The influence of cobaltous chloride modification on physical properties and microstructure of modified PAN fiber during carbonization

Modification of polyacrylonitrile (PAN) fibers with cobaltous chloride has increased crystal size, crystallinity, and density, and also improved tensile strength and modulus of the resulting carbon fibers. In this study, the effect of cobaltous chloride modification on the physical properties, microstructure, and elemental composition of PAN fibers during the carbonization process was examined. The resultant carbon fibers developed from modified PAN fibers had a lower formation temperature of carbon basal planes than those fibers that developed from the original one. The modification process not only improved the tensile strength but also increased the tensile modulus by about 15% of the resulting carbon fibers at carbonization temperature of 1300°C. A higher stacking size (L_c), or a greater carbon basal plane in crystalline, is one of the reasons to improve the modulus and conductivity of the final carbon fibers. The modification process also increased the electrical conductivity by about 15% at 1300°C and by about 150% at 2500°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2409–2415, 1998     

Tensile,flow, and thermal properties of CaCO3‐filled LDPE/LLDPE composites

Calcium carbonate (CaCO₃)‐filled low‐density polyethylene (LDPE)/linear low‐density polyethylene (LLDPE) composites were fabricated by means of a twin‐screw extruder, and the tensile mechanical properties of the tubing with thickness of 0.5 mm made from these composites were measured at room temperature to identify the effect of the filler concentration on the properties of these composites. The results showed that the tensile elastic modulus increased roughly linearly with increasing weight fraction (?_f) of the fillers. The tensile fracture strength (σ_b) along longitudinal direction was obviously higher than that along transverse direction under the same test conditions, especially at higher filler concentration. The values of σ_b of the specimens along both the two directions achieved minimum at ?_f = 20%. Furthermore, the melt flow rate (MFR) and heat enthalpy (ΔH) of the composite materials were measured. It was found that both the MFR and the ΔH decreased with the addition of ?_f. The ΔH for the composite with LDPE/LLDPE ratio of 70/30 was higher than that of the composite with LDPE/LLDPE ratio of 50/50 at the same filler concentration, but contrary to the MFR. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1692–1696, 2007     

Processing and modeling of the mechanical behavior of natural fiber thermoplastic composite: Flax/polypropylene

A proposed modeling approach to calculate the mechanical properties of thermoplastic matrices reinforced with natural fibers is suggested. This model aims to solve the great deviation trends observed in the fiber content especially out of the range 10–40% volume fraction v_f. The model considers the transfer of fiber load hand over from fibers pull out to fiber load bearing. Different cases of the matrices are studied. Namely, matrix with either elastic or elastic plastic behavior, matrix with either brittle or ductile failure strain in comparison with the reinforcing fiber. Length and orientation efficiency factors for stiffness and strength are exploited. Another factor describing the even distribution of the fibers and the amount of corresponding matrix in adhesion is developed. This factor gives insight to the compounding process. Experimental plan is carried out to investigate the fiber loading of 0–50% v_f and different matrices namely polypropylene PP and maleated anhydride polypropylene MAPP. The suggested model is tested versus both the current experimental data and the literature results. The model shows good matching with the experimental results in a big domain of the fiber v_f. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mechanical properties of transparent poly(methyl methacrylate) nanocomposites reinforced with core–shell polyacrylonitrile/poly(methyl methacrylate) nanofibers

Having considered the mechanical and optical properties related to microstructure, the authors of the present work did a study of the in situ interface formation between polyacrylonitrile/poly(methyl methacrylate) (PAN/PMMA) core–shell nanofibers and PMMA resin so as to prepare reinforced PMMA nanocomposites (NCs). The NCs were produced using the dip-coating method. The core–shell nanofibers were generated via phase separation of PAN/PMMA solution during the conventional electrospinning. The results of attenuated total reflection-Fourier transform infrared spectroscopy, transmission electron microscope, and energy dispersive X-ray spectrometer confirmed the formation of core–shell structure of the PAN/PMMA nanofibers. According to the findings of the study, the NCs reinforced with 1.7% volume fractions (v _f) of the core–shell nanofibers, having the composition of 50/50 (PAN/PMMA), had the highest tensile and bending properties. The obtained results showed that by increasing the v _f of nanofibers from 1.7 to 2.9%, the tensile and bending moduli increased by 29.9 and 44.2%, respectively. Increasing v _f to 5.7% decreased the just-mentioned properties. Moreover, the transparency of NCs decreased by less than 1, 10, and 18%, respectively, when the aforementioned volume fractions were applied. The theoretical values for the tensile modulus were calculated using the models proposed by Manera, Pan, and Halpin–Tsai–Nielsen. The best prediction was made when the model proposed by Halpin–Tsai–Nielsen was applied.     

Discontinuous carbon fiber/polyamide composites with microencapsulated paraffin for thermal energy storage

This work focuses on the development of multifunctional thermoplastic composites with thermal energy storage capability. A polyamide 12 (PA12) matrix was filled with a phase change material (PCM), constituted by paraffin microcapsules (T_melt = 43 °C), and reinforced with carbon fibers (CFs) of two different lengths (chopped/CF “long”[CFL] and milled/CF “short” [CFS]). DSC tests showed that the melting/crystallization enthalpy values increase with the PCM weight fraction up to 60 J/g. The enthalpy was 41–94% of the expected value and decreased with an increase in the fiber content, because the capsules were damaged by the increasing viscosity and shear stresses during compounding. Long CFs increased the elastic modulus (+316%), tensile strength (+26%), and thermal conductivity (+54%) with respect to neat PA12. Thermal imaging tests evidenced a slower cooling for the samples containing PCM, and once again the CFS-containing samples outperformed those with CFL, due to the higher effective PCM content. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47408.     

Auxetic polypropylene films

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (～0.15‐mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in‐plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being ν_xy = ?1.12 ± 0.06 and E_x = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are ν_yx = ?0.77 ± 0.01 and E_y = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517–528, 2005. © 2005 Society of Plastics Engineers     

Electrical and thermal conductivities of polyethylene composites filled with biaxial oriented short-cut carbon fibers

Polyethylene composites filled with various types of carbon fiber were prepared for electrical and thermal conductivity measurements. By estimation of the anisotropic parameter (Hermans' parameter), the fibers were confirmed to be significantly biaxially oriented in the composites. The critical volume fractions in the electrical conductivity of these composites for the two oriented directions (X and Y) were equal to each other and smaller than that for a direction (Z) vertical to the above. The electrical anisotropy, i.e., ratio of electrical conductivity of the composite for the Z direction to the X and Y directions varied drastically with increase in filler content. The longer the length of carbon fiber was, the higher became the electrical conductivity of the biaxially oriented carbon fiber composites for all directions. But, the thermal conductivity of the composite was almost unchanged for the Z direction, even if fiber length was sufficiently long. Our equation, previously proposed, proved adaptable to these thermal conductivities. The factors of C_p and C_f in the equation are kept unchanged, in spite of increasing fiber length. © 1994 John Wiley & Sons, Inc.     

Elastic constants and thermal expansivity of gel-spun polyethylene fiber and its composites

The five independent stiffness constants, C₁₁, C₃₃, C₄₄, C₆₆, and C₁₃, and the axial and transverse thermal expansivity of unidirectional gel-spun polyethylene fiber reinforced composites have been measured as functions of fiber volume fraction V_f. The axial extensional modulus C₃₃ and axial Poisson's ratio v₁₃ follow the rule of mixtures, while the axial shear modulus C₄₄, transverse shear modulus C₆₆, and transverse plane-strain bulk modulus C_t ( = C₁₁ − C₆₆) obey the Halpin-Tsai equation. Extrapolation to V_f = 1 gives the five stiffness constants of gel-spun polyethylene fiber. The tensile property of the fiber is highly anisotropic, with the axial Young's modulus about 40 times higher than the transverse Young's modulus. In contrast, the axial shear modulus exceeds the transverse shear modulus by only 5%. A similar treatment of the thermal expansivity data in terms of the Schapery equations gives an axial thermal expansivity of −1.25 × 10⁻⁵ K⁻¹ and a transverse thermal expansivity of 11.7 × 10⁻⁵ K⁻¹ for the fiber.     

Thermal conductivity of ramie fiber drawn in water in low temperature

To understand the effect of extension of molecular chain in amorphous region in polymer fibers to thermal conductivity, the thermal conductivity, tensile modulus and crystal orientation angle of ramie fibers and those drawn by the stress of 17.4 kg/mm² (water treatment) in the water were investigated. The tensile modulus of ramie fiber in fiber direction increased from 61 to 130 GPa by drawing in the water. The crystal orientation angles of ramie fiber with and without water treatment were measured by X‐ray diffraction. The orientation degrees of ramie fibers without and with water treatment were estimated as 92.9 and 93.6%, respectively. Therefore, the tensile modulus increases two times as that of blank ramie by water treatment although crystal orientation angle does not change distinctly. The increasing of tensile modulus of ramie fiber by water treatment was explained by extension of the molecular chains in the amorphous region. Thermal conductivities of ramie fibers with and without water treatment were measured in the fiber direction in the temperature range from 10 to 150 K. Thermal conductivity of ramie fiber in the fiber direction increased by water treatment. The increasing ratio of thermal conductivity by water treatment agreed to that of sound velocity induced by increasing tensile modulus. Those results suggest that thermal conductivity of polymer fiber increase by the extension of molecular chains in the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2196–2202, 2006     

Improvement of high-temperature stability of PIP SiCf/SiC material through in situ grown BNNTs

In this paper, the effect of in situ grown boron nitride nanotubes (BNNTs) and preparation temperature on mechanical behavior of PIP (Precursor Infiltration and Pyrolysis) SiC_f/SiC minicomposites under monotonic and compliance tensile is investigated. In situ BNNTs are grown on the surface of SiC fibers using ball milling–annealing process. Composite elastic modulus, tensile strength, fracture strain, tangent modulus, and loading/unloading inverse tangent modulus (ITM) are obtained and adopted to characterize the mechanical properties of the composites. Microstructures of in situ grown BNNTs and tensile fracture surfaces are observed under scanning electronic microscopic (SEM). For SiC_f/SiC minicomposites with BNNTs, the elastic modulus, tensile strength, and fracture strain are all lower than those of SiC_f/SiC minicomposites without BNNTs, mainly due to high preparation temperature and the oxidation of the PyC interphase during the annealing process. Tensile stress–strain curves of SiC_f/SiC minicomposites with and without BNNTs are predicted using the developed micromechanical constitutive model. The predicted results agreed with experimental data. This work will provide guidance for predicting the service life of SiC_f/SiC composite materials and may enable these materials to become a backbone for thermal structure systems in aerospace applications.     

Theoretical study on composition-dependent properties of ZnO·nAl2O3 spinels. Part II: Mechanical and thermophysical

Knowledge on the mechanical and thermophysical properties of ZnO·nAl₂O₃ is essential for practical applications. Based on the first-principles calculations and the bond valence method, the disordered spinel-type structure of ZnO·nAl₂O₃ (n = 1–4) was constructed to investigate the composition-dependent mechanical and thermophysical properties. The effects of cation substitution on the hardness, elastic modulus, thermal expansion, and thermal conductivity were revealed from the insights into the chemical bonds. At a higher n, the tetrahedral bond is stronger, manifested as its higher hardness and bulk modulus as well as smaller thermal expansion coefficient. Meanwhile, the octahedral bond is weaker, leading to the lower hardness and bulk modulus, along with the larger expansion coefficient. In consequence, the hardness and elastic moduli of ZnO·nAl₂O₃ are improved moderately while the expansion coefficient is decreased with the rise of n. Due to the different vibration characteristics of Zn^IV and Al^IV, the cation disorder in the 8a site provides the primary source of phonon scattering, resulting in the dramatic reduction of thermal conductivity as n increases. The understanding offers guidance on the application-oriented design of new oxide spinels.     

Effect of different coagents on physico‐chemical properties of electron beam cured NBR/HDPE composites reinforced with HAF carbon black

The effect of different coagents on the physico‐chemical properties of NBR/HDPE composites reinforced with 40 phr (part per hundred part of rubber by weight) HAF carbon black and cured with accelerated electrons was investigated. The coagents N,N′‐methylene bisacrylamide (MBAAm) and trimethylol propane trimethacrylate (TMPTMA) were used at a constant content of 10 phr. The physico‐chemical properties such as tensile strength, tensile modulus at 50% elongation (M₅₀), elongation at break (E_b), hardness, soluble fraction (SF), swelling number (SN), electrical conductivity, and thermal properties were studied. The results obtained showed that the TMPTMA as a coagent is more effective than MDA in enhancing the mechanical and physical properties of NBR/HDPE vulcanized composites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Temperature dependence of the tensile strength of glass fiber–epoxy and glass fiber–unsaturated polyester composites

Epoxy and unsaturated polyester resins reinforced with random-planar orientation of short glass fibers were prepared and the temperature dependence of their tensile strength was studied. The tensile strength decreases as the temperature increases, and this tendency can be expressed in terms of critical fiber length l_c and apparent interfacial shear strength τ: where σ_cs is the tensile strength of composite reinforced with random-planar orientation of short fibers, L is the fiber length, d is the fiber diameter, σ_f is the tensile strength of fiber, σ_m is the tensile strength of matrix, u_f is the volume fraction of fiber, v_m is the volume fraction of matrix, and σ′_m is the stress of the matrix at fracture strain of the composite. The experimental strength values at room temperature are considerably smaller than the theoretical values, and this difference can be explained by the thermal stress produced during molding due to the large difference in the thermal expansion coefficient between glass fiber and matrix resin.     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

Ultrahigh molecular weight polyethylene fibers prepared using conical dies with varying dimensions

Dimensions of conical dies were found to have a significant influence on thermal, morphological, orientation, ultradrawing, and dynamic mechanical properties of the as‐prepared and/or drawn ultrahigh molecular weight polyethylene (UHMWPE) fiber specimens prepared in this study. Many demarcated “micro‐fibrils” were found paralleling to fiber direction of the as‐prepared UHMWPE fiber specimens. The percentage crystallinity, melting temperatures, orientation factor (f_o) and achievable draw ratio (D_ra) values of each as‐prepared UHMWPE fiber specimen prepared at a fixed length of outlet land reach a maximum value, as the entry angles of the conical die approach the optimum value at 75°. The maximum f_o and D_ra values obtained for each F₂₀^75‐y as‐prepared fiber series specimens prepared using the optimum entry angle reach another maximum value as their length of outlet land approach the optimum value of 6.5 mm. The ultimate tensile strengths and moduli of the drawn UHMWPE fibers prepared at the optimum entry angle and length of outlet land are significantly higher than those of fibers prepared at other conditions but stretched to the same draw ratio. Possible reasons accounting for the above interesting properties were discussed in this study. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Enskog modulus,bρχ, for the gaseous and liquid states of carbon dioxide

The PVT behavior of carbon dioxide was used to establish a correlation for the Enskog modulus, bρχ in the dense gaseous and liquid regions. This modulus is presented for reduced temperatures ranging from T_R = 0.90 up to T_R = 3.5 and reduced pressures up to P_R = 40. The Enskog modulus finds use in the calculation of the effect of pressure on viscosity, thermal conductivity, and self-diffusivity. The value of the Enskog modulus for carbon dioxide at the critical point has been calculated to be (bρχ)_c = 0.885.     

Polyacrylonitrile solution homogeneity study by dynamic shear rheology and the effect on the carbon fiber tensile strength

Poly(acrylonitrile‐co‐methacrylic acid) (PAN‐co‐MAA)/N,N‐dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70°C, the polymer solution became less elastic (more liquid‐like) with a ～60% reduction in the zero‐shear viscosity. Relaxation spectra of the PAN‐co‐MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, τ_d), corresponding to an about 8% decrease in viscosity average molecular weight. The log‐log plot of G′ (storage modulus) versus G″ (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN‐co‐MAA/DMF solutions were prepared, and the precursor fibers were processed using gel‐spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G′ versus G″ log‐log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber. POLYM. ENG. SCI., 56:361–370, 2016. © 2016 Society of Plastics Engineers     

Thermal,mechanical, and rheological properties of biodegradable polybutylene succinate/carbon nanotubes nanocomposites

Biodegradable poly(butylene succinate)/carbon nanotubes nanocomposites were prepared by melt mixing process, and the influence of carbon nanotubes on the properties of the nanocomposites was investigated. Differential scanning calorimetry showed that crystallization temperature (T_c) increase with increasing carbon nanotube content. Improvement of tensile modulus was observed by the addition of carbon nanotubes compared with pure poly(butylene succinate). Electrical conductivity showed that conductivity of polybutylene succinate/carbon nanotube composites increased with addition of carbon nanotube content. The storage moduli of polybutylene succinate/carbon nanotube composites are higher than the neat polybutylene succinate. The processability of polybutylene succinate/carbon nanotubes composites was improved and more pronounced in higher content of carbon nanotubes. POLYM. COMPOS., 31:1309–1314, 2010. © 2009 Society of Plastics Engineers     

Interrelation of mechanical and optical properties of plasticized epoxy polymers

A series of cold-setting epoxy polymers, plasticized with different amounts of plasticizer, ranging between 0 and 90% by weight of the amount of the epoxy prepolymer, were studied for their mechanical, optical, and fracture behavior properties. Quantities defining the mechanical properties were considered: the elastic modulus E, Poisson's ratio v, and fracture tensile stress σ_f. These were accurately measured with electric strain gauges in specimens tested in a 5-ton Instron tester. The optical behavior was characterized by the stress optical coefficients of the materials in both principal directions, α and β, as well as by the coefficient of optical anisotropy, ζ. The values of these quantities were measured by a Fizeau interferometric method. Finally, the optical method of caustics was applied to cracked epoxy polymer specimens to provide a new experimental technique for determining the stress optical properties of these polymers in terms of their mechanical properties. This method was used to check the previous results found by established experimental methods.     

Effect of tensile strain on the use of the WLF equation

The effect of finite elongation on superposed infinitesimal torsional oscillations has been determined on two propellants, a carbon black-filled rubber and Solithane 113 (Galcit I), as a function of temperature at various fixed frequencies. Torsional storage modulus—temperature data for carbon black-filled rubber and propellant show that the effect of the imposed tensile elongation cannot be explained by any simple temperature–elongation shift relationship. The shift factors for the torsional moduli of these two polymeric systems have been calculated as a function of temperature at various tensile elongations. The WLF constants C₁ and C₂ have been computed for these systems as a function of the elongation. The constants decrease with increasing elongation. The values of the constants at 0% elongation are larger than those commonly found in unfilled materials. The temperature dependence of the shift factor of the torsional storage modulus was found to differ from that of the loss modulus in the cases of carbon black-filled rubber and propellant. This difference is slight for the rubber and large for the propellant. The effect of increased elongation is to increase the difference in the shift behavior of the moduli for each of these filled polymers. The shape of the loss tangent curve of the propellants examined indicates that these propellants are not thermorheologically simple.