Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.     

Properties of acrylonitrile butadiene rubber (NBR)/poly(lactic acid) (PLA) blends and their foams

Abstract

Thermoplastic elastomers and their foams were prepared by blending elastomeric acrylonitrile butadiene rubber (NBR) and rigid poly(lactic acid) (PLA) with various PLA compositions ranging between 0 and 40%. The thermal and mechanical properties and the morphologies of the blends with various PLA contents were investigated through universal testing machine, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscope analysis. The rheological properties during gel formation were in situ monitored through the evolution of torque with curing time. Furthermore, the microcellular structures and physical properties of the NBR/PLA foams prepared using organic blowing agents were studied. The NBR/PLA blends showed a two-phase morphology made of a continuous NBR matrix and micron or submicron nodules and the tensile strength and modulus; also, hardness of the NBR/PLA blends increased with the increase of the added PLA content. While the foamed samples exhibited a similar cell structure and foaming ratio to that of the pure NBR, the cell formation was considerably reduced as the added PLA content exceeded 30%. We conclude that the mechanical properties of NBR thermoplastic elastomer as well as its foams can be controlled by a judicious introduction of rigid and biodegradable PLA.     

Mechanical Properties Comparison of Various Ratios of L-Lactide Grafted Sisal Fibers and Untreated Sisal Fibers Reinforced Poly (lactic acid) Composites

Composites composed of the mixed fibers of L-lactide (LA) grafted sisal fiber (SF-g-LA) and untreated sisal fiber (USF) in a poly (lactic acid) (PLA) matrix were prepared with SF-g-LA/USF fibers ratios of 0, 1:9, 3:7, 5:5, 7:3, 9:1, and 1. The mechanical properties and the interfacial performance of the mixed SF reinforced PLA composites were investigated. The results of the study showed that the introduction of SF-g-LA improved the tensile strength, tensile modulus, flexural strength and flexural modulus of the mixed SF reinforced PLA composites compared with pure PLA or PLA composites with only USF, resulting from the improved interfacial adhesion between SF-g-LA and the PLA matrix. In addition, the introduction of some amount of USF enhanced the reinforcing efficiency of the mixed SF in the composites compared to the PLA composites with only SF-g-LA, owing to the good mechanical properties of USF itself. Furthermore, as for the tensile strength and tensile modulus of the mixed SF reinforced PLA composites, the optimal ratio of SF-g-LA and USF was 7:3, whereas for the flexural modulus of the mixed SF reinforced PLA composites, the optimal mixed ratio of SF-g-LA and USF was 3:7.     

Designing and Characterization of Poly(L-Lactide)/Poly(ϵ-Caprolactone) Multiblock Copolymers

A series of poly(L-lactide)/poly(?-caprolactone) (PLA/PCL) biodegradable multiblock copolymers was synthesized by a two-step process and characterized. Ring-opening polymerization was used to prepare a series of HO-PLA-PCL-PLA-OH copolymers initiated by hydroxyl-terminated PCL. Then the triblock copolymers and 1,6-hexamethylene diisocyanate (HDI) were reacted with different copolymer/HDI weight ratios. Consequently, a series of PLA/PCL multiblock copolymers with designed molecular chain structure was obtained. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and ¹H NMR were used to characterize these copolymers and the results showed that the designed PLA/PCL copolymers had been synthesized. Dynamic mechanical analysis (DMA) was applied to characterize their thermal properties. Stress–strain curves showed that a PLA/PCL copolymer with adjustable mechanical properties had been achieved.     

Designing and Characterization of Biodegradable Multiblock Poly(L-Lactic Acid)/Polybutadiene Elastomers

A series of poly(L-lactic acid)/polybutadiene (PLA/PB) biodegradable multiblock elastomers was synthesized and characterized. A two-step process to prepare PLA/PB multiblock elastomers was applied. Melt polymerization was used to prepare poly(L-lactic acid) (PLA) terminated with hydroxyl groups and, at the same time, hydroxyl-terminated polybutadiene (HTPB) and 1,6-hexamethylene diisocyanate (HDI) were employed to synthesize diisocyanate-terminated polybutadiene (ITPB). Then, PLA and ITPB were reacted with different PLA/PB weight ratios. Consequently, a series of PLA/PB biodegradable poly(ester-urethane)s with crosslinked chains was obtained. Swelling characteristics and crosslink density of the crosslinked elastomer were investigated. DMA was applied to characterize its thermal properties. The measurement of mechanical properties showed that a PLA/PB elastomer with adjustable mechanical properties was synthesized. Micromorphology, hydrophobicity, and degradability of the material were also characterized.     

Properties and Morphology of Poly(Lactic Acid)/Calcium Carbonate Whiskers Composites Prepared by a Vane Mixer based on an Extensional Flow Field

Binary composites of poly(lactic acid) (PLA)/calcium carbonate whiskers (CCW) with different weight fractions were prepared with a vane mixer based on extensional rheology. The mechanical properties, thermostability, crystallization behavior, rheology behaviors and micromorphology of the composites were analysed to study the effect of the CCW fibers on the composite's properties; a pure PLA sample was also prepared for comparison. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that the CCW fibers had excellent compatibility with the PLA matrix and the CCW fibers were dispersed and distributed evenly in the PLA matrix under the action of the extensional flow field produced by the vane mixer. Differential scanning calorimetric (DSC) analysis showed that introducing a vane mixer into the PLA processing could increase the degree of crystallization (χ_c) of the composites significantly, and moderate CCW fibers adding could further increase its χ_c value. Thermogravimetric analysis (TGA) revealed that adding the CCW fibers reduced the thermostability of the composites. The G′, G″, η* and the torque, T_N, of the composites, obtained from rheology analyses, declined obviously, because of the hydrolysis and chains scission induced by residual water and fatty acid when the CCW content less than 4%. Tensile tests proved that filling moderate amounts of CCW fibers into PLA could increase its tensile strength and strain at break, increasing by 5% and 29.6%, respectively.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Fiber Structure,Tensile Behavior and Antibacterial Activity of Polylactide/Poly(butylene terephthalate) Bicomponent Fibers Produced by High-Speed Melt-Spinning

Abstract

Various types of bicomponent fibers composed of polylactide (PLA) and poly(butylene terephthalate) (PBT) with different molecular weights, arranging the polymers separately in the skin or core, were produced by high-speed melt-spinning. The bicomponent spinning, arranging the PLA with high molecular weight (melt flow rate =1.9?g/10?min, L-lactide content = 98.7%) in the skin and the PBT with low molecular weight (IV = 0.835–0.865 dL/g) in the core, resulted in orientation-induced crystallization in the PLA component at the spinning speed of 2?km/min. This crystallization effect was ascribed to a chain-extending treatment applied to the original PLA (MFR = 4.0?g/10?min) to increase its molecular weight. By the treatment the PLA could crystallize when spun even at 1?km/min in its single-component spinning. On the other hand, the bicomponent spinning system interfered with the orientation-induced crystallization of PBT in the core. As a result, the critical spinning speed needed to generate the orientation-induced crystallization in the core PBT was elevated to 4?km/min. The inferior tensile behavior of the bicomponent fibers, as compared to the single-component PLA or PBT fibers, suggested poor compatibility between PLA and PBT. Transesterification reactions rarely occurred at the interface of the two polymers. The bicomponent fibers prepared from high molecular weight PLA and low molecular weight PBT, however, showed sufficient antibacterial activity and physical properties to be suitable for designing medical clothing materials.     

Mechanical,Biodegradation and Morphological Properties of Sisal Fiber Reinforced Poly(Lactic Acid) Biocomposites

Sisal fiber-reinforced poly(lactic acid) (SF/PLA) biocomposites were prepared by melt mixing and subsequent compression molding. The effect of fiber content and sodium hydroxide (NaOH) concentration, used for the fiber mercerization, on the properties of the biocomposites was investigated. It was found that the SFs had a large potential for improving the mechanical properties of the biocomposites. The tensile strength and impact strength increased linearly up to a fiber content of 20%, and then decreased due to the fiber agglomeration. The water absorption was enhanced with increasing the SF content owing to the SFs containing an abundance of hydroxyl groups. The biodegradability of the SF/PLA biocomposites increased similarly. Furthermore, the mercerization led to an increase of the mechanical properties of the biocomposites, which normally depended on the fiber-matrix adhesion. The mercerization had competing effects on the water absorption and biodegradability, including not only the positive function of the improved hydrophilicity of the mercerized-SF but also the negative role of the increase of fiber-matrix interfacial adhesion. Overall, the optimum SF load for mechanical properties was 20?wt% due to a good balance between the reinforcement and distribution of the SFs, whereas the 6% NaOH concentration was optimal owing to the resulting fibers yielding the highest mechanical properties and acceptable water resistance and biodegradability.     

Cellulose-based biocomposites: comparison of different multiphasic systems

Biocomposites (biodegradable composites) are obtained by blending biodegradable polymers and fillers. Since the main components are biodegradable, the composite as a whole is also expected to be biodegradable. This paper presents various biocomposites that have been elaborated with cellulose or lignocellulose fibers from diverse sources, with different lignin contents. This paper is targeted on the analysis of 'fiber–matrix' interactions of two types of biocomposites based on agropolymer (plasticized wheat starch) and biopolyester (polybutylene adipate-co-terephthalate), named APB and BPB, respectively. Processing and main properties of both biocomposites are shown and compared. Polyolefin-based composite (PPC), which is known to present very poor 'fiber–matrix' interactions, is used as a reference. Through the Young's modulus, mechanical properties have shown that the reinforcement, by increasing fiber content, is much more significant for APB compared to BPB. The evolution of chains mobility, evidenced through shift of T _g values, according to the increase in fiber content and thence in interfacial area, have shown that the fiber–matrix interactions are higher for APB. BPB presents intermediate values, higher than PPC ones. These results are in agreement with the analysis of the composite morphologies performed by SEM on cryogenic fractures. Finally, by determining the theoretical works of adhesion and the interfacial tensions from contact angle measurements, it is shown that these parameters are partially able to predict the level of interaction between the fibers and the matrix. We could show that the perspectives of such work seem to be of importance to tailor new materials with a controlled end-use.     

Thermoplastic Vulcanizate Based on Poly(lactic acid) and Acrylic Rubber Blended with Ethylene Ionomer

A new thermoplastic vulcanizate (TPV) was developed by meltblending of poly(lactic acid) (PLA), acrylic rubber (ACM), and ethylene-methacrylic acid with sodium ions (EMAA-Na). The PLA/ACM/EMAA-Na blend showed low-yield strength, low modulus, and excellent strain recovery. It also demonstrated an increase in complex viscosity and decrease in melting temperature due to the interfacial reaction between the PLA and the ACM phases. The Fourier transform infrared spectroscopy results indicate that EMAA-Na can interact with both PLA and ACM, and that the Na⁺ ions act as a catalyst for the interfacial reaction between PLA and ACM, while PLA does not react with ACM without EMAA-Na. Moreover, the tensile strength at break of the PLA/ACM/EMAA-Na blend was observed to be extremely improved by the addition of hexamethylenediaminecarbamate (HMDC) due to the increasing of the cross-link density inside the rubber phase. The morphology of the PLA/ACM/EMAA-Na blend with HMDC was finer than that of PLA/ACM/EMAA-Na without HMDC. From the results, it is suggested that the interfacial reaction between the PLA and the ACM phases, the cross-linking in the ACM phase, and the finer morphology improved the mechanical properties of the blend.     

Ultrasound-assisted modification of functional properties and biological activity of biopolymers: A review

In this review, the recent applications of power ultrasound technology in improving the functional properties and biological activities of biopolymers are reviewed. The basic principles of ultrasonic technology are briefly introduced, and its main effects on gelling, structural, textural, emulsifying, rheological properties, solubility, thermal stability, foaming ability and foaming stability and biological activity are illustrated with examples reviewing the latest published research papers. Many positive effects of ultrasound treatment on these functional properties of biopolymers have been confirmed. However, the effectiveness of power ultrasound in improving biopolymers properties depends on a variety of factors, including frequency, intensity, duration, system temperature, and intrinsic properties of biopolymers such as macromolecular structure. In order to obtain the desired outcomes, it is best to apply optimized ultrasound processing parameters and use the best conditions in terms of frequency, amplitude, temperature, time, pH, concentration and ionic strength related to the inherent characteristics of each biopolymer. This will help employ the full potential of ultrasound technology for generating innovative biopolymers functionalities for various applications such as food, pharmaceuticals, and other industries.     

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few microns, which are in the desirable range for constructing “biomimicking” fibrous scaffolds for tissue engineering applications.     

Calcium Sulfate as High-Performance Filler for Polylactide (PLA) or How to Recycle Gypsum as By-product of Lactic Acid Fermentation Process

Reinforcing of polylactide (PLA) with fillers can be an interesting solution to reduce its global price and to improve specific properties. Starting from calcium sulfate (gypsum) as by-product of the lactic acid fermentation process, novel high performance composites have been produced by melt-blending PLA and this filler after a previous specific dehydration performed at 500°C for min. 1 h. Due to PLA sensitivity towards hydrolysis, it has first been demonstrated that formation of β-anhydrite II (AII) by adequate thermal treatment of calcium sulfate hemihydrate is a prerequisite. Then, the modification of filler interfacial properties with different coating agents such as stearic acid (SA) and stearate salts has been considered. The effect of surface treatment on molecular, thermal and mechanical properties has been examined together with the morphology of the resulting composites. To take advantage of the improved lubricity and better wetting characteristics, the filler was coated by up to 2% (by weight) SA. The coating of the filler leads to PLA–AII composites that surprisingly exhibit thermal stability, cold crystallization and enhanced impact properties. Such remarkable performances can be accounted for by the good filler dispersion as evidenced by SEM–BSE imaging of fractured surfaces. As far as tensile proprieties are concerned, notable utilization of uncoated filler or filler coated by stearate salts leads to PLA–AII composites characterized by higher tensile strength and Young's modulus values. The study represents a new approach in formulating new melt-processable grades with improved characteristic features by using PLA as polymer matrix.     

Electronics with and on paper

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, driven mainly by low‐cost and disposable applications. Adding to this interest, we must recognise the importance of the dream of wireless auto‐sustained and low‐energy‐consumption electronics. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. Most of the paper used up to now is optimised in terms of the required mechanical and physical properties to be used as the support of inks of different origins. In the future, specific electronic heterogeneous paper sheets should be fabricated aiming to get paper fibers with required bulk and surface functionalities, proper water/vapour barrier, size and diameter/thickness of the fibrils and full paper thickness. This will be the function of components/devices to be incorporated/integrated such as thin‐film transistors, complementary metal oxide semiconductor devices, passive electronic components (resistances, inductors and capacitors), memory transistors, electrochromics and thin‐film paper batteries. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vitamin C functionalized multi-walled carbon nanotubes and its reinforcement on poly(ester-imide) nanocomposites containing L-isoleucine amino acid moiety

The aim of this research was to prepare poly(ester–imide) (PEI)-based nanocomposites (NCs) through the functionalization of carboxylated-multiwalled carbon nanotubes (MWCNT)s with ascorbic acid, in order to ensure better filler dispersion and good interfacial adhesion between filler and matrix. Chiral and biodegradable PEI was synthesized from amino acid-based diacid with 4,4′-thiobis(2-tert-butyl-5-methylphenol) by a direct polycondensation method. Using the solution mixing technique, the NCs containing modified MWCNTs with different loading levels of 5,10, 15 wt% were produced and examined in terms of chemical structure, morphology, and thermal stability by FT-IR spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). TEM and FE-SEM photographs of the obtained NCs indicated well-dispersed morphologies and strong interaction between the functionalized MWCNTs and the polymer matrix. TGA results revealed that the addition of MWCNT resulted in a significant increase of the thermal stability and char yields of the NCs compared to those of the neat PEI.     

Effect of interfacial debonding and matrix cracking on mechanical properties of multidirectional composites

In composites, debonding at the fiber–matrix interface and matrix cracking due to loading or residual stresses can effect the mechanical properties. Here three different architectures — 3-directional orthogonal, 3-directional 8-harness satin weave and 4-directional in-plane multidirectional composites — are investigated and their effective properties are determined for different volume fractions using unit cell modeling with appropriate periodic boundary conditions. A cohesive zone model (CZM) has been used to simulate the interfacial debonding, and an octahedral shear stress failure criterion is used for the matrix cracking. The debonding and matrix cracking have significant effect on the mechanical properties of the composite. As strain increases, debonding increases, which produces a significant reduction in all the moduli of the composite. In the presence of residual stresses, debonding and resulting deterioration in properties occurs at much lower strains. Debonding accompanied with matrix cracking leads to further deterioration in the properties. The interfacial strength has a significant effect on debonding initiation and mechanical properties in the absence of residual stresses, whereas, in the presence of residual stresses, there is no effect on mechanical properties. A comparison of predicted results with experimental results shows that, while the tensile moduli E ₁₁, E ₃₃and shear modulus G ₁₂ match well, the predicted shear modulus G ₁₃ is much lower.     

A Fiber-Bundle Pull-out Test for Surface-Modified Glass Fibers in GF/Polyester Composite

The development of high-performance polymer composites is tightly bound with the functional surface modification of reinforcements. A new method, based on the principle of the fiber-bundle pull-out test, is proposed to analyze the interfacial properties between the long fibers in the form of a bundle and the polymer matrix. Specimen geometry and a test fixture were designed using finite element analysis. The method was verified for unsized and sized glass fibers embedded in polyester resin to demonstrate its applicability for a wide range of adhesion between fibers and the polymer matrix. The pull-out test can be used for a relative comparison of different surface modifications if the bundle geometry is unknown. The results of high reproducibility and sensitivity for interfacial properties make the method attractive.     

Correlation of the Morphological and Mechanical Properties of a Biodegradable Blend Based on Polylactic Acid

A series of binary and ternary blends composed of polylactic acid (PLA), low-density polyethylene (LDPE), and chitosan (CS) were prepared and characterized in terms of their morphological and mechanical properties. The mechanical properties of the prepared blends, including tensile properties and impact strength, were compared with neat PLA. In addition, the effect of incorporation of maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA) as a compatibilizing agent, and the order of mixing on the mechanical and morphological properties of the ternary blends were also studied. It was observed that addition of CS enhanced the stiffness of PLA/LDPE blends while it decreased the toughness and tensile strength. It was demonstrated that addition of LLDPE-g-MA, up to 10 wt%, had no significant compatibilizing effect. However, the mechanical results indicated that when 15 wt% of LLDPE-g-MA was loaded, it started to play a compatibilizing role and caused an improvement in the toughness properties of ternary blend.     

Preparation and Characterization of Poly(L-lactide-co-glycolide-co-ε-caprolactone)/Nano-biaoactive Glass-Nano-β-tricalcium Phosphate Composite Scaffolds

Abstract

Polymeric/ceramic composite scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. In this work a series of poly(L-lactide-co-glycolide-co-ε-caprolactone)/nano-biaoactive glass-nano-β-tricalcium phosphate composite scaffolds were successfully fabricated and the influences of the inorganic content and freezing temperature on the physical properties were studied. The composite scaffolds with various inorganic contents showed an interconnected pore structure with irregular shapes. The composite scaffolds had a porosity that was reduced with increasing inorganic content and decreasing freezing temperature. The incorporation of inorganic fillers and decreasing freezing temperature improved the mechanical properties of the hybrid scaffolds. By appropriate control of these two factors (10.0?wt% content of NBAG and β-TCP with freezing at ?30?°C) a suitable composite scaffold was prepared as a potential bone tissue engineering implant.