Development of bacterial cellulose nanowhiskers reinforced EVOH composites by electrospinning

In the current study, hybrid electrospun ethylene vinyl alcohol (EVOH) fibers reinforced with bacterial cellulose nanowhiskers (BCNW) were developed and characterized. Additionally, electrospinning was suggested as a method for the incorporation of well‐dispersed BCNW into an EVOH matrix by melt compounding. With the aim of maximizing the BCNW's loading in the electrospun fibers, an optimized method was applied for generating fibers from solutions containing up to 40 wt % BCNW. As demonstrated by FTIR spectroscopy, it was possible to incorporate BCNW concentrations up to ～ 24 wt %, although a complete incorporation of the nanofiller into the fibers was only achieved with solutions containing up to 20 wt % of the filler, DSC analyses suggested that the incorporation of the nanofiller reduced the crystallinity of the as‐obtained EVOH fibers and produced an increase in the glass transition temperature of these during the second heating run. Thermogravimetric analyses showed that even though EVOH protects the nanowhiskers from thermal degradation, the electrospun hybrid fibers present a relatively lower thermal stability than the pure EVOH fibers. FTIR analyses of the samples subjected to different thermal treatments confirmed that the stiffening effect observed by DSC only occurs after melting of the EVOH phase and is cooperative with a partial acid chemical development in the BCNW, which promotes strong chemical interactions between the polymeric matrix and the nanofiller. Finally, the hybrid electrospun fibers were incorporated into pure EVOH by melt compounding to produce composite films. This methodology showed higher stability and dispersion of the BCNW than direct addition of the freeze‐dried nanofiller to EVOH. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nanocomposites of ethylene vinyl alcohol copolymer with thermally resistant cellulose nanowhiskers by melt compounding (II): Water barrier and mechanical properties

In the present work, the crystallinity and crystalline morphology, thermal stability, water barrier, and mechanical properties of ethylene vinyl alcohol copolymer (EVOH) nanocomposites prepared by melt compounding and incorporating both plant (CNW) and bacterial cellulose nanowhiskers (BCNW) are reported. An improvement in the water barrier performance was observed, that is, 67% permeability drop, only for the microcomposite sample incorporating 2 wt % of bacterial cellulose fibrils. No significant differences in the water‐barrier properties of the nanocomposites generated through the two studied preincorporation methods were observed despite the fact that an excellent dispersion was observed in the previous study. On the other hand, direct melt‐mixing of the freeze‐dried nanofiller with EVOH resulted in increased water permeation. The aggregation of the filler in the latter nanocomposite was also ascribed to the detrimental effect on the mechanical properties. Interestingly, by using the precipitation method, an increase in the elastic modulus and tensile strength of ～36 and 22%, respectively, was observed for a 3 wt % BCNW loading, which was thought to coincide with the percolation threshold. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effect of plasticizer and cellulose nanowhisker content on the dispersion and properties of cellulose acetate butyrate nanocomposites

We studied the effects of plasticizer and cellulose nanowhisker content on the dispersion and properties of cellulose acetate butyrate (CAB)‐based bionanocomposites. The cellulose nanowhiskers in an aqueous medium were solvent‐exchanged to nonaqueous polar solvent (acetone) and used for nanocomposite processing by solution casting. The plasticized and unplasticized nanocomposites with 5 and 10 wt % cellulose nanowhisker content were prepared. Atomic force microscopy indicated nanoscale dispersion of whiskers in the CAB matrix. The dynamic mechanical analysis showed an increase in storage modulus with addition of cellulose nanowhiskers, especially above the glassy‐rubbery transition region. Thermogravimetric analysis showed an improvement in thermal stability with increased whisker content for both unplasticized and plasticized nanocomposites. The plasticized nanocomposites showed better transparency than the unplasticized composites, indicating a better dispersion of cellulose nanowhiskers in CAB, in the presence of a plasticizer. The dynamic mechanical properties and thermal stability increased, whereas transparency decreased with increased CNW content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal properties and crystallinity of PCL/PBSA/cellulose nanocrystals grafted with PCL chains

Bionanocomposite films of poly(?‐caprolactone) (PCL) and poly(butilene succinate‐co ‐adipate) (PBSA) blends with cellulose nanocrystals (CNW) grafted with PCL chains (CNW‐g ‐PCL) were prepared by solution casting and their thermal properties and crystallinity were studied. The CNW surface was modified with PCL chains by grafting “from” approaches, in an effort to improve their compatibility with the polymer blends. The grafting efficiency was evidenced by FTIR and TGA analysis. The acicular morphology of CNW‐g ‐PCL was characterized by SEM. The TGA results showed an increase in the thermal stability of the CNW grafted with PCL chains. The PCL/PBSA blends showed higher thermal stability in comparison with the neat polymers and PCL/PBSA/CNW‐g ‐PCL bionanocomposites. DSC results showed the CNW‐g ‐PCL act as a nucleating agent in the bionanocomposites. Additionally, a better interaction of the CNW‐g ‐PCL in the blends of 30/70 composition in comparison with the blends of 50/50 composition was characterized. The results obtained for aforementioned films prepared by solution casting encourage the production of such bionanocomposites by melt compounding (extrusion), aiming the achievement of new bionanocomposites materials with improved thermal and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44493.     

Assessment of ball milling methodology to develop polylactide‐bacterial cellulose nanocrystals nanocomposites

In this work, ball milling is evaluated as a methodology to develop polylactide (PLA)‐bacterial cellulose nanocrystals (BCNC) nanocomposites. This technique, widely used for clay‐based nanocomposites, is effective in breaking up to a very large extent the freeze‐dried nanocellulose aggregates, giving raise to transparent films similar to the neat PLA films. Incorporation of the nanofiller through this methodology enhances the polymer crystallinity index. An increase in the onset degradation temperature and a significant reinforcing effect in terms of an increase in the storage modulus and in the tan delta peak are also observed. Improved barrier to oxygen at high relative humidity (80%) is also noticed, reaching the best performance at the lowest BCNC loading (0.5 wt %). These improvements are related to the relatively good nanocellulose dispersion and distribution attained for low loadings of the nanofiller. Thus, the ball milling methodology appears as a feasible processing methodology for developing PLA‐BCNC nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41605.     

Pre‐dispersing of montmorillonite nanofiller: Impact on morphology and performance of melt compounded ethyl vinyl acetate nanocomposites

Ethyl vinyl acetate (EVA) copolymers are potential materials for biomedical applications due to their exceptional mechanical properties and biocompatibility. As new medical device designs continue to reduce in size, new materials are required that exhibit improved strength and toughness. In this research, EVA nanocomposites containing synthetic montmorillonite (MMT) are being investigated as new biomedical materials with similar flexibility, biocompatibility, and biostability to neat EVA, but with far superior tensile strength and toughness. We show that the pre‐dispersing of the organo‐MMT prior to melt compounding with the EVA matrix can facilitate nanofiller exfoliation and dispersion in the EVA, thereby enabling significant improvement of EVA nanocomposite performance when high organo‐MMT loading (5 wt %) was added. It was observed that the polarity of pre‐dispersing medium influenced the nanofiller's surfactant organization and distribution, organo‐MMT exfoliation, and dispersion in the EVA, and also interphases of the host copolymer. Consequently, changes in morphology have brought noticeable effects on the mechanical and thermal properties of the EVA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43204.     

Effects of ionizing radiation in ethylene-vinyl alcohol copolymers and in composites containing microfibrillated cellulose

This study reports on the effect of gamma radiation on morphological, thermal, and water barrier properties of pure ethylene vinyl alcohol copolymers (EVOH29 and EVOH44) and its biocomposites with the nanofiller microfibrillated cellulose (2 wt %). Added microfibrillated cellulose (MFC) preserved the transparency of EVOH films but led to a decrease in water barrier properties. Gamma irradiation at low (30 kGy) and high doses (60 kGy) caused some irreversible changes in the phase morphology of EVOH29 and EVOH44 copolymers that could be associated to crosslinking and other chemical alterations. Additionally, the EVOH copolymers and the EVOH composites reduced the number of hygroscopic hydroxyl functionalities during the irradiation processing and novel carbonyl based chemistry was, in turn, detected. As a result of the above alterations, the water barrier properties of both neat materials and composites irradiated at low doses were notably enhanced, counteracting the detrimental effect on water barrier of adding MFC to the EVOH matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Melt‐spun polylactic acid fibers: Effect of cellulose nanowhiskers on processing and properties

Bio‐based continuous fibers were processed from polylactic acid (PLA) and cellulose nanowhiskers (CNWs) by melt spinning. Melt compounding of master batches of PLA with 10 wt % CNWs and pure PLA was carried out using a twin‐screw extruder in which compounded pellets containing 1 and 3 wt % of CNWs were generated for subsequent melt spinning. The microscopy studies showed that the fiber diameters were in the range of 90‐95 µm, and an increased surface roughness and aggregations in the fibers containing CNWs could be detected. The addition of the CNWs restricted the drawability of the fibers to a factor of 2 and did not affect the fiber stiffness or strength, but resulted in a significantly lower strain and slightly increased crystallinity. Furthermore, CNWs increased the thermal stability, creep resistance and reduction in thermal shrinkage of PLA fibers, possibly indicating a restriction of the polymer chain mobility due to the nanoscale additives. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites

Bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was reinforced with cellulose nanowhiskers (CNW) in 1-5 wt.% concentrations using a solvent casting method. The CNW was prepared from microcrystalline cellulose (MCC) using sulfuric acid hydrolysis. The influence of CNW on the PHBV crystallization, thermal, dynamic mechanical and mechanical properties were evaluated using polarized optical microscope (POM), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), tensile and bulge tests, respectively. POM test results demonstrated that CNW was an effective PHBV nucleation agent. Tensile strength, Young’s modulus and toughness of PHBV increased with the increasing concentration of CNW. DMA results showed an increased tan δ peak temperature and broadened transition peak, indicating restrained PHBV molecular mobility in the vicinity of the CNW surface. Storage modulus of the PHBV also increased with the addition of CNW, especially at the temperatures higher than the PHBV glass transition temperature. These results indicated that the CNW could substantially increase the mechanical properties of PHBV and this increase could be attributed to the strong interactions between these two phases.     

Effect of the variation in the weight percentage of the loading and the reduction in the nanosizes of CaSO4 on the mechanical and thermal properties of styrene–butadiene rubber

The incorporation of fillers into elastomers has profound effects on the mechanical, physical, and thermal properties of the nanocomposites that form. In this study, styrene–butadiene rubber as a matrix was reinforced separately with 10‐, 15‐, or 23‐nm CaSO₄, which was synthesized by an in situ deposition technique. The mixing and compounding were performed on a two‐roll mill, and sheets were prepared in a compression‐molding machine. Properties such as the swelling index, specific gravity, tensile strength, elongation at break, modulus at 300% elongation, Young's modulus, hardness, and abrasion resistance were measured. The morphology of the rubber nanocomposites was also performed with scanning electron microscopy to study the dispersion of the nanofiller in the rubber matrix. The thermal decomposition of the rubber nanocomposites was studied with thermogravimetric analysis, and the results were compared with those of commercial CaSO₄‐filled styrene–butadiene rubber. A reduction in the nanosizes of CaSO₄ led to an enhancement of the mechanical, physical, and thermal properties of the rubber nanocomposites. Above a 10 wt % filler loading, the styrene–butadiene rubber showed a reduction in all properties. This effect was observed because of the agglomeration of the nanoparticles in the rubber matrix. The thermodynamic parameters were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2018–2026, 2007     

竹纤维素纳米晶须的结构与性质

利用酸水解制备竹纤维纳米晶须(CNW),借助原子力显微镜(AFM)和核磁共振,研究了酸水解不同时间对制备的竹纤维纳米晶须形貌和结构的影响。结果表明:硫酸水解15 min之前NCW的形貌呈棒状结构,超过15 min转变为较细的针状结构;在酸水解时间为20 min时长径比最大,结晶度最高,次晶含量最低,晶粒尺寸最大。通过偏光显微镜观察CNW悬乳液,其具有形成手性向列相液晶指纹状结构的性质。CNW质量分数为1%时,浓度太低晶须之间不能相互作用,当CNW质量分数达到2.5%(2.5%～7.5%),随着CNW悬乳液浓度增加,形成的手性向列相液晶的指纹间距减小。     

Deformation and fracture behavior of polypropylene–ethylene vinyl alcohol blends compatibilized with ionomer Zn2+

This work investigated the deformation and fracture behavior of polypropylene–ethylene vinyl alcohol (PP/EVOH) blends compatibilized with ionomer Zn²⁺. Uniaxial tensile tests and quasistatic fracture experiments were performed for neat PP and for 10 and 20 wt % EVOH blends with different ionomer contents. The addition of EVOH copolymer to PP led to an increase in the Young's modulus whereas the yield strength was decreased with the EVOH content as a consequence of the higher stiffness of EVOH and the poor interfacial adhesion between PP and EVOH, respectively. Furthermore, the incorporation of EVOH into PP promoted stable crack growth. Neat PP displayed nonlinear load‐displacement behavior with some amount of slow crack growth preceding unstable brittle fracture, whereas most PP/EVOH blends exhibited “pseudostable” fracture characterized by slow crack growth that could not be externally controlled. All blends exhibited lower resistance to crack initiation than PP but the fracture propagation resistance was significantly improved. For 10 wt % EVOH blends, the resistance to crack initiation was roughly constant with the ionomer content up to 5%, then it increased with the further addition of compatibilizer. Conversely, for 20 wt % EVOH blends, the resistance to crack initiation appeared to be independent of the ionomer content. The better resistance to crack initiation exhibited by the 10 wt % EVOH blends could be attributed to a higher level of compatibilization in these blends. By contrast, 20 wt % EVOH blends with ≤2% ionomer content showed completely stable crack growth. In addition, J–R curves and valid plane strain fracture toughness values for these blends could also be determined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1271–1279, 2005     

Cellulose nanocrystals extracted from okra fibers in PVA nanocomposites

Cellulose nanocrystals (CNC) were extracted from okra bahmia (Abelmoschus Esculentus) bast fibers and inserted in different tenors (1, 2, 5, and 10 wt %) as the reinforcement of a poly(vinyl alcohol) (PVA) matrix. The extraction of cellulose was carried out in a two‐step procedure: the first chemical treatment led to the production of holocellulose by the gradual removal of lignin, while the subsequent sulphuric acid hydrolysis process allowed obtaining cellulose nanocrystals in an aqueous suspension. The dispersion of CNC in the composite appeared effective at low cellulose content (1 wt %), while it presented more problems for higher contents. However, a 5 wt % cellulose content proved ideal to promote a direct mechanical interaction between the PVA and cellulose structures. Thermal analysis demonstrated that the presence of okra did not have a large effect on glass transition temperature, while it sensibly modified the melting temperature of the PVA matrix, as well as the crystallization temperature, due to the nucleating action of the nanofillers. FTIR spectroscopy performed during the exposure to UV light underlined that no oxidative reactions occur after a short‐time exposure and that a longer irradiation times are required to produce oxidation on neat matrix and PVA/CNC nanocomposites. The results confirmed that the presence of CNC does not affect the stability of the neat PVA matrix to the photodegradation after UV irradiation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poly(?-caprolactone) based nanocomposites reinforced by surface-grafted cellulose nanowhiskers via extrusion processing: Morphology, rheology, and thermo-mechanical properties

Poly(ε-caprolactone)-grafted cellulose nanowhiskers (extracted from ramie: CNWr) synthesized by ring-opening polymerization of the corresponding lactone [1] were studied as “masterbatches” by melt-blending within its commercial poly(ε-caprolactone) matrix (PCL). For sake of comparison, unmodified CNWr were also dispersed in PCL. The goal of this study consists to evidence the impact of the covalent grafting of CNWr surface on thermo-mechanical properties of the commercial matrices. Atomic force microscopy (AFM) attests of the excellent dispersion of the cellulose nanowhiskers within PCL matrix. As a result of the excellent interfacial compatibility between the nanofiller and the matrix, the thermo-mechanical and rheological performances were largely enhanced.     

Morphological investigation of cellulose acetate/cellulose nanocrystal composites obtained by melt extrusion

Composites were prepared from cellulose acetate (CA) and cellulose nanocrystals (CNC) by melt extrusion using two methods for the introduction of CNC: direct mixing and predispersion in CA solution. CNC were isolated using hydrochloric acid to increase thermal stability allowing the composites to be processed above 150 °C. The effect of CNC dispersion on the composites morphology, thermal, and mechanical properties was investigated. Field emission scanning electron microscopy and transmission electron microscopy results indicated that the predispersion method allows better CNC dispersion and distribution when compared to the direct mixture method. In addition, predispersion promotes preferential CNC orientation in relation to the injection flow. The predispersion method also showed a 14% Young's modulus increase in composites containing 15 wt % CNC while no significant change was observed when using the direct mixing. The results obtained in this work show that, to achieve the percolation threshold, nanoparticle distribution is as important as their content. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44201.     

Reprocessing effects on polypropylene/silica nanocomposites

A polypropylene matrix was melt compounded with a given amount (2 vol %) of both untreated (hydrophilic) and surface treated (hydrophobic) fumed silica nanoparticles with the aim to investigate the influence of the time under processing conditions on the microstructure and thermo‐mechanical properties of the resulting materials. Chain scission reactions induced by thermal processing caused a remarkable decrease of the melt viscosity, as revealed by the melt flow index values of both neat matrix and nanocomposites, but the degradative effect was significantly hindered by the presence of silica nanoparticles. It was observed that the size of nanofiller aggregates noticeably decreased as the compounding time increased, especially when hydrophobic silica nanofiller was considered. While the melting temperature seemed to be unaffected by the processing time, a remarkable embrittlement of the samples was observed for prolonged compounding times. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40242.     

Sustainable bionanocomposite from d,l‐lactide/δ‐valerolactone triblock and bionanowhiskers: Preparation,characterization, and properties

Bionanocomposites were prepared using d ,l ‐lactide–δ‐valerolactone–d ,l ‐lactide triblock and unmodified and modified cellulose nanowhiskers (CNs) at different loadings (0, 2, 4, 8 wt %). Poly(δ‐valerolactone) chains were grafted on CNs for modification. These were characterized by various techniques. The broadening of OH (hydroxyl) stretching region and the presence of low‐intensity peaks at 1064 cm^?1 for C? O/C? C stretching vibration and 1426 cm^?1 for bending vibration of CH₂ group_, were evident in Fourier transform infrared spectra of the nanocomposites. The increase in crystallinity was noticed as the amount of nanowhiskers was increased. The nanowhiskers having the width in the range of 80–300 nm were uniformly dispersed in the triblock matrix. The tensile strength and modulus increased by 130% and 50% respectively at 8 wt % of filler loading. The storage modulus, loss modulus, complex viscosity, and tan δ values increased with increased filler loading. Further improvement in mechanical properties was observed with the modified CNs. The modulus mapping from atomic force microscopy confirmed the effective reinforcement behavior of the nanowhiskers. Scaffold fabrication using the bionanocomposite exhibited porous nature, having a homogeneous dispersion of CNs on the surface of the scaffold. The 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay confirmed the suitability of the composite material for scaffold application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 135, 46035.     

Thermal and barrier properties of EVOH/EFG nanocomposite films for packaging applications: Effect of the mixing method

Ethylene‐vinyl alcohol copolymer (EVOH)/exfoliated graphite (EFG) nanocomposite films were prepared by precoating EFG on the EVOH surface and conducting a successive melt‐extrusion process. Their physical properties were strongly dependent on the EFG content and the mixing method, which strongly affected the morphology and surface properties of the nanocomposite films. The hydrophobicity and water resistance property of EVOH increased by incorporating hydrophobic EFG and their effects were more pronounced in the precoating method, which is related to good dispersion of EFG in EVOH and an enhanced crystalline structure. The incorporation of EFG into EVOH by the precoating method more effectively diminished the dependence of the relative humidity on the oxygen transmission rate of pure EVOH and increased the oxygen barrier properties of EVOH at a high relative humidity. The incorporation of EFG into EVOH by the precoating method also induced relatively more enhanced thermal stability. These results suggest the feasibility of the application of moisture‐sensitive EVOH resin for food packaging films. POLYM. COMPOS., 37:1744–1753, 2016. © 2014 Society of Plastics Engineers     

Melt rheological investigation of polylactide‐nanographite platelets biopolymer composites

This study is an analytical investigation of processability of biopolymer‐carbon based nanofiller composites primarily through rheological investigation of samples. The composites were fabricated via dry mixing and melt‐blending of biodegradable polylactide (PLA) and nanographite platelets (NGP) in a Brabender twin screw extruder. A range of different nanofiller contents (1, 3, 5, 7, and 10 wt %) were studied for NGP containing composites. The morphology was studied with X‐ray diffraction and transmission electron microscopy techniques and showed poor dispersion, with agglomerates, tactoids, and exfoliated layers present. Mechanical properties showed an optimum at 3 wt % filler. Results showed that the composites exhibited higher elastic and viscous moduli than neat PLA. The rheological percolation threshold predicted by changes in slope (α) as well as liquid–solid transition theory of samples was found around 3 wt % through the change from liquid‐like behavior to pseudo‐solid‐like behavior at terminal region during dynamic oscillatory measurements. NGP nanofillers were found to enhance the viscoelastic and mechanical properties of PLA at low concentrations; however, an efficient dispersion of nanofillers within polymer by melt intercalation method of mixing was not achieved. POLYM. ENG. SCI., 54:175–188, 2014. © 2013 Society of Plastics Engineers     

Processing-microstructure-property relationship in conductive polymer nanocomposites

The processing-microstructure-property relationship in conductive polymer nanocomposites was investigated. Nanocomposites of vapor grown carbon nanofiber (VGCNF)/high density polyethylene (HDPE) with different levels of nanofiber dispersion were formulated by changing the nanocomposites’ compounding temperature. Direct (SEM and optical microscopy) and indirect methods (linear viscoelastic properties) were used to characterize the dispersion of nanofiller. VGCNF aspect ratio before and after mixing was measured. Increasing processing temperature was found to increase the nanofiller agglomeration and reduce the breakage of nanofiller because of the decrease in the mixing shear stress and energy. The electrical and electromagnetic interference (EMI) shielding properties of the VGCNF/HDPE nanocomposites decreased with increase in processing temperature from 180 °C to 220 °C because the increase in the agglomeration of VGCNF was more significant than the preservation of the VGCNF aspect ratio. This finding does not mean that the increase in processing temperature will always lead to decrease in the electrical conductivity and EMI shielding properties for all polymer composites. For some composites, it is possible to preserve the filler aspect ratio enough so that the increase in agglomeration is less of a factor.