Novel toughened polylactic acid nanocomposite: Mechanical,thermal and morphological properties

The objective of the study is to develop a novel toughened polylactic acid (PLA) nanocomposite. The effects of linear low density polyethylene (LLDPE) and organophilic modified montmorillonite (MMT) on mechanical, thermal and morphological properties of PLA were investigated. LLDPE toughened PLA nanocomposites consisting of PLA/LLDPE blends, of composition 100/0 and 90/10 with MMT content of 2 phr and 4 phr were prepared. The Young’s and flexural modulus improved with increasing content of MMT indicating that MMT is effective in increasing stiffness of LLDPE toughened PLA nanocomposite even at low content. LLDPE improved the impact strength of PLA nanocomposites with a sacrifice of tensile and flexural strength. The tensile and flexural strength also decreased with increasing content of MMT in PLA/LLDPE nanocomposites. The impact strength and elongation at break of LLDPE toughened PLA nanocomposites also declined steadily with increasing loadings of MMT. The crystallization temperature and glass transition temperature dropped gradually while the thermal stability of PLA improved with addition of MMT in PLA/LLDPE nanocomposites. The storage modulus of PLA/LLDPE nanocomposites below glass transition temperature increased with increasing content of MMT. X-ray diffraction and transmission electron microscope studies revealed that an intercalated LLDPE toughened PLA nanocomposite was successfully prepared at 2 phr MMT content.     

Processing of cellulose nanowhiskers/cellulose acetate butyrate nanocomposites using sol-gel process to facilitate dispersion

Biobased nanocomposites based on cellulose nanowhiskers (CNWs) and cellulose acetate butyrate (CAB) were prepared using solvent exchange of CNWs to ethanol by sol-gel method followed by casting. The strong flow birefringence of the solutions indicated evenly dispersed cellulose nanowhiskers in the dissolved polymer CAB. Scanning electron microscopy of the nanocomposites confirmed well dispersed CNWs in the CAB matrix, which was further supported by the high transparency exhibited by the nanocomposites. The results of tensile tests indicated significant improvements in the mechanical properties of nanocomposites by increasing the CNWs contents. The Young’s modulus and strength increased 83% and 70%, respectively, for nanocomposites with 12 wt% of CNW, and the strain was not suppressed compared to the neat CAB. The dynamic mechanical thermal analysis demonstrated significant improvement in storage modulus with increasing CNW contents, and the tan δ peak position was moved towards higher temperature when CNW was added. It is expected that solvent exchange by the sol-gel route followed by casting of nanocomposites from the same solvent will provide a promising route for obtaining cellulose nanocomposites with well dispersed CNW, leading to improved mechanical properties, even with low nanowhisker contents.     

Flammability and tensile properties of polylactide nanocomposites with short carbon fibers

Nanocomposites of polylactide (PLA) with aluminum hydroxide (ATH), short carbon fibers (CF), and montmorillonite (MMT) were prepared via direct melt blending. The exfoliated and intercalated clay structures with some aggregations in the PLA matrix were observed. The tensile strength and elongation at break of the PLA composite caused by the high content of the retardant ATH were improved by adding modified MMT and CF to replace a portion of ATH in the PLA matrix. The thermal degradation temperatures and char residue of the PLA/ATH/MMT/CF nanocomposites as determined by thermogravimetric analysis were higher than without MMT. Furthermore, a novel method was proposed to analyze the flammability of composite using an infrared camera, which could capture the apparent thermal image of the sample during UL 94 V test. It was found that, with addition of the MMT and short CF, a more effective insulation layer could be formed on the ablating surface of the PLA/ATH composite, and the high thermal conductivity of the CF might increase the release rate of heat from the surface composite during burn, thus the PLA/ATH/MMT nanocomposite containing short carbon fibers having a V-0 rating without flaming dripping could be obtained.     

Properties of poly(lactic acid)/montmorillonite/carbon nanotubes nanocomposites: determination of percolation threshold

Incorporation of rigid nanoparticles is the most effective means of improving polymer properties. Montmorillonite (MMT) and multi-walled carbon nanotubes (MWCNTs) are legendary in this field for their individual exceptional properties. A synergistic phenomenon is induced between these two particles when they are simultaneously incorporated into polymers. At a definite nanofillers concentration, called the percolation threshold, there is a sudden change in nanocomposite properties due to the formation of a 3D-structured network of the nanoparticles within the matrix. In this work, the properties of poly(lactic acid) (PLA) nanocomposites filled with different fractions of MMT/MWCNTs hybrid (0.5–2.0 wt%) were analyzed. In particular, the percolation threshold of the MMT/MWCNTs hybrid was uniquely identified by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis. The structural studies by X-ray diffraction and Fourier-transform infrared spectroscopy were also associated with the percolation threshold of MMT/MWCNTs in PLA. At 1.0 wt% MMT/MWCNTs concentration, the complete exfoliation of the particles was maintained, and the thermal characteristics such as glass transition, crystallization and melting temperatures reached their plateau at this hybrid concentration. Moreover, the thermal degradation and viscoelastic parameters showed their peak values at this critical point, which is correlated with the formation of the percolation threshold within the matrix. The morphological studies confirmed the homogeneous dispersion of MMT/MWCNTs in PLA up to a concentration of 1.0 wt%. At 2.0 wt% MMT/MWCNTs, few aggregations occurred in the PLA-based composite, confirming that the percolation threshold was formed at a lower concentration of MMT/MWCNTs nanoparticles.

     

Morphology,thermal and mechanical properties of PVC/MMT nanocomposites prepared by solution blending and solution blending + melt compounding

Two types of montmorillonite (MMT), natural sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT), in different amounts of 1, 2, 5, 10 and 25 phr (parts per hundred resin), were dispersed in rigid poly (vinyl chloride) by two different methods: solution blending and solution blending + melt compounding. The effects on morphology, thermal and mechanical properties of the PVC/MMT nanocomposites were studied by varying the amount of Na-MMT and OMMT in both methods. SEM and XRD analysis revealed that possible intercalated and exfoliated structures were obtained in all of the PVC/MMT nanocomposites. Thermogravimetric analysis revealed that PVC/Na-MMT nanocomposites have better thermal stability than PVC/OMMT nanocomposites and PVC. In general, PVC/MMT nanocomposites prepared by solution blending + melt compounding revealed improved thermal properties compared to PVC/MMT nanocomposites prepared by solution blending. Vicat tests revealed a significant decrease in Vicat softening temperature of PVC/MMT nanocomposites prepared by solution blending + melt compounding compared to unfilled PVC.     

Electron beam irradiation enhanced of Hibiscus cannabinus fiber strengthen polylactic acid composites

This paper reported the effects of increasing Hibiscus cannabinus fiber (also known as kenaf fiber) loading level on properties of electron beam irradiated polylactic acid/low density polyethylene (PLA/LDPE). PLA and LDPE were compounded with 5–20 parts per hundred resins (phr) of kenaf respectively to enhance mechanical properties. The compounded kenaf added PLA/LDPE samples were electron beam irradiated from 15 to 60 kGy. The physical properties of kenaf added PLA/LDPE samples were characterized using gel content, X-Ray diffraction and scanning electron microscopy analysis. The results showed that the increasing of irradiation dosages in PLA/LDPE have gradually increased the gel content and tensile strength due to the formation of crosslinking networks in polymer matrix. However, the higher loading level of kenaf and irradiation dosages could decrease the elongation at break of PLA/LDPE samples. This is due to the restriction of polymer chains mobility as resulted by the poor interfacial adhesion between polymer matrix and kenaf particles as well as the formation of crosslinking networks in polymer matrix limits the sliding of polymer chains. Meanwhile, the increasing of kenaf loading level also has gradually increased the crystallinity of PLA/LDPE matrix. It is concluded that the electron beam irradiation dosages and amount of kenaf fiber in PLA/LDPE matrix should be kept at maximum 45 kGy and 15 phr, respectively for better combination to enhance the properties of the composites.     

Study on mechanical and ablative properties of EPDM/OMMT thermal insulating nanocomposites

In order to enhance the elongation at break, the ablation resistant properties as well as the tensile strength of the thermal insulating materials, organo-montmorillonite (OMMT) was introduced into the short aramid fibers reinforced Ethylene-Propylene-Diene Monomer (EPDM) based nanocomposites. The effects of OMMT content on the mechanical and ablative properties of the nanocomposites were investigated systematically. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that EPDM-matrix has been intercalated into OMMT interlayers after a mixing process on a two-roll mill. The brittle fracture of nanocomposites also indicates that OMMT can lubricate aramid fiber to weaken the interfacial adhesive strength between the fibers and the matrix. As a result, the tensile strength and elongation at break are both improved sharply with OMMT content increasing from 1 phr to 7 phr. However, thanks to the inevitable agglomeration of OMMT with high loading inside the nanocomposites, the tensile strength and elongation at break reduce gently once OMMT is over 7 phr. Furthermore, the ablation resistant properties are improved greatly by increasing OMMT from 1 phr to 11 phr. Therefore, the optimal content of OMMT is 7-11 phr for the thermal insulating nanocomposites with big elongation and excellent ablation resistant properties.     

Hybrid Composite Using Natural Filler and Multi-Walled Carbon Nanotubes (MWCNTs)

This paper presents an experimental study on the development of hybrid composites comprising of multi-walled carbon nanotubes (MWCNTs) and natural filler (oil palm shell (OPS) powder) within unsaturated polyester (UP) matrix. The results revealed that the dispersion of pristine MWCNTs in the polymer matrix was strongly enhanced through use of the solvent mixing method assisted by ultrasonication. Four different solvents were investigated, namely, ethanol, methanol, styrene and acetone. The best compatibility with minimum side effects on the curing of the polyester resin was exhibited by the styrene solvent and this produced the maximum tensile and flexural properties of the resulting nanocomposites. A relatively small amount of pristine MWCNTs well dispersed within the natural filler polyester composite was found to be capable of improving mechanical properties of hybrid composite. However, increasing the MWCNT amount resulted in increased void content within the matrix due to an associated rapid increase in viscosity of the mixture during processing. Due to this phenomenon, the maximum tensile and flexural strengths of the hybrid composites were achieved at MWCNT contents of 0.2 to 0.4 phr and then declined for higher MWCNT amounts. The flexural modulus also experienced its peak at 0.4 phr MWCNT content whereas the tensile modulus exhibited a general decrease with increasing MWCNT content. Thermal stability analysis using TGA under an oxidative atmosphere showed that adding MWCNTs shifted the endset degradation temperature of the hybrid composite to a higher temperature.     

Physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly(lactic acid)

A range of nanocomposites were prepared using cellulose nanowhiskers (CNWs) and poly(lactic acid) (PLA) via a solvent casting process. Acid hydrolysis process was used to produce CNWs from bleached cotton. Structural morphology and surface topography of the CNWs and nanocomposites were examined using transmission (TEM) and scanning electron microscopy. TEM images revealed rod-like whiskers in the nano-scale region which were dispersed within the PLA matrix. The presence of the functional groups of CNWs and PLA were confirmed via FTIR analysis. Tensile tests were conducted on thin films and the nanocomposites containing 1 wt% CNWs showed a 34 and 31% increase in tensile strength and modulus, respectively, compared to pure PLA. The dynamic mechanical analysis showed that the tensile storage modulus also increased in the visco-elastic temperature region with increasing CNWs content in the nanocomposites. Thermogravimetric analysis showed that all the materials investigated were thermally stable from room temperature to 210 °C. A positive effect of CNWs on the crystal nucleation of PLA polymer in the nanocomposites was observed using differential scanning calorimetry and X-ray diffraction analysis. The degradation profiles of the nanocomposites in deionised water over 1 week revealed a mass loss of 1.5–5.6% at alternate temperatures (25, 37 and 50 °C) and at the same conditions the swelling ratio and water uptake were seen to increase with CNWs content in the nanocomposites, which was strongly influenced by the presence of crystalline CNWs.     

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.     

聚氯乙烯/丁腈橡胶/蒙脱土/ABS复合材料的表征与性能

在不添加插层剂的情况下,将蒙脱土原土(MMT)与丁腈胶乳(NBR)在水相中高速搅拌,使蒙脱土原土在稀释的丁腈胶乳基体中均匀分散,制备了丁腈胶乳/蒙脱土原土杂化物。采用该杂化物作为第三组分加入PVC/ABS共混体系中,经熔融共混制备了PVC/NBR/MMT/ABS复合材料。研究了NBR/MMT杂化物的用量对复合材料力学性能的影响。结果表明,当NBR/MMT用量在15 phr时,PVC/NBR/MMT/ABS复合材料的冲击强度提高近3倍,其综合力学性能达到最佳值。SEM和TEM观察结果表明,在PVC/NBR/MMT/ABS复合材料中,分散相分布较精细均匀,且以一定的取向分布;基体与分散相界面模糊,各相之间具有良好的相容性。     

Characterization of starch based nanocomposites

The goal of this study was to characterize the nanostructure and the properties of starch based nanocomposites with either cellulose nano whiskers (CNW) or layered silicates (LS) (synthetic hectorite) as reinforcements. Modified potato starch was used as matrix with water and sorbitol as plasticizers and with 5 wt.% of either of the reinforcements. Two methods were explored to prepare samples for transmission electron microscopy (TEM) examination; chemical fixation and freeze etching. It was possible to characterize the nanostructure both parallel and perpendicular to the nanocomposite surface by the freeze etching technique. Both nanocomposites showed well-distributed reinforcements in the starch matrix. Dynamic mechanical thermal analysis showed that the storage modulus was significantly improved at elevated temperatures, especially for the layered silicate nanocomposite. Both nanocomposites showed a significant improvement in tensile properties compared to the pure matrix.     

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.     

Fracture behavior of nitrile rubber-cellulose II nanocomposites

Nanocomposites of nitrile rubber (NBR) and cellulose II (Cel II) were prepared by co-coagulation of nitrile rubber latex and cellulose xanthate mixtures. The effect of the addition of increasing amounts of Cell II, varying from 0 to 30 phr, on the mechanical behavior of a NBR was analyzed. The fracture mechanisms of the nitrile rubber-cellulose II (NBR/Cel II) nanocomposites after tension and tear tests was investigated by scanning electron microscopy (SEM) and correlated to the test results. It was found that the addition of Cell II to NBR leads to a gradual change in the stress at break, and the samples with 20 phr of Cel II showed the highest resistance; as the cellulose content is increased to 30 phr, the strain at break decreases. The SEM fractographic analyses of NBR/Cel II nanocomposites, with cellulose content up to 30 support the observed mechanical behavior of the material. The results are presented and discussed. The obtainment of NBR/Cel II nanocomposites was proven by transmission electron microscopy (TEM).     

The effect of crystallization of PLA on the thermal and mechanical properties of microfibrillated cellulose-reinforced PLA composites

This paper describes the thermal and mechanical properties of nanocomposites based on polylactic acid (PLA) and microfibrillated cellulose (MFC). The primary objective of this study was to improve the storage modulus of PLA at a high temperature. MFC and PLA were mixed in an organic solvent with various fiber contents up to 20 wt%, followed by drying, kneading and hot pressing into sheets. The nanocomposites were prepared in two different states, fully amorphous and crystallized. Differential scanning calorimetry (DSC) measurements revealed that the presence of MFC accelerates the crystallization of PLA. The tensile modulus and strength of neat PLA were improved with an increase of MFC content in both amorphous and crystallized states. The addition of 20 wt% of MFC in PLA improved the storage modulus of crystallized PLA at a high temperature (120 °C) from 293 MPa to 1034 MPa.     

Environmentally friendly polymer hybrids Part I Mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites

As an attempt to develop environmentally friendly polymer hybrids, biodegradable thermoplastic starch (TPS)/clay nanocomposites were prepared through melt intercalation method. Natural montrorillonite (Na⁺ MMT; Cloisite Na⁺) and one organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were chosen in the nanocomposite preparation. TPS was prepared from natural potato starch by gelatinizing and plasticizing it with water and glycerol. The dispersion of the silicate layers in the TPS hybrids was characterized by using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). It was observed that the TPS/Cloisite Na⁺ nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites as well as the pristine TPS, due to the formation of the intercalated nanostructure. The effect of clay contents on the tensile, dynamic mechanical, and thermal properties as well as the barrier properties of the nanocomposites were investigated.     

挤出法乙丙橡胶/蒙脱土纳米复合材料制备和表征

采用一种新型的有机土蒙脱土(OMM T),通过熔融挤出法制备出了具有优异性能的乙丙橡胶/OMM T复合材料,并与炭黑补强体系进行了对比。透射电子显微镜考察表明,所制备的乙丙橡胶/OMM T纳米复合材料为剥离型结构;力学性能测试结果表明,当有机土含量仅为3份时,复合材料硫化胶的扯断强度是纯胶体系的5.2倍,比同量的高耐磨炭黑增强体系的硫化胶也提高了284%,与加入15份高耐磨炭黑的硫化胶相当;有机土体系撕裂强度也明显高于炭黑体系。还利用门尼黏度测试表征了材料的加工性能。     

Synthesis and characterization of thermoplastic polyurethane/montmorillonite nanocomposites produced by reactive extrusion

The novel polyurethane/montmorillonite (PU/MMT) nanocomposites based on poly (propylene oxide) glycol (POP), 4,4′-diphenymethylate diisocyanate (MDI), 1,4-butanediol (1,4-BD) and MMT has been synthesized using a one-step direct polymerization-intercalation technique by twin-screw extruder. Its structure and thermal properties are characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and High-resolution electron microscopy (HREM), Fourier-transform infrared spectroscopy (FTIR) and Thermogravimetry analysis (TGA), respectively. The results of XRD and HREM analyses show that the silicate layer is well dispersed in PU matrix and this mesostructure can be considered as a delaminated nanocomposites. The TGA analysis indicates that the thermal stability properties of the PU/MMT nanocomposites are increased slightly compared with the pristine PU, due to the increase of the char residue. The mechanical and flammability performances are examined by electronic Universal Tester and Cone calorimetry, respectively. The layered silicate, which acts as a high aspect ratio reinforcement, enhances tensile strength of the PU. Specifically, there is a 25% increase in the tensile strength of PU nanocomposites containing 4 wt.% MMT compared with that of pristine PU. However, the elongation at break of PU/MMT nanocomposites is lower than that of pristine PU. The loading of MMT leads to the remarkably decrease of heat release rate (HRR), contributing to the improvement of flammability performance.     

Experimental and theoretical analyses of mechanical properties of PP/PLA/clay nanocomposites

Compatibilized and non-compatibilized blends of polypropylene (PP) and poly(lactic acid) (PLA) with various compositions containing nanoclay particles were prepared by one step melt compounding in a twin screw extruder. Two nanocomposite systems with different matrices i.e. PP-rich (75/25 composition) containing Cloisite 15A and PLA-rich (25/75 composition) containing Cloisite 30B were selected for investigation of effect of nanoclays and n-butyl acrylate glycidyl methacrylate ethylene terpolymers (PTW) as compatibilizer on mechanical properties of PP/PLA/clay nanocomposites. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. Tensile modulus and strength of the blends were increased while elongation at break decreased by increasing PLA content. There was an irregular relationship between impact strength of the blends and PLA content. Several proposed models for blends and nanocomposites were used for prediction of tensile modulus of the samples. Most of the proposed models for blends could predict the tensile modulus of the blends successfully at low content of PLA. Another notable point was that most of the micromechanical models for nanocomposites fitted well to experimental values at low content of the clays and showed deviations at high clay loadings.     

Microstructure and mechanical properties of epoxy hybrid nanocomposites modified with acrylic tri-block-copolymer and layered-silicate nanoclay

In this study, processing, morphology and mechanical properties of acrylic tri-block-copolymer and organophilic layered-silicate nanoclay modified epoxy hybrid nanocomposites were investigated. The acrylic tri-block-copolymer preferentially self-assembled into spherical micelles in the epoxy matrix, and predominantly intercalated and few exfoliated platelets were observed with nanoclay. Three-phase ternary nanocomposites showed coexistence of both intercalated nanoclay and nanostructured block-copolymer in epoxy. Experimental results revealed that the block-copolymer significantly enhanced fracture toughness. Increased toughness of epoxy coincided with a reduction of tensile stiffness and strength. The nanoclay filled nanocomposites exhibited superior stiffness and slight improvement in tensile strength while compromising ductility. Optimum property enhancement was observed in the case of epoxy hybrid nanocomposites. Mechanical properties of the hybrid nanocomposites depend on microstructure, dispersion state and the ratio between organic and inorganic nanofiller contents.