of the strength was proportional to the square root of the diameter as suggested by the Griffith theory. Extrapolation to a zero diameter yielded an ultimate tensile strength of 2.4±0.1 GPa for a fiber having a maximum achieved tensile modulus of 35±1 GPa.     

Study on the acidic hydrolysis process of poly(N‐vinylformamide/acrylonitrile) fiber

A convenient method of preparing chelating fiber with amine groups on the fiber surface was developed. The precursor polymer of Poly(N‐vinylformamide/acrylonitrile) (P(NVF/AN)) was synthesized via solution polymerization, using N‐vinylforaimde as a functional monomer. The solution of P(NVF/AN) was spun through a wet spinning method and the precursor fiber was hydrolyzed in the hydrochloric acid solution to convert formamide moieties to the corresponding amine. The influence of hydrolytic conditions on hydrolysis degree, such as hydrolysis temperature, hydrolysis time, and hydrochloric acid concentrations were examined experimentally. The hydrolysis degree of the precursor fiber was evaluated by potentiometric and conductometric titrations. The changes of the structure and properties of the fibers were characterized through infrared spectroscopy, scanning electron microscopy, and tensile strength tester. The results showed that the hydrolysis degree was limited in acidic hydrolysis because of the electrostatic repulsion among the cationic amine groups and proton. The hydrolysis degree of precursor fiber reached nearly 60%, and the chelating fiber remained the adequate mechanical properties under the suitable hydrolysis condition. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Reinforcing performance of recycled PET microfibrils in comparison with liquid crystalline polymer for polypropylene based composite fibers

Recycled polyethylene terephthalate (rPET) used as an alternative reinforcing additive for polypropylene (PP) based composite fibers, compared with liquid crystalline polymer (LCP), was investigated. Both PP-LCP and PP-rPET composites were prepared as fiber using hot drawing process. The effects of draw ratios and compatibilizer dosages on morphology in relation to tensile properties of both types of the composite systems were studied. The variation of draw ratios resulted in much change of stress–strain behavior in compatibilized rPET composite system owing to the obvious difference in morphological change of rPET dispersed phase upon drawing. Tensile strength and extensibility of both composites system were significantly improved with compatibilizer loading. The tensile strength of compatibilized rPET-composite fibers was higher than that of the compatibilized LCP system. The obtained results demonstrated the high potential of rPET as a well-defined reinforcing material for PP based composite fiber under the improved interfacial adhesion promoted by compatibilizer.     

Producing high‐quality precursor polymer and fibers to achieve theoretical strength in carbon fibers: A review

The precursor fiber quality has a large impact on carbon fiber processing in terms of its performance, production yield, and cost. Polyacrylonitrile precursor fibers have been used commercially to produce strong carbon fibers with average tensile strength of 6.6 GPa. There is a scope to improve the average tensile strength of carbon fibers, since only 10% of their theoretical strength has been achieved thus far. Most attempts to increase the tensile strength of carbon fibers have been made during the conversion of precursor fiber to carbon fiber. This review highlights the potential opportunities to enhance the quality of the polyacrylonitrile‐based precursor fiber during polymer synthesis, spinning, and postspinning. These high‐quality precursor fibers can lead to new generation carbon fibers with improved tensile strength for high‐performance applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43963.     

Effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers

In this paper, polyborosilazane precursor was synthesied from HMDZ, HSiCl₃, BCl₃ and CH₃NH₂ using a multistep method. By controlling the storage conditions, parts of the polyborosilazane fibers were hydrolyzed. FT-IR, NMR, XRD, TEM and monofilament tensile strength test were employed to study the effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers. FT-IR and NMR results indicate that Si-N group in PBSZ reacts with H₂O to form Si-O-Si group. After pyrolysis reaction at 1400℃, Si-O-Si group will finally transformed into highly ordered cristobalite and β-quartz, resulting in formation of the wrinkled surface of the obtained SiBN ceramic fiber. The strip-like defects on fiber surface, according to monofilament tensile strength test, had a significant effect on mechanical property of the obtained SiBN ceramic fiber and caused no increase in fiber tensile strength of hydrolytic polyborosilazane fiber before and after pyrolytic process.