Poly Lactic Acid Foams Research Articles

Preparation of biomass fiber/polylactic acid foam using an oven-type free foaming method for energy savings and performance enhancement

Given the inherent challenges of low melt strength and slow crystallization rate associated with polylactic acid (PLA), this study introduces a sustainable and efficacious approach to enhance PLA crystallization utilizing biomass tomato peel pomace powder (TP) as a heterogeneous nucleating agent. ZnO-modified azodicarbonamide (ADC) was used as the chemical blowing agent. The blends were prepared with the aid of a torque rheometer, and TP/PLA composite foams were successfully prepared by the oven-type free foaming method. The empirical results demonstrate that the TP/PLA composite foam exhibits reduced processing requirements and superior comprehensive properties compared to pure PLA foam. Specifically, the composite containing 5 wt% TP achieved optimal foaming performance with 3 phr blowing agents and a foaming duration of 10 min. Furthermore, the annealing treatment markedly enhanced the compression modulus and strength of the foams. Under annealing conditions of 110 °C for 30 min, the compressive strength of the foam increased by 483.5 % relative to the untreated sample. The development of this composite foam signifies a novel direction for energy-efficient performance enhancement and holds significant potential for applications in building insulation and packaging industries.

Investigating Polylactic Acid Foam–Plant Fiber Composites for Sound Absorption and Insulation

Investigating Polylactic Acid Foam–Plant Fiber Composites for Sound Absorption and Insulation

Tuning pore size and density of rigid polylactic acid foams through thermally induced phase separation and optimization using response surface methodology

Rigid polylactic acid (PLA) foams fabricated via thermally induced phase separation (TIPS) utilizing a ternary solution of PLA, Tetrahydrofuran (THF), and water. The PLA gels were stabilized mechanically by the substituting of the THF/water solvent mixture with ethanol as non-solvent and subsequently vacuum dried. A comprehensive characterization of PLA foams was achieved by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD) and Brunauer–Emmett–Teller (BET) analyses. The BET area obtained in the PLA foam is up to 18.76 m2/g. The Response Surface Methodology (RSM) was utilized to assess the impacts of four independent variables (polymer concentration, solvent composition, quench temperature, and aging time) on the pore size and density of PLA foam. The experimental findings demonstrated that the fabrication parameters could be fine-tuned to govern the morphology of the pores, comprising their size and density. The optimal values of parameters for cell size were identified by RSM to be 8.96 (wt%), 91.60 (w/w), 5.50 °C, and 3.86 h for the optimum cell size of 37.96 µm (37.78 by Genetic Algorithm). Optimum density by RSM 88.88 mgr/cm3 (88.38 mgr/cm3 by Genetic Algorithm) was obtained at 5.00 (wt%), 89.33 (w/w), 14.40 °C and 2.65 h.

Preparation of tomato peel pomace powder/polylactic acid foams under supercritical CO2 conditions: Improvements in cell structure and foaming behavior

Polylactic acid (PLA) is an eco-friendly material that can help address the problems of petroleum depletion and pollution. Blending renewable biomass materials with PLA to create composite foams with a tunable pore structure, superior performance, and low cost is a green technique for improving the pore structure and mechanical characteristics of single PLA foams. PLA/TP composites were created using melted tomato peel pomace powder (TP), which has a lamellar structure, as a reinforcing agent. Then, the relationship between the vesicle structure, morphology, and properties of the PLA/TP composite foams produced through supercritical CO2 intermittent foaming were investigated. The findings revealed that TP considerably enhanced the rheological characteristics and crystalline behavior of PLA. The PLA/TP composite foam had a better cell structure, compression characteristics, and wettability than pure PLA. The expansion ratio of the PLA/TP composite could reach 18.8, and its thermal conductivity decreased from 174.2 mW/m·K at 100 °C to 57.8 mW/m·K at 120 °C. Furthermore, annealing before foaming decreased the average composite foam blister size from 110.09 to 66.53 μm, and the annealing process also improved compression performance. This study contributes to solving environmental difficulties and creating PLA foams with controlled bubble structures, uniform bubble sizes, and outstanding overall performance.

Insights into heterogeneous surface induced bubble nucleation mechanisms in cellulose reinforced polylactic acid foams

As the most abundant natural homo-polymer, cellulose has the potential to enhance polymer properties reducing the cost of raw materials. In this work, the carboxylate cellulose nanofiber (CNF-C) was selected to modify polylactic acid (PLA) foams, and the density functional theory was constructed to help analyze the foaming mechanism quantitatively. The theoretical results showed that the ordered structure, the carboxyl and the hydroxyl of CNF-C were more conducive to providing much stronger CO2 adsorption for bubble nucleation, where the predicted critical bubble size decreased and the cell density increased with the addition of CNF-C. The experimental results revealed that the CNF-C promoted the rheological properties and crystallization behaviors of PLA samples, the PLA/CNF-C foams were characterized with uniform structures, the average cell size decreased from 21.39 μm to 0.19 μm, and the cell number density increased from 2.65×1010cell/cm3 to 2.30×1014cell/cm3. Those improvements resulted in an increase of 394.0 % for the compressive strength of the prepared foams. Generally, the high-performance PLA/CNF-C foams were fabricated successfully without compromising the properties of bio-based and biodegradable, the foaming mechanism was analyzed combining theoretical results with experimental data, and it was believed to provide a guide for cellulose reinforcing biodegradable polymer materials.

Development of toughened and heat-resistant biodegradable injection-molded polylactide acid-based blend foams via enhancing interfacial bonding and PLA phase crystallization

Polylactic acid (PLA) foam is gaining increased attention as a biodegradable alternative to traditional petroleum-based plastic foams, which pose significant environmental pollution issues post-use. However, its potential application is greatly limited by inherent shortcomings such as brittleness and diminished heat resistance post-melting. Herein, high-performance biodegradable PLA/poly(butylene succinate) (PBS) blend foams with well-defined cell structure, high ductility, and enhanced heat resistance were fabricated using a core-back foam injection molding (FIM) process coupled with a straightforward annealing procedure. To enhance compatibility and tailor the dispersed phase morphology into a more fibrillar structure, an epoxy-functional chain extender (ADR) was incorporated. This addition resulted in a substantial increase in the notched impact strength, elevating it to 7.0 kJ/m2, compared to the mere 1.5 kJ/m2 of unmodified PLA foam. Moreover, with the inclusion of 1.0 phr ADR, the notched impact strength of the foam post-annealing soared to 20.7 kJ/m2, a 13.8-fold enhancement compared to pure PLA foam. The formation of a uniformly distributed and interlocked “shish-kebab" crystal structure in the blend facilitated effective stress transfer and distribution, leading to shear yield in the PLA matrix. Additionally, the heat deflection temperature of the annealed blend foam showed a significant increase significantly to 94.7 °C, in contrast to the mere 55.6 °C of pure PLA foam. This study demonstrates a viable and feasible strategy for preparing fully biodegradable PLA foams with high-toughness and heat resistance.

Effect of the interchain interaction on the crystallization kinetics and crystal structure of polylactic acid under nitrogen

In order to prepare polylactic acid (PLA) foam material with excellent performance by utilizing nitrogen (N2), the crystallization behavior of PLA under N2 has been studied.

Structure-tunable polyether block amide/polylactic acid foams with shape memory performance using supercritical CO2 foaming

Lightweight and structure-tunable shape memory polyether block amide (PEBA)/polylactic acid (PLA) foams were prepared using an efficient, green microcellular foaming technology. PLA is conducive to increasing the shape fixing ratio of PEBA/PLA, whereas PEBA is favorable for enhancing the shape recovery ratio. The shape memory performance and mechanical properties of PEBA/PLA foams can be modified by adjusting the expansion ratio and cellular structure. When the blend ratio of PEBA/PLA is 80/20, the expansion ratio above 6.4 can enhance both the shape fixing ratio and the shape recovery ratio. A cell size of 23.3–43.6 µm significantly improves the shape fixing ratio, while a cell size of 7.0–10.4 µm is advantageous for enhancing the shape recovery ratio. PEBA/PLA foams have a density of 0.17 g/cm3 and shape memory properties with a shape fixing ratio of 87.2% and shape recovery ratio of 90.5%.

High-Expansion Open-Cell Polylactide Foams Prepared by Microcellular Foaming Based on Stereocomplexation Mechanism with Outstanding Oil-Water Separation.

Biodegradable polylactic acid (PLA) foams with open-cell structures are good candidates for oil-water separation. However, the foaming of PLA with high-expansion and uniform cell morphology by the traditional supercritical carbon dioxide microcellular foaming method remains a big challenge due to its low melting strength. Herein, a green facile strategy for the fabrication of open-cell fully biodegradable PLA-based foams is proposed by introducing the unique stereocomplexation mechanism between PLLA and synthesized star-shaped PDLA for the first time. A series of star-shaped PDLA with eight arms (8-s-PDLA) was synthesized with different molecular weights and added into the PLLA as modifiers. PLLA/8-s-PDLA foams with open-cells structure and high expansion ratios were fabricated by microcellular foaming with green supercritical carbon dioxide. In detail, the influences of induced 8-s-PDLA on the crystallization behavior, rheological properties, cell morphology and consequential oil-water separation performance of PLA-based foam were investigated systemically. The addition of 8-s-PDLA induced the formation of SC-PLA, enhancing crystallization by acting as nucleation sites and improving the melting strength through acting as physical cross-linking points. The further microcellular foaming of PLLA/8-s-PDLA resulted in open-cell foams of high porosity and high expansion ratios. With an optimized foaming condition, the PLLA/8-s-PDLA-13K foam exhibited an average cell size of about 61.7 μm and expansion ratio of 24. Furthermore, due to the high porosity of the interconnected open cells, the high-absorption performance of the carbon tetrachloride was up to 37 g/g. This work provides a facile green fabrication strategy for the development of environmentally friendly PLA foams with stable open-cell structures and high expansion ratios for oil-water separation.

Preparation of superhydrophobic, green, and eco-friendly modified polylactic acid foams for separation oil from water

Developing a facile and green strategy to fabricate polymer foams with super hydrophobicity and eco-friendliness for large-scale oil-water separation remains a challenge. In this study, biocompatible polylactic acid polymer foam modified by nanochitosan and stearic acid was used to remove petroleum and organic contaminants in water. All three materials used to prepare and modify this foam are green and inexpensive. F4d foam (prepared by solvent displacement method) and F8d foam (prepared by freeze dryer) can selectively remove oil pollutants in water with a contact angle of 164.01° and 168.51°, respectively. The maximum absorption capacity of oil pollutants by F4d and F8d are related to chloroform with values of 32.7 g/g and 48.51 g/g, respectively. Also, the minimum absorption capacity is related to n-hexane with values of 24.83 g/g and 32.06 g/g. The absorption percentage range of F4d and F8d foams after 15 cycles of absorption-desorption for chloroform is 82.56 % and 87.81 %, respectively, and for n-hexane, is 77.28 % and 85.99 %, respectively. During the continuous water-oil pumping test, the efficiency of foam can be maintained for >15 h, which shows promising hope for large-scale oil pollution cleaning.

Polylactic Acid Chemical Foaming Assisted by Solid-State Processing: Solid-State Shear Pulverization and Cryogenic Milling.

A chemical foaming process of polylactic acid (PLA) was developed via the solid-state processing methods of solid-state shear pulverization (SSSP) and cryogenic milling. Based on the ability of solid-state processing to enhance the crystallization kinetics of PLA, chemical foaming agents (CFA) are first compounded before foaming via compression molding. Specifically, the effects of the pre-foaming solid-state processing method and CFA concentration were investigated. Density reduction, mechanical properties, thermal behavior, and cell density of PLA foams are characterized. Solid-state processing of PLA before foaming greatly increases the extent of PLA foaming by achieving void fractions approximately twice that of the control foams. PLA's improved ability to crystallize is displayed through both dynamic mechanical analysis and differential scanning calorimetry. The solid-state-processed foams display superior mechanical robustness and undergo low stress relaxation. The cell density of the PLA foams also increases with solid-state processing, especially through SSSP. Additionally, crosslinking of PLA during the pre-foaming processing step is found to result in the greatest enhancement of crystallization but decreased void fraction and foam effectiveness. Overall, SSSP and cryogenic milling show significant promise in improving chemical foaming in alternative biopolymers.

Foaming of Polylactic Acid/Cellulose Nanocrystal Composites: Pickering Emulsion Templating for High-Homogeneity Filler Dispersions

Polylactic acid (PLA)/cellulose nanocrystal (CNC) composite foams have attracted much attention due to their biodegradability and potential to replace petroleum-based foams. However, the dispersion of (unmodified) CNCs in PLA remains challenging. Here, we used the Pickering emulsion templating method of unmodified CNCs to stabilize PLA microspheres and prepare a concentrated masterbatch. This masterbatch was used in conventional melt blending of pristine PLA to obtain well-dispersed CNCs in PLA with a CNC loading of up to 5 wt %. In comparison, PLA/CNC composites prepared by direct melt blending of CNCs in PLA showed visual agglomerates of CNCs. PLA/CNC composites were batch foamed with CO2 as a physical blowing agent. We demonstrate that the good CNC dispersion obtained by the Pickering emulsion route is favorable for preparing PLA foams with smaller and more uniform cell sizes and with a higher cell density. These results demonstrate that the Pickering emulsion approach to prepare CNC masterbatches for subsequent dispersion in thermoplastics by conventional processing seems promising for numerous industrial applications.

Preparation of high-expansion open-cell polylactic acid foam with superior oil-water separation performance

Environmentally friendly and non-toxic polylactic acid (PLA) foam has shown great application prospects in heat preservation, adsorption and other fields. However, it is still challenging to prepare high-expansion PLA foam. Herein, a cooling batch foaming process under supercritical CO2 (sc-CO2), based on pre-melted non-crystalline state, was proposed to prepare PLA foams with high expansion ratio. The CO2 dissolved in the polymer melt will lower the crystallization temperature of PLA. Due to the lack of crystallization, the foaming temperature of PLA can be reduced, which increases the CO2 saturation and helps foam. When foaming is triggered before crystallization, ultrahigh expansion foam can be produced. Based on pre-melting treatment, the maximum expansion ratio of PLA has reached 59.7-fold. At the same time, an open-pore structure is produced by this method, which can selectively absorb oil from water. In addition, the adsorption capacity of CCl4 reaches 15 g/g, and there is no significant attenuation in 20 adsorption-desorption cycles. This work provides a green, solvent-free method to prepare biodegradable oil-adsorbing foam.

Compostable, fully biobased foams using PLA and micro cellulose for zero energy buildings

Ecological, health and environmental concerns are driving the need for bio-resourced foams for the building industry. In this paper, we examine foams made from polylactic acid (PLA) and micro cellulose fibrils (MCF). To ensure no volatile organic compounds in the foam, supercritical CO2 (sc-CO2) physical foaming of melt mixed systems was conducted. Mechanical and thermal conductivity properties were determined and applied to a net zero energy model house. The results showed that MCF had a concentration dependent impact on the foams. First structurally, the presence of MCF led to an initial increase followed by a decrease of open porosity, higher bulk density, lower expansion ratios and cell size. Differential Scanning Calorimetry and Scanning Electron Microscopy revealed that MCF decreased the glass transition of PLA allowing for a decrease in cell wall thickness when MCF was added. The mechanical performance initially increased with MCF and then decreased. This trend was mimicked by thermal insulation which initially improved. Biodegradation tests showed that the presence of cellulose in PLA improved the compostability of the foams. A maximum comparative mineralization of 95% was obtained for the PLA foam with 3 wt.% MCF when expressed as a fractional percentage of the pure cellulose reference. Energy simulations run on a model house showed that relative to an insulation of polyurethane, the bio-resourced foams led to no more than a 12% increase in heating and cooling. The energy efficiency of the foams was best at low MCF fractions.

Density Measurement, Tensile and Morphology Properties of Polylactic Acid Biocomposites Foam Reinforced with Different Kenaf Filler Loading

This paper investigates the performance of polylactic acid (PLA)/kenaf fiber (KF) composites foamed using azodicarbonamide (AC) in terms of density, mechanical, and morphology aspects. The KF loading was varied in the range of 20-40 wt. %. The mixtures were compounded using a co-rotating twin-screw extruder and followed by hotcold pressing in order to prepare test specimens for characterization. The density of the foamed composites showed a fluctuate trend where it decreased at lower KF loading (0-20 wt. %) while further increasing fiber loading (30-40 wt. %) resulted in an increase of the composites density. Tensile results showed that the optimum loading of KF was achieved at 30 wt. % with an improvement of 135, 153, and 27.6% for stress at yield, strain at break and Young modulus, respectively, as compared to neat PLA foam. Field emission scanning electron microscope (FESEM) micrographs confirmed the fiber dispersion and morphological interaction between PLA and KF components.

Foaming of PLA Composites by Supercritical Fluid-Assisted Processes: A Review.

Polylactic acid (PLA) is a well-known and commercially available biopolymer that can be produced from different sources. Its different characteristics generated a great deal of interest in various industrial fields. Besides, its use as a polymer matrix for foam production has increased in recent years. With the rise of technologies that seek to reduce the negative environmental impact of processes, chemical foaming agents are being substituted by physical agents, primarily supercritical fluids (SCFs). Currently, the mass production of low-density PLA foams with a uniform cell morphology using SCFs as blowing agents is a challenge. This is mainly due to the low melt strength of PLA and its slow crystallization kinetics. Among the different options to improve the PLA characteristics, compounding it with different types of fillers has great potential. This strategy does not only have foaming advantages, but can also improve the performances of the final composites, regardless of the implemented foaming process, i.e., batch, injection molding, and extrusion. In addition, the operating conditions and the characteristics of the fillers, such as their size, shape factor, and surface chemistry, play an important role in the final foam morphology. This article proposes a critical review on the different SCF-assisted processes and effects of operating conditions and fillers on foaming of PLA composites.

Cell structure and mechanical properties of microcellular PLA foams prepared via autoclave constrained foaming

Microcellular polylactic acid (PLA) foams with various cell size and cell morphologies were prepared using supercritical carbon dioxide (sc-CO2) solid-state foaming to investigate the relationship between the cell structure and mechanical properties. Constrained foaming was used and a wide range of cell structures with a constant porosity of ∼75% by tuning saturation pressure (8–24 MPa) was developed. Experiments varying the saturation pressure while holding other variables’ constant show that the mean cell size and the mean cell wall thickness decreased, while the cell density and the open porosity increased with increase of pressure. Tensile modulus of PLA foams decreased with increasing the saturation pressure, but the specific tensile modulus of PLA foams was still 15–80% higher than that of solid PLA. Tensile strength and elongation at break first increased with increasing saturation pressure up to 16 MPa and then decreased with further increasing saturation pressure (20 MPa and 24 MPa) at which opened-cell structure produced. Compressive modulus, compressive strength, and compressive yield stress also followed the same variation trend. The results indicated that not only cell size plays an important role in properties of PLA foams but also cell morphology can influence these properties significantly.

Highly expanded fine-cell foam of polylactide/polyhydroxyalkanoate/nano-fibrillated polytetrafluoroethylene composites blown with mold-opening injection molding

To manufacture entirely biodegradable polylactic acid (PLA) foam with a high expansion ratio and a fine-cell structure, we attempted to design economically viable material recipe as well as the injection foam molding (FIM) process. It is well-known that PLA foam featuring high expansion and fine cells is challenging to achieve on FIM technique due to its intrinsically low melt strength. To overcome the inferior foaming characteristics of PLA in this study, nano-fibrils of polytetrafluoroethylene (PTFE) were added expecting an increase of molecular chain entanglements. Another bio-based biodegradable polymer, polyhydroxyalkanoate (PHA) was also blended with PLA to improve the impact strength of the final foams. High-pressure FIM process combined with mold-opening technique was performed to make highly expanded PLA foams with varied material recipes. A constant amount (0.6 wt%) of supercritical nitrogen was injected into FIM system and uniformly mixed with various polymer compositions. The gas-laden melt was injected into the mold cavity to create the foamed PLA samples. Finally, we could demonstrate that it is clearly feasible to manufacture entirely biodegradable PLA foams having a high expansion ratio and a desirable cellular structure using an advanced FIM process.

Mechanical Behaviour of Polylactic Acid Foam as Insulation Under Increasing Temperature

Abstract Measures to increase the share of renewables in heat generation, combined with increased energy efficiency provide a direct emissions reduction on the heating sector. Energy efficiency measures, as well as the role-out of sustainable heating technologies such as district heating networks have one key actor: insulation. However, state of the art insulating materials such as polyurethane or polystyrene have severe environmental drawbacks incompatible with today’s transition to the circular economy, and are the Achilles’ heel of the sector in terms of sustainability. Biobased and biodegradable polylactic acid (PLA) foam could be a promising replacement for fossil-based polymeric insulating foams. This study provides data on the mechanical behaviour of expanded PLA foam under different temperatures, which will help to assess its potential use as insulation where the foam is subject to heat.

Strong and thermally insulating polylactic acid/glass fiber composite foam fabricated by supercritical carbon dioxide foaming

Environmental friendly and non-toxic polylactic acid (PLA) foam exhibits a promising perspective in many areas. However, PLA shows very poor foaming ability. Herein, silane-modified glass fiber (GF) was compounded with PLA to improve its foaming ability. Thanks to the increased melt viscoelasticity and melt strength, and the enhanced crystallization by adding GF, PLA/GF composites show dramatically improved foaming ability, characterized by widened processing window, increased expansion ratio, and improved cellular uniformity. Compared with pure PLA foam, PLA/GF composite foam shows dramatically enhanced mechanical properties in compressive strength and modulus. For foams with the same expansion ratio of 20-fold, the incorporation of 10 wt% GF led to increased compressive strength and modulus by 44.8% and 92.0%, respectively. The PLA/GF composite foam with an expansion ratio of 24.2-fold has a low thermal conductivity of 31.4 mW/m·K, which is comparable with the excellent thermal insulation performance of commercial polymer foams.