Heat and humidity performance of injection molded PLA for durable applications

The durability of a commercially available injection molding grade polylactide (PLA) was assessed by exposure to conditions of elevated temperature and humidity over a period of several weeks. Moisture absorption, molecular weight, and mechanical performance were monitored over time and as a function of crystallinity level. At 50°C and 90% relative humidity, both amorphous and crystalline samples of PLA showed significant moisture absorption, allowing hydrolysis to occur. The study showed that while crystalline content had an effect on the initial moisture absorption behavior, the overall longer term effects on degradation were surprisingly minor. A cumulative damage model was used to relate the overall degradation due to moisture uptake and hydrolysis to long‐term durability in environments typical of automotive interiors. The study showed that the injection molding grade PLA resins that are currently commercially available are not suitable for use in applications that require long‐term durability in environments subject to elevated temperature and humidity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polylactic acid and its blends with petroleum‐based resins: Effects of reprocessing and recycling on properties

Environmental and economic reasons make the use of bioplastics and biocomposites increasingly coveted in sectors other than packaging. Recycling of all wasted or rejected durable plastics is highly desired and biobased plastics are no exception. Therefore, the investigation of pre‐ and post‐consumer recycling of products made from biobased plastics is of great interest. Polylactic acid (PLA) and its blends have been chosen for this study because it is an excellent representative of mass‐produced bioplastics for industrial applications. As part of the “Sustainable Recycling of ‘Green’ Plastics” project, the current study addresses the durability issues related to the reprocessing and post‐consumer recycling of a PLA virgin resin and two commercially available blends of PLA namely one with polycarbonate (PC) and one with polyethylene (PE). The materials were investigated using methods that simulate post‐processing and post‐consumer recycling. Accelerated ageing was performed at elevated temperature and humidity to simulate the usage period of the materials. The materials were analyzed using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and their mechanical strength was evaluated by tensile and impact testing. The flow properties of the materials were characterized by the melt flow index (MFI). Multiple processing of pure PLA did not affect the impact strength or the glass transition temperature (T_g), but caused crystallization and increase in the MFI, indicating that degradation occurred during processing. DSC thermograms of the blends revealed that the components in the blends were not miscible. Multiple processing of the blends did not significantly affect the elastic modulus of the materials, but affected the elongation at break. The results indicated that multiple processing of the PLA/HDPE blend caused increased dispersion and thus increased elongation at break, while the dominating mechanism in the PLA/PC blend was degradation that caused a decrease in elongation at break. Post‐consumer recycling of the PLA/PC blend was simulated and the results clearly showed that ageing corresponding to one year of use caused a significant degradation of PLA. Pure PLA was severely degraded after only one ageing cycle. Although the PLA/PC blend showed some improved mechanical properties and resistance to degradation compared with pure PLA, one ageing cycle still caused a severe degradation of the PLA and even the PC was degraded as indicated by the formation of small amounts of bisphenol A. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43916.     

Retarding hydrolytic degradation of polylactic acid: Effect of induced crystallinity and graphene addition

The combination of elevated temperature and humidity leads to rapid degradation of polylactic acid (PLA) because of hydrolysis. Consequently, PLA, which is a bio‐derived and biodegradable polymer, is not currently used for durable applications since properties cannot always be maintained over time. In this work, the ability of polymer crystals to reduce the rate of degradation during accelerated aging tests was studied. Also examined was the influence of addition of 2 wt % graphene nanoplatelets to act as moisture transport barriers in the polymer. PLA samples were immersed in aqueous media of different pH or exposed to 100% relative humidity at 50 °C for different lengths of time to study the hydrolytic degradation behavior. In addition to monitoring the loss in mass of the samples, the values of crystallinity, melt viscosity, and mechanical properties, among others, were measured as functions of aging time using techniques such as DSC and rheometry. It was found that both crystallization and graphene addition are able to slow down the rate of degradation at short times, but significant degradation of PLA still occurs at long times. This is because PLA crystallites and graphene nanoplatelets can only reduce, but not eliminate, moisture diffusion into the polymer sample. Between the use of nanoplatelets and crystals, though, the former approach may be the better choice since enhanced crystallization tends to make PLA brittle. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44166.     

Formulation and characterization of compatibilized poly(lactic acid)‐based blends and their nanocomposites with silver‐loaded kaolinite

Biodegradable polymer nanocomposites have been developed in this study as materials for use in the packaging of moisture‐sensitive products. Poly(lactic acid) (PLA) was the main component of the nanocomposites with poly(butylene adipate‐co‐terephthalate) (PBAT) as flexibility enhancer. Tetrabutyl titanate was also added as a compatibilizer to enhance the interfacial affinity between PLA and PBAT by inducing the formation of some PLA/PBAT via transesterification during the melt blending process, thereby improving the mechanical properties of the blends. Silver‐loaded kaolinite synthesized via chemical reduction was also incorporated into the compatibilized blends for further property improvement. Herein, we report a novel biodegradable quaternary nanocomposite system with intercalated‐exfoliated clay dispersion that was uniquely achieved by increasing the interlamellar space between kaolinite layers through silver nanoparticle insertion. The resultant nanocomposites containing as little as 4 phr modified clay reduced the elongation at break from 213.0 ± 5.85% to 53.8 ± 1.81%, enhanced thermal stability (initial decomposition temperature increased from 378 °C to 399 °C) and exhibited a water vapor permeability reduction of 41.85%. On the basis of these properties, the developed nanocomposites are considered to be promising candidates for use in bio‐packaging applications to replace non‐biodegradable and petro‐based plastics. © 2014 Society of Chemical Industry     

Morphology,mechanical properties,and durability of poly(lactic acid) plasticized with Di(isononyl) cyclohexane‐1,2‐dicarboxylate

Di(isononyl) cyclohexane‐1,2‐dicarboxylate (DINCH) was used as a new plasticizer for poly(lactic acid) (PLA), and the effects of DINCH and tributyl citrate ester (TBC) on the morphology, mechanical and thermal properties, and durability of PLA were compared. DINCH has limited compatibility with PLA, leading to PLA/DINCH blends with phase separation in which DINCH forms spherical dispersed phase. TBC is compatible with PLA and evenly distributed in PLA. Plasticized PLA with 10 and 20 phr DINCH have a constant glass transition temperature (T_g) of 50°C and are stiff materials with high elongation at break and impact strength. TBC could significantly decrease the T_g and increase the crystallinity of PLA, and PLA/TBC (100/20) blend is a soft material with a T_g of 24°C. The durability of plasticized PLA was characterized by weight loss measurement under water immersion, mechanical properties, and thermal analysis. The results reveal that PLA/DINCH blends have better water resistance and aging resistance properties than PLA/TBC blends, which is attributed to the relatively high hydrophobicity of DINCH and high T_g of PLA/DINCH blends. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Shear properties and load–deflection response of cross–ply glass–epoxy composite short–beams subjected to three‐point‐bending tests,and the effect of moisture absorption

The extensive use of composites in aerospace, chemical, marine, and structural applications leads to exposure to humidity and water immersion. Hence, there is a need to study the effect of moisture absorption on the mechanical properties of composite materials, especially the matrix dominated properties, such as the interlaminar shear strength (ILSS). The horizontal shear test with a short‐beam specimen in three‐point‐bending is used as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In this work, the ILSS of cross‐ply glass‐epoxy resin composites is determined in seven different fiber directions with short‐beam three‐point‐bending tests, before and after moisture conditioning. It is found that moisture absorption reduces ILSS and stiffness of the examined composites whereas it leads to larger failure deflections. It is also found that the direction of fibers strongly affects the load–deflection response and the ILSS of the dry and conditioned specimens. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Compatibilization of Polymer Blends from Poly(butadiene‐g‐poly(styrene‐co‐acrylonitrile)) and Polycarbonate through Oxazoline‐ and Benzoxazole‐Modification of ABS

Blends of poly(butadiene‐g‐poly(styrene‐co‐acrylonitrile) (ABS) with polycarbonate (PC) are some of the most successful multiphase materials, with applications in the automotive and electronics industries. The mechanical properties of the complete incompatible blends are mainly determined by the interaction between the poly(styrene‐co‐acrylonitrile) (S/AN) component of the ABS and the PC as well as through the dispersion of the elastomeric component poly(butadiene) in the thermoplastic S/AN‐matrix. The aim of our work is to optimize the modification process by the use of new substituted amino alcohols and amino phenols, as well as the use of a more efficient catalyst. Both reactive and non reactive compatibilization of polymer blends should be performed with the new ABS‐modifications.     

Incorporating amylopectin in poly(lactic acid) by melt blending using poly(ethylene‐co‐vinyl alcohol) as a thermoplastic carrier. II. Physical properties

This study adds to a previous morphological work (paper I) with further characterization of the developed poly(lactic acid) (PLA) blends containing amylopectin, which made use of an ethylene‐vinyl alcohol copolymer (EVOH) as a melt‐compoundable carrier for the polysaccharide in the biopolyester. The effect of using glycerol as compatibilizer was also characterized. Water and oxygen transport parameters, mechanical properties, and comparative biodegradability tests were evaluated for the blends. From the results, the barrier properties to oxygen were only seen to improve at 0%RH and mostly for the PLA‐EVOH blends, which furthermore showed a positive deviation from the rule of mixtures. At high relative humidity, the blends showed somewhat poorer barrier performance due to the comparatively higher improvement in barrier of the neat PLA at 80% RH. Interestingly, room temperature biodegradability testing suggested that low additions of the blending elements seemed to facilitate the biodegradability of the biopolyester. Despite the fact that properties were not so dramatically improved, incorporating renewable resources within PLA seems as a potentially viable route to reduce PLA supply dependency, retain good optical properties and to overcome some drawbacks associated to the use of this biopolyester. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties and morphological changes of poly(lactic acid)/polycarbonate/poly(butylene adipate‐co‐terephthalate) blend through reactive processing

The mechanical properties and morphological changes of poly(lactic acid) (PLA), polycarbonate (PC), and poly(butylene adipate‐co‐terephthalate) (PBAT) polymer blends were investigated. Several types of blend samples were prepared by reactive processing (RP) with a twin‐screw extruder using dicumyl peroxide (DCP) as a radical initiator. Dynamic mechanical analyses (DMA) of binary polymer blends of PC/PBAT indicated that each component was miscible over a wide range of PC/PBAT mixing ratios. DMA of PLA/PBAT/PC ternary blends revealed that PBAT is miscible with PC even in the case of ternary blend system and the miscibility of PLA and PBAT can also be modified through RP. As a result, the tensile strain and impact strength of the ternary blends was increased considerably through RP, especially for PLA/PBAT/PC = 42/18/40 (wt/wt/wt) with DCP (0.3 phr). Scanning electron microscopy (SEM) analysis of the PLA/PBAT/PC blends revealed many small spherical island phases with a domain size of approximately 0.05–1 μm for RP, whereas it was approximately 10 μm without RP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Biorenewable blends of polyamide‐11 and polylactide

Polyamide‐11(PA11) is melt blended with polylactide (PLA) using 0.00 to 0.10 wt% titanium isopropoxide catalyst to investigate potential compatibilizing reactions. Blend properties are characterized by differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile and impact testing. DSC shows two separate glass transition temperatures indicating only partial miscibility. Base etching to remove PLA domains followed by field emission scanning electron microscopy confirms the two phase nature of the blends. Storage and tensile moduli of the blends increase monotonically with increasing PLA content. Interchange reactions during reactive mixing were investigated by ¹³C‐NMR spectroscopy but the analysis shows little evidence of interchange reactions. This is true irrespective of catalyst level and mixing time over the temperature range from 185°C to 225°C. At the upper end of the temperature range investigated, significant degradation is observed. The combined results indicate that degradation reactions dominate over compatibilizing interchain transreactions. POLYM. ENG. SCI., 54:1523–1532, 2014. © 2013 Society of Plastics Engineers     

Moisture diffusion properties of HFPE‐II‐52 polyimide

Moisture diffusion properties of the polyimide HFPE‐II‐52 were determined using weight gain, weight loss, and swelling experiments over a temperature range of 25–200°C. Below 100°C, diffusivity was measured using standard weight loss and weight gain methods. Above 100°C, diffusivity is found by weight loss experiments performed by placing moisture saturated samples in an oven and recording weight loss dynamically. The diffusivity of the polyimide was found to obey the Arrhenius relation over the entire range of temperature. Weight gain experiments were performed to determine the equilibrium level of moisture absorbed by the polyimide as a function of relative humidity. Swelling experiments were performed to measure swelling strain as a function of moisture absorption. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3471‐3479, 2006     

Mechanical and thermal properties of thermoplastic polyurethane‐toughened polylactide‐based nanocomposites

The crystallinity and mechanical and thermal properties of polylactide (PLA)‐based biodegradable‐engineered plastic nanocomposites were determined. The nanocomposites were composed of thermoplastic polyurethane (TPU)‐toughened PLA, Talcum (Talc) and organic modified clay (montmorillonite; OMC). The tensile and flexural tests showed that PLA blended with 10 wt% TPU, 4 wt% Talc powder and 2 wt% OMC had the highest modulus and strength without a loss of elongation. The heat distortion temperature (HDT) tests demonstrated that the thermally treated PLA‐based nanocomposites had an HDT of nearly double the HDT for untreated specimens. An analysis of the polymer using scanning electron microscopy demonstrated that the incorporation of inorganic fillers altered the heterogeneous morphology of the PLA/TPU blend. This study investigated the feasibility of using PLA‐based nanocomposites for practical use, including applications in the automotive and furniture industries. POLYM. COMPOS., 35:1744–1757, 2014. © 2013 Society of Plastics Engineers     

Moisture uptake and resulting mechanical response of bio‐based composites. II. composites

The durability of entirely bio‐based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio‐based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross‐ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio‐based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity. POLYM. COMPOS., 36:1510–1519, 2015. © 2014 Society of Plastics Engineers     

Design of highly tough poly(l‐lactide)‐based ternary blends for automotive applications

Technical renewable poly(l ‐lactide) (PLA)‐based blends represent an elegant way to achieve attractive properties for engineering applications. Recently, the miscibility between PLA and poly(methyl methacrylate) (PMMA) gave rise to new formulations with enhanced thermo‐mechanical properties but their high brittleness still remains a challenge to be overcome. This work here focuses on rubber‐toughened PLA/PMMA formulations for injection‐molding processes upon the addition of a commercially available ethylene‐acrylate impact modifier (BS). The miscibility between PLA and PMMA is not altered by the presence of BS but the incorporation of BS (17% by weight) into a PLA/PMMA matrix could enhance both ductility and toughness of PLA/PMMA blends for PMMA content up to 50 wt %. An optimum range of particle sizes (d_n ～0.5 µm) of the dispersed domains for high impact toughness is identified. These bio‐based ternary blends appear as promising alternatives to petro‐sourced blends such as ABS‐based blends in engineering injection‐molding parts. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43402.     

Crystallization behavior of fully biodegradable poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Both poly(lactic acid) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) are fully biodegradable polyesters. The disadvantages of poor mechanical properties of PLA limit its wide application. Fully biodegradable polymer blends were prepared by blending PLA with PBAT. Crystallization behavior of neat and blended PLA was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WAXD). Experiment results indicated that in comparison with neat PLA, the degree of crystallinity of PLA in various blends all markedly was increased, and the crystallization mechanism almost did not change. The equilibrium melting point of PLA initially decreased with the increase of PBAT content and then increased when PBAT content in the blends was 60 wt % compared to neat PLA. In the case of the isothermal crystallization of neat PLA and its blends at the temperature range of 123–142°C, neat PLA and its blends exhibited bell shape curves for the growth rates, and the maximum crystallization rate of neat PLA and its blends all depended on crystallization temperature and their component. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of moisture content and heat treatment on the physical properties of starch and poly(lactic acid) blends

Starch, a hydrophilic renewable polymer, has been used as a filler for environmentally friendly plastics for about 2 decades. Starch granules become swollen and gelatinized when water is added or when they are heated, and water is often used as a plasticizer to obtain desirable product properties. The objective of this research was to characterize blends from starch and poly(lactic acid) (PLA) in the presence of various water contents. The effects of processing procedures on the properties of the blends were also studied. Blends were prepared with a lab‐scale twin‐screw extruder, and tensile bars for mechanical testing were prepared with both compression and injection molding. Thermal and mechanical properties of the blends were analyzed, and the morphology and water absorption of the blends were evaluated. The initial moisture content (MC) of the starch had no significant effects on its mechanical properties but had a significant effect on the water absorption of the blends. The thermal and crystallization properties of PLA in the blend were not affected by MC. The blends prepared by compression molding had higher crystallinities than those prepared by injection molding. However, the blends prepared by injection molding had higher tensile strengths and elongations and lower water absorption values than those made by compression molding. The crystallinities of the blends increased greatly with annealing treatment at the PLA second crystallization temperature (155°C). The decomposition of PLA indicated that PLA was slightly degraded in the presence of water under the processing temperatures used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3069–3082, 2001     

In‐line analysis of the influence of monomeric and oligomeric hindered amine on the hydrolysis of polycarbonate in a PC/ABS blend

The polycarbonate/polyacrylonitrile butadiene styrene (PC/ABS) blends lose mechanical properties when exposed to outdoor conditions. This is due to the ultraviolet (UV) induced photo‐oxidation of the PC phase and the polybutadiene portion of the ABS. It is known that ABS can be stabilised against terrestrial light by the use of hindered amine in combination with a UV absorber. However, such hindered amine cannot be used when PC is present in a multi component polymer blend. The hydrolysis of PC is accelerated when a small amount of hindered amine light stabilisers (HALS) is incorporated in the resin and is exposed to elevated temperature. In this article the effect of monomeric and oligomeric hindered amine on the hydrolysis of PC during the compounding of PC/ABS blend in a twin screw extruder at 240°C is observed by means of in‐line UV‐vis spectroscopy. Tinuvin 765 was used as monomeric hindered amine and Tinuvin 622 as oligomeric hindered amine. The molecular weight of the compounded sample was determined by gel permeation chromatography (GPC) and the rheological properties were observed using an online viscometer. It was found that the extent of hydrolysis induced by the oligomeric hindered amine is less compared to monomeric amine. It was also observed that polymeric hindered amine imparts better dispersion of the ABS phase into the polymer blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compression molding and melt‐spinning of the blends of poly(lactic acid) and poly(butylene succinate‐co‐adipate)

Poly(lactic acid) (PLA) is a biobased polymer made from biomass having high mechanical properties for engineering materials applications. However, PLA has certain limited properties such as its brittleness and low heat distortion temperature. Thus, the aim of this study is to improve toughness of PLA by blending with poly(butylene succinate‐co‐adipate) (PBSA), the biodegradable polymer having high toughness. Polymer blends of PLA and PBSA were prepared using a twin screw extruder. The melt rheology and the thermal property of the blends were examined. Further the blends were fabricated into compression molded parts and melt‐spun fiber and were subjected to tensile and impact tests. When the PBSA content was low, PBSA phase was finely dispersed in the PLA matrix. On the other hand, when the PBSA content was high, this minor phase dispersed as a large droplet. Mechanical properties of the compression molded parts were affected by the dispersion state of PBSA minor component in PLA matrix. Impact strength of the compression molded parts was also improved by the addition of soft PBSA. The improvement was pronounced when the PBSA phase was finely dispersed in PLA matrix. However, the mechanical property of the blend fibers was affected by the postdrawing condition as well as the PBSA content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41856.     

Compatibilization method applied to the chitosan‐acid poly(L‐lactide) solution

We are testing the compatibilization of the chitosan/PLA blends by addition of diisocyanate and at studying the effect of several MDI concentrations (0.5 and 2.5% of the global blend mass, w/w). To evaluate the MDI efficiency as a compatibilizer of chitosan/PLA blends, we worked with the following methods: IRTF spectra with higher peak at 1558 cm⁻¹ is due to the  NH bonds that exist in urea and urethane, thermal properties shows that the temperature of the endothermic peaks of the chitosan/PLA blends with MDI is very close to the temperature of pure chitosane and SEM micrography shows that MDI addition decreases the PLA particles size in the chitosan mixture; they also comply with the compatibilization theory. After that the mechanical properties have been characterized: we can notice that the MDI compatibilized chitosan/PLA blends have a higher Young's modulus than the noncompatibilized blends. we are showed that the use of 0.5% MDI is not enough sufficient to obtain a compatibilization, because a part of the MDI can be consumed by water. The addition of MDI increases the performance of the mechanical properties of the blends. Therefore, with this compatibilization, we could obtain some chitosan/PLA blends that would be water‐resistant and that would also keep their mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Interfacial micromechanics and effect of moisture on fluorinated epoxy carbon fiber composites

Carbon fiber composites have witnessed an increased application in aerospace and other civil structures due to their excellent structural properties such as specific strength and stiffness. However, unlike other structural materials, carbon fiber composites have not been as widely studied. Hence, their increased application is also accompanied with a serious concern about their long‐term durability. Many of these applications are exposed to multiple environments such as moisture, temperature, and UV radiation. Composites based on conventional epoxies readily absorb moisture. However, recently synthesized fluorinated epoxies show reduced moisture absorption and hence potentially better long‐term durability. The aim of this project is to study the effect of moisture absorption on fluorinated‐epoxy‐based carbon fiber composites and their comparison with conventional epoxy carbon fiber‐based composites. Microbond tests are performed on fluorinated and nonfluorinated epoxy‐based single fiber samples before and after boiling water degradation. It is found that fluorinated epoxy‐based single fiber coupons showed relatively reduced degradation of interface when compared with the nonfluorinated epoxy single fiber coupons. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers