Biocomposites based on chemically modified cellulose fibers with renewable fatty‐acid‐based thermoplastic systems: Effect of different fiber treatments

Advanced biocomposites, based on binary and ternary systems, were developed with thermoplastic matrices such as thermoplastic polyurethane (TPU) and polyamide (DAPA) obtained from dimers of fatty acids, and cellulose fibers (CF). The CF were modified to display high interfacial adhesion and compatibility with the rather hydrophobic matrices. Different routes were considered such as grafting onto with prepolymers, or grafting from with aromatic isocyanate or fatty acid. An original approach of this work is to consider CF as a polyol with an equivalent hydroxyl index obtained by titration. In order to understand better the effect of each phase, the resulting modified CF were tested with neat TPU and DAPA matrices. The most promising fibers treatments were then tested with 80/20 and 50/50 wt %/wt % TPU/DAPA blends. Properties at the molecular and macromolecular scale were investigated. Improvement of the interfacial adhesion between the fibers and the polymers were observed. From the different grafting approaches tested, the best performing were the isocyanate‐terminated prepolymer and the silane‐terminated prepolymer modifications. In comparison with neat CF, modification with isocyanate‐terminated prepolymer improved threefold the storage and Young's modulus of TPU biocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43878.     

Permeability and mechanical property correlation of bio based epoxy reinforced with unidirectional sisal fiber mat through vacuum infusion molding technique

The present investigation is focused to study the permeability of natural fiber during vacuum infusion (VI) process and the effect of the surface treatments of natural fiber, fiber loading direction, resin flow direction and process parameter on the tensile properties of developed composites (sisal/bio based epoxy). The bio based resin exhibits good flow characteristics in NaOH and isocyanate treated fibers which may be attributed to change in polarity. The surface treatments appear to provide an appreciable enhancement in tensile strength through enhanced bonding between fiber and matrix. The longitudinal tensile strength has been found to be higher than that of the transverse direction and the flow along the fiber provides maximum tensile strength. It has also been demonstrated that VI process provides improved mechanical properties as compared to hand‐layup process. Morphological studies of fractured developed composites were performed by scanning electron microscopy (SEM) to understand the de‐bonding of fiber/matrix adhesion. POLYM. COMPOS., 38:2192–2200, 2017. © 2015 Society of Plastics Engineers     

Effect of fiber surface treatments on the properties of short sisal fiber/poly(lactic acid) biocomposites

Sisal fiber (SF)‐reinforced poly(lactic acid) (PLA) biocomposites were prepared from biodegradable PLA and surface‐untreated or ‐treated short SF by melt mixing and subsequent compression molding. It is found that the surface treatments facilitate good adhesion between SFs and PLA matrix, which is consistent with the higher mechanical properties of the treated‐SF/PLA biocomposites. Moreover, the surface treatments have similar effects on the biodegradability and water absorption of the biocomposites with the order as following: neat PLA < acetylated SF (A‐SF)/PLA biocomposite ≈ silane‐treated SF (S‐SF)/PLA biocomposite < permanganate‐treated SF (P‐SF)/PLA biocomposite < mercerized SF (M‐SF)/PLA biocomposite < untreated fiber (U‐SF)/PLA biocomposite. In terms of overall consideration of the properties, acetylation treatment seems to be the most desirable surface method owing to the maximum tensile strength and water resistance, medium impact strength, and minimum degradability of the A‐SF/PLA biocomposite. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of surface modification of rice straw on mechanical and flow properties of TPU‐based green composites

In this study, rice straw (RS) which was one of the major agricultural residues was used as filler in bio‐based thermoplastic polyurethane (TPU). Several treatments including hot water, alkali, permanganate, peroxide and silane were applied for modifying the surface of RS. The effects of surface modifications on mechanical, flow, morphological, and water absorption properties of green composites were investigated at a constant 30 wt% RS loading. Silane treatment performed after alkaline treatment gave the highest tensile strength, elastic and storage modulus in mechanical tests and gave the lowest water uptake properties. POLYM. COMPOS., 37:1596–1602, 2016. © 2014 Society of Plastics Engineers     

Electrospinning of plant oil‐based,non‐isocyanate polyurethanes for biomedical applications

Non‐isocyanate polyurethanes (NIPU) have rapidly emerged as a sustainable, less toxic, and environmentally friendly alternative to traditional isocyanate‐based thermoplastic polyurethane (TPU) synthesis. TPU is widely used in the medical industry due to its excellent mechanical properties and elasticity. However, little work has been done to synthesize and electrospin NIPU into fibrous mats for biomedical applications. In this work, melt polymerization of a plant oil‐based cyclic carbonate monomer with polyether soft segments and various diamines yielded isocyanate‐free, segmented poly(amide hydroxyurethane)s (PAHUs). Electrospinning of segmented PAHUs afforded ductile, free‐standing fibrous mats with Young's modulus values between 7 and 8 MPa, suitable for tissue scaffold applications. PAHU fiber mats exhibited 3–4 times greater water uptake than the electrospun TPU control, demonstrating potential utility in drug delivery. Fibroblasts adhered to electrospun PAHU fibrous mats with viability values over 90% after 72‐h, validating its biocompatibility. The results highlight the high performance and potential of electrospun isocyanate‐free polyurethanes mats for biomedical application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46464.     

Blends of thermoplastic polyurethane and polypropylene. I. Mechanical and phase behavior

Pure thermoplastic polyurethane (TPU), polypropylene (PP), and TPU/PP blends with different weight ratios prepared in a twin‐screw extruder were investigated by dynamic mechanical analysis (DMA), the universal tester for mechanical investigation, and by wide‐angle X‐ray diffraction (WAXD). The addition of PP above 20 wt % to the TPU stepwise changed the ductility and Young's modulus, i.e., apparently a kind of ductile → brittle transition occurred between TPU/PP 80/20 and TPU/PP 60/40 blends. This fact and the result of analysis of WAXD curves indicated matrix → dispersed phase inversion in this concentration region. TPU melt enabled easier migration of the PP chains and prolonged crystallization of PP matrix during solidification process affecting thus crystallite size, orientation, and crystallinity. In accordance to this fact, DMA results indicated partial miscibility of PP with polyurethane in the TPU/PP blends due to the lack of interfacial interaction and adhesion between the nonpolar crystalline PP and polar TPU phases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3980–3985, 2007     

Preparation and characterization of thermoplastic polyurethane/organoclay nanocomposites by melt intercalation technique: Effect of nanoclay on morphology,mechanical, thermal,and rheological properties

Nanocomposites based on thermoplastic polyurethane (TPU) and organically modified montmorillonite (OMMT) were prepared by melt blending. Organically modified nanoclay was added to the TPU matrix in order to study the influence of the organoclay on nanophase morphology and materials properties. The interaction between TPU matrix and nanofiller was studied by infrared spectroscopy. Morphological characterization of the nanocomposites was carried out using X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy techniques. The results showed that melt mixing is an effective process for dispersing OMMT throughout the TPU matrix. Nanocomposites exhibit higher mechanical and thermal properties than pristine TPU. All these properties showed an increasing trend with the increase in OMMT content. Thermogravimetric analysis revealed that incorporation of organoclay enhances the thermal stability of nanocomposites significantly. Differential scanning calorimetry was used to measure the melting point and the glass transition temperature (T_g) of soft segments, which was found to shift toward higher temperature with the inclusion of organoclays. From dynamic mechanical thermal analysis, it is seen that addition of OMMT strongly influenced the storage and loss modulus of the TPU matrix. Dynamic viscoelastic properties of the nanocomposites were explored using rubber process analyzer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Contribution of surface silanization process on mechanical characteristics of TPU-based composites involving feldspar and quartz minerals

In this study, quartz and feldspar powders were surface treated using a silane coupling agent to achieve a more compatible mineral surface with the polymer matrix. Details of surface characteristics of minerals were examined by energy-dissipative X-ray spectroscopy, contact angle measurements, and infrared spectroscopy. Thermoplastic polyurethane-TPU was compounded with minerals using the melt-blending technique. Mechanical, thermo-mechanical, melt-flow, and morphological characterizations of TPU and relevant composites were performed by utilizing tensile and Shore hardness tests, dynamic mechanical analysis (DMA), melt flow index (MFI) measurements, and scanning electron microscopy (SEM), respectively. Water repellency of TPU and composites were also evaluated experimentally. Effects of surface treatments were discussed by comparing the results of composites filled with pristine and modified minerals. Results revealed that enrichment of quartz and feldspar surfaces confer mechanical and thermo-mechanical performance of composites. Mineral inclusions caused no drastic changes to the MFI parameter of TPU. The silane layer on the mineral surface displayed a barrier effect to water uptake of composites. Homogeneous dispersion and improved interfacial adhesion of mineral particles to the TPU phase were confirmed with help of SEM observations. Quartz exhibited slightly higher performance thanks to its silica-rich composition. The findings of this research exhibited the considerable influence of the silane layer on the mineral surface on the mechanical performance of TPU-based composites.     

Mechanical properties of surface‐treated banana fiber/polylactic acid biocomposites: A comparative study of theoretical and experimental values

Current study evaluates the effect of fiber surface treatments on the mechanical properties of banana fiber (BF) reinforced polylactic acid (PLA) biocomposites. Experimental results indicate increase in tensile modulus and strength upon surface treatments of BF with various silanes (APS and Si69) and NaOH. Approximately, an increase of 136% in tensile strength and 49% in impact strength was obtained in case of biocomposites with Si69‐treated BF compared with the untreated BF biocomposites. Also, experimentally determined mechanical modulus of untreated and surface‐treated BF biocomposite has been compared with the mechanical modulus calculated using various micromechanical models. Models such as Hirsch's, modified Bawyer and Bader's, and Brodnyan model showed good agreement with the experimentally determined results. Similarly, other models like Halpin‐Tsai, Nielson modified Halpin‐Tsai, and Cox's model also have been tried for the comparative study with the experimental data. Surface modification of BF showed increased interfacial adhesion between the fiber and the matrix which was evident from lowered difference between the experimentally and theoretically derived mechanical modulus. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of fiber treatment on the mechanical properties of hybrid fiber reinforced polystyrene composites. Part II. Use of glass fiber and wood pulp as hybrid fiber

The mechanical properties of polystyrene reinforced with a mixture of hardwood aspen chemithermomechanical pulp (CTMP) and surface-treated glass fiber have been studied. The adhesion of cellulose fiber to glass fiber as well as to thermoplastics improved thanks to various surface treatments of CTMP, e.g. coating with polymer+isocyanate or with silane, and grafting with polystyrene. In general, compared with non-treated CTMP-filled composites, the mechanical properties improved when surface-treated wood fiber was used as a filler. Experimental results indicate better compatibility between treated wood fiber and surface-treated glass fiber as well as polystyrene and, consequently, the mechanical properties were enhanced.     

Maleic anhydride‐grafted‐polybutadiene as a controlled defibrillating and dispersing agent for short aramid fiber reinforced thermoplastic polyurethane composite with improved mechanical properties

The reinforcing effect of resorcinol formaldehyde latex (RFL) coated short aramid fiber on an ester‐based thermoplastic polyurethane (TPU) was investigated on the basis of mechanical properties. Short fibers having different fiber length were used for the reinforcement. The exceptionally high Young's modulus and low strain modulus indicate the reinforcing effect of this fiber on to the TPU matrix. It has been observed that fibers of 3 mm length at 10 phr loading and 6 mm length even at a loading of 5 phr start to exhibit severe fibrillation: the longitudinal splitting of fiber having larger diameter into thinner fibrils during processing. Fibrillation favorably affects the mechanical bonding with the matrix because of the large surface area as well as surface irregularities provided by the fibrillated fiber. However, fibrillation adversely affects the fiber dispersion by enhancing the fiber aggregation. This leads to a greater disturbance in the strain hardening behavior of the TPU matrix and subsequently reducing the tensile strength and elongation at break especially at high fiber loading. Therefore, to control the degree of fibrillation a pre‐treatment has been applied on the aramid fiber surface with maleic anhydride‐grafted‐polybutadiene (PB‐g‐MA) prior to mixing it with the TPU matrix. A good quality of fiber dispersion with improved tensile strength and elongation at break has been achieved even with 6 mm short fiber at a loading of 10 phr with the treatment of only 5 phr of PB‐g‐MA. The tensile fractured surface morphological analyses of PB‐g‐MA coated fiber filled TPU composite strongly advocate these results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2205–2216, 2013     

Studies of the effect of fiber surface and matrix rheological properties on nonwoven reinforced elastomer composites

The influence of fiber type and fiber-surface properties on matrix flow behavior was investigated using structural reaction injection-molding (SRIM). The influence of fiber type, fiber-surface properties, and matrix type on strength properties in elastomeric composites reinforced with nonwoven fibrous structures was investigated using tensile tests on elastomer composite samples from SRIM and latex coagulation (LC) fabrication methods and the microbond strength method on individual fibers. The fibers used were PET, LLDPE, and p-aramid. Fibers were treated with epoxy, styrene, and isocyanate derivatives, which make the surface chemically reactive. Treatments were also made with NaOH and a copolymer of polyester and polyol ether, causing a change in the fiber surface energy. The matrix types were polyurethane elastomer and natural rubber. The results show that the surface treatments which produced a change in the surface energy influenced the flow rate of the matrix polymer during the composite fabrication process. The treatments resulted in chemically reactive fiber surfaces which improved the fiber-matrix bond strength without affecting the Young's modulus of the composite material. Good correlation was found between bond strength and surface energy including the dispersive component of surface energy in the case of polyurethane elastomer and surface-modified PET fibers. The age of the polyurethane matrix has a marked influence on the bond strength. The fiber volume fraction in composites has a strong influence on the Young's modulus of the elastomer composite. © 1995 John Wiley & Sons, Inc.     

Short glass fiber reinforced ABS and ABS/PA6 composites: Processing and characterization

In this study acrylonitrile‐butadiene‐styrene (ABS) terpolymer was reinforced with 3‐aminopropyltrimethoxysilane (APS)‐treated short glass fibers (SGFs). The effects of SGF concentration and extrusion process conditions, such as the screw speed and barrel temperature profile, on the mechanical properties of the composites were examined. Increasing the SGF concentration in the ABS matrix from 10 wt% to 30 wt% resulted in improved tensile strength, tensile modulus and flexural modulus, but drastically lowered the strain‐at‐break and the impact strength. The average fiber length decreased when the concentration of glass fibers increased. The increase in screw speed decreased the average fiber length, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength were affected negatively and the strain‐at‐break was affected positively. The increase in extrusion temperature decreased the fiber length degradation, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength increased. At higher temperatures the ABS matrix degraded and the mechanical strength of the composites decreased. To obtain a strong interaction at the interface, polyamide‐6 (PA6) at varying concentrations was introduced into the ABS/30 wt% SGF composite. The incorporation and increasing amount of PA6 in the composites broadened the fiber length distribution (FLD) owing to the low melt viscosity of PA6. Tensile strength, tensile modulus, flexural modulus, and impact strength values increased with an increase in the PA6 content of the ABS/PA6/SGF systems due to the improved adhesion at the interface, which was confirmed by the ratio of tensile strength to flexural strength as an adhesion parameter. These results were also supported by scanning electron micrographs of the ABS/PA6/SGF composites, which exhibited an improved adhesion between the SGFs and the ABS/PA6 matrix. POLYM. COMPOS. 26:745–755, 2005. © 2005 Society of Plastics Engineers     

Dynamic mechanical properties of nanoclay filled TPU/PP blends with compatibiliser

Abstract

Blends of thermoplastic polyurethane (TPU) and polypropylene (PP) are highly incompatible because of large differences in polarities and high interfacial tensions. On one hand, PP is added to TPU to improve TPU's thermal stability, chemical properties, mechanical properties (modulus, strength and hardness) and processing performance and to reduce TPU's cost. On the other hand, TPU is blended with PP to improve PP's properties (e.g. abrasion, flexibility, tear strength, shock absorbing capabilities, impact strength, adhesion and paintability/printability). Earlier works in polyurethane/organoclay nanocomposites, PP/organoclay nanocomposites and TPU/PP blends were studied. In our experimental work, both ester and ether based TPU nanocomposites were prepared by melt blending using 3?wt-% Cloisite 10A (organically modified montmorillonite clay) as the nanoscale reinforcement and blended with PP with/without PP-graft-maleic anhydride as the compatibiliser. Blends of nanoclay filled TPU/PP were evaluated for dynamic mechanical properties such as storage modulus E′, loss modulus E″ and dissipation factor tanδ.     

Enhanced properties of polyvinyl chloride modified by graphene reinforced thermoplastic polyurethane

Graphene sheets with a range of unusual properties and thermoplastic polyurethane (TPU ) were combined to modify polyvinyl chloride (PVC ), and the enhanced properties such as flexibility, thermal stability and mechanical properties of the PVC were investigated. In order to avoid the C ? Cl bonds in PVC being weakened, graphene was incorporated into TPU in the melting state first and then this TPU was employed as a modifier to enhance and plasticize PVC in another melt blending step. In comparison with the ternary blending method, this step‐by‐step melt blending method was more efficient and convenient. The distribution of graphene sheets in the polymer matrix is uniform and no C ? Cl bond weakened effect can be observed. Due to the similar polarity, TPU showed good compatibility with PVC and its plasticizing effect allowed a broader range of low temperature flexibility of the modified PVC matrix. Moreover, other properties of the resultant PVC matrix (PTG ‐x ) including mechanical properties, thermal stability and plasticizer migration resistance were all found to be improved. With innovative applications in mind, the development of new graphene‐based materials will certainly lead to many future advances in science and technology. © 2017 Society of Chemical Industry     

Effect of fiber surface treatment on the properties of biocomposites from nonwoven industrial hemp fiber mats and unsaturated polyester resin

Biocomposites were made with nonwoven hemp mats and unsaturated polyester resin (UPE). The hemp fiber volume fraction was optimized by mechanical testing. The effect of four surface treatments of industrial hemp fibers on mechanical and thermal properties of biocomposites was studied. The treatments done were alkali treatment, silane treatment, UPE (matrix) treatment, and acrylonitrile treatment. Bending strength, modulus of elasticity, tensile strength, tensile modulus, impact strength, storage modulus, loss modulus, and tan δ were evaluated and compared for all composites. The mechanical as well as thermal properties of the biocomposites improved after surface treatments. The properties of the above biocomposites were also compared with E‐glass–mat composite. To achieve balance in properties, a hybrid composite of industrial hemp and glass fibers was made. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1055–1068, 2006     

Preparation and characterization of nanoclay‐filled polyurethane/polypropylene blends

Ester‐based thermoplastic polyurethane (TPU) nanocomposites were prepared by melt blending at 190°C, using 3 wt% Cloisite 10A (organically modified montmorillonite clay) as the nanoscale reinforcement [TPU(C10A)]. The nanocomposites were subsequently melt‐blended with polypropylene (PP) using maleic anhydride–grafted polypropylene (MA‐g‐PP) as a compatibilizer [in the ratio of 70/30‐TPU/PP, 70/25/5‐TPU/PP/MA‐g‐PP, 70/25/5‐TPU (C10A)/PP/MA‐g‐PP]. Besides giving substantial increase in modulus, tensile strength, and other properties, organoclay reinforcement functions as a surface modifier for TPU hard segment resulting in improved dispersion. The morphology and other characteristics of the nanocomposite blends were investigated in terms of X‐ray diffraction, fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile properties, scanning electron microscopy, and atomic force microscopy. The results indicate that the ester‐TPU(C10A)/PP/MA‐g‐PP exhibited better dispersion than other blend systems; abrasion resistance and water absorption resistance were also better for this system. POLYM. ENG. SCI., 50:1878–1886, 2010. © 2010 Society of Plastics Engineers     

Viscoelastic,mechanical, and thermal characterization of fly ash‐filled ABS composites and comparison of fly ash surface treatments

In the present investigation, viscoelastic, mechanical, thermal properties, and microstructural analysis of ABS reinforced with various surface treated fly ash (FA) has been studied. FA particles were surface treated with various chemical reagents, i.e., Ca(OH)₂, NaOH, and Bis(3‐triethoxysilylpropyl)tetrasulfane (Si69) to improve the interfacial adhesion between ABS and FA. DMA tests confirmed an increase in the stiffness in the surface treated composites. Hybrid ABS/FA composites showed optimum storage modulus and T_g as compared with the virgin matrix. TGA analysis also showed higher thermal stability of ABS/FA composites than virgin matrix with the surface treatments of FA. The treated FA composites also show improved mechanical properties compared to untreated FA composite. The morphology of virgin matrix, untreated and treated FA composites was studied employing SEM. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Effects of thermoplastic polyurethane on the properties of poly(lactic acid)/organo‐montmorillonite nanocomposites based on novel vane extruder

Polylactic acid (PLA)/organo‐montmorillonite (OMMT) nanocomposites toughened with thermoplastic polyurethane (TPU) were prepared by melt‐compounding on a novel vane extruder (VE), which generates global dynamic elongational flow. In this work, the mechanical properties of the PLA/TPU/OMMT nanocomposites were evaluated by tensile, flexural, and tensile tests. The wide‐angle X‐ray diffraction and transmission electron microscopy results show that PLA/TPU/OMMT nanocomposites had clear intercalation and/or exfoliation structures. Moreover, the particles morphology of nanocomposites with the addition of TPU was investigated using high‐resolution scanning electronic microscopy. The results indicate that the spherical TPU particles dispersed in the PLA matrix, and the uniformity decreased with increasing TPU content (≤30%). Interestingly, there existed abundant filaments among amount of TPU droplets in composites with 30 and 40 wt% TPU. Furthermore, the thermal properties of the nanocomposites were examined with differential scanning calorimeter and dynamic mechanical analysis. The elongation at break and impact strength of the PLA/OMMT nanocomposites were increased significantly after addition of TPU. Specially, Elongation at break increased by 30 times, and notched impact strength improved 15 times when TPU loading was 40 wt%, compared with the neat PLA. Overall, the modified PLA nanocomposites can have greater application as a biodegradable material with enhanced mechanical properties. POLYM. ENG. SCI., 54:2292–2300, 2014. © 2013 Society of Plastics Engineers     

Electrical and Mechanical Properties of Thermoplastic Polyurethane and Polytetrafluoroethylene Powder Composites

To determine the possibility of using polytetrafluoroethylene (PTFE) powder as reinforcing filler in the thermoplastic matrix, the thermoplastic polyurethane (TPU) as the matrix and PTFE powder as reinforcing filler were used to prepare a particulate reinforced composite, in order to determine testing data for electrical and mechanical properties of the composites according to the filler loading in respect to TPU polymer matrix. The TPU and PTFE powder composites were prepared by the milling TPU with 2.5, 5, 7.5, and 10 wt% of PTFE powder in a two roll mill and the milled material is compression moulded to make sheets. From the sheets, the test specimens were made and tested for electrical properties—dielectric strength, dielectric constant, surface, and volume resistivity; fire resistance—rate of burning; mechanical properties—tensile strength and elongation, impact strength, hardness; density and melt flow index. The incorporation of PTFE powder has significantly improved the electrical properties—dielectric strength, dielectric constant, surface and volume resistivity; and fire resistance—rate of burning of thermoplastic polyurethane. However, the tensile strength decreased from 24.91 to 14.71 MPa and tensile elongation increased from 620 to 772 percentage.