Morphology,biodegradability, mechanical,and thermal properties of nanocomposite films based on PLA and plasticized PLA

In this study, melt intercalation method is applied to prepare poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG)‐plasticized PLA nanocomposite films including 0, 3, and 5% organoclay (Cloisite 30B) using a laboratory scale compounder, which is connected to a microcast film device. To evaluate the nanomorphology and the dispersion state of the clays, X‐ray diffraction (XRD) and transmission electron microscopy (TEM) are conducted. Tensile tests are performed to characterize the mechanical behavior of the films. Biodegradation rate is determined by degradation tests in composting medium. Differential scanning calorimeter (DSC) is applied to observe the thermal behavior of the films. XRD and TEM show that the exfoliation predominantly occurrs in plasticized PLA nanocomposites, whereas unexfoliated agglomerates together with exfoliated clays are observed in the nonplasticized PLA. Tensile tests indicate that the addition of 3% clay to the neat‐PLA does not affect the strength; however, it enhances the modulus of the nanocomposites in comparison to neat‐PLA. Incorporation of 3% clay to the plasticized PLA improves the modulus with respect to PLA/PEG; on the other hand, the strain at break value is lowered ～ 40%. The increase in the rate of biodegradation in composting medium is found as in the order of PLA > PLA/PEG > 3% Clay/PLA/PEG > 5% Clay/PLA/PEG > 3% Clay/PLA. DSC analysis shows that the addition of 3% clay to the neat PLA results in an increase in T_g. The addition of 20% PEG as a plasticizer to the neat‐PLA decreases T_g about 30°C, however incorporation of clays increases T_g by 4°C for the plasticized PLA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological aspects of injected polypropylene/clay nanocomposite materials

Polypropylene (PP) clay nanocomposites were injection‐molded using two different coupling agents based on maleic anhydride‐grafted PP (MA‐g‐PP) and two clay loadings. The morphological aspects of these materials were studied by depth profiling. Molecular chain and clay orientations were characterized using attenuated total reflectance‐infrared analysis and transmission electron microscopy (TEM). Both clay platelets and PP molecular chain orientations were found to decrease from the surface toward the core of the injection–molded specimens. Clay intercalation, characterized by both complementary X‐ray diffraction and TEM, was found to be significantly influenced by both the characteristics of the coupling agent used and the type of residual stresses generated at each layer across the thickness of the injection‐molded parts. The use of low‐molecular weight (M_w) MA‐g‐PP led to a uniform intercalation but with no further exfoliation. The use of higher molecular weight MA‐g‐PP led to a heterogeneous intercalation with some signs of exfoliation. The crystallization behavior of PP clay nanocomposites studied by differential scanning calorimetry showed an increase in the level of crystallinity from the surface to the core of the specimens; these results were also confirmed by scanning electron microscopy. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Morphology and rheological behavior of polylactic acid/clay nanocomposites

The investigated rheological properties of polylactic acid (PLA)/clay nanocomposite are important to understand the effect of organically modified layered silicates (OMLS) (clay) on processing as well as the change in viscoelastic properties due to polymer filler interaction. The time sweep result revealed that the thermal stability improved with addition of nanoclay due to the formation of percolating network structure. It was also supported by multi wave ramp test. The frequency sweep analysis showed that the dynamic moduli increased with addition of nanoclay. Viscoelastic spectra (DMTA) showed an increase of the storage and loss moduli with the increase in the clay content. Wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of intercalation, or exfoliation and nanostructure level of clay dispersion on PLA nanocomposites. XRD data demonstrated complete exfoliation at lower nanoclay content. On increasing the nanoclay content, exfoliated and partially intercalated structures were obtained. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Interfacially compatibilized poly(lactic acid) and poly(lactic acid)/polycaprolactone/organoclay nanocomposites with improved biodegradability and barrier properties: Effects of the compatibilizer structural parameters and feeding route

Nanocomposites with enhanced biodegradability and reduced oxygen permeability were fabricated via melt hybridization of organomodified clay and poly (lactic acid) (PLA) as well as a PLA/polycaprolactone (PCL) blend. The nanocomposite microstructure was engineered via interfacial compatibilization with maleated polypropylene (PP‐g‐MA). Effects of the compatibilizer structural parameters and feeding route on the dispersion state of the nanolayers and their partitioning between the PLA and PCL phases were evaluated with X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy. Although highly functionalized PP‐g‐MA with a low molecular weight was shown to be much more effective in the intercalation of PLA and the PLA/PCL blend into the clay gallery spaces, composite samples compatibilized by high‐molecular‐weight PP‐g‐MA with a lower degree of maleation exhibited lower oxygen permeability as well as a higher rate of biodegradation, which indicated the accelerating role of the dispersed nanolayers and their interfaces in the enzymatic degradation of PLA and PLA/PCL matrices. This evidenced a correlation between the nanocomposite structure and rate of biodegradation. The size of the PCL droplets in the PLA matrix was reduced by nanoclay incorporation, and this revealed that the nanolayers were preferentially wetted by PCL in the blend. However, PCL appeared as fine and elongated particles in the microstructure of the PLA/PCL/organoclay hybrids compatibilized by higher molecular weight and less functionalized PP‐g‐MA. All the PLA/organoclay and PLA/PCL/organoclay hybrids compatibilized with high‐molecular‐weight PP‐g‐MA displayed a higher dynamic melt viscosity with more pseudo solid‐like melt rheological responses, and this indicated the formation of a strong network structure by the dispersed clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel strategy for nanoclay exfoliation in thermoset polyimide nanocomposite systems

A novel method of nanoclay exfoliation in the synthesis of nanocomposites of PMR type thermoset resins was investigated. The method involves nanoclay intercalation by lower molecular weight PMR monomer prior to dispersion in primary, higher molecular weight PMR resin and resin curing to obtain the final composites. The resultant mechanical and thermal properties were evaluated as functions of clay type, degree of clay exfoliation, and clay intercalation strategies. It was found that sonication of clay at the time of intercalation by lower molecular weight PMR resin helps to achieve higher degree of exfoliation. In addition, clays obtained from ion exchange with a 50:50 mixture of N-[4(4-aminobenzyl)phenyl]-5-norborene-2,3-dicarboximide (APND), and dodecylamine (C12) showed better exfoliation than Cloisite^® 30B clay. The resultant nanocomposites show higher thermal stability and higher tensile modulus.     

X‐ray pole figures to assess orientation in PVC sheets

A series of X‐ray pole figures were obtained from oriented and unoriented rigid polyvinyl chloride sheets. From these, information about crystallite orientation in uniaxially and biaxially drawn sheets stretched at 90°C was obtained. Uniaxial orientation produced two crystallite orientations with the extent of orientation increasing with draw ratio; for biaxial samples the chain direction (c) was distributed uniformly in the plane of the sheet, with the planar orientation improving as draw ratio increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 528–535, 2007     

Intercalation and exfoliation behaviour of clay layers in branched polyol and polyurethane/clay nanocomposites

The exfoliation of clay layers was realized in a tri‐hydroxyl branched polyether polyol by direct mixing and the corresponding exfoliated polyurethane/clay nanocomposite was prepared by further in situ curing. The effects of various surface‐modified organoclays and various polyol types on the intercalation and exfoliation behaviour of clay layers were investigated. The interaction between the polyol and clay and the mixing temperature plays an important role in the occurrence of exfoliation and intercalation. The relationship between rheological data of polyol/clay dispersion and the intercalation or exfoliation state of the clay was established. This provides a convenient and efficient way to evaluate the dispersion state of the clay. Based on the experimental results, a possible layer‐by‐layer exfoliation mechanism is proposed. Copyright © 2006 Society of Chemical Industry     

Poly(ethylene terephthalate)/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate)/clay nanocomposites: Effects of biaxial stretching

In this study, we fabricated poly(ethylene terephthalate) (PET)/clay, PET/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG), and PET/PETG/clay nanocomposite plates and biaxially stretched them into films by using a biaxial film stretching machine. The tensile properties, cold crystallization behavior, optical properties, and gas and water vapor barrier properties of the resulting films were estimated. The biaxial stretching process improved the dispersion of clay platelets in both the PETG and PET/PETG matrices, increased the aspect ratio of the platelets, and made the platelets more oriented. Thus, the tensile, optical, and gas‐barrier properties of the composite films were greatly enhanced. Moreover, strain‐induced crystallization occurred in the PET/PETG blend and in the amorphous PETG matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42207.     

Effects of process conditions and mixing protocols on structure of extruded polypropylene nanocomposites

Polymer melt‐direct intercalation or exfoliation is a promising approach for the preparation of nanocomposites. The structure of nanoclay platelets in the nanocomposites depends not only on the properties of polymer matrix and nanoclay, but also on the operating conditions during processing. The objective of the present work is to investigate the effects of clay chemical modifiers, mixing protocols, and operating conditions upon the clay structure in nanocomposites prepared with a corotating twin‐screw extruder. Two mixing methods were used for the nanocomposite preparation: two‐step mixing and one‐step mixing. Experimental results obtained from melt flow index and complex viscosity measurements suggest that nanoclay C15A is more exfoliated than C30B in a polypropylene homopolymer containing a maleic anhydride grafted PP (PB) as compatibilizer. The two‐step mixing method results in better exfoliation for the nanofillers than the one‐step mixing method. A numerical simulation has been carried out to evaluate the mean residence time and shear rate in different screw configurations under various process conditions. X‐ray diffraction experiments indicate that the residence time is a dominant factor in producing satisfactory nanocomposites in extruders. However, high shear rate coupled with long residence time might result in poor exfoliation of clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1891–1899, 2004     

Characterisation of biaxial orientation gradients in poly(ethylene terephthalate) films and bottles using polarised attenuated total reflection FTIR spectroscopy

Polarised attenuated total reflection (ATR) infrared spectroscopy has been used to quantify biaxial orientation in commercially manufactured poly(ethylene terephthalate) (PET) films and stretch-blow moulded bottles. Using a single-bounce accessory with a high refractive index element, and applying appropriate data normalisation prior to measuring band intensities, measurement of the average square direction cosines that describe the orientation is simple. Using this technique it was shown that uniaxially drawn PET films were actually biaxially oriented, and there were significant gradients in orientation through the film thickness. Bulk measurements, or methods that assume uniaxial orientation, would give incorrect results from these materials. The bottles exhibited complex orientation patterns that depended on preform and mould design, and again there were strong orientation gradients through the bottle walls. Kratky's model (pseudo-affine) was used in an attempt to predict the biaxial orientation gradients as a function of preform and bottle dimensions.     

Nanoindentation and nanoscratch testing of uniaxially and biaxially drawn poly(ethylene terephthalate) film

Nanoindentation and nanoscratch testing have revealed large differences in nanomechanical behaviour on uniaxially and biaxially drawn poly(ethylene terephthalate) films. Differences can be ascribed to the processing history of the film. The biaxial material exhibited significantly higher hardness and elastic modulus than the uniaxial film, presumably due to increased crystallinity from the second draw. The biaxially drawn material was also less susceptible to creep deformation. The plasticity index, the ratio of the dissipated energy to the total indentation energy, was greater on the uniaxial film, indicating that it exhibits less plastic deformation than the biaxially stretched film. The differences in processing also affected the resistance of the films to nanoscratching wear. The wear resistance of the films correlated with the ratio of the hardness to the modulus.     

Tapioca starch‐poly(lactic acid)‐Cloisite 30B nanocomposite foams

Tapioca starch (TS), poly(lactic acid) (PLA), and Cloisite 30B nanocomposite foams, with four clay contents of 1, 3, 5, 7 wt%, were prepared by a melt‐intercalation method. Selected structural, thermal, physical, and mechanical properties were characterized using X‐ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetry analyses, and an Instron universal testing machine, respectively. XRD results indicated that intercalation of TS/PLA into the nanoclay layers occurred in all four nanocomposite foams. At the same time, tactoid structures were observed in all nanocomposite foams but to a lesser extend with 1 and 3 wt% clay contents. Effect of clay content on melting temperature (T_m), onset degradation temperature, radial expansion ratio, unit density, bulk compressibility and bulk spring index of the nanocomposites were investigated. Among the four nanocomposites, 3 wt% clay content produced significantly different (p < 0.05) properties. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Multilayer coextrusion of graphene polymer nanocomposites with enhanced structural organization and properties

A potential advantage of platelet‐like nanofillers as nanocomposite reinforcements is the possibility of achieving two‐dimensional (2D) stiffening through planar orientation of the platelets. Forced assembly by multilayer coextrusion, which enables the in‐plane orientation of platelet‐like fillers in alternating layers, was used in this work to produce poly(lactic acid) (PLA)/graphene multilayer films. These films exhibited a multilayer structure made of alternating layers of neat PLA and PLA containing graphite nanoplatelets (GNPs). Electron microscopy revealed information on the orientation of the individual GNPs. X‐ray diffraction results indicated that the thickness of the individual GNPs was reduced during the multilayer coextrusion process. A significant reinforcement of 120% at an overall GNP loading of 1 wt % in PLA was achieved. This high effective reinforcement was attributed to the high degree of planar alignment, improved dispersion and exfoliation and increased aspect ratio of the GNPs in the composite layers after multilayer coextrusion. Improved water vapor barrier properties were also achieved as a result of the highly organized 2D nanofillers in the multilayer films. These industrial scalable multilayer nanocomposite films open up possibilities for lightweight and strong packaging materials for food and industrial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46041.     

Kinetic studies of the preparation of nanocomposites based on encapsulated Cloisite 30B in poly[styrene‐co‐(butyl acrylate)] via mini‐emulsion polymerization

Mini‐emulsion polymerization of poly[styrene‐co‐(butyl acrylate)] encapsulating various contents of Cloisite 30B was performed. The kinetic behaviours of mini‐emulsions were investigated using the gravimetric method and the effect of nanoclay content on the polymerization rate was investigated. The average number of radicals per particle was estimated by calculating the number of particles. The results showed that by increasing the nanoclay content, the average diameter of polymer particles increased. Studies of the polymerization rate indicated that the increase in particle size provided a greater average number of reactive radicals per polymer particle, which increased from 0.0520 for the neat copolymer to 0.2462 for the nanocomposite containing 5.3 wt% encapsulated nanoclay. This study also confirmed our previous claim about the role of sodium dodecylsulfate (SDS) molecules in the exfoliation of nanoclay platelets. On increasing the clay content, fewer SDS molecules will be available on particle surfaces resulting in larger particles at the end of the reaction. Copyright © 2011 Society of Chemical Industry     

Microstructure of biaxially drawn ultrahigh molecular weight polyethylene

The microstructure of ultrahigh molecular weight polyethylene (UHMW-PE) sheets biaxially drawn in the molten state was investigated by means of wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and electron microscopy. The crystallographic c-axis tended to be oriented in the sheet plane by the biaxial drawing in the molten state. The microstructure of the biaxially drawn UHMW-PE was shown to depend upon molecular weight of UHMW-PE. The biaxially drawn sheet of higher molecular weight (M_v = 2,700,000) showed a fibrous structure, while the lower molecular weight sample (M_v 700,000) had a lamellar structure. The result of DSC measurements suggested that a small number of nucleating extended chain crystals was produced by biaxial melt drawing of the UHMW-PE sheet with higher molecular weight.     

Morphology and mechanical properties of heterophasic PP–EP/EVA/organoclay nanocomposites

The effect of vinyl acetat (VA) on the morphological, thermal stability, and mechanical properties of heterophasic polypropylene–(ethylene‐propylene) copolymer (PP–EP)/poly(ethylene vinyl acetate) (EVA)/organoclay nanocomposites was studied. Tailored organoclay C20A was selected to enhance the exfoliation of the clay platelets. Depending on the VA content, there were two morphological organoclay populations in the systems. Both populations were directly observed by scanning transmission electron microscopy and measured by wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The content of VA in EVA originated spherical and elongated morphologies in the resultant nanocomposites. High‐VA content led to a better intercalation of the organoclay platelets. Measurement of thermal properties suggested that higher VA decreases thermal stability in samples both with and without organoclay, although nanocomposites had higher thermal stability than samples without clay. The storage modulus increased both with nanoclay and VA content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Micro- and nano-structure in polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites prepared by melt blending using different clays and coupling agents based on maleic anhydride-grafted PP (MA-PP) were studied. Clay dispersion using field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscopy (TEM), and PP matrix morphology were characterized. Clay dispersion was improved in the presence of MA-PP, as shown by the higher particles surface density (number of particles/mm²) at all micro-, sub-micro- and nano-levels. The PP spherulite diameter was affected by both the presence of MA-PP and clay dispersion. Clay intercalation, characterized by both complementary X-ray diffraction (XRD) and TEM, was greatly influenced by the characteristics of MA-PP. The use of low molecular weight (M_w) MA-PP led to a good and uniform intercalation but with no further possibility to exfoliation. The use of higher M_w MA-PP led to a heterogeneous intercalation with signs of exfoliation. The crystallization behavior of nanocomposites was studied by differential scanning calorimetry (DSC). When fine clay dispersion was achieved with MA-PP, clay-nucleating effect was limited and lower crystallization temperature and rates were observed. It was also shown by wide angle X-ray diffraction (WAXD) that clay induced some orientation of α-phase PP crystallites.     

Biaxial orientation of poly(vinyl chloride) compounds: Interaction between drawing,structure, and properties

Rigid poly(vinyl chloride) (PVC) sheets were stretched uniaxially (at constant width), equally biaxially, and unequally biaxially to various draw ratios. Tensile properties, density, and birefringence of the stretched sheets were measured, and their wide angle X-ray diffraction traces recorded. Comparison of results showed the highest crystallite and overall orientation and density in the uniaxial samples, and lowest values for the equal biaxial samples. Drawing resulted in the alignment of some existing crystallites in the plane of the film, together with the formation of new mesomorphous structures. Changes in tensile strength were attributed to overall orientation.     

Effect of rubber matrix type on the morphology and reinforcement effects in carbon black‐nanoclay hybrid composites—A comparative assessment

Carbon black (B)–nanoclay (NC) hybrid composites, based on millable polyurethane and brominated isoprene isobutylene rubber (BIIR), were prepared. The carbon black loading was fixed at 20 phr and organically modified sodium montmorillonite clay loading varied from 5 to 20 phr in each rubber compounds. The nanocomposites were prepared in laboratory by mixing two‐roll mill. The state of dispersion of the layered silicate was studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM results indicated intercalation of PU and BIIR into the silicate interlayers, followed by exfoliation of the silicate layers into the elastomer matrices. However, the level of intercalation and exfoliation varied considerably with the type of elastomer. The reinforcing effects obtained were found to depend strongly on the extent and degree of the dispersion of the carbon black and silicate layers into the rubber matrices. Mechanical and dynamic mechanical properties were evaluated for each composite. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Short‐ and long‐term loss of carvacrol from polymer/clay nanocomposite film – a chemometric approach

A combination of partial least squares (PLS) regression and design of experiments was used to analyse and define the short‐ and long‐term loss mechanisms of carvacrol from polymer/clay nanocomposite films used as an antimicrobial food packaging material. Three formulation x variables were evaluated: type of nanoclay, concentration of nanoclay and concentration of compatibilizer agent. Five experimental y responses were measured: loss of carvacrol from the films stored at room conditions on the third and fifth days (short‐term loss); on the forty‐fifth and sixtieth days (long‐term loss); and the polymer/clay level of intercalation. All variables and responses were simultaneously calibrated by an ANOVA‐validated (P < 0.05) comprehensive PLS interaction model with a satisfactory R² = 0.956 and Q² = 0.505. A differentiation and discrimination of the mechanisms that control the loss of carvacrol over different periods of time was observed. Short‐term loss seems to be controlled mainly by direct molecular interactions in the interlayer space between carvacrol and the nanoclay organomodifier. Long‐term loss seems to be mainly controlled by diffusion within the nanocomposite matrix once carvacrol has left the nanoclay interlayer space, and it is closely related to the levels of intercalation reached in the nanocomposite. © 2016 Society of Chemical Industry