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1.
  • Al-Maqdasi, Zainab, 1986-, et al. (author)
  • Time-dependent properties of high-density polyethylene with wood/graphene nanoplatelets reinforcement
  • 2023
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 44:1, s. 465-479
  • Journal article (peer-reviewed)abstract
    • The effect of graphene nanoplatelets (GNPs) on the long-term performance of wood fiber/high-density polyethylene (HDPE) composite is investigated by using short-term creep tests with an efficient, faster data analysis approach. Previously, it was shown that the addition of GNPs at 15 wt% into HDPE reduces the viscoplastic (VP) strain developed during 2 h creep by ~50%. The current study shows that 25 and 40 wt% wood content in HDPE reduce the VP strains developed during 2 h creep time by >75% with no noticeable effect of the increased wood content. However, further addition of GNPs results in more than 90% total reduction in the VP strains. The current study shows that the development of the VP strains in the hybrid composites follows Zapas model. Viscoelastic (VE) response of these composites is nonlinear and thus is described by Schapery's model. Parameters for VP and VE models are obtained from the creep experiments and were validated in a separate loading-unloading test sequence. Results show a very good agreement between experiments and predictions for the studied materials as long as the micro-damage is not present.
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2.
  • Almgren, Karin M., et al. (author)
  • Contribution of wood fiber hygroexpansion to moisture induced thickness swelling of composite plates
  • 2010
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:5, s. 762-771
  • Journal article (peer-reviewed)abstract
    • One of the main drawbacks of wood fiber-based composite materials is their propensity to swell due to moisture uptake. Because the wood fibers are usually the main contributor to hygroexpansion, it is of interest to quantify the hygroexpansion coefficient of wood fibers, to compare and rank different types of fibers. This investigation outlines an inverse method to estimate the transverse hygroexpansion coefficient of wood fibers based on measurements of moisture induced thickness swelling of composite plates. The model is based on composite micromechanics and laminate theory. Thickness swelling has been measured on polylactide matrix composites with either bleached reference fibers or crosslinked fibers. The crosslinking modification reduced the transverse hygroexpansion of the composites and the transverse coefficient of hygroexpansion of the fibers was reduced from 0.28 strain per relative humidity for reference fibers to 0.12 for cross-linked fibers
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3.
  • Almgren, Karin M., et al. (author)
  • Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials
  • 2009
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:12, s. 1809-1816
  • Journal article (peer-reviewed)abstract
    • Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA-modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out-of-plane hygroexpansion of PLA and PLA/PP composites, under water-immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA-modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out-of-plane hygroexpansion, with a high-fiber fraction leading to large hygroexpansion. Fiber-matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 30:1809-1816, 2009.
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4.
  • Alsalmah, Hessa A., et al. (author)
  • Synthesis and characterization of PEG/CS-AgNO3 polymer nanocomposites for flexible optoelectronic and energy storage applications
  • 2024
  • In: Polymer Composites. - : WILEY. - 0272-8397 .- 1548-0569.
  • Journal article (peer-reviewed)abstract
    • The Polyethylene glycol (PEG) and Chitosan (CS)/silver nitrate (AgNO3) thin films were prepared by utilizing the casting technique to enhance their optical, dielectric, and electrical properties. Their physicochemical characteristics were investigated using a variety of techniques. The FT-IR study demonstrates that the addition of AgNO3 NPs results in a discernible difference in the intensities and locations of vibrational peaks of all bands, supporting the incorporation of AgNO(3)NPs inside the PEG/CS. The XRD analysis indicates that the peak at 2 theta = 23.1(degrees) broadens and strengthens proportionally with the increase of AgNO3 NPs. This observation suggests that the incorporation of AgNO3 NPs into PEG/CS results in a greater degree of amorphous characteristics compared to the PEG/CS blend. Additionally, when the amount of AgNO3 NPs increases in the PEG/CS, the energy band gap decreases, resulting in the creation of localized states between the valence and conduction bands. These polymer nanocomposite films' electrical conductivity, dielectric constant, and dielectric loss all increased with frequency increased and showed variance for various composite concentrations. These AgNO(3)NPs/PEG/CS films can be promising options for frequency-tunable nanodielectrics, flexible dielectric substrates, and bandgap-regulated materials for upcoming microelectronic, capacitive energy storage, and optoelectronic technologies, according to the experimental results.
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5.
  • Andersons, Janis, et al. (author)
  • Progressive cracking mastercurves of the transverse ply in a laminate
  • 2009
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:8, s. 1175-1182
  • Journal article (peer-reviewed)abstract
    • In this study, progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation-controlled and propagation-controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates.
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6.
  • Andersons, J., et al. (author)
  • Stiffness and strength of flax fiber/polymer matrix composites
  • 2006
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 27:2, s. 221-229
  • Journal article (peer-reviewed)abstract
    • Flax fiber composites with thermoset and thermoplastic polymer matrices have been manufactured and tested for stiffness and strength under uniaxial tension. Flax/polypropylene and flax/maleic anhydride grafted polypropylene composites are produced from compound obtained by coextrusion of granulated polypropylene and flax fibers, while flax fiber mat/vinylester and modified acrylic resin composites are manufactured by resin transfer molding. The applicability of rule-of-mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is considered.
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7.
  • Andersson, H.M., et al. (author)
  • Application of digital speckle photography to measure thickness variations in the vacuum infusion process
  • 2003
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 24:3, s. 448-455
  • Journal article (peer-reviewed)abstract
    • A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in-house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross-correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm. The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross-linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross-linking is reached.
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8.
  • Andersson, Magnus, et al. (author)
  • Computational fluid dynamics applied to the vacuum infusion process
  • 2005
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 26:2, s. 231-239
  • Journal article (peer-reviewed)abstract
    • An all-purpose computational fluid dynamics software is used for simulations of the vacuum infusion process. The study comprises simulations of a full three-dimensional two-phase flow through a porous medium. The medium that has an anisotropic, spatial- and time-dependent permeability is located in a complex mold with moving boundaries. With this generalization, different material combinations, processing conditions, and even other manufacturing techniques can be evaluated. The strength of the presented approach is exemplified by simulations of mold filling of a real part, using a typical vacuum infusion set-up. In addition to the overall development of the model, a number of specific aspects and phenomena are investigated and evaluated. Local lead of the flow front and a minor influence in overall flow front lead-lag, with no influence on the fill time, is the result of simulations of edge effects due to poor preform fitting.
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9.
  • Andersson, Magnus, et al. (author)
  • Flow-enhancing layers in the vacuum infusion process
  • 2002
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 23:5, s. 895-901
  • Journal article (peer-reviewed)abstract
    • The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.
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10.
  • Asp, Leif, et al. (author)
  • Prediction of failure initiation in polypropylene with glass beads
  • 1997
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 9-15
  • Journal article (peer-reviewed)abstract
    • The effect of glass bead content and residual stresses on failure initiation in isotactic polypropylene composites has been investigated by finite element analysis for the cases of interfacial debonding, plastic yielding, and cavitation. Residual thermal stresses are demonstrated to have a large effect on global failure initiation stress. Yielding and cavitation occur at higher global stresses than debonding. Modeling results, as well as previous experimental data, support debonding as the initial failure mechanism
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11.
  • Azhdar, Bruska, et al. (author)
  • Polymer-nanofiller prepared by high-energy ball milling and high velocity cold compaction
  • 2008
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 29:3, s. 252-261
  • Journal article (peer-reviewed)abstract
    • High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves.
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12.
  • Aziz, Shazed, et al. (author)
  • Experimental evaluation of the interfacial properties of carbon nanotube coated carbon fiber reinforced hybrid composites
  • 2015
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 36:10, s. 1941-1950
  • Journal article (peer-reviewed)abstract
    • A floating catalyst chemical vapor deposition (CVD) unit was utilized to grow CNT onto the surface of carbon fiber (CF). The surface morphology of the resultant fibers, CNT population density and alignment pattern were found to be depended on the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. In contrast to the neat‐CF reinforced composites, improved interfacial shear strength (IFSS) between CF and matrix were obtained when the surface of CF was coated by CNT. Particularly, CF treatment condition for CNT‐coating with 700°C reaction temperature and 30 min reaction time has shown a considerable increase in IFSS approximately of 45% over that of the untreated fiber from which it was processed. The proper justification of fiber–matrix adhesion featured by composite interfacial properties was explained through IFSS.
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13.
  • Bengtsson, Magnus, et al. (author)
  • Profile Extrusion and Mechanical Properties of Crosslinked Wood-Thermoplastic Composites
  • 2006
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 27:2, s. 184-194
  • Journal article (peer-reviewed)abstract
    • Challenges for wood-thermoplastic composites to be utilized in structural applications are to lower product weight and to improve the long-term load performance. Silane crosslinking of the composites is one way to reduce the creep during long-term loading and to improve the mechanical properties. In this study, silane crosslinked wood-polyethylene composites were produced by reactive extrusion and subsequently manufactured into rectangular profiles. The silane crosslinked composites were stored in a sauna at 90 °C to increase the degree of crosslinking. The toughness of the silane crosslinked composites was significantly higher than for the non-crosslinked composites. Improved adhesion between the wood and polyethylene phases is most likely the reason for the improved toughness of the crosslinked composites. There was no significant difference in flexural modulus between the crosslinked and non-crosslinked composites. In addition, impact testing showed that the impact strength of the crosslinked composites was considerable higher (at least double) than the non-crosslinked. The effect of temperature on the impact strength of the composites indicated slightly higher impact strength at _30 °C than at 0° and at 25 °C, and then an incrase in impact strength at 60 °C. Crosslinking also reduced the creep response during short-term loading. Moreover, scanning electron microscopy on the fracture surface of the crosslinked composites revealed good adhesion between the polyethylene and wood phases.
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14.
  • Doroudgarian, Newsha, et al. (author)
  • Moisture uptake and resulting mechanical response of bio-based composites. II. Composites
  • 2015
  • In: Polymer Composites. - : John Wiley and Sons Inc.. - 0272-8397 .- 1548-0569. ; 36:8, s. 1510-1519
  • Journal article (peer-reviewed)abstract
    • The durability of entirely bio-based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio-based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross-ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio-based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity. 
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15.
  • Enqvist, Evelina, et al. (author)
  • The effect of ball milling time and rotational speed on ultra high molecular weight polyethylene reinforced with multiwalled carbon nanotubes
  • 2016
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 37:4, s. 1128-1136
  • Journal article (peer-reviewed)abstract
    • Ultra high molecular weight polyethylene (UHMWPE) composites reinforced with multiwalled carbon nanotubes (MWCNT) were produced using planetary ball milling. The aim was to develop a more wear resistant composite with increased mechanical properties to be used in stress bearing joints. The manufacturing technique, using ball-milling to incorporate MWCNT into UHMWPE matrix was investigated. The effect of manufacturing parameters such as effect of ball milling time and rotational speed on final composite was analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), particle size distribution and contact angle measurements. Ball milling as mixing technique for UHMWPE based composites is not a new approach but yet, the effect of time, rotational speed, loading of milling jar and type of ball mill has not been reported properly for UHMWPE. 0.5 and 1 wt% UHMWPE/MWCNTs were manufactured at different rotational speed and mixing time. The results indicate that rotational speed rather than mixing time is important for dispersing MWCNTs
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16.
  • Ericson, Mats L., et al. (author)
  • The effect of microstructure on the elastic modulus and strength of performed and commercial GMTs
  • 2003
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 14:1, s. 35-41
  • Journal article (peer-reviewed)abstract
    • A new technique was used to fabricate performed glass fiber/polypropylene GMTs. The method utilizes thermoplastic powder and fiber roving in a spray-up procedure in which a porous perform in fabricated, heated and molded. The objective was to compare the properties of various preformed GMT composition with two commercial GMTs and to relate the mechanical properties to the microstructure of the materials. Preformed GMTs were fabricated with various fiber lengths and with or without a fiber/matrix adhesion promotor. Processing observation, microstructure, tensile creep modulus, and tensile strength of these preformed GMTs are reported. Fiber length and the addition of a fiber/matrix adhesion promotor had generally little effect on the modulus and strength of the preformed GMT. Comparisons with two structurally different commercial GMTs also showed negligible effects on modulus and strength. The major reason for this is suggested to be the inhomogeneities of the materials. The mechanical properties are controlled by local inhomogeneities rather than by the general microstructure of the material. These inhomogeneities arise from the fiber arrangement in the semi-finished sheet or perform. Since the microstructure of preformed GMT can be controlled, this material is well suited for future studies on the effect of better fiber dispersion.
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17.
  • Eslah, Farnaz, et al. (author)
  • Chemical modification of soybean flour-based adhesives using acetylated cellulose nanocrystals
  • 2018
  • In: Polymer Composites. - : Blackwell Publishing. - 0272-8397 .- 1548-0569. ; 39:10, s. 3618-3625
  • Journal article (peer-reviewed)abstract
    • In this study, two types of new bioadhesives formulated from abundant and renewable soybean flour (SF), acetylated soybean flour based adhesive (ASF), and soybean flour-based adhesive, were modified with acetylated cellulose nanocrystal (ACNC). The apparent viscosity and morphology of the adhesive formulations were characterized. The chemical composition of the formulations was evaluated by FT-IR spectroscopy and the effect of polyethilenimine (PEI) on the formulations was investigated using the proton nuclear magnetic resonance (1H NMR) spectra. Moreover, water resistance of produced plywood composites bonded with the bioadhesives was measured. The results of FT-IR and 1H NMR confirmed that chemical modifications of the SF occurred. The scanning electron microscopy (SEM) images showed less holes and cracks on the cross section of the ASF/PEI/NaOH and SF/PEI/NaOH/ACNC formulations. The results showed that the plywood specimens bonded with formulations of the ASF/PEI/NaOH (with a dry weight ratio of ASF/PEI: 5/1 and 6/1), and SF/PEI/NaOH/ACNC had good resistance to water. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers
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18.
  • España, J. M., et al. (author)
  • Antioxidant and antibacterial effects of natural phenolic compounds on green composite materials
  • 2012
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 33:8, s. 1288-1294
  • Journal article (peer-reviewed)abstract
    • The aim of this study is to establish the thermal performance of a biocomposite (Arbofill kokos®), stabilized with different natural phenolic additives, to check the antioxidant capacity of the resulting compounds. Different phenolic compounds (thymol, carvacrol, α-tocopherol, and tannic acid) were used as biobased additives and the concentrations ranged between 0.5 wt% and 2 wt%. The results obtained were compared with formulations containing a typical industrial petroleum-based antioxidant agent (octadecyl-3-(3,5-di-tert- butyl-4-hydroxyphenyl) propionate). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the antioxidant performance of the selected natural additives. The antimicrobial effect of these natural phenolic compounds was also studied by analyzing the growth of bacterial colonies. The comparison between the natural phenolic compounds and the petroleum-based antioxidant compound showed good antioxidant action for natural phenolic compounds; in all the mixtures of biocomposite and antioxidant agent the oxidation onset temperature (OOT) increased in a remarkable way, but the highest stabilization effect was achieved with α-tocopherol with provides a % increase on OOT of about 45%. With regard to antibacterial activity of the different natural phenolic compounds, thymol, and carvacrol showed interesting antibacterial properties against Staphylococcus aureus. Copyright © 2012 Society of Plastics Engineers.
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19.
  • Ferrero, B., et al. (author)
  • Green composites based on wheat gluten matrix and posidonia oceanica waste fibers as reinforcements
  • 2013
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 34:10, s. 1663-1669
  • Journal article (peer-reviewed)abstract
    • In this work, green composites from renewable resources were manufactured and characterized. A fibrous material derived from Posidonia oceanica wastes with high cellulose content (close to 90 wt% of the total organic component) was used as reinforcing material. The polymeric matrix to bind the fibers was a protein (wheat gluten) type material. Composites were made by hot-press molding by varying the gluten content on composites in the 10-40 wt% range. Mechanical properties were evaluated by standardized flexural tests. Thermo-mechanical behavior of composites was evaluated with dynamic mechanical analysis (torsion DMA) and determination of heat deflection temperature. Morphology of samples was studied by scanning electronic microscopy and the water uptake in terms of the water submerged time was evaluated to determine the maximum water uptake of the fibers in the composites. Composites with 10-40 wt% gluten show interesting mechanical performance, similar or even higher to many commodity and technical plastics, such as polypropylene. Water resistance of these composites increases with the amount of gluten. Therefore, the sensitiveness to the water of the composites can be tailored with the amount of gluten in their formulation.
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20.
  • Fällström, Karl-Evert, et al. (author)
  • A nondestructive method to determine material properties in anisotropic plates
  • 1991
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 12:5, s. 293-305
  • Journal article (peer-reviewed)abstract
    • Material parameters in anisotropic rectangular plates are determined in a nondestructive way. Real-time, TV-holography is used to determine frequencies and shapes of the first five modes of vibration of plates with free-free boundary conditions. According to rules given in the paper, finite element analysis is then used to determine two effective Young's moduli, the shear modulus, and the Poisson's ratio
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21.
  • Fällström, Karl-Evert (author)
  • Determining material properties in anisotropic plates using Rayleigh's method
  • 1991
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 12:5, s. 306-314
  • Journal article (peer-reviewed)abstract
    • Material parameters of anisotropic plates are determined. Rectangular anisotropic plates are tuned by changing the quotient between the length of the sides, so that the second and third modes of vibration, for free-free boundary conditions, degenerate into the well-known cross-shaped and ring-shaped modes, respectively. The first three modes of vibrations for these plates are determined by optical methods. The propagation of bending waves, generated by the impact of a ballistic pendulum on the plates, has also been optically studied. It is found that bending waves generated in the middle of the tuned plates will reach the boundaries of the plates simultaneously. This gives a relationship between main material parameters. Using this relation and Rayleigh's method for the first three modes of vibrations, the main material parameters for the plates, that is, the effective two Young's moduli, the shear modulus, and the Poisson's ratio, are determined
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22.
  • Fällström, Karl-Evert, et al. (author)
  • Nondestructive method to determine material properties in orthotropic plates
  • 1987
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 8:2, s. 103-108
  • Journal article (peer-reviewed)abstract
    • An electronic speckle pattern interferometer (ESPI) is used to determine modes of vibration in rectangular, orthotropic, free-free-plates; that is using a noncontact, nondestructive, optical method. It is shown, using the finite element method (FEM), that each of the first three modes of vibration in rectangular orthotropic plates has a strong dependence upon only one of the main material parameters, namely the in-plane shear modulus and the two Young's moduli, respectively. With this one-variable dependence it is a simple task to determine the effective material parameters. This method has several obvious advantages compared to the use of test bars and it can be extended to give a measure of the damping parameters and probably also be used for production control. Preliminary results are presented and discussed
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23.
  • Gebart, Rikard, et al. (author)
  • Measurement of in-plane permeability of anisotropic fiber reinforcements
  • 1996
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 17:1, s. 43-51
  • Journal article (peer-reviewed)abstract
    • Three of the most common methods (two with parallel flow and one with radial flow) for determination of the in-plane permeability tensor are studied both theoretically and experimentally. An error analysis shows that the difference between the methods is negligible if the error levels are equal. However, the radial flow method is found to be susceptible to large errors from mold deflection in an experimental comparison between the methods. Additional experiments with the radial flow method in a stiffer mold show that the method gives the same values for the permeability tensor as the other two methods. A new method with multiple cavities in parallel is proposed that combines the simplicity of the radial flow method with the stiff mold of the parallel flow method. Only mass and time need to be measured in one experiment and it eliminates the need to measure fluid viscosity, temperature, and injection pressure. The method depends on the availability of a reference material with known permeability.
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24.
  • Gong, Guan, et al. (author)
  • Toughening effect of cellulose nanowhiskers on polyvinyl acetate : Fracture toughness and viscoelastic analysis
  • 2011
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 32:10, s. 1492-1498
  • Journal article (peer-reviewed)abstract
    • The toughening effect of cellulose nanowhiskers (CNWs) on modified polyvinyl acetate (PVAc) was analyzed with the help of morphology, relaxation, and creep behavior. The CNWs together with bound moisture at the matrix/whisker interfaces resulted in significant improvement in resistance to crack initiation and propagation. The magnitude of plastic deformation of the nanocomposites was higher than that of the neat PVAc. The relaxation temperature decreased, while the width of the damping peak increased with increasing CNW and moisture contents. The results from creep modeling showed that the instantaneous elastic modulus first increased and then decreased with the addition of CNWs, while the time-dependent elasticity and viscosity decreased. The results suggested that the reinforcing effect of the CNWs was overwhelmed by the plasticizing effect of the bound moisture. Furthermore, low concentrations of CNWs significantly improved the fracture toughness of PVAc at the minor cost of strength, stiffness, and creep resistance. In this article, we present a novel approach to studying the toughening effect of CNWs on polymers using fracture tests and viscoelastic modeling
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25.
  • Hagstrand, P.-O., et al. (author)
  • Mechanical properties and morphology of flax fiber reinforced melamine-formaldehyde composites
  • 2001
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 22:4, s. 568-578
  • Journal article (peer-reviewed)abstract
    • The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber-matrix interface. In contrast, melamine-formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber-matrix interface. This suggests that the fiber-matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements
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26.
  • Hallander, Per, et al. (author)
  • Fast forming of multistacked UD prepreg using a high-pressure process
  • 2019
  • In: Polymer Composites. - : WILEY. - 0272-8397 .- 1548-0569. ; 40:9, s. 3550-3561
  • Journal article (peer-reviewed)abstract
    • In this article, the opportunities of fast forming of multistacked UD prepreg when using high-pressure forming were examined in an experimental study. Forming is often considered a bottleneck in manufacturing of composite aircraft parts and speeding up the process is, therefore, of great interest. A Quintus Flexform fluid cell press was used to create pressure of 100 to 400 bars. In the study, different lay-up sequences and thicknesses were tested for manufacturing of c-shaped coupons. Tests were performed at different temperatures and some of the samples were sandwiched with mild steel sheets referred to as a steel sheet dummy. A case study was also performed on a double-curved spar geometry. It was found that forming at a relatively high overall pressure level combined with an elevated temperature, created squeeze flow-related wrinkle formations, and radius thinning. With high pressure forming, material compression/compaction mechanisms showed to have great influence on the forming result. This differs to low pressure vacuum forming, where intraply shear, interply shear, and ply bending are the dominant forming mechanisms. The steel sheet dummy minimized the squeeze flow related wrinkle in the web and flanges. Instead the forming temperature was found to exert the greatest influence on radius thinning. When forming at room temperature, radius thinning was almost eliminated and instead bending-related wrinkles in the flange below the radii appeared. POLYM. COMPOS., 40:3550-3561, 2019.
  •  
27.
  • Hallander, Per, 1970-, et al. (author)
  • Forming of composite spars including interlayers of aligned, multiwall, carbon nanotubes : an experimental study
  • 2016
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569.
  • Journal article (peer-reviewed)abstract
    • Carbon nanotubes offer the potential for improved or changed matrix properties, thereby enabling the creation of novel, multifunctional composite materials. By using highly-aligned, multiwall, carbon nanotubes (MWCNT) with thermoset resins, good dispersion and distribution of nanotubes is obtained. To date, research has mainly focused on improving the growth process of the aligned MWCNTs, however little has been done on the processing of composites that include MWCNTs as interlayers in the stack.  The aim of this work is to study how the aligned MWCNTs are affected within composite part forming. The study shows that MWCNTs are influenced by the shearing that occurs during forming, but still maintain their integrity. To some extent, the shear pattern observed in the MWCNTs after deformation provides an indication of deformation modes. However, the presence of MWCNTs also significantly influences the forming characteristics of the prepreg stack.
  •  
28.
  • Hammami, A., et al. (author)
  • Analysis of the vacuum infusion molding process
  • 2000
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 21:1, s. 28-40
  • Journal article (peer-reviewed)abstract
    • The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1-D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part.
  •  
29.
  • Hosseini, Seyedehsan, 1994, et al. (author)
  • Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene
  • 2024
  • In: Polymer Composites. - 1548-0569 .- 0272-8397. ; 45:1, s. 825-835
  • Journal article (peer-reviewed)abstract
    • Alkyl ketene dimers (AKDs) are known to efficiently react with cellulose with a dual polarity in their structure: a polar component and a nonpolar component. AKD of three different carbon chain lengths, 4, 10, and 16 carbons have been synthesized, and thermomechanical pulp (TMP) fibers were modified by them. The modification of TMP fibers with AKD resulted in an increased water contact angle, showing the presence of the AKDs on the TMP fibers and a new carbonyl peak in the IR spectra, suggesting modification of the TMP fibers with AKD groups. Calculating the Hansen solubility parameters of AKD and AKD conjugated to TMP in polypropylene (PP) indicates improved compatibility, especially of longer chain AKD and TMP AKD. The rheological studies of the composites showed that the AKD with the longest carbon chain decreases the melt viscosity of the PP-TMP-AKD composite, which combined with the shape and the color of the extruded composite filaments indicates improved flow properties and reduced stress build up during processing. The research findings demonstrate the ability of AKD to enhance the dispersibility and compatibility of natural fibers with PP.
  •  
30.
  • Hosseini, Seyedehsan, 1994, et al. (author)
  • Molybdenum disulphide—A traditional external lubricant that shows interesting interphase properties in pulp-based composites
  • 2021
  • In: Polymer Composites. - : Wiley. - 1548-0569 .- 0272-8397. ; 42:9, s. 4884-4896
  • Journal article (peer-reviewed)abstract
    • Compression molded composites were prepared through a water-assisted mixing of an aqueous suspension of poly(ethylene-co-acrylic acid), additive, and pulp fibers [thermomechanical pulp (TMP) or dissolving pulp (DP)]. The lubricating additives used were magnesium stearate (MgSt) and molybdenum disulphide (MoS2). The composite materials had dry pulp contents ranging from 30 to 70 wt% and 5 wt% additive relative to the weight of the pulp. The adsorption of the additives onto the fibers was confirmed by scanning electron microscopy and energy dispersive X-ray analysis. DMA showed that MgSt and MoS2 gave similar interphase properties for the TMP samples at all loading contents, but the combination of MgSt and MoS2 improved the overall properties of the DP-based composites. The tensile modulus, at 70 wt% fiber content (TMP or DP), increased compared to the matrix by a factor of 6.3 and 8.1, without lubricants, and by a factor of 8 and 10.7, with lubricants, respectively. The increase in melt viscosity observed for the lubricated samples was greater for the TMP-based samples containing MoS2. At a lubricant content of 5 wt%, in 30 wt% TMP, the MoS2 behaved as both a lubricant and compatibilizer.
  •  
31.
  • Jose, T, et al. (author)
  • Thermal and crystallization behavior of cotton : Polypropylene commingled composite systems
  • 2010
  • In: Polymer Composites. - : Wiley-Blackwell. - 0272-8397 .- 1548-0569. ; 31:8, s. 1487-1494
  • Journal article (peer-reviewed)abstract
    • Techniques like thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy were used to study the thermal and crystallization behavior of cotton-polypropylene (PP) commingled composite system. Thermal analysis was used to understand the structure-property relationship and also to quantify the amount of moisture and volatiles, which causes the deterioration of the composite performance. Thermal stability of the composite was found be intermediate between that of PP and cotton fibers. Presence of treated reinforcements had increased the crystallinity of PP. Also, fibers act as heterogeneous nucleants and favor the early crystallization of PP in the composites. The crystallization and onset crystallization temperature values were increased by the presence of cotton fibers. The theories of heterogeneous nucleation and crystal growth kinetics were used to explain the growth of transcrystalline layer (TCL) of PP on cotton fibers. The interfacial free energy difference for nucleation of PP on fiber was found to be smaller compared with that in the bulk PP. This favors the formation and growth of TCL. The thickness of TCL and radius of the spherulites increase with the increase in the crystallization temperature. Fiber surface roughness and thermal stresses facilitate the growth of transcrystallinity on cotton fiber.
  •  
32.
  • Kumar, S., et al. (author)
  • Buckling behavior of non-uniformly heated 3D printed plain and functionally graded nanocomposites
  • 2023
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 44, s. 5450-5463
  • Journal article (peer-reviewed)abstract
    • The functionalized multi-walled carbon nanotubes (MWCNTs) (0.5–5 wt.%) are compounded with high density polyethylene (HDPE), and, subsequently, used for extruding nanocomposite filaments to fabricate nanocomposites (NCs) and functionally graded nanocomposites (FGNCs) through 3D printing. The 3D printed NCs are investigated for coefficient of thermal expansion (CTE), and buckling under different non-uniform temperature distributions (case-1: left edge heating, case-2: centre heating, and case-3: left and right edge heating). A significant reduction in CTE is observed with MWCNT addition and gradation. The highest reduction in CTE is observed for H5 (5 wt.% of MWCNT in HDPE) NC and H1 ⟶ H3 ⟶ H5 (FGNC-2) among the NCs and the FGNCs. It is noted that Tcr (critical buckling temperature) is highest for case-3 and lowest for case-2. The highest deflection is noticed in case-2, while no significant difference is observed in case-1 and case-3 heating conditions. It is also observed that Tcr increases with gradation and MWCNTs addition. The H5 NC and FGNC-2 exhibited the highest Tcr among the NCs and FGNCs, respectively. The maximum deflection is noticed for HDPE, whereas the minimum deflection is noticed for FGNC-2 and H-5 NC among the tested samples. The results also revealed that Tcr is very sensitive to type of heating. © 2023 Society of Plastics Engineers.
  •  
33.
  • Kupka, Vojtech, et al. (author)
  • Well-dispersed polyurethane/cellulose nanocrystal nanocomposites synthesized by a solvent-free procedure in bulk
  • 2019
  • In: Polymer Composites. - : WILEY. - 0272-8397 .- 1548-0569. ; 40, s. E456-E465
  • Journal article (peer-reviewed)abstract
    • Polyurethane (PU) nanocomposites utilizing cellulose nanocrystals (CNCs) as nanofiller and amorphous PU matrix were synthesized in a novel solvent-free bulk process. A green nanofiller, CNCs, was studied as reinforcement and was further modified by grafting poly(ethylene glycol) (PEG) on the CNC surface (CNC-PEG). Transmission electron microscopy revealed an excellent dispersion of the PEGylated CNC nanoparticles in the PU matrix, whereas as-received CNCs formed agglomerates. The results indicated strong improvements in tensile properties with Young's modulus increasing up to 50% and strength up to 25% for both, PU/CNC and PU/CNC-PEG nanocomposites. The enhanced tensile modulus was attributed to stiff particle reinforcement together with an increase in glass transition temperature.
  •  
34.
  • Lindhagen, Johan, et al. (author)
  • Notch sensitivity and damage mechanisms of glass mat reinforced polypropylene
  • 1997
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 40-47
  • Journal article (peer-reviewed)abstract
    • Notch Sensitivities of two structurally different glass-mat reinforced polypropylene materials (GMT) were investigated. Center hole notches in tensile specimens were used in the tests. The results show that the short fiber material has higher unnotched strength, but also higher notch sensitivity compared to a swirled mat material. Reasons for this are discussed, focusing on microstructural differences. Predictions from four different failure criteria were compared with the experimental notched strength data. The point stress and damage zone criteria were found to give the best descriptions.
  •  
35.
  • Lundström, Staffan (author)
  • Bubble transport through constricted capillary tubes with application to resin transfer molding
  • 1996
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 17:6, s. 770-779
  • Journal article (peer-reviewed)abstract
    • This paper describes and expounds a theoretical and experimental study of bubble motion through constricted capillary tubes. In the experiment, two liquidfilled capillaries are used. They have unequal radii and are glued together. Gas bubbles are injected into the larger capillary. Then the pressure required to force the bubbles through the constriction is measured for various liquids, bubble lengths, capillary radii and constriction geometry. It appears that the pressure directly follows Young's-Laplace law for capillary pressure. The results of the study are used to understand the bubble transport through fiber reinforcements, which generally takes place during the manufacturing of composites. The bubbles are carried if: (i) the pressure gradient is high enough, (ii) the surface tension of the liquid is low enough, (iii) the cross-sectional area of the channels in the reinforcement is sufficiently uniform. The theory reveals that the bubbles are more likely to be trapped on a small scale, i.e. within fiber bundles rather than on a large scale, i.e. between the bundles. It is also concluded that, if the bubbles are trapped at the resin flow front, a converging flow is better for the transport of the voids than a diverging flow.
  •  
36.
  • Lundström, Staffan, et al. (author)
  • Influence from process parameters on void formation in resin transfer molding
  • 1994
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 15:1, s. 25-33
  • Journal article (peer-reviewed)abstract
    • The influence of different process variables on the void content in resin transfer modling (RTM) has been investigated experimentally. The moldings were made in a flat mold filled by a parallel flow from one edge of the laminate to the other. The viods were found concentrated in a narrow region close to the ventilation side of the laminate. The void volume fraction in this region was almost constant and dropped over a short distance to basically no voids in the rest of the laminate. Micrographs from cross sections in different directions revealed that the voids were of two different types, long cylinderical bubbles inside the fiber bundles. An efficient way of reducing the void content was to use vacuum assistance during mold filling. This technique was benefical both for the magnitude of the void content and for the extent of the void region. The void content with the highest level of vacuum assistance (≈ 1 kPa absolute pressure), was practically negligible. Strong indications for void generation by mechanical entrapment at the flow front was found. The lowering of the void content with vacuum assistance can be interpreted as aresult of compression of voids when the vacuum is released and a higher mobility of voids created at a lower pressure.
  •  
37.
  • Lundström, T. Staffan, et al. (author)
  • In-plane permeability measurements on fiber reinforcements by the multi-cavity parallel flow technique
  • 1999
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 20:1, s. 146-154
  • Journal article (peer-reviewed)abstract
    • This report discusses the advantages and drawbacks of the multi-cavity parallel flow technique for permeability measurements. An experimental series with repeated measurements on material from the same roll shows that the repeatability of the technique is very good considering the manufacturing variability of the fabric. The measured standard deviation in the repeatability study is about 10%. It is, however, shown that the permeability can vary considerably- between reinforcements of similar geometry. Furthermore, computer simulations were used to estimate the errors when highly anisotropic materials are oriented at an angle to the material principal direction in the parallel flow technique. The conclusion based on the simulations is that the length to width ratio of the cavity should be larger than the anisotropy of the reinforcement for an acceptable error.
  •  
38.
  • Moriana, Rosana, et al. (author)
  • Assessing the influence of cotton fibers on the degradation in soil of a thermoplastic starch-based biopolymer
  • 2010
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:12, s. 2102-2111
  • Journal article (peer-reviewed)abstract
    • Biocomposites consisting of cotton fibers and a commercial starch-based thermoplastic were subjected to accelerated soil burial test. Fourier transform infrared (FTIR) spectrometry analysis was carried out to provide chemical-structural information of the polymeric matrix and its reinforced biocomposites. The effects that take place as a consequence of the degradation in soil of both materials were studied by FTIR-ATR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). When the polymeric matrix and the reinforced biocomposite are submitted to soil burial test, the infrared studies display a decrease in the C=O band associated to the ester group of the synthetic component as a consequence of its degradation. The crystalline index of both materials decreased as a function of the degradation process, where the crystalline structure of the reinforced biocomposite was the most affected. In accordance, the degraded reinforced biocomposite micrographs displayed a more damaged morphology and fracture surface than the degraded polymeric matrix micrographs. On the other hand, the same thermal decomposition regions were assessed for both materials, regardless of the degradation time. Kissinger, Criado, and Coats-Redfern methods were applied to analyze the thermogravimetric results. The kinetic triplet of each thermal decomposition process was determined for monitoring the degradation test. The thermal study confirms that starch was the most biodegradable polymeric matrix component in soil. However, the presence of cotton fiber modified the degradation rate of both matrix components; the degradability in soil of the synthetic component was slightly enhanced, whereas the biodegradation rate of the starch slowed down as a function of the soil exposure time. © 2010 Society of Plastics Engineers.
  •  
39.
  • Mårtensson, Per, et al. (author)
  • Cost and weight efficient partitioning of composite automotive structures
  • 2015
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569.
  • Journal article (peer-reviewed)abstract
    • To make carbon fiber composites not only weight but also cost effective in high volume production the different cost drivers need to be addressed and new design philosophies considered. This study analyzes integral and differential design approaches when partitioning large complex composite structures. The influence of different partition philosophies are investigated based on a framework of composites manufacturing cost modelling and structural optimization and the effects are exemplified by a case study. The results show that depending on how the partitioning is made the structural performance and the manufacturing cost is affected. More particularly, if the partitioning is made with the most beneficial philosophy differential designs can improve both these important parameters.
  •  
40.
  • Nilsson, Greger, et al. (author)
  • Flow induced fiber orientation in compression molded glass mat thermoplastics
  • 2000
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 21:6, s. 1007-1013
  • Journal article (peer-reviewed)abstract
    • This study examines how the mechanical properties in GMT are affected by axisymmetric flow during compression molding. Two types of GMT with different architecture are used, swirled mat and short fiber GMT. Tree different grades are tested for each fiber architecture 20, 30, and 40% fiber content by weight. These are in principle the grades of GMT commercially available today. It is found that the flow reduced the tensile strength by 30 to 50% and the tensile modulus up to 30% in the flow direction. The reduction in mechanical properties, which is mainly caused by flow-induced fiber orientation, is larger at high fiber contents. The study also showed that there is no major difference in behavior between swirled mat and short fiber GMT regarding flow induced fiber orientation.
  •  
41.
  • Nordlund, Markus, et al. (author)
  • An investigation of particle deposition mechanisms during impregnation of dual-scale fabrics with micro particle image velocimetry
  • 2010
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:7, s. 1232-1240
  • Journal article (peer-reviewed)abstract
    • Injection moulding processing of composite materials most often includes infiltration of a thermoset resin into a multi-scale porous fabric. Controlling the fluid flow within the multi-scale fabric is essential for the quality of the final composite material, since the transport of fluid between regions with different scales is of importance for phenomena such as void formation and filtration of particle doped resins. Hence, the transient flow behaviour in dual scale porous media is investigated in detail with Micro Particle Image Velocimetry. These experiments show that the fluid transport between the two scales can be controlled by the injection velocity. Validation of the measured velocity fields furthermore shows excellent agreement with theory and that transport between the two scales can be substantial at the flow front but negligible up-stream it. POLYM. COMPOS
  •  
42.
  • Nättinen, Kalle, et al. (author)
  • Naturally compatible : starch acetate/cellulosic fibre composites. Part I: Processing and properties
  • 2010
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:3, s. 524-535
  • Journal article (peer-reviewed)abstract
    • Composite compounds based on hemp and flax fibers in triethyl citrate plasticized starch acetate were prepared by melt processing. For better properties and processability, compounds with plasticizer contents in the range 20-35 wt% were screened. Composites were prepared with fiber contents up to 50 wt%. The composite mechanical properties were measured from injection molded test specimens. A Young's modulus of 8.3 GPa and stress at maximum load of 51 MPa were obtained with 40 wt% flax fiber in a plasticized starch acetate with 20 wt% triethyl citrate. Decreasing the plasticizer and increasing the fiber content, the tensile properties were consistently improved. An almost linear relation between fiber content and the tensile properties was found. The increase of the fiber content first improved the impact strength, but at higher fiber contents resulted in a reduction of impact strength. The quality of the produced materials was found to be good; the variation in properties between duplicated compounds was acceptable low, the variation in density and fiber content along a single tensile specimen was low, and finally, the porosity content was low even at high fiber content. The latter result was verified with scanning electron microscope images of fracture surfaces of the composites.
  •  
43.
  • Oldenbo, Magnus, et al. (author)
  • A constitutive model for non-Linear behavior of SMC accounting for linear viscoelasticity and micro-damage
  • 2005
  • In: Polymer Composites. - : Society of Plastics Engineers. - 0272-8397 .- 1548-0569. ; 26:1, s. 84-97
  • Journal article (peer-reviewed)abstract
    • An approach for modeling sheet molding compound (SMC) composites as viscoelastic damageable material is presented. Continuum damage mechanics theory by Chow and Wang (Int. J. Fract., 33, 3 (1987)) was used in combination with linear viscoelasticity. The model was applied to a modern SMC composite material containing both hollow glass spheres for low density and toughening additive for improved impact resistance. Tensile tests and uniaxial creep test were employed to build the constitutive model. Validation was done by comparing test data with simulations of uniaxial creep on material with different degrees of damage. The model has good accuracy at moderate damage levels under controlled time-dependent crack propagation. Tensile testing at two different fixed strain rates was simulated using quasi-elastic method to calculate relaxation modulus. The model predicts the stress-strain curve with good accuracy until the region is close to failure, where new mechanisms not accounted for are taking place. Finally, a simulation of a cyclic tensile test with increasing maximum strain per cycle was performed, and since both damage and viscoelasticity are included in the model, the slope change, accumulation of residual strain, and hysteresis in the stress-strain, loading-unloading curve are predicted.
  •  
44.
  • Petkov, Valeri Ivanov, et al. (author)
  • Thermal oxidative aging of satin weave and thin-ply polyimide composites
  • 2022
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 43:5, s. 2615-2627
  • Journal article (peer-reviewed)abstract
    • The weight loss and damage development of satin weave and thin-ply carbon fiber-reinforced polyimide composites are studied during high temperature (288 and 320°C) aging in air. Two distinct regions are identified in the weight loss measurements—a rapid initial desorption and a subsequent slower weight loss, which is attributed to matrix degradation. The initial desorption stage is modeled by combining material constitutive properties from literature, micro-mechanics and a one-dimensional Fickian diffusion model. Two different damage patterns are observed by using optical microscopy and X-ray computed tomography on specimens before and after aging. Crack clusters form a network in satin weave composites, while edge delaminations are observed in thin-ply laminates, which are known for their enhanced resistance to matrix cracking.
  •  
45.
  • Pupure, Liva, et al. (author)
  • Moisture uptake and resulting mechanical response of biobased composites. I. constituents
  • 2014
  • In: Polymer Composites. - : John Wiley and Sons Inc.. - 0272-8397 .- 1548-0569. ; 35:6, s. 1150-1159
  • Journal article (peer-reviewed)abstract
    • The mechanical properties of the biobased fiber and resins have been characterized and moisture influence on the behavior of these materials has been studied. Commercially available biobased thermoset resins (Tribest, EpoBioX, Palapreg, Envirez SA, and Envirez SB) and regenerated cellulose fibers (Cordenka) have been conditioned at different levels of relative humidity (as received, dried, 41, 70, and 90%) to obtain materials with different moisture content. The following properties of polymers were measured: tensile, flexural (3P-bending), impact strength (unnotched Charpy), and fracture toughness (compact tension). The results of characterization of biobased thermosets were compared against data for epoxy Araldite LY556, which is used as reference resin. RCF bundles (with and without twist, extracted from fabric) as well as single fibers separated from these bundles were tested in tension. In general biobased resins performed well, moreover EpoBioX showed better properties than synthetic epoxy.
  •  
46.
  • Roy, Amit, et al. (author)
  • Tribological properties of polyimide coating filled with carbon nanotube at elevated temperatures
  • 2020
  • In: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 41:7, s. 2652-2661
  • Journal article (peer-reviewed)abstract
    • This work mainly focuses on the development and characterization of polyimide (PI) based composite coatings filled with multi‐walled carbon nanotubes (MWCNT) on a steel substrate. The tribological properties of PI/MWCNT composite coatings at different temperatures ranging from room temperature (RT) to 200°C were investigated. Also, the influence of MWCNT and thermal & mechanical properties of PI composites coatings were measured. The addition of MWCNT could reduce the friction coefficient as well as wear volume at elevated temperatures. The PI/3MWCNT composites coatings show better wear‐resistant properties as compared to other composites. Also, the PI/MWCNT composites showed improved mechanical properties such as micro‐hardness and nanoindentation. Formation of an organic‐inorganic structure due to the inclusion of MWCNT, enhance the mechanical properties and reduce the thermo‐degradation of composites coatings. The glass transition temperature (Tg) of the PI/MWCNT composites was improved as the MWCNT content increases from 0.1 to 5 wt%.
  •  
47.
  • Rybak, Andrzej, et al. (author)
  • Graphene nanoplatelet-silica hybrid epoxy composites as electrical insulation with enhanced thermal conductivity
  • 2018
  • In: Polymer Composites. - : Wiley. - 1548-0569 .- 0272-8397. ; 39, s. E1682-E1691
  • Journal article (peer-reviewed)abstract
    • The efficient management of heat is a key issue when considering the performance of electrical devices. To reduce the probability of their failure an effective heat dissipation should be ensured. The thermal conductivity of pure epoxy is low and can be improved through the addition of fillers. Graphene has been considered as an adequate filler, due to its excellent thermal conductivity. However, graphene-based composites also show a high electrical conductivity, which limits their application as an electrical insulation considerably. The presented work shows that it is possible to enhance thermal conductivity through the incorporation of a new class of hybrid filler, namely a masterbatch of graphene nanoplatelets (GNPs) and a standard filler like silica. This unique structural design combines the advantages of both, GNPs and silica powder, resulting in composites that not only show high thermal conductivity, but also preserve electrical insulation functionality. A modified processing method leads to the improvement of thermal conductivity. GNPs-silica hybrid epoxy composites with only 2 wt% of GNPs reached 1.54 W/mK, whereas the volume resistivity remained at the level of 1015 Ω cm. The unique scientific aspect, namely temperature dependence of thermal conductivity, was studied. The presented novel hybrid composites show great potential in applications requiring electrical insulation with enhanced thermal conductivity in high voltage devices. POLYM. COMPOS., 39:E1682–E1691, 2018.
  •  
48.
  • Seldén, Ragnar, et al. (author)
  • UV aging of poly(propylene)/wood-fiber composites
  • 2004
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 25:5, s. 543-553
  • Journal article (peer-reviewed)abstract
    • The effect of accelerated UV-aging on properties of PP/wood-flber composites has been studied. Plates containing 0, 25 and 50 wt% wood-fibers were subjected to accelerated UV-aging in a QUV weatherometer for up to 8 weeks. Stabilization against UV-degradation was made by adding 3% of a UV stabilizer. The results showed that both the unfilled PP and the PP/wood-fiber composites displayed good UV resistance with regard to mechanical properties. The color of the PP/wood-fiber composite plates changed from brown to chalky white at the exposed area because of the formation of a thin, strongly degraded surface layer. Physical and chemical analysis of these surface layers using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy showed that degradation of the PP matrix had occurred, leading to chemicrystallization and extensive surface cracking. A decrease in PP melting temperature was also noted, due to molecular chain scission and the formation of extraneous groups, such as carbonyls and hydroperoxides. These results indicate that the wood-fibers act as chromophores when incorporated in the PP matrix. Increasing the fiber content from 25 to 50 wt% increases the rate of degradation of the PP matrix by approximately a factor of two. © 2004 Society of Plastics Engineers.
  •  
49.
  • Sjögren, B.A., et al. (author)
  • Failure mechanisms in polypropylene with glass beads
  • 1997
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 1-8
  • Journal article (peer-reviewed)abstract
    • The effect of glass beads on the stress-strain behavior of isotactic polypropylene has been examined. Poisson's ratio and secant compliance as a function of strain have been measured. Both sets of data are consistent with interfacial debonding as the initial damage mechanism. Interfacial debonding is then followed by extensive plastic yielding of the matrix at the debond sites. The maximum stress and strain to failure decrease with glass bead content and glass bead diameter. Impact properties correlate with the ability of the composites to reach high strain to failure. The proposed failure mechanisms are supported by fractography and in-situ deformation studies by scanning electron microscopy.
  •  
50.
  • Sjögren, B.A., et al. (author)
  • Toughening mechanisms in rubber-modified glass fiber/unsaturated polyester composites
  • 1999
  • In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 20:5, s. 705-712
  • Journal article (peer-reviewed)abstract
    • An important case of composite failure is the leakage of pipes and pressure vessels subjected to internal pressure. The primary damage mechanism leading to leakage is transverse cracking parallel to the fibers. Effects of matrix toughening on transverse cracking strains were therefore investigated for GF/UP cross-ply laminates with matrices of different liquid rubber content. The strain to the first transverse crack was increased from 0.2 to 0.6% with 10 wt% rubber. Debonding occurred at similar strains in GF/UP and GF/UP-rubber. However, whereas debonding was almost simultaneous with transverse cracking in GF/UP, gradual growth of debonds to short cracks took place initially in GF/UP-rubber. This was followed by slow extension of short cracks to a critical flaw size corresponding to unstable growth
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