Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid)

Nanodiamond (ND)/poly (lactic acid) (PLA) nanocomposites with potential for biological and biomedical applications were prepared by using melting compound methods. By means of transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyses (TGA), Dynamic mechanical analyses (DMA), Differential scanning calorimetry (DSC) and Tensile test, the ND/PLA nanocomposites were investigated, and thus the effect of ND on the structural, thermal and mechanical properties of polymer matrix was demonstrated for the first time. Experimental results showed that the mechanical properties and thermal stability of PLA matrix were significantly improved, as ND was incorporated into the PLA matrix. For example, the storage modulus (E′) of 3 wt% ND/PLA nanocomposites was 0.7 GPa at 130 °C which was 75% higher than that of neat PLA, and the initial thermal decomposition was delayed 10.1 °C for 1 wt% ND/PLA nanocomposites compared with the neat PLA. These improvements could be ascribed to the outstanding physical properties of ND, homogeneous dispersion of ND nanoclusters, unique ND bridge morphology and good adhesion between PLA matrix and ND in the ND/PLA nanocomposites.     

Thermal,mechanical and rheological properties of polylactide toughened by expoxidized natural rubber

This paper concerns on the use of epoxidized natural rubber (ENR) as toughening agent for polylactide (PLA). ENR with epoxidation content of 20 mol% (ENR20) and 50 mol% (ENR50) were separately melt blended with PLA using an internal mixer. DSC results suggested that PLA/ENR blends were amorphous after melt blending while they were crystalline and revealed two melting peaks in the thermograms after being annealed at 100 °C. Mechanical tests showed that the introduction of ENR reduced the tensile modulus and strength but enhanced the elongation and the impact strength of PLA. The impact strength of the 20 wt% ENR20/PLA and ENR50/PLA blends increased to 6-fold and 3-fold, respectively, compared to that of pure PLA. This enhancement was due to a good interfacial adhesion between ENR and PLA. Both ENR20/PLA and ENR50/PLA blends performed very strong shear thinning behavior, and the complex viscosity, storage and loss modulus of the blends also increased after blending with ENR.     

The effect of silane treated- and untreated-talc on the mechanical and physico-mechanical properties of poly(lactic acid)/newspaper fibers/talc hybrid composites

This paper evaluates the effect of the addition of silane treated- and untreated- talc as the fillers on the mechanical and physico-mechanical properties of poly(lactic acid) (PLA)/recycled newspaper cellulose fibers (RNCF)/talc hybrid composites. For this purpose, 10 wt% of a talc with and without silane treatment were incorporated into PLA/RNCF (60 wt%/30 wt%) composites that were processed by a micro-compounding and molding system. PLA is utilized is a bio-based polymer that made from dextrose, a derivative of corn. Talc is also a natural product. The RNCF and talc hybrid reinforcements of PLA polymer matrix were targeted to design and engineer bio-based composites of balanced properties with added advantages of cost benefits besides the eco-friendliness of all the components in the composites. In this work, the flexural and impact properties of PLA/RNCF composites improved significantly with the addition of 10 wt% talc. The flexural and impact strength of these hybrid composites were found to be significantly higher than that made from either PLA/RNCF. The hybrid composites showed improved properties such as flexural strength of 132 MPa and flexural modulus of 15.3 GPa, while the unhybridized PLA/RNCF based composites exhibited flexural strength and modulus values of 77 MPa and 6.7 GPa, respectively. The DMA storage modulus and the loss modulus of the PLA/RNCF hybrid composites were found to increase, whereas the mechanical loss factor (tan delta) was found to decrease. The storage modulus increased with the addition of talc, because the talc generated a stiffer interface in the polymer matrix. Differential scanning calorimetry (DSC) thermograms of neat PLA and of the hybrid composites showed nearly the similar glass transition temperatures and melting temperatures. Scanning electron microscopy (SEM) micrographs of the fracture surface of Notched Izod impact specimen of 10 wt% talc filled PLA/RNCF composite showed well filler particle dispersion in the matrix and no large aggregates are present. The comparison data of mechanical properties among samples filled with silane-treated- and untreated- talc fillers showed that the hybrid composites filled with silane treated talc displayed the better mechanical prosperities relative to the other hybrid composites. Talc-filled RNCF-reinforced polypropylene (PP) hybrid composites were also made in the same way that of PLA hybrid composites for a comparison. The PLA hybrid bio-based composites showed much improvement in mechanical properties as compared to PP-based hybrid counterparts. This suggests that these PLA hybrid bio-based composites have a potential to replace glass fibers in many applications that do not require very high load bearing capabilities and these recycled newspaper cellulose fibers could be a good candidate reinforcement fiber of high performance hybrid biocomposites.     

Isolation of nanofibers from soybean source and their reinforcing capability on synthetic polymers

The focus of this work is to study nanofibers in three different polymers: polyvinyl alcohol (PVA), polypropylene (PP) and polyethylene (PE). The nanofibers were isolated from a soybean source by combining chemical and mechanical treatments. Isolated nanofibers were shown to have diameter between 50 and 100 nm and the length in micrometer scale which results in very high aspect ratio. The mechanical properties demonstrated an increase in tensile strength from 21 MPa of PVA/UNF5 (untreated-fiber (5 wt%) reinforced PVA) and 65 MPa of pure PVA to 103 MPa of PVA/SBN5 (nanofiber (5 wt%) reinforced PVA). The increased stiffness of PVA/SBN5 nanocomposites was also very promising; it was 6.2 GPa compared to 2.3 GPa of pure PVA and 1.5 GPa of PVA/UNF5. In solid phase melt-mixing, nanofiber was directly incorporated into the polymer matrix using a Brabender. The nanofiber addition significantly changed the stress–strain behavior of the composites: modulus and stress were increased with coated nanofibers by ethylene–acrylic oligomer emulsion as a dispersant; however, elongation was reduced. The dynamic mechanical analysis showed the addition of the soybean nanofiber (SBN) improved the thermal properties for PVA and how the addition of different contents of SBN influenced the tan δ peak and storage modulus of PVA.     

Ductile PLA nanocomposites with improved thermal stability

Polylactide (PLA) is used as a biomedical material because it is biodegradable, but the vast majority of biodegradable polymers in clinical use are composed of rather stiff materials that are unsuitable for use in numerous applications because they exhibit limited extendibility, weak mechanical strength, and poor thermal stability. We modified PLA with 2-methacryloyloxyethyl isocyanate (MOI) to prepare ductile PLA materials. By utilizing a novel sol–gel process, PLA nanocomposites were further prepared with improved mechanical properties and thermal stability. The 10% thermal decomposition temperature for PLA modified with 5% MOI and 5–10% silica was 21–32 °C higher than that of original pristine PLA. Elongation at break increased by 4–13 times when compared to neat PLA while the tensile strength was maintained at 30–40 MPa. These synthesized PLA nanocomposites can be applied as biomaterials with improved mechanical and thermal properties.     

Mechanically improved and optically transparent polycarbonate/clay nanocomposites using phosphonium modified organoclay

The present study deals with the properties of polycarbonate (PC)/clay nanocomposites prepared through melt and solution blending at two different clay loadings (0.5 phr and 1 phr) with preserved optical transparency of PC. The organoclay was prepared by exchanging the Na⁺ ions presented in the clay galleries of Na-MMT with butyltriphenylphosphonium (BuTPP⁺) ions, and denoted as BuTPP-MMT. The outstanding thermal stability of the BuTPP-MMT (∼1.44 wt% loss at 280 °C, after 20 min), concomitant with the increase in gallery height from 1.24 nm to 1.83 nm, proved its potentiality as nanofiller for melt-blending with PC. The X-ray diffraction analysis (XRD) revealed the destruction of the ordered geometry of aluminosilicate layers in the nanocomposites. However, from direct visualization through transmission electron microscopy, a discernible amount of clay was found to be localised in PC matrix in the 1 phr clay loaded nanocomposites (TEM). The differential scanning calorimetric (DSC) study revealed a nominal increase in glass transition temperature (T_g) of the PC in the nanocomposites. The thermal stability of the nanocomposites was increased with increase in clay loading. The nanocomposites possessed improved tensile strength and modulus than that of the virgin PC and the properties were related to the amount of clay loading and degree of clay dispersion. The dynamic mechanical analysis (DMA) revealed that the storage modulus increased in both the glassy and rubbery region with increase in clay loadings in the nanocomposites. Moreover, the optical transparency of the PC was retained in the PC/clay nanocomposites without development of any colour in the nanocomposites.     

Structure and thermal properties of poly(lactic acid)/cellulose whiskers nanocomposite materials

The goal of this work was to produce nanocomposites based on poly(lactic acid) (PLA) and cellulose nanowhiskers (CNW). The CNW were treated with either tert-butanol or a surfactant in order to find a system that would show flow birefringence in chloroform. The nanocomposites were prepared by incorporating 5 wt% of the different CNW into a PLA matrix using solution casting. Field emission scanning electron microscopy showed that untreated whiskers formed flakes, while tert-butanol treated whiskers formed loose networks during freeze drying. The surfactant treated whiskers showed flow birefringence in chloroform and transmission electron microscopy showed that these whiskers produced a well dispersed nanocomposite. Thermogravimetric analysis indicated that both whiskers and composite materials were thermally stable in the region between 25 °C and 220 °C. The dynamic mechanical thermal analysis showed that both the untreated and the tert-butanol treated whiskers were able to improve the storage modulus of PLA at higher temperatures and a 20 °C shift in the tan δ peak was recorded for the tert-butanol treated whiskers.     

Morphology,interfacial and mechanical properties of polylactide/poly(ethylene terephthalate glycol) blends compatibilized by polylactide-g-maleic anhydride

Polylactide/poly(ethylene terephthalate glycol) (PLA/PETG 80/20 wt) blends compatibilized with polylactide-g-maleic anhydride (PLA-g-MAH) were prepared by melt blending and the rheological, morphological and mechanical properties of the blends were studied. PLA/PETG (80/20 wt) blend formed a typical sea-island morphology, while upon compatibilization, the size and size distribution of the dispersed phase decreased significantly and the 3 wt% PLA-g-MAH compatibilized blend exhibited the smallest phase size and the narrowest distribution of the dispersed particles. The interfacial tension between PLA and PETG was determined from the morphological characteristics and the viscoelastic response of PLA/PETG blends via using two emulsion models. A minimum for PLA/PETG blend containing 3 wt% PLA-g-MAH was observed from both Palierne model and G–M model. The elongation-at-break increased by ∼320%, from 6.9% for PLA to 28.7% for the blend containing 3 wt% PLA-g-MAH without significant loss in the tensile modulus and tensile strength.     

Structure and properties of hybrid PLA nanocomposites with inorganic nanofillers and cellulose fibers

Polylactide reinforced with 3 wt% of organo-modified montmorillonite, 5 wt% of stearic acid-modified calcium carbonate nanoparticles, 15 wt% of cellulose fibers (PLA/MMT, PLA/NCC, PLA/CF) and hybrid composites containing 15 wt% of fibers in addition to montmorillonite (PLA/MMT/CF) or calcium carbonate (PLA/NCC/CF) were prepared and examined. The nanoparticles were dispersed in polylactide almost homogeneously; montmorillonite was exfoliated during processing. T_g of polylactide remained unaffected but its cold crystallization was enhanced; the cold-crystallization behavior of the hybrid composites was dominated by nanofillers nucleating ability. The fibers and calcium carbonate decreased whereas exfoliated montmorillonite improved the thermal stability of the materials. Polylactide, PLA/NCC and PLA/MMT exhibited ability to plastic deformation, although the latter the weakest. Tensile behavior of the hybrid composites was strongly influenced by the fibers and similar to that of PLA/CF. All the fillers increased the storage modulus below T_g; that of PLA/MMT/CF and PLA/NCC/CF was improved with respect to polylactide by 50% and 45%, respectively.     

Effect of composition ratio on the thermal and physical properties of semicrystalline PLA/PHB-HHx composites

In this study, composites of semicrystalline, biodegradable polylactide (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-HHx) were prepared by direct melt compounding. The physical and thermal properties of the composites were investigated as a function of the composition ratio. Differential scanning calorimetry analysis indicated that PLA and PHB-HHx formed immiscible composites over the observed range of composition. The crystallization of PLA was gradually suppressed by increasing proportions of PHB-HHx. Dynamic mechanical analysis results confirmed that the innate ductility of PHB-HHX and its inhibiting effect on PLA crystallization improved the stiffness of the composite compared to those of neat PLA. The infrared spectra of the immiscible PLA/PHB-HHx composites at two crystallization temperatures (30 °C, 130 °C) were obtained and presented. At 30 °C, PHB-HHx existed as crystalline domains in the PLA matrix, while, amorphous phase of molten PHB-HHx was diffused within the crystalline phase of PLA at 130 °C. The interaction between PHB-HHX and PLA could not be elucidated from the temperature data. Mechanical tests showed that the addition of PHB-HHx improves ductility of PLA/PHB-HHx composite. Morphological analysis revealed that small proportions of PHB-HHx exhibited less tendency to aggregate, which resulted in greater plastic deformation and improved toughness. From this study, PLA blended with small portions of PHB-HHx may further expand the use of bio-friendly resources in a variety of applications such as flexible films, food packaging and something like that.     

Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites

The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m², and a fracture toughness of 3 MPa m^1/2.     

Synthesis of multiblock thermoplastic elastomers based on biodegradable poly (lactic acid) and polycaprolactone

A new biodegradable (AB)_n type of multiblock copolymers derived from poly (ε-caprolactone) (PCL) and poly (lactic acid) (PLA) was prepared via the method of the chain extending reaction among PCL oligomers, PLA oligomers and hexamethylene diisocyanate (HDI). Fourier transform infrared spectra (FTIR), ¹H NMR, thermal gravity analysis (TGA) and derivative thermograms (DTG) were used to characterize the copolymers and the results showed that PCL and PLA were coupled by the reaction between –NCO groups and terminal –OH and –COOH groups of PCL and PLA, respectively. The material displayed enhanced mechanical properties: Young's modulus was as low as 2.7 ± 0.7 MPa and elongation at break value was above 790% at the composition of PCL/PLA = 80/20 (w/w). Moreover, according to SEM micrographs interfacial adhesion of the composites was improved. Thermal degradation temperature of the composites was higher than PLA but was lower than PCL, which is an advantage for industry process.     

PLA/algae composites: Morphology and mechanical properties

Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.     

Investigation of the effect of nanoclay and processing parameters on the tensile strength and hardness of injection molded Acrylonitrile Butadiene Styrene–organoclay nanocomposites

Polymer–clay nanocomposites have attracted considerable interest over recent years due to their dramatic improved mechanical properties. In the present study, compatibility of Acrylonitrile Butadiene Styrene (ABS) and organically modified montmorillonite nanoclay (Cloisite 30B) and composition capability of them are investigated. Polymethylmethacrylate (PMMA) in varying amount (0, 2, and 4 wt%) is used as the compatibilizer. In order to produce nanocomposite parts, the material is first compounded using a twin-screw extruder and then injected into a mold. The effect of the nanoclay percentage and processing parameters on the tensile strength and hardness of nanocomposite parts is also explored using Taguchi Design of Experiments method. Nanoclay content (in three levels: 0, 2 and 4 wt%), melt temperature (in three levels: 190, 200 and 210 °C), holding pressure (in three levels: 80, 105 and 130 MPa) and holding pressure time (in three levels: 1, 2.5 and 4 s) are considered as the variable parameters. Moreover, distribution of nanoclay layers is analyzed using Wide Angle X-ray Diffraction (XRD) test. XRD results displayed that with the presence of PMMA, nanoclay in ABS matrix is compounded in more exfoliated and less intercalated dispersion mode. Adding PMMA also leads to a remarkable increase in the fluidity of the melt during injection molding process. Results also illustrated that nanocomposites with medium loading level (i.e. 2%) of nanoclay have the highest tensile strength, while the highest hardness number belongs to nanocomposites with 4 wt% nanoclay. Obtained results also indicated that injection temperature has the most important effect on tensile strength and hardness of ABS–clay nanocomposites.     

Effects of extrusion temperature on the rheological,dynamic mechanical and tensile properties of kenaf fiber/HDPE composites

The effects of extrusion processing temperature on the rheological, dynamic mechanical analysis and tensile properties of kenaf fiber/high-density polyethylene (HDPE) composites were investigated for low and high processing temperatures. The rheological data showed that the complex viscosity, storage and loss modulus were higher with high processing temperature. Complex viscosities of pure HDPE and 3.4 wt% composite with zero shear viscosity of ⩽2340 Pa s were shown to exhibit Newtonian behavior while composites of 8.5 and 17.5 wt% with zero shear viscosity ⩾30,970 Pa s displayed non-Newtonian behavior. The Han plots revealed the sensitivity of rheological properties with changes in processing temperature. An increase in storage and loss modulus and a decrease in mechanical loss factor were observed for 17.5 wt% composites at high processing temperature and not observed at low processing temperature. Processing at high temperature was found to improve the tensile modulus of composites but displayed diminished properties when processed at low processing temperature especially at high fiber content. At both low and high processing temperatures, the tensile strength and strain of the composite decreased with increased content of the fiber.     

Optimising industrial hemp fibre for composites

The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10 wt% NaOH solution at a maximum processing temperature of 160 °C with a hold time of 45 min was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40 wt% fibre and 3 wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.     

High thermal and mechanical properties enhancement obtained in highly filled polybenzoxazine nanocomposites with fumed silica

Highly filled polybenzoxazine nanocomposites filled with nano-SiO₂ particles were investigated for their mechanical and thermal properties as a function of filler loading. The nanocomposites were prepared by high shear mixing followed by compression molding. A very low A-stage viscosity of benzoxazine monomer gives it excellent processability having maximum nano-SiO₂ loading as high as 30 wt% (18.8 vol%) with negligible void content. Moreover, thermal analysis of the curing process of the compound of the PBA-a/nano-SiO₂ composites was found to be autocatalytic in nature with average activation energy of 79–92 kJ mol⁻¹. Microscopic analysis (SEM) performed on the PBA-a/nano-SiO₂ composite fracture surface indicated a nearly homogeneous distribution of the nano-scaled silica in the polybenzoxazine matrix. In addition, the enhancement in storage modulus of the nano-SiO₂ filled polybenzoxazine composites was found to be significantly higher than that of the recently reported nano-SiO₂ filled epoxy composites. The dependence of the nanocomposites’ modulus on the nano-SiO₂ particles content is well fitted by the generalized Kerner equation. Furthermore, the relatively high micro-hardness of the PBA-a/nano-SiO₂ composites up to about 600 MPa was achieved. Finally, the substantial enhancement in the glass transition temperature (T_g) of the PBA-a/nano-SiO₂ composites was also observed with the ΔT_g up to 16 °C at the nano-SiO₂ loading of 30 wt%. The resulting PBA-a/nano-SiO₂ composite is a highly attractive candidate as coating material in electronic packaging or other related applications.     

Thermal and rheological properties of highly concentrated PET composites with ferrite nanoparticles

Ferrite nanoparticles were introduced into poly(ethylene terephthalate) (PET) in a melt state at 270 °C upto 20 wt%, and the thermal and rheological properties of the nanocomposites were investigated. The introduction of ferrite nanoparticles increased a little the crystallization temperature (T_c) of PET by ca. 3 °C, while it had little effect on the melting temperature (T_m). In addition, it increased both heat of crystallization (ΔH_c) and heat of fusion (ΔH_m) with ferrite content. PET nanocomposites with ferrite 5 wt% and above exhibited an increased thermal stability and a two-stage degradation. The dynamic viscosity of PET nanocomposites was increased with ferrite content. However, ferrite loading of 5 wt% and above produced a high degree of shear thinning leading to even lower viscosity in a high frequency range than that of pure PET. The nanocomposites gave a non-zero positive value of yield stress, which was notably increased particularly from 5 wt% loading. In the Cole–Cole plot, at contents 1 wt% and above, ferrite nanoparticles caused the deviation from the master curve and a reduced slope. In addition, the relaxation time was increased with ferrite content and an increasing degree was more notable at a lower frequency.     

Single-wall carbon nanotubes/epoxy elastomers exhibiting high damping capacity in an extended temperature range

In nanocomposites containing single-wall or multi-wall carbon nanotubes (SWCNT and MWCNT) high damping can be achieved by taking advantage of the weak bonding and interfacial friction between individual nanotubes and the matrix. The increase in damping capacity has already been proved for stiff epoxies and in this study it is extended to epoxy elastomers. Variable amounts (0.5–3 wt%) of oxidized SWCNT were dispersed by ultrasonication in precursors of an epoxy elastomer based on the reaction of diglycidylether of bisphenol A (DGEBA) and a polyoxypropylene with average molar mass of 2000, end-capped with primary amine groups. The quality of the initial dispersion was assessed by the constancy of the storage modulus with frequency in the low-frequency range. A rheological percolation threshold of 0.41 wt% SWCNT was found. Cured elastomers exhibited a large increase of the loss modulus with increasing amounts of SWCNT. For 3 wt% SWCNT, the increase in loss modulus was 1400% at room temperature. When temperature was increased up to 140 °C the loss modulus of the nanocomposite was practically constant while the one of the matrix dropped to a negligible value. The damping capacity at high temperatures opens important practical applications.     

Multi-scale hybrid biocomposite: Processing and mechanical characterization of bamboo fiber reinforced PLA with microfibrillated cellulose

In this research we develop novel hybrid biocomposites based upon a biodegradable poly(lactic acid) (PLA) matrix reinforced with microfibrillated cellulose (MFC) and bamboo fiber bundles. Due to the relative difference in scale between microfibrillated cellulose and bamboo, a hierarchy of reinforcement is created where bamboo fiber bundles are the primary load-carrying reinforcement and cellulose creates an interphase in the polymer matrix around the bamboo fiber that prevents sudden crack growth. The influence of MFC dispersion on the properties of the PLA matrix was investigated and substantial improvements in the strain energy until fracture observed. By adding just 1 wt% of MFC with a high degree of dispersion an increase in fracture energy of nearly 200% was obtained. In the hybrid bamboo/MFC/PLA composites there is also a dramatic change in the fracture morphology around the bamboo fiber bundles.