Extruded PLA/clay nanocomposite foams blown with supercritical CO2

The effects of nanoclay (Cloisite 30B) on the foamability of polylactide (PLA) were investigated in continuous extrusion foaming using supercritical CO₂ as the blowing agent. PLA samples containing 0–5 wt% of nanoclay were prepared. The X-ray diffraction and transmission electron microscopy images showed a high degree of exfoliation of clay nanoparticles within PLA. A single-screw tandem extruder was used to produce foams with 5 wt% and 9 wt% supercritical CO₂. The crystallization behavior of the samples was analyzed using regular and high-pressure differential scanning calorimeters and using a rotational rheometer under small amplitude oscillatory shearing. In the presence of dissolved CO₂, clay, and shear action, the PLA crystallization kinetics was significantly enhanced. The foamed results showed that both the cell density and the expansion ratio were greatly promoted with increased clay content and the dissolved CO₂, as well as by the possibly nucleated crystals. By further use of Cloisite 20A nanoclay particles with poor disperse-ability in PLA, we also proved that a high degree of dispersion significantly promoted the cell density and the expansion ratio of the PLA nanocomposites. Further, by varying the temperature profile within second extruder of the tandem-line, it was confirmed that the more rapid crystallization along the second extruder was responsible for the enhanced cell density and expansion ratio. The final crystallinity of the foamed samples was also enhanced at higher expansion ratios due to the strain induced crystallization.     

Preparation and properties of foamed cellulose acetate/polylactic acid blends

In order to improve the foaming performance of pure cellulose acetate (CA), blends were prepared by mixing polylactic acid (PLA) in CA and foamed by supercritical CO₂ (ScCO₂) in this study. The effect of PLA content (percentage by mass of blend) on structure, thermal properties, rheological properties, foaming properties and mechanical properties of the blends was investigated. The results showed that the addition of PLA destroyed the original hydrogen bonds of CA, while the blends had good crystallization properties. At the same time, compared with pure CA, the glass transition temperature (T_g) of the blends decreased, and the initial decomposition temperature (T₀) was reduced from 349.41°C (pure CA) to 334.68°C (CA/20%PLA). In addition, the rheological properties of the blends were improved, and the viscosity was reduced, which was obviously beneficial to foaming process. The pore size and density of the foamed blends both reached the maximum value at 20%PLA. The presence of PLA could degrade the mechanical properties of the blends. However, the overall drop (1.01 KJ/m²) of impact strength of the blends after foaming is much smaller than that before foaming (12.11 KJ/m²), indicating that the improvement of foaming performance was beneficial to improve its impact strength.     

Compatibility improvement of poly(lactic acid)/thermoplastic starch blown films using acetylated starch

The present research aims to improve the compatibility between relatively hydrophobic poly(lactic acid) (PLA) and hydrophilic thermoplastic starch (TPS) and the properties of the PLA/TPS blends by replacing TPS from native cassava starch (TPSN) with TPS from acetylated starch (TPSA). The effects of the degree of acetylation (DA) of acetylated starch, that is, 0.021, 0.031, and 0.074, on the morphological characteristics and properties of PLA/TPS blend are investigated. The melt blends of PLA and TPS with a weight proportion of PLA:TPS of 50:50 are fabricated and then blown into films. Scanning electron microscopy confirms the dispersion of TPS phase in the PLA matrix. Better dispersion and smaller size of the TPS phase are observed for the PLA/TPSA blend films with low DA of acetylated starch, resulting in improved tensile and barrier properties and increased storage modulus, thermal stability, and T_g, T_cc, and T_m of PLA. Elongation at break of the PLA/TPSA blend increases up to 57%, whereas its water vapor permeability and oxygen permeability decrease about 15%. The obtained PLA/TPSA blend films have the potential to be applied as biodegradable flexible packaging.     

Binary and ternary blends of polylactide, polycaprolactone and thermoplastic starch

In this study binary and ternary blends of polylactide (PLA), polycaprolactone (PCL) and thermoplastic starch (TPS) are prepared using a one-step extrusion process and the morphology, rheology and physical properties are examined. The morphology and quantitative image analysis of the 50/50 PLA/TPS blend transverse phase size demonstrate a bimodal distribution and the addition of PCL to form a ternary blend results in a substantial number of fine dispersed particles present in the system. Focused ion beam irradiation, followed by atomic force microscopy (AFM) shows that dispersed PCL forms particles with a size of 370 nm in PLA. The TPS phase in the ternary blends shows some low level coalescence after a subsequent shaping operation. Dynamic mechanical analysis indicates that the temperature of the tan δ peak for the PLA is independent of TPS blend composition and that the addition of PCL in the ternary blend has little influence on the blend transitions. Both the α and β transitions for the thermoplastic starch are highly sensitive to glycerol content. When TPS of high glycerol content is blended with PLA, an increase in the ductility of the samples is achieved and this effect increases with increasing volume fraction of TPS. The ternary blend results in an even greater ductility with an elongation at break of 55% as compared to 5% for the pure PLA. A substantial increase in the notched Izod impact energy is also observed with some blends demonstrating three times the impact energy of pure PLA. The mechanical properties for the ternary blend clearly indicate a synergistic effect that exceeds the results obtained for any of the binary pairs. Overall, the ternary blend approach with PLA/TPS/PCL is an interesting technique to expand the property range of PLA materials.     

Morphology and properties of compatibilized polylactide/thermoplastic starch blends

This paper investigates the properties and interfacial modification of blends of polylactide (PLA) and glycerol-plasticized thermoplastic starch (TPS). A twin-screw extrusion process was used to gelatinize the starch, devolatilize the water to obtain a water-free TPS and then to blend into the PLA matrix. The investigated TPS concentration ranged from 27 to 60 wt%. In the absence of interfacial modification, the TPS/PLA blend morphology observed through scanning electron microscopy was very coarse with TPS particles sizes between 5 and 30 μm. Interfacial modification was achieved by free-radical grafting of maleic anhydride (MA) unto the PLA and then by reacting the modified PLA with the starch macromolecules. Blends comprising MA-grafted PLA showed much finer dispersed phase size, in the 1–3 μm range and exhibited a dramatic improvement in ductility. The paper discusses the effects of two interfacial modification strategies on the blend morphology and tensile properties and investigates the compatibilization efficiency for glycerol plasticizer contents between 30 and 39 wt% and for starches from three different sources: wheat, pea and rice.     

Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid)

A batch processing method is used to fabricate foams comprising of a blend of poly(lactic acid) (PLA) and Novatein, a protein‐based thermoplastic. Various compositions of Novatein/PLA are prepared with and without a compatibilizer, PLA grafted with itaconic anhydride (PLA‐g‐IA). Pure Novatein cannot form a cellular structure at a foaming temperature of 80 °C, however, in a blend with 50 wt % of PLA, microcells form with smaller cell sizes (3.36 µm) and higher cell density (8.44 × 10²¹ cells cm^?3) compared to pure PLA and blends with higher amounts of PLA. The incorporation of 50 wt % of semicrystalline Novatein stiffens the amorphous PLA phase, which restrains cell coalescence and cell collapse in the blends. At a foaming temperature of 140 °C, NTP₃₀–PLA₇₀ shows a unique interconnected porous morphology which can be attributed to the CO₂‐induced plasticization effect. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45561.     

Gas foaming of segmented poly(ester amide) films

Biodegradable segmented poly(ester amide)s, based on dimethyl adipate, 1,4-butanediol and N,N′-1,2-ethanediyl-bis[6-hydroxy-hexanamide], with two distinct melting transitions were gas foamed using carbon dioxide (CO₂). Polymer films were saturated with CO₂ at 50 bar for 6 h after which the pressure was released. The samples were immersed in octane at the desired temperature after which foaming started immediately. Just above the lower melt transition the polymers retain adequate mechanical properties and dimensional stability, while the chain mobility increased sufficiently to nucleate and expand gas cells during the foaming process. In this way semi-crystalline poly(ester amide)s can be gas foamed below the flow temperature.Two poly(ester amide)s with 25 mol% (PEA2,5-25) and 50 mol% (PEA2,5-50) of bisamide segment content were foamed at 70 and 105 °C, respectively. The storage modulus (G′) of both pure polymers at the onset foaming temperature is 50-60 MPa. Closed-cell foams were obtained with a maximum porosity of ∼90%. The average pore size of PEA2,5-25 ranges from 77 to 99 μm. In contrast, the average pore size of PEA2,5-50 is in between 2 and 4 μm and can be increased to 100 μm by lowering the CO₂ saturation pressure to 20 bar. The porosity of PEA2,5-50 foams using this saturation pressure decreased to 70%.     

Effect of supercritical carbon dioxide on PMMA/rubber and polystyrene/rubber blending: Visosity ratio and phase inversion

Supercritical carbon dioxide (scCO₂) was added during blending of polystyrene or poly(methyl‐methacrylate) (PMMA) and a rubber impact modifier (SP 2207). The resulting blend morphologies were compared. The compounding took place in a Leistritz ZSE‐27 twin‐screw extruder at 100 RPM, at a temperature of 200°C, and with 2.0 wt% CO₂ Injection. The viscosity reduction of PMMA, polystyrene, and SP 2207 was measured using a slit die rheometer attached to the twin‐screw extruder. A viscosity reduction of up to 84% was seen with PMMA, 70% with polystyrene and 30% with SP 2207. The solubility of CO₂ in these polymers was measured in a high‐pressure vessel at 200°C and 13.78 MPa (2000 psi). A solubility of 5.79 wt% CO₂ was seen with PMMA, 3.65 wt% with polystyrene, and 2.60 wt% with SP 2207. The injection of CO₂ reduced the size of the dispersed rubber phase in both polystyrene and PMMA. For both blends (polystyrene/SP 2207 and PMMA/SP 2207) with and without the injection of CO₂, the extruder length for phase inversion was shortened by about L/D = 4, or 10% of the total extruder length. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26% by the addition of CO₂. The improvement in impact strength was not as large for blends of PMMA and SP 2207.     

Fabrication and characterization of polyetherimide/polyvinyl acetate polymer blend membranes for CO2/CH4 separation

This article presents fabrication, characterization, and performance evaluation of polyetherimide (PEI)/polyvinyl acetate (PVAc) blend membranes. Polymer blend membranes with various blend ratios of PEI/PVAc were prepared by solution casting and evaporation technique. Morphology and miscibility of polymer blend membranes were characterized by field emission scanning electron microscope (FESEM) and differential scanning calorimetry (DSC), respectively. The interaction between blend polymers was analyzed by FTIR analysis. Gas separation performance was evaluated in terms of permeability and selectivity. FESEM results revealed that pure polymer and blend membranes were homogeneous and dense in structure. A single glass transition temperature of polymer blend membranes was found in DSC analysis which indicated the miscibility of PEI/PVAc blend. FTIR analysis confirmed the presence of molecular interaction between blend polymers. The permeation results showed that the presence of PVAc (3 wt%) in blend membranes has improved CO₂ permeability up to 95% compared to pure PEI membrane. In addition, CO₂/CH₄ selectivity was found to be 40% higher than pure PEI membrane. This study shows that blending a small fraction of PVAc can improve the gas separation performance of PEI/PVAc blend membranes. POLYM. ENG. SCI., 59:E293–E301, 2019. © 2018 Society of Plastics Engineers     

Suppressing the effect of cullet composition on the formation and properties of foamed glass

The process of foaming glass is very dependent on the chemical composition of the glass. In this study we used a foaming-agent/oxidizing-agent couple and a crystallization inhibitor to foam cullets of flat, container and CRT-panel glass. Foamed glass with a density of 110–120?kg?m^–3, a thermal conductivity of 50–52?mW?m^–1 K^–1 and a homogeneous pore structure was obtained from a mixture of panel glass, 0.33?wt% carbon and 4.45?wt% Fe₂O₃. We also showed that it is possible to fabricate foamed glass with the same density or pore structure as mentioned above by adding up to 50?wt% container cullet or 70?wt% flat glass to the mixture. In the foamed samples with a low content of panel glass, crystals form, resulting in an increased open porosity, density and inhomogeneous pore structure. The crystallization can, however, be inhibited by adding calcium phosphate, so enabling the preparation of high-quality foamed glass from flat glass or flat/container-glass mixture. The pore gas is predominantly CO₂ and the pressure inside the pores is 0.36–0.47?bar. The reduced effect of the composition on the foaming process suggests that there is a great potential for stabilizing the production of foamed glass and ensuring the product's quality.     

苹果酸对聚乳酸/热塑性淀粉共混物结构与性能的影响

将天然淀粉用甘油改性后制得了热塑性淀粉(TPS),再通过熔融共混法制备了聚乳酸(PLA)/TPS共混物。通过SEM、TG、DSC分析和拉伸性能、吸水性能、流变性能测试,研究了苹果酸对TPS和PLA/TPS共混物结构和性能的影响。结果表明:苹果酸能促进淀粉酸解,使TPS分散相尺寸减小,在PLA基体中的分布更加均匀;苹果酸能提高PLA/TPS共混物的拉伸性能;苹果酸对PLA/TPS共混物的玻璃化转变温度、熔融温度及冷结晶温度影响较小;少量的苹果酸可降低PLA/TPS共混物的吸水率。     

In situ fibre‐reinforced composite films of poly(lactic acid)/low‐density polyethylene blends: effects of composition on morphology,transport and mechanical properties

This study aimed to investigate the effects of blend composition on packaging‐related properties of poly(lactic acid) (PLA) and low density polyethylene (LDPE) blown films. Blend films with PLA contents of 5–20 wt% were produced and compared. Scanning electron micrographs of cross‐sectional cryofractured surfaces of the blend films revealed that in situ fibre‐reinforced composites were obtained. Viscosity ratio of the polymer components of ca 1 confirmed that fibre formation was favourable for this blend system. PLA microdomains were dispersed throughout the film in forms of long fibres (length‐to‐diameter ratio > 100) and ribbons. The number of fibres and ribbons increased with an increase of PLA content. Critical content of PLA was found to be 20 wt% for effective improvement of both moduli and gas barrier properties. Incorporation of poly[ethylene‐co‐(methyl acrylate)] compatibilizer showed minimal effect on PLA structure. However, it did improve moduli and O₂ barrier properties when sufficient amount (1.5 pph) was used in 10 wt% PLA/LDPE. In short, flow behaviour, ratio of polymer components and degree of compatibility together played intricate roles in the morphology and hence mechanical and transport properties of PLA/LDPE immiscible blends. © 2017 Society of Chemical Industry     

From microstructure to mechanical properties of compatibilized polylactide/thermoplastic starch blends

Bio‐degradable polymer blends of polylactic acid/thermoplastic starch (PLA/TPS) were prepared via direct melt blending varying order of mixing of ingredients fed into the extruder. The effect of interface interactions between PLA and TPS in the presence of maleic anhydride (MA) compatibilizer on the microstructure and mechanical properties was then investigated. The prepared PLA/TPS blends were characterized by scanning electron microscopy, differential scanning calorimetry (DSC), tensile, and rheological measurements. Morphology of PLA/TPS shows that the introduction of MA into the polymer matrix increases the presence of TPS at the interface region. DSC results revealed the reduction of glass transition temperature of PLA with contributions from both TPS and MA. The crystallization temperature was decreased by the addition of MA leading to reduction of overall crystallization of PLA/TPS blend. The mechanical measurements show that increasing MA content up to 2 wt % enhances the modulus of PLA/TPS more than 45% compared to the corresponding blends free of MA compatibilizer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44734.     

Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2

In this study, the outcome of operating conditions of extrusion assisted by supercritical CO₂ for the manufacture of poly(lactic acid) foams was investigated. It was found that the temperature before and inside the die was the most prominent parameter to tune the foam properties. Foam porosity as high as 96% could be obtained (for die temperature between 109 and 112 °C), representing a total expansion exceeding 30. In this temperature range, low crystallinity (≈6%) was induced giving foams with high radial expansion i.e., large diameters and open porosity. At 112 °C, the CO₂ was able to greatly expand the foams, providing 73% of its potential blowing effect. On the other hand, a low die temperature (below a die temperature of 107 °C) induces a significantly higher level of crystallinity resulting in foams with closed‐porosity and a large longitudinal expansion due to higher strength of the polymer melt. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45067.     

Comparison of solvent performance for CO2 capture from coal-derived flue gas: A pilot scale study

The performance of a proprietary solvent (CAER-B2), an amine-carbonate blend, for the absorption of CO₂ from coal-derived flue gas is evaluated and compared with state-of-the-art 30 wt% monoethanolamine (MEA) under similar experimental conditions in a 0.1 MWth pilot plant. The evaluation was done by comparing the carbon capture efficiency, the overall mass transfer rates, and the energy of regeneration of the solvents. For similar carbon loadings of the solvents in the scrubber, comparable mass transfer rates were obtained. The rich loading obtained for the blend was 0.50 mol CO₂/mol amine compared to 0.44 mol CO₂/mol amine for MEA. The energy of regeneration for the blend was about 10% lower than that of 30 wt% MEA. At optimum conditions, the blend shows promise in reducing the energy penalty associated with using industry standard, MEA, as a solvent for CO₂ capture.     

Extrusion of PE/PS blends with supercritical carbon dioxide

The effects of dissolved supercritical carbon dioxide on the viscosity and morphological properties were investigated for polyethylene/polystyrene blends in a twin-screw extruder. The viscosities of the blend/CO₂ solutions were measured using a wedge die mounted on the extruder. A considerable reduction of viscosity was found when CO₂ was dissolved in the blend. It was observed that the dissolution of CO₂ into PE/PS blends, regardless of the CO₂ content used, led to decreased shear thinning behavior resulting in an increase of the power law index from 0.29 to 0.34. The cell structures of foamed PE/PS blends showed a typical dependence of pressure and CO₂ concentration, with higher operating pressures and CO₂ content leading to a smaller cell size. Also, it was noted that the size of the dispersed PS phase in the PE/PS phase blends decreased by increasing the CO₂ concentration, and that the dispersed PS phase domains were highly elongated in the direction normal to the cell radius.     

Diffusion and desorption of CO2 in foamed polystyrene film

Based on the existence of the pores in foamed polystyrene (PS), foamed‐non‐Fickian diffusion (FNFD) model was proposed, for the first time, to regress the desorption data obtained by gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO₂ out of foamed PS, and well predict the solubility of CO₂ in foamed PS. The characterization of scanning electron microscopy indicated that there were abundant pores in the foamed PS, and the pores store most of CO₂, which would diffuse in the pores, adsorb to the wall of the pores, penetrate across walls of the pores, diffuse in the matrix of PS, and desorb out of PS. The mass of CO₂ in the pores of foamed PS was expressed as a function of foaming pressure and temperature according to foaming kinetics. Results showed that the values calculated by this function agreed well with the values obtained from the FNFD model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45645.     

Physical extruder foaming of poly(lactic acid)—processing and foam properties

The article describes extrusion foaming of poly(lactic acid) (PLA) using carbon dioxide in the supercritical state as foaming agent emphasizing the steps required to establish a stable extrusion process. Low melt strength of PLA plays a role in optimizing processing conditions. The tests included PLA grades of different viscosity in addition to a chain extender. Processing at low temperature is possible due to the plasticizing effect of the CO₂ on the PLA melt and a sufficiently low melt temperature is also a prerequisite in production of stable foams due to improved melt strength. Foams were characterized by density, cell structure, crystallinity, and mechanical properties in compression. Low density, microcellular foams with density down to 20–30 kg/m³ were obtained for three different PLA grades. Varying die temperature and pressure drop rate we can explain observed abrupt drops in density with increasing CO₂ content by the interplay between cell nucleation and gas diffusivity at given temperatures. An effect on melt strength similar to using a chain extender is achieved by lowering the melt temperature at the die. Observed variations in sample crystallinity do not correlate with foam density. The PLA foams have good energy absorption capability. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Batch Foam Processing of Polypropylene/Polydimethylsiloxane Blends

Batch foaming processes were employed to prepare plastic foams from polypropylene (PP)/polydimethylsiloxane (PDMS) blends. Various amounts of PDMS were added to a PP matrix, and the resulting blends were batch foamed at different saturation pressures using carbon dioxide (CO₂) as the blowing agent. Ultimately, the blend foams exhibited better cell morphologies and higher cell densities in comparison with those prepared from PP alone. The increased solubility of CO₂ in PDMS made it as a CO₂ reservoir to induce more nucleation. When the PDMS content exceeded a certain level, however, it exerted a negative influence on cell density. Moreover, as the saturation pressure was raised, the cell density of the blend foams increased significantly. It was also noted that the addition of PDMS to the PP matrix generated some very small cells in the larger cell walls.     

Novel ternary blends of natural rubber/linear low-density polyethylene/thermoplastic starch: influence of epoxide level of epoxidized natural rubber on blend properties

Novel degradable materials based on ternary blends of natural rubber (NR)/linear low-density polyethylene (LLDPE)/thermoplastic starch (TPS) were prepared via simple blending technique using three different types of natural rubber (i.e., unmodified natural rubber (RSS#3) and ENR with 25 and 50 mol% epoxide). The evolution of co-continuous phase morphology was first clarified for 50/50: NR/LLDPE blend. Then, 10 wt% of TPS was added to form 50/40/10: NR/LLDPE/TPS ternary blend, where TPS was the particulate dispersed phase in the NR/LLDPE matrix. The smallest TPS particles were observed in the ENR-50/LLDPE blend. This might be attributed to the chemical interactions of polar functional groups in ENR and TPS that enhanced their interfacial adhesion. We found that ternary blend of ENR-50/LLDPE/TPS exhibited higher 100 % modulus, tensile strength, hardness, storage modulus, complex viscosity and thermal properties compared with those of ENR-25/LLDPE/TPS and RSS#3/LLDPE/TPS ternary blends. Furthermore, lower melting temperature (T _m) and heat of crystallization of LLDPE (?H) were observed in ternary blend of ENR-50/LLDPE/TPS compared to the other ternary blends. Also, neat TPS exhibited the fastest biodegradation by weight loss during burial in soil for 2 or 6 months, while the ternary blends of NR/LLDPE/TPS exhibited higher weight loss compared to the neat NR and LLDPE. The lower weight loss of the ternary blends with ENR was likely due to the stronger chemical interfacial interactions. This proved that the blend with ENR had lower biodegradability than the blend with unmodified NR.