Alma Hodzic | The University of Sheffield (original) (raw)
Papers by Alma Hodzic
Journal of Adhesion, 2003
An overview is presented of the properties and effective thickness of the interphase formed betwe... more An overview is presented of the properties and effective thickness of the interphase formed between fibres and polymer matrices. Chemical and physical characterization of the interphase is discussed to portray molecular interactions comprising the interphase layers in silane-treated glass-fibre composites. The gap between physico-chemical investigation on one side and bulk material testing on the other side is bridged by implementation of novel techniques, such as nanoindentation, nanoscratch tests, and atomic force microscopy (AFM), which have been successfully used for nanoscopic characterization of the interphase in the past few years. Salient differences are identified between the major findings of these studies in terms of hardness/modulus of the interphase relative to the bulk matrix material. While there is a significant "fibre stiffening" effect that may cause misinterpretation of the interphase hardness very close to the fibre, the formation of both a softer and a harder interphase is possible, depending on the combination of reinforcement, matrix, and coupling agent applied. This is explained by different interdiffusion behaviour, chemical reactions, and molecular conformation taking place at the interphase region in different composite systems. The effective interphase thickness is found to vary from as small as a few hundred nanometers to as large as 10 µm, depending on the constituents, coupling agent, and ageing conditions.
Journal of Applied Polymer Science, 2006
Natural fiber composites were designed and optimized to achieve good mechanical properties and re... more Natural fiber composites were designed and optimized to achieve good mechanical properties and resistance to growth of living organisms. Composite materials were prepared from poly(lactic acid) (PLA) with flax fibers, which had been subjected to interstitial polymerization to replace the water in the cellulose fibers. Prior to the polymerization, the flax fibers were extracted with sodium hydroxide and acetone to remove lignin, pectin, and waxes from the cellulose. Differential scanning calorimetry was used to study the crystallization and melting of the composites compared to pure PLA. The surface wetting of the fibers and morphology of the composites were studied by scanning electron microscopy and optical microscopy. Mechanical properties were studied using dynamic mechanical analysis. The influence of the interstitial polymerization on the dynamic storage modulus was found to be significant. The composites of polymerization treated flax with acetone washed fibers had higher storage moduli than the unwashed fiber composites, which suggested that the adhesion between the flax fibers and the matrix was improved by the treatments. The composites were subjected to moist environmental conditions in order to test for development of mold and fungi, and the acetone washed polymerization treated flax composites were resistant to these growths. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3620–3629, 2006
Journal of Applied Polymer Science, 2004
Crystal structure and mechanical properties of cellulose fibers were studied to investigate the e... more Crystal structure and mechanical properties of cellulose fibers were studied to investigate the effect of chemical treatment on the fiber. Pretreatment by acetone extraction, mercerization with 3–20% wt/v sodium hydroxide (NaOH), and acrylonitrile (AN) grafting initiated by azo-bis-isobutylonitrile were performed. From Fourier transform infrared spectroscopy and wide-angle X-ray diffraction quantitative measurements, the pretreated fibers showed an induced slight decrease of crystallinity index. The structural transformation of the fibers from cellulose I to cellulose II was observed at high NaOH concentration of 10–20% wt/v. The amount of grafting, 1.56, 2.94, 6.04, 8.34, or 10.46%, was dependent upon the initiator concentration and the volume of monomer in the reactor. The AN grafted fibers had no transformation of crystalline structure as observed after mercerization. Only a variation of X-ray crystallinity index with grafting amount was observed. Moisture regain of pretreated and modified fibers depended on the structure of the fiber and the amount of grafting. The mechanical properties performed by a single fiber test method were strongly influenced by the cellulose structure, lateral index of crystallinity, and fraction of grafting. Scanning electron microscopy was used for analysis of surface morphologies of treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2456–2465, 2004
Polymer Engineering and Science, 2003
The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites wa... more The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites was investigated. The plasticizes chosen were triethyl citrate (TEC), tributyl citrate (TBC) and glycerol triacetate (GTA), which were derived from natural sources. Characterization was performed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The morphology was examined from scanning electron microscopy (SEM) and optical microscopy (OM). The results showed that the plasticizer caused a marked increase in the storage modulus of the composites, which could be due to an improvement in the morphology of the matrix and a smoother surface coverage of the fibers by the matrix. The thermal properties were also affected, in which the glass transition temperature (Tg), the crystallization temperature (Tc) and the crystallinity (Xc) were reduced depending on the plasticizer. The citrate esters revealed to be the most effective plasticizers of those tested.
Journal of Applied Polymer Science, 2005
A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-... more A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber-reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005
Journal of Applied Polymer Science, 2004
Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bi... more Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bipolyesters (PHB). The biopolyesters consist of the homopolyester PHB and its copolymers with 5 and 12% 3-hydroxyvalerate (PHV). These biopolymer–natural fiber composites provide structures totally composed of biodegradable and renewable resources. The adhesion between the fibers and the polyesters was better than for analogous polypropylene composites. Wetting of the fibers by the polyesters was observed using scanning electron microscopy. The composites were limited by the properties of the polyesters. PHB is a brittle polymer though flexibility is improved in its copolymers with PHV, but at the expense of crystallization rate. Nucleation was increased by the fibers and silane coupling agent used as adhesion promoter. The melting temperature was influenced by the promoted adhesion and copolymerization. The bending modulus was increased in the composites and dynamic mechanical analysis provided storage modulus of as much as 4 GPa at 25°C with a smaller component as the loss modulus. The maximum in the loss modulus curve was taken as the glass transition temperature, and this increased in the composites. The influence of silane coupling agent was found beneficial for the material properties of the biopolyester–flax composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2114–2121, 2004
Composites Science and Technology, 2004
Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) an... more Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) and flax fibres was provided by addition of 4, 4′-thiodiphenol (TDP) at various concentrations up to 10% v/v. The additive TDP is known to form hydrogen bonds ...
Macromolecular Materials and Engineering, 2005
Polymer Testing, 2005
Creep, the deformation over time of a material under stress, is one characteristic of composites ... more Creep, the deformation over time of a material under stress, is one characteristic of composites that has resulted in poor performance in certain applications. This work was undertaken to investigate the advantages of using PP fibres in random poly(propylene-co-ethylene) (PPE) with different fibre concentrations. Addition of long polypropylene fibres into PPE greatly improved the creep resistance and modulus of elasticity
Macromolecular Materials and Engineering, 2004
Composites Science and Technology, 2007
ABSTRACT The interfacial shear strength (IFSS), evaluated by single fibre pull-out tests was quan... more ABSTRACT The interfacial shear strength (IFSS), evaluated by single fibre pull-out tests was quantified for various biopolymer-flax fibre composites that were modified with additives. The additives included a plasticiser (glycerol triacetate) (GTA) absorbed onto/into the fibres, 4,4′-thiodiphenol (TDP) that is capable of forming hydrogen bonds between the matrix and cellulose from the fibres, and a hyperbranched polyester (HBP) to impart improved fracture toughness. Fibres were washed with acetone to remove the surface impurities and dried under vacuum before absorption of plasticiser and adsorption of thiodiphenol. It was found that the different additives significantly influenced the IFSS for the biopolymer-flax fibre systems while extraction with acetone had a no effect on the IFSS compared with the untreated fibres. The use of TDP imparted the most significant increase in IFSS whilst the HBP had an opposing effect. The use of ESEM corroborated with the findings of the single fibre pull-out tests.
Macromolecular Materials and Engineering, 2002
Journal of Applied Polymer Science, 2006
Natural fiber composites were designed and optimized to achieve good mechanical properties and re... more Natural fiber composites were designed and optimized to achieve good mechanical properties and resistance to growth of living organisms. Composite materials were prepared from poly(lactic acid) (PLA) with flax fibers, which had been subjected to interstitial polymerization to replace the water in the cellulose fibers. Prior to the polymerization, the flax fibers were extracted with sodium hydroxide and acetone to remove lignin, pectin, and waxes from the cellulose. Differential scanning calorimetry was used to study the crystallization and melting of the composites compared to pure PLA. The surface wetting of the fibers and morphology of the composites were studied by scanning electron microscopy and optical microscopy. Mechanical properties were studied using dynamic mechanical analysis. The influence of the interstitial polymerization on the dynamic storage modulus was found to be significant. The composites of polymerization treated flax with acetone washed fibers had higher storage moduli than the unwashed fiber composites, which suggested that the adhesion between the flax fibers and the matrix was improved by the treatments. The composites were subjected to moist environmental conditions in order to test for development of mold and fungi, and the acetone washed polymerization treated flax composites were resistant to these growths. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3620–3629, 2006
Journal of Applied Polymer Science, 2004
Crystal structure and mechanical properties of cellulose fibers were studied to investigate the e... more Crystal structure and mechanical properties of cellulose fibers were studied to investigate the effect of chemical treatment on the fiber. Pretreatment by acetone extraction, mercerization with 3–20% wt/v sodium hydroxide (NaOH), and acrylonitrile (AN) grafting initiated by azo-bis-isobutylonitrile were performed. From Fourier transform infrared spectroscopy and wide-angle X-ray diffraction quantitative measurements, the pretreated fibers showed an induced slight decrease of crystallinity index. The structural transformation of the fibers from cellulose I to cellulose II was observed at high NaOH concentration of 10–20% wt/v. The amount of grafting, 1.56, 2.94, 6.04, 8.34, or 10.46%, was dependent upon the initiator concentration and the volume of monomer in the reactor. The AN grafted fibers had no transformation of crystalline structure as observed after mercerization. Only a variation of X-ray crystallinity index with grafting amount was observed. Moisture regain of pretreated and modified fibers depended on the structure of the fiber and the amount of grafting. The mechanical properties performed by a single fiber test method were strongly influenced by the cellulose structure, lateral index of crystallinity, and fraction of grafting. Scanning electron microscopy was used for analysis of surface morphologies of treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2456–2465, 2004
Polymer Engineering and Science, 2003
The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites wa... more The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites was investigated. The plasticizes chosen were triethyl citrate (TEC), tributyl citrate (TBC) and glycerol triacetate (GTA), which were derived from natural sources. Characterization was performed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The morphology was examined from scanning electron microscopy (SEM) and optical microscopy (OM). The results showed that the plasticizer caused a marked increase in the storage modulus of the composites, which could be due to an improvement in the morphology of the matrix and a smoother surface coverage of the fibers by the matrix. The thermal properties were also affected, in which the glass transition temperature (Tg), the crystallization temperature (Tc) and the crystallinity (Xc) were reduced depending on the plasticizer. The citrate esters revealed to be the most effective plasticizers of those tested.
Journal of Applied Polymer Science, 2005
A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-... more A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber-reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005
Journal of Applied Polymer Science, 2004
Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bi... more Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bipolyesters (PHB). The biopolyesters consist of the homopolyester PHB and its copolymers with 5 and 12% 3-hydroxyvalerate (PHV). These biopolymer–natural fiber composites provide structures totally composed of biodegradable and renewable resources. The adhesion between the fibers and the polyesters was better than for analogous polypropylene composites. Wetting of the fibers by the polyesters was observed using scanning electron microscopy. The composites were limited by the properties of the polyesters. PHB is a brittle polymer though flexibility is improved in its copolymers with PHV, but at the expense of crystallization rate. Nucleation was increased by the fibers and silane coupling agent used as adhesion promoter. The melting temperature was influenced by the promoted adhesion and copolymerization. The bending modulus was increased in the composites and dynamic mechanical analysis provided storage modulus of as much as 4 GPa at 25°C with a smaller component as the loss modulus. The maximum in the loss modulus curve was taken as the glass transition temperature, and this increased in the composites. The influence of silane coupling agent was found beneficial for the material properties of the biopolyester–flax composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2114–2121, 2004
Composites Science and Technology, 2004
Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) an... more Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) and flax fibres was provided by addition of 4, 4′-thiodiphenol (TDP) at various concentrations up to 10% v/v. The additive TDP is known to form hydrogen bonds ...
Macromolecular Materials and Engineering, 2005
Polymer Testing, 2005
Creep, the deformation over time of a material under stress, is one characteristic of composites ... more Creep, the deformation over time of a material under stress, is one characteristic of composites that has resulted in poor performance in certain applications. This work was undertaken to investigate the advantages of using PP fibres in random poly(propylene-co-ethylene) (PPE) with different fibre concentrations. Addition of long polypropylene fibres into PPE greatly improved the creep resistance and modulus of elasticity
Journal of Adhesion, 2003
An overview is presented of the properties and effective thickness of the interphase formed betwe... more An overview is presented of the properties and effective thickness of the interphase formed between fibres and polymer matrices. Chemical and physical characterization of the interphase is discussed to portray molecular interactions comprising the interphase layers in silane-treated glass-fibre composites. The gap between physico-chemical investigation on one side and bulk material testing on the other side is bridged by implementation of novel techniques, such as nanoindentation, nanoscratch tests, and atomic force microscopy (AFM), which have been successfully used for nanoscopic characterization of the interphase in the past few years. Salient differences are identified between the major findings of these studies in terms of hardness/modulus of the interphase relative to the bulk matrix material. While there is a significant "fibre stiffening" effect that may cause misinterpretation of the interphase hardness very close to the fibre, the formation of both a softer and a harder interphase is possible, depending on the combination of reinforcement, matrix, and coupling agent applied. This is explained by different interdiffusion behaviour, chemical reactions, and molecular conformation taking place at the interphase region in different composite systems. The effective interphase thickness is found to vary from as small as a few hundred nanometers to as large as 10 µm, depending on the constituents, coupling agent, and ageing conditions.
Journal of Applied Polymer Science, 2006
Natural fiber composites were designed and optimized to achieve good mechanical properties and re... more Natural fiber composites were designed and optimized to achieve good mechanical properties and resistance to growth of living organisms. Composite materials were prepared from poly(lactic acid) (PLA) with flax fibers, which had been subjected to interstitial polymerization to replace the water in the cellulose fibers. Prior to the polymerization, the flax fibers were extracted with sodium hydroxide and acetone to remove lignin, pectin, and waxes from the cellulose. Differential scanning calorimetry was used to study the crystallization and melting of the composites compared to pure PLA. The surface wetting of the fibers and morphology of the composites were studied by scanning electron microscopy and optical microscopy. Mechanical properties were studied using dynamic mechanical analysis. The influence of the interstitial polymerization on the dynamic storage modulus was found to be significant. The composites of polymerization treated flax with acetone washed fibers had higher storage moduli than the unwashed fiber composites, which suggested that the adhesion between the flax fibers and the matrix was improved by the treatments. The composites were subjected to moist environmental conditions in order to test for development of mold and fungi, and the acetone washed polymerization treated flax composites were resistant to these growths. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3620–3629, 2006
Journal of Applied Polymer Science, 2004
Crystal structure and mechanical properties of cellulose fibers were studied to investigate the e... more Crystal structure and mechanical properties of cellulose fibers were studied to investigate the effect of chemical treatment on the fiber. Pretreatment by acetone extraction, mercerization with 3–20% wt/v sodium hydroxide (NaOH), and acrylonitrile (AN) grafting initiated by azo-bis-isobutylonitrile were performed. From Fourier transform infrared spectroscopy and wide-angle X-ray diffraction quantitative measurements, the pretreated fibers showed an induced slight decrease of crystallinity index. The structural transformation of the fibers from cellulose I to cellulose II was observed at high NaOH concentration of 10–20% wt/v. The amount of grafting, 1.56, 2.94, 6.04, 8.34, or 10.46%, was dependent upon the initiator concentration and the volume of monomer in the reactor. The AN grafted fibers had no transformation of crystalline structure as observed after mercerization. Only a variation of X-ray crystallinity index with grafting amount was observed. Moisture regain of pretreated and modified fibers depended on the structure of the fiber and the amount of grafting. The mechanical properties performed by a single fiber test method were strongly influenced by the cellulose structure, lateral index of crystallinity, and fraction of grafting. Scanning electron microscopy was used for analysis of surface morphologies of treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2456–2465, 2004
Polymer Engineering and Science, 2003
The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites wa... more The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites was investigated. The plasticizes chosen were triethyl citrate (TEC), tributyl citrate (TBC) and glycerol triacetate (GTA), which were derived from natural sources. Characterization was performed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The morphology was examined from scanning electron microscopy (SEM) and optical microscopy (OM). The results showed that the plasticizer caused a marked increase in the storage modulus of the composites, which could be due to an improvement in the morphology of the matrix and a smoother surface coverage of the fibers by the matrix. The thermal properties were also affected, in which the glass transition temperature (Tg), the crystallization temperature (Tc) and the crystallinity (Xc) were reduced depending on the plasticizer. The citrate esters revealed to be the most effective plasticizers of those tested.
Journal of Applied Polymer Science, 2005
A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-... more A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber-reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005
Journal of Applied Polymer Science, 2004
Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bi... more Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bipolyesters (PHB). The biopolyesters consist of the homopolyester PHB and its copolymers with 5 and 12% 3-hydroxyvalerate (PHV). These biopolymer–natural fiber composites provide structures totally composed of biodegradable and renewable resources. The adhesion between the fibers and the polyesters was better than for analogous polypropylene composites. Wetting of the fibers by the polyesters was observed using scanning electron microscopy. The composites were limited by the properties of the polyesters. PHB is a brittle polymer though flexibility is improved in its copolymers with PHV, but at the expense of crystallization rate. Nucleation was increased by the fibers and silane coupling agent used as adhesion promoter. The melting temperature was influenced by the promoted adhesion and copolymerization. The bending modulus was increased in the composites and dynamic mechanical analysis provided storage modulus of as much as 4 GPa at 25°C with a smaller component as the loss modulus. The maximum in the loss modulus curve was taken as the glass transition temperature, and this increased in the composites. The influence of silane coupling agent was found beneficial for the material properties of the biopolyester–flax composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2114–2121, 2004
Composites Science and Technology, 2004
Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) an... more Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) and flax fibres was provided by addition of 4, 4′-thiodiphenol (TDP) at various concentrations up to 10% v/v. The additive TDP is known to form hydrogen bonds ...
Macromolecular Materials and Engineering, 2005
Polymer Testing, 2005
Creep, the deformation over time of a material under stress, is one characteristic of composites ... more Creep, the deformation over time of a material under stress, is one characteristic of composites that has resulted in poor performance in certain applications. This work was undertaken to investigate the advantages of using PP fibres in random poly(propylene-co-ethylene) (PPE) with different fibre concentrations. Addition of long polypropylene fibres into PPE greatly improved the creep resistance and modulus of elasticity
Macromolecular Materials and Engineering, 2004
Composites Science and Technology, 2007
ABSTRACT The interfacial shear strength (IFSS), evaluated by single fibre pull-out tests was quan... more ABSTRACT The interfacial shear strength (IFSS), evaluated by single fibre pull-out tests was quantified for various biopolymer-flax fibre composites that were modified with additives. The additives included a plasticiser (glycerol triacetate) (GTA) absorbed onto/into the fibres, 4,4′-thiodiphenol (TDP) that is capable of forming hydrogen bonds between the matrix and cellulose from the fibres, and a hyperbranched polyester (HBP) to impart improved fracture toughness. Fibres were washed with acetone to remove the surface impurities and dried under vacuum before absorption of plasticiser and adsorption of thiodiphenol. It was found that the different additives significantly influenced the IFSS for the biopolymer-flax fibre systems while extraction with acetone had a no effect on the IFSS compared with the untreated fibres. The use of TDP imparted the most significant increase in IFSS whilst the HBP had an opposing effect. The use of ESEM corroborated with the findings of the single fibre pull-out tests.
Macromolecular Materials and Engineering, 2002
Journal of Applied Polymer Science, 2006
Natural fiber composites were designed and optimized to achieve good mechanical properties and re... more Natural fiber composites were designed and optimized to achieve good mechanical properties and resistance to growth of living organisms. Composite materials were prepared from poly(lactic acid) (PLA) with flax fibers, which had been subjected to interstitial polymerization to replace the water in the cellulose fibers. Prior to the polymerization, the flax fibers were extracted with sodium hydroxide and acetone to remove lignin, pectin, and waxes from the cellulose. Differential scanning calorimetry was used to study the crystallization and melting of the composites compared to pure PLA. The surface wetting of the fibers and morphology of the composites were studied by scanning electron microscopy and optical microscopy. Mechanical properties were studied using dynamic mechanical analysis. The influence of the interstitial polymerization on the dynamic storage modulus was found to be significant. The composites of polymerization treated flax with acetone washed fibers had higher storage moduli than the unwashed fiber composites, which suggested that the adhesion between the flax fibers and the matrix was improved by the treatments. The composites were subjected to moist environmental conditions in order to test for development of mold and fungi, and the acetone washed polymerization treated flax composites were resistant to these growths. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3620–3629, 2006
Journal of Applied Polymer Science, 2004
Crystal structure and mechanical properties of cellulose fibers were studied to investigate the e... more Crystal structure and mechanical properties of cellulose fibers were studied to investigate the effect of chemical treatment on the fiber. Pretreatment by acetone extraction, mercerization with 3–20% wt/v sodium hydroxide (NaOH), and acrylonitrile (AN) grafting initiated by azo-bis-isobutylonitrile were performed. From Fourier transform infrared spectroscopy and wide-angle X-ray diffraction quantitative measurements, the pretreated fibers showed an induced slight decrease of crystallinity index. The structural transformation of the fibers from cellulose I to cellulose II was observed at high NaOH concentration of 10–20% wt/v. The amount of grafting, 1.56, 2.94, 6.04, 8.34, or 10.46%, was dependent upon the initiator concentration and the volume of monomer in the reactor. The AN grafted fibers had no transformation of crystalline structure as observed after mercerization. Only a variation of X-ray crystallinity index with grafting amount was observed. Moisture regain of pretreated and modified fibers depended on the structure of the fiber and the amount of grafting. The mechanical properties performed by a single fiber test method were strongly influenced by the cellulose structure, lateral index of crystallinity, and fraction of grafting. Scanning electron microscopy was used for analysis of surface morphologies of treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2456–2465, 2004
Polymer Engineering and Science, 2003
The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites wa... more The effect of modified flax fibers by plasticizer absorption in poly(L-lactic acid) composites was investigated. The plasticizes chosen were triethyl citrate (TEC), tributyl citrate (TBC) and glycerol triacetate (GTA), which were derived from natural sources. Characterization was performed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The morphology was examined from scanning electron microscopy (SEM) and optical microscopy (OM). The results showed that the plasticizer caused a marked increase in the storage modulus of the composites, which could be due to an improvement in the morphology of the matrix and a smoother surface coverage of the fibers by the matrix. The thermal properties were also affected, in which the glass transition temperature (Tg), the crystallization temperature (Tc) and the crystallinity (Xc) were reduced depending on the plasticizer. The citrate esters revealed to be the most effective plasticizers of those tested.
Journal of Applied Polymer Science, 2005
A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-... more A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber-reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005
Journal of Applied Polymer Science, 2004
Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bi... more Natural fiber–biopolymer composites have been prepared using flax and poly(3-hydroxylbutyrate) bipolyesters (PHB). The biopolyesters consist of the homopolyester PHB and its copolymers with 5 and 12% 3-hydroxyvalerate (PHV). These biopolymer–natural fiber composites provide structures totally composed of biodegradable and renewable resources. The adhesion between the fibers and the polyesters was better than for analogous polypropylene composites. Wetting of the fibers by the polyesters was observed using scanning electron microscopy. The composites were limited by the properties of the polyesters. PHB is a brittle polymer though flexibility is improved in its copolymers with PHV, but at the expense of crystallization rate. Nucleation was increased by the fibers and silane coupling agent used as adhesion promoter. The melting temperature was influenced by the promoted adhesion and copolymerization. The bending modulus was increased in the composites and dynamic mechanical analysis provided storage modulus of as much as 4 GPa at 25°C with a smaller component as the loss modulus. The maximum in the loss modulus curve was taken as the glass transition temperature, and this increased in the composites. The influence of silane coupling agent was found beneficial for the material properties of the biopolyester–flax composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2114–2121, 2004
Composites Science and Technology, 2004
Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) an... more Improvement of the interfacial properties of composites consisting of poly (3-hydroxybutyrate) and flax fibres was provided by addition of 4, 4′-thiodiphenol (TDP) at various concentrations up to 10% v/v. The additive TDP is known to form hydrogen bonds ...
Macromolecular Materials and Engineering, 2005
Polymer Testing, 2005
Creep, the deformation over time of a material under stress, is one characteristic of composites ... more Creep, the deformation over time of a material under stress, is one characteristic of composites that has resulted in poor performance in certain applications. This work was undertaken to investigate the advantages of using PP fibres in random poly(propylene-co-ethylene) (PPE) with different fibre concentrations. Addition of long polypropylene fibres into PPE greatly improved the creep resistance and modulus of elasticity