Investigation on two modification strategies for the reinforcement of biodegradable lignin/poly(lactic acid) blends

In this work, biodegradable lignin/poly(lactic acid) (PLA) blends were prepared with melting compounding method. Dicumyl peroxide (DCP) and maleic anhydride (MA)/biphenyl peroxide (BPO) were used for the modification of the polymer blends, respectively. Structure of the polymer blends was characterized with Fourier transformed infrared spectroscopy and field emission scanning electron microscopy. Mechanical properties of the samples were determined with universal test machine and dynamic mechanical analysis. Thermal behaviors and thermal stability of the blends were all characterized with a thermal gravimetric analysis/differential scanning calorimetry simultaneous thermal analyzer. Lignin reinforced the mechanical strength of the blends while the thermal stability was not improved. At low content, DCP and MA/BPO apparently enhanced the mechanical strength of lignin/PLA blends. However, excessive DCP led to decreased tensile strength and elongation at break. Both DCP and MA/BPO resulted in lower glass transition temperature and melting temperature of PLA in the blends, while the thermal stability of the polymer blends was poorer after modification.     

Two in One: Modified Polyurethane Foams by Dip‐Coating of Halloysite Nanotubes with Acceptable Flame Retardancy and Absorbency

Poor flame retardancy of polyurethane foam (PUF) limits its practical application in many fields. Here, flame‐retardant performance of PUF is improved by a simple dip‐coating method. Halloysite nanotube (HNT) coating can be uniformly bonded to PUF surfaces via hydrogen‐bonding interactions, which is confirmed by element mapping and X‐ray photoelectron spectra. Density and mechanical properties of PUF increase with the concentration of HNT suspension, while porosity of the foam decreases with HNT loading. Weight ratio of HNTs to PUF in the composite can be achieved as high as 65.2%. Surfaces of PUF transfer from hydrophobic to super‐hydrophilic after HNT coating, and the water contact angle decreases from 116° to 0° after HNT coating. As a result, methylene blue adsorption capacity of HNTs‐coated PUF increases from 0.02 to 0.15 mg g^?1, and adsorption efficiency can reach 98% after 10 s. HNT coating can prevent PUF from burning and dripping, which suggests that flame‐retardant performance of PUF is significantly improved by HNTs. This work establishes a general procedure for improving flame retardancy and dye absorbency of polymer materials by simple dip‐coating of environmental‐friendly clay nanotubes, which shows great potential in high‐performance polymer and functional composite materials.     

Halloysite nanotube reinforced biodegradable nanocomposites using noncrosslinked and malonic acid crosslinked polyvinyl alcohol

Halloysite nanotubes (HNTs) based thin membrane‐like fully biodegradable nanocomposites were produced by blending individualized HNT dispersion with polyvinyl alcohol (PVA). Stable individualized HNT dispersion was obtained using several separation techniques, sequentially, prior to blending with PVA. PVA was crosslinked using malonic acid (MA) as crosslinker and phosphoric acid as catalyst, to increase the mechanical and thermal properties of HNT–PVA nanocomposites. Crosslinking was also intended to make PVA water‐insoluble and hence more useful in commercial applications. Examination of the composites indicated that HNTs were uniformly dispersed in both PVA as well as crosslinked PVA. Excellent mechanical properties of the HNT–PVA nanocomposites were achieved. These nanocomposites are intended to be composted at the end of their life rather than ending up in landfills as most of today's traditional petroleum based non‐biodegradable plastics. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Morphologies,crystallization, and mechanical properties of PLA-based nanocomposites: Synergistic effects of PEG/HNTs

In this study, the compounding modifier poly(ethylene glycol)/halloysite nanotubes (PEG/HNTs) was prepared by supersonic vibration and dynamic vacuuming. A series of poly(lactic acid) (PLA)/PEG and PLA/PEG/HNT composites were fabricated using a twin-screw extruder. Fourier transform infrared spectroscopy indicated that the hybrid between PEG and HNTs had no evident chemical interaction via supersonic vibration and dynamic vacuuming. The dispersed morphology of the compounding modifier in the PLA matrix was tested by high-resolution scanning electronic microscopy and transmission electron microscopy. The results showed that the low content of PEG/HNTs presented a good dispersion morphology. The binding energy of the PLA-based composites was studied through contact angle measurements. The results showed that PEG and PEG/HNTs can decrease the water contact angle of PLA, and that the binding energy between PEG and HNTs is higher than that of PLA/HNTs, which leads to more location of HNTs in the PEG phase. The crystallization behavior of PLA-based composites was examined by wide-angle X-ray diffraction and differential scanning calorimetry. The results suggested that the addition of PEG and PEG/HNTs effectively enhanced the crystallization of PLA and that the diffraction peak intensity of the PLA-based composites reached a maximum when the content of PEG/HNTs was 1.2 wt %. The spherulite morphology indicated that the addition of PEG resulted in perfect spherulites. The mechanical properties of PLA-based composites were analyzed with a universal testing machine and impact tester, which confirmed that the tensile strength and impact strength of the PLA-based composites increased slightly when the content of the PEG/HNT modifier was 1.2 wt %, while the tensile modulus of the PLA-based composites increased distinctly. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47385.     

Epoxidized natural rubber toughened poly(lactic acid)/halloysite nanocomposites with high activation energy of water diffusion

Poly(lactic acid)/halloysite nanotube (PLA/HNT) nanocomposites were prepared using melt compounding followed by compression molding. Epoxidized natural rubber (ENR) was used to toughen the PLA nanocomposites. The properties of PLA/HNT nanocomposites were characterized by impact tests, thermal analysis (DSC), morphological analysis (FESEM, TEM), and Fourier transform infrared spectroscopy (FTIR). Water absorption tests were performed at three immersion temperature (30, 40, 50°C). The maximum water absorption (M_m), diffusion coefficient (D), and the activation energy of water diffusion (E_a) were determined. The impact strength of PLA/HNT6 nanocomposites was increased significantly to ～296% by the addition of 15 wt % ENR. The incorporation of HNT and ENR increase its nucleation effect and assist in the crystallization process of PLA. The HNT has good affinity with PLA and ENR, which was revealed by TEM and FTIR. The M_m of PLA was increased in the presence of HNT and ENR. Nevertheless, the D value and the E_a of the PLA nanocomposites were found to be affected by the HNT and ENR contents. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42850.     

Biocompatible regenerated cellulose/halloysite nanocomposite fibers

Regenerated cellulose (RC) bio-nanocomposite fibers reinforced with halloysite nanotubes (HNT) were fabricated through wet spinning technique via ionic liquid as a green solvent. Mechanical properties, water uptake, thermal stability, and cytocompatibility of the obtained fibers were examined. FTIR spectra indicated the uniform dispersion of HNT in the cellulose network. XRD analysis, together with FE-SEM images indicated that HNT was dispersed homogenously in the polymer. Moreover, mechanical and thermal stabilities of the nanocomposite fibers were notably increased through the addition of HNT. Eventually, human skin fibroblasts proliferation on nanocomposite fibers demonstrated good cyto-compatibility. These findings highlight the potential of HNT nanocomposite fibers for biological and biomedical applications.     

Mechanical and thermal properties of biocomposites from poly(lactic acid) and DDGS

Distillers dried grains with solubles (DDGS), an ethanol industry coproduct, is used mainly as a low‐value feedstuff. Poly(lactic acid) (PLA) is a leading biodegradable polymer, but its applications are limited by its relatively high cost. In this study, low‐cost, high‐performance biodegradable composites were prepared through thermal compounding of DDGS and PLA with methylene diphenyl diisocyanate (MDI) as a coupling agent. Mechanical, morphological, and thermal properties of the composites were studied. The coupling mechanism of MDI in the PLA/DDGS system was confirmed via Fourier‐transform infrared spectra. The PLA/20% DDGS composite with 1% MDI showed tensile strength (77 MPa) similar to that of pure PLA, but its Young's modulus was 25% higher than that of pure PLA. With MDI, strong interfacial adhesion was established between the PLA matrix and DDGS particles, and the porosity of the composites decreased dramatically. Crystallinity of PLA in the composites was higher than that in pure PLA. Composites with MDI had higher storage moduli at room temperature than pure PLA. This novel application of DDGS for biocomposites has significantly higher economic value than its traditional use as a feedstuff. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of halloysite nanotubes and kaolin loading on the tensile,swelling, and oxidative degradation properties of poly(vinyl alcohol)/chitosan blends

[Halloysite nanotubes (HNT)]‐filled and kaolin filled composite films based on poly(vinyl alcohol) (PVA)/chitosan (CS) blend were prepared via solution casting method. Tensile properties, fracture morphology, FTIR spectra, thermal stability, swelling properties, moisture absorption, and oxidative degradation of the composite films were investigated. Addition of 0.5 wt% of filler led to the optimum tensile properties of the films. Increased roughness and tearing in the fracture surface morphology supported the tensile results. The FTIR results indicated there were physical interactions present in the composite films. Thermal stability of the composite films differed slightly where PVA/CS/HNT composite films showed better thermal stability than PVA/CS/kaolin composite films. Moreover, the presence of HNT and kaolin fillers in the blend reduced the swelling and moisture absorption properties of the films. Finally, the composite films were degraded by using Fenton's reagent. Degradation percentage of the composite films decreased with increasing filler loading. J. VINYL ADDIT. TECHNOL., 19:55–64, 2013. © 2013 Society of Plastics Engineers     

Engineering of Poly Lactic Acids (PLAs) for melt processing: Material structure and thermal properties

Bottles and other packaging account for approximately 70% of the global market of biopolymers, which include both biodegradable and durable materials. Durable materials account for the vast majority of the market, especially the bottles. Degradable polymers are instead refrained by the often‐insufficient mechanical and thermal properties, which limit their usage to single‐use packaging items at ambient temperature and in dry conditions. In this respect, the present work deals with the development and manufacturing of innovative and custom‐built Poly Lactic Acids (PLAs) for injection and compression molding, which are designed to be compostable, suitable for food contact and characterized by a good compromise of mechanical properties and thermal stability. A commercial grade PLA was, therefore, compounded in a twin‐screw co‐rotating extruder by the addition of maleated and glycidyl methacrylate PLAs as chain extenders and micro‐lamellar talc as mineral filler and nucleation promoter. Compatibilization between PLA, chain extenders and mineral filler was, therefore, investigated. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to evaluate the material structure and thermal response of the pellets after reactive compounding extrusion. The experimental findings show that material structure and, especially, crystallization of the PLA can be controlled by fine‐tuning the compound formulation as well as by setting of the operational parameters. In addition, achievement of the appropriate crystallization degree in the polymer is found to lead to composite materials, which can boast very good thermal stability. Accordingly, the custom‐built PLA formulations feature the potential to expand significantly the fields of application of non‐durable polymers, thus posing a valid alternative to both durable biopolymers and conventional plastics in injection and compression molding process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44504.     

Effects of thermoplastic polyurethane on the properties of poly(lactic acid)/organo‐montmorillonite nanocomposites based on novel vane extruder

Polylactic acid (PLA)/organo‐montmorillonite (OMMT) nanocomposites toughened with thermoplastic polyurethane (TPU) were prepared by melt‐compounding on a novel vane extruder (VE), which generates global dynamic elongational flow. In this work, the mechanical properties of the PLA/TPU/OMMT nanocomposites were evaluated by tensile, flexural, and tensile tests. The wide‐angle X‐ray diffraction and transmission electron microscopy results show that PLA/TPU/OMMT nanocomposites had clear intercalation and/or exfoliation structures. Moreover, the particles morphology of nanocomposites with the addition of TPU was investigated using high‐resolution scanning electronic microscopy. The results indicate that the spherical TPU particles dispersed in the PLA matrix, and the uniformity decreased with increasing TPU content (≤30%). Interestingly, there existed abundant filaments among amount of TPU droplets in composites with 30 and 40 wt% TPU. Furthermore, the thermal properties of the nanocomposites were examined with differential scanning calorimeter and dynamic mechanical analysis. The elongation at break and impact strength of the PLA/OMMT nanocomposites were increased significantly after addition of TPU. Specially, Elongation at break increased by 30 times, and notched impact strength improved 15 times when TPU loading was 40 wt%, compared with the neat PLA. Overall, the modified PLA nanocomposites can have greater application as a biodegradable material with enhanced mechanical properties. POLYM. ENG. SCI., 54:2292–2300, 2014. © 2013 Society of Plastics Engineers     

The effect of halloysite nanotubes reinforced epoxy filler on the crushing behavior of aluminum tubes

Crash box is one of the equipment to minimize the damage that may occur during an accident in vehicles. Many studies are conducted to improve the performance of crash boxes. Some of these studies were aimed at filling thin-walled crash boxes. Halloysite nanotubes (HNT) were used as filling material in this study. HNT can be found in nature and is in nanotube structure by nature. For this reason, it is inexpensive compared to other nanotubes like carbon nanotube. Within the scope of the study, epoxy-based mixtures with 0%, 5%, 10%, and 15% HNT were prepared and filled into aluminum tubes. The powders used were ~20–100 nm in size and in the form of cylindrical tubes. Investigated were the effects of the HNT ratio and the thin-walled aluminum construction. Nine diverse types of specimens were created. The vacuuming principle was used as the production method. The reason for this is to minimize the air bubbles that may occur during mixing. The effect of aluminum tube and HNT ratio on energy absorption and mechanical strength was investigated. For this, quasi-static tests were conducted. The absorbed energies of the specimens were determined by integrating the acquired contact force–displacement curves, and the specific absorbed energy was determined by dividing the absorbed energy by the specimen weights. SEM images were taken for internal structure characterization. In addition, FTIR analysis was performed to determine whether the composite was cured. According to the results obtained, the mechanical characteristics and specific absorbed energy of the filled specimens were superior to those of the unfilled ones. Specimen containing 5% HNT showed maximum energy absorption and mechanical strength. Although the HNT additive has a positive effect on the mechanical and energy absorption in general, it has been determined that the HNT additive affects the performances negatively from 10%.     

Review on Polymer/Halloysite Nanotube Nanocomposite

Halloysite nanotube (HNT) is a unique type of nanofiller, i.e., structurally much similar to nanoclay, whereas geometrically analogous to carbon nanotube. Due to nanosize, surface area, low cost, and natural availability, HNT offers up to date latent for polymeric nanocomposite. Polymer/HNT nanocomposites have been prepared using different techniques; however, melt mixing technique was widely used. Thermal stability, mechanical robustness, and nonflammability of polymer nanocomposite have been found to increase by HNT addition. Application areas discovered so far include materials for flame retardancy, stimuli-response, anticorrosion, dye removal, and drug delivery. Future research is desired to expand the potential of polymer/HNT nanocomposite.     

Poly(lactic acid)–thermoplastic starch–cotton composites: Starch-compatibilizing effects and composite biodegradability

Poly(lactic acid) (PLA) is a biodegradable, brittle, and high-cost polymer, which can be applied over structural components and green packaging. In this study, we reinforced PLA with natural cotton (10 wt %) and thermoplastic starch (TPS; 3 wt %) to obtain a biodegradable and lower cost composite. TPS was incorporated in three distinct ways: it was blended, coated, and blended and coated. In this study, we investigated the compatibilization of TPS in the improvement of matrix-reinforcement adhesion and increase in the tensile behavior without a compromise in biodegradation. The samples were investigated with thermal analysis, dynamic mechanical thermal analysis, tensile testing, scanning electron microscopy, confocal laser scanning microscopy, and hydrolytic degradation. The results show that the coupling effect was more pronounced in the PLA_TPS–cotton_TPS (hybrid system with PLA and cotton) hybrid system. This formulation presented a higher glass-transition temperature, thermal stability, storage modulus, wettability, and ductility. The TPS addition improved the adhesion between the matrix and starched cotton fiber and retarded abiotic biodegradation. These properties will allow for green applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47490.     

Effects of halloysite nanotubes on the performance of plasticized poly(lactic acid)‐based composites

The objective of this study is processing and characterization of Halloysite nanotube (HNT)/poly(lactic acid) (PLA) nanocomposites. As HNT filler, a domestic source was used (ESAN HNT). The results obtained from this HNT were compared with a well‐known reference HNT (Nanoclay HNT). To achieve the desired physical properties and clay dispersion, composites were compounded via direct melt mixing in a laboratory twin‐screw compounder. However, the constituents were observed to be incompatible without a compatibilizer. To improve the flexibility of nanocomposites and provide compatibilization between PLA and HNT, two types of blends were prepared: PLA plasticized with poly(ethylene glycol) (PEG) denoted as P‐PLA and PLA toughened with a thermoplastic polyurethane (TPU) denoted as T‐PLA. Despite the limited improvement in the P‐PLA blends, TPU addition improved the flexibility of PLA/HNT without deteriorating the tensile strength in a great manner. This was attributed to the relatively better compatibilization effect of TPU and the role of nanotubes acting as bridges between the TPU and PLA phases. POLYM. COMPOS., 37:3134–3148, 2016. © 2015 Society of Plastics Engineers     

生物可降解聚乳酸基复合材料研究进展

生物可降解高分子材料的研究开发是解决石油基塑料对环境污染的有效方法之一。其中,聚乳酸（PLA）具有可完全生物降解、可加工、可再生、力学性能优良等特点,是代替石油基塑料的必然趋势。但是PLA的疏水性大、性脆、价格贵等缺点限制了其应用和发展。论文主要综述了近年来国内外有关聚乳酸与天然高分子共混、合成高分子共混改性的研究进展,介绍了加工工艺、表面处理、添加剂等对复合体系性能的影响。在现有研究成果的基础上,可以通过加入柔性高分子、表面活性剂、纤维等以改善复合材料的脆性、相容性以及强度,以推动聚乳酸基复合材料的广泛发展。     

Toughening linear low‐density polyethylene with halloysite nanotubes

Linear low‐density polyethylene (LLDPE)‐based composites were prepared through melt compounding and hot pressing using both untreated and treated halloysite nanotubes (HNT) up to filler contents of 8 wt% to assess the role of the filler exfoliation and surface treatment on the thermal, mechanical, and rheological properties of the resulting composites. The addition of treated nanoparticles resulted in a better dispersion of the filler within the matrix, as confirmed by observations conducted at scanning and transmission electron microscopies. A decrease in both complex viscosity and shear storage modulus was recorded for all LLDPE‐HNT nanocomposites in the molten state. Differential scanning calorimetry analysis evidenced that HNT addition produced an increase of the crystallization peak temperature, while thermogravimetric analysis showed a remarkable improvement of the thermal stability with the nanofiller content. The addition of treated HNT nanoparticles induced better improvements in elastic modulus and tensile properties at break without significant loss in ductility. The fracture toughness, evaluated by the essential work of fracture approach, showed remarkable improvements (up to a factor of 2) with addition of treated HNT. Conversely, incorporation of untreated HNT produced an adverse effect on the fracture toughness when considering the nanocomposite filled with 8 wt% HNT. Both creep tests and dynamic mechanical analyses showed an overall enhancement of the viscoelastic properties due to addition of HNT, revealing higher improvements in nanocomposites added with treated HNT. POLYM. COMPOS., 36:869–883, 2015. © 2014 Society of Plastics Engineers     

Development of dual purpose,industrially important PLA–PEG based coated abrasives and packaging materials

Fabrication of industrially valuable PLA based coated abrasive and packaging products are made using bio-polymeric blends of PLA–PEG without involving the use of hazardous halogen based solvents, such as, chloroform and dichloromethane. Accordingly, an attempt has been made in our study to substitute a relatively less harmful ethyl acetate (EA) solvent in place of the toxic halogenated solvents to dissolve both PLA and PEG polymer blends to produce an environmentally safe PLA–PEG coating and film formulation in EA. This attempt in turn eliminates and replaces the use of non-degradable polymer coatings, (such as, acrylates, PVC, and synthetic latex) on Kraft paper thereby contributing to sustainability and environmental safety besides reduction in waste disposal to realize a cleaner environment. PLA is a hard and brittle polymer, which restricts its unexplored industrial user applications. On the other hand, PEG toughens the brittle PLA due to its plasticizing action. Hence, PLA–PEG polymer blends were prepared using increasing percentage of PEG content systematically from 5% to 25% and the % of PEG in PLA was optimized to 10% to get the maximum toughening effect in PLA–PEG formulation, which is ascertained by differential scanning calorimetry analysis. FTIR analysis confirmed the possible interaction that occurred between PLA and PEG, due to which a shift in vibration frequency of the PLA carbonyl group is observed. The other important test results from mechanical properties, contact angle, surface roughness, Cobb values, WVTR, and SEM analysis support to reveal that PLA–PEG (10%) blend is the best coating and film forming material on Kraft paper for the fabrication of industrially valuable both coated abrasive and packaging products to demonstrate its dual purpose applications.     

Ductile PLA modified with methacryloyloxyalkyl isocyanate improves mechanical properties

The majority of the biodegradable polymers in clinical use are composed of stiff materials that exhibit limited extendibility with unsuitably high Young’s modulus and low elongation at break values that make them non-optimal for various biomedical applications. Polylactide (PLA) is often used as a biomedical material because it is biodegradable, but the physical and mechanical properties of PLA need to be improved for biomedical applications. In order to improve the flexibility and strength of biodegradable PLA, various reaction conditions were studied. Urethane structure polymer materials were prepared; PLA was reacted with a small amount of methacryloyloxyethyl isocyanate (MOI) to obtain a ductile PLA with markedly improved mechanical properties. Elongation at break increased by 20 times when compared to neat PLA. Impact resistance (notched) improved 1.6 times. Thus, this modified PLA biodegradable polymer may have greater application as a biomedical material with increased mechanical properties.     

Preparation of ductile PLA materials by modification with trimethyl hexamethylene diisocyanate

Polylactide (PLA) is biodegradable and has been useful in various biomedical applications. Since the majority of the biodegradable polymers in clinical use are rather stiff materials that exhibit limited extendibility with low elongation at break values, the physical and mechanical properties of PLA must be improved to allow for more biomedical applications. Poly(ester-urethane) structure polymer materials were prepared; PLA was reacted with a small amount of trimethyl hexamethylene diisocyanate to obtain ductile PLA with markedly improved mechanical properties. Elongation at break was increased by more than 20 times while maintaining relatively high tensile stress when compared to pristine PLA. Impact resistance (notched) improved 1.6 times. Thus, the modified PLA biodegradable polymers presented here may have greater application as a biomedical material due to its enhanced mechanical properties.     

Nanocomposites of halloysite and polylactide

Naturally occurred halloysite (Hal) nanotubes compounded with polylactide (PLA) via melt mixing formed biodegradable and biocompatible clay polymer nanocomposites (CPN). The hydrogen bonding interactions between Hal and PLA were confirmed by Fourier transform infrared spectroscopy (FTIR). The modulus, strength and toughness of the Hal-PLA nanocomposites were substantially higher than those of neat PLA. Storage modulus and glass transition temperature of the Hal-PLA nanocomposites also increased with Hal loading as observed by dynamic mechanical analysis. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that Hal was uniformly dispersed and oriented in the CPN. X-ray diffraction (XRD) of the CPN showed the absence of Hal reflection at around 20°, indicating interactions of the PLA molecular chains in the interlayer space of Hal. Hal could nucleate PLA, leading to the decreased cold crystallization temperature and increased crystallinity. The vicat softening temperature and the degradation temperature of the CPN increased with Hal loading. Owing to the high performance and biocompatibility of the CPN, the prepared Hal-PLA nanocomposites had potential applications in biodegradable plastic and biomedical areas.