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Polylactide (PLA) is one of the most important bioplastics worldwide and thus represents a good potential substitute for bead foams made of the fossil-based Polystyrene (PS). However, foaming of PLA comes with a few challenges. One disadvantage of commercially available PLA is its low melt strength and elongation properties, which play an important...
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Context 1
... this process, cleavage takes place at the hydrolyzable groups, such as esters, by water molecules. The structural formula of PLA is shown below in Figure 1, with the functional groups color-coded. hydrolysis, a distinction must be made between two different types, acidic and basic ester hydrolysis. ...
Citations
... Figure 10B demonstrates that the PLA exhibits higher water uptake due to its hydrophilic nature and the presence of specific functional groups, such as hydroxyl and carboxyl groups, that interact with water molecules. 47 PMMA shows lower water absorption compared to PLA because PMMA is less hydrophilic compared to PLA due to its ester functional groups. 41 This might have an F I G U R E 9 Compressive testing of 3D-printed specimens (A) testing setup (B) Compressive strength of neat and blended polymers. ...
This research article focused on the blending of poly(lactic acid)/poly(methyl methacrylate) (PLA/PMMA) polymer materials to overcome PLA's inherent weaknesses, such as low glass transition temperature, brittleness, and lack of melt strength. Consolidated feasible characteristic investigations, such as mechanical, thermal, and aging behavior, were carried out for PLA/PMMA blended polymer materials. Initially, the miscibility of PLA/PMMA blend filaments was prepared at various blend ratios (91/9, 82/18, and 73/27) and samples were printed by fused deposition modeling (FDM). Differential scanning calorimetry (DSC) and Fourier infrared spectroscopy (FTIR) analysis have been utilized to evaluate the glass transition temperature (Tg) and intermolecular interaction, respectively, on blended polymer materials. Experimental tensile, compression, and flexural strength testing were performed on neat polymers and blended polymer composites. Compared to neat PLA materials, blended composites had 13.24% and 19.07% higher flexural and compression strengths. Besides, the interfacial interaction of neat and blended polymers has been done using dynamic mechanical analysis (DMA). Furthermore, Tg, storage modulus, and aging behavior of blended polymer materials have significantly improved over neat PLA materials. Altogether, the development of PMMA/PLA blends as sustainable biomaterials for dental applications aligns with environmental concerns and the need for biocompatible materials in dentistry.
Highlights
Blending of PLA and PMMA helps mitigate the inherent constraints of PLA.
Blended composites exhibited greater compressive and flexural strengths.
Better glass transition temperature and intermolecular interaction.
Excellent thermal stability and water aging imply viable dental biomaterials.
... The followed methodology enabled the fabrication of high-expansion PLA foams with improved thermal insulation and compressive performance. Dreier et al. [147] used reactive extrusion on a twin-screw extruder to modify PLA with dicumyl peroxide as a melt strength enhancer and polycarbodiimide as a hydrolysis stabilizer, in order to protect PLA against thermal degradation and hydrolysis and to improve its melt strength during batch foaming. Li et al. [148] introduced longchain branching structures into PLA by employing soybean oil under the initiation of trace amounts of cyclic peroxide to improve the melt strength of PLA and its crystallization performance during a batch foaming process. ...
The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.
... Due to restrictions and the low CO 2 footprint of PLA [3] it can be a promising alternative to EPS and EPP. There is limited work in the field of biobased bead foams [4][5][6][7][8][9] For example, Nofar et al. focused on a stirred autoclave method to produce expanded PLA [4,[8][9][10]. Another method to produce bead foams is an extrusion process [11,12]. ...
Nowadays, bead foams are of great interest due to their high lightweight potential. The processing of such foams strongly depends on the crystallization and rheological behavior of the polymers used. By blending polymers, these properties can be tailored to obtain beaded foams with low density, small cell size and high cell density. As a bio-based polymer, PLA is of great interest due to its renewable carbon source. PLA suffers from its low thermal and rheological properties, which can be compensated by using blends. The correlation between the PLA/PHBV ratio and the rheological as well as the crystallization behavior was investigated. The use of PHBV as a minor phase significantly changes the rheological properties and increases the crystallization behavior of PLA. These findings were applied to the foam extrusion process to obtain low density bead foams. Bead foams with densities below 100 kg/m³, mean cell sizes below 50 µm and cell densities of 1 × 10⁷ cells/cm³ were obtained.
... The values corresponding to the MC for PLA resins are around 0.5% [75]. The quantification of MC for films produced from PLA is essential since the main form of degradation of PLA occurs by hydrolysis [76][77][78]. Despite the relevance of moisture penetration in evaluating the performance, degradation, and life cycle of polymer products, the available literature on moisture transport in PLA to packaging is still quite limited [79]. ...
Poly (Lactic Acid) (PLA) is considered one of the most promising polymers. However, neat PLA films have limitations. An effective strategy to overcome these problems is incorporating clay or essential oils. Cloisite 30B (C30B) is an organoclay widely used to improve the properties of polymers. Notably, the development of films incorporating Oregano Essential Oil (OEO) has attracted significant attention. Compression molding manufactured neat PLA, PLA/C30B, and PLA/C30B/OEO films in this manuscript. The visual evaluation indicated that the films had a good surface finish, and the films thickness varied between 0.15–0.19 mm. The moisture content increased with the incorporation of C30B and OEO. Optical microscopy showed a good distribution of clay particles. The transparency of the films increased with OEO, while with C30B, it presented greater opacity. Incorporating C30B/OEO in the PLA matrix is a promising film proposal that can be directed to the packaging sector. However, other analyses must be done better to understand the films performance for such an application.
... As shown in Figure 2, the preparation of bead foams is mainly carried out by autoclave foaming and extrusion foaming. Autoclave foaming is a batch process during which polymer pellets are saturated with high pressure gas under temperatures lower than their melting point, and foaming occurs upon rapid depressurization [3,26]. By comparison, extrusion foaming is a continuous process to prepare bead foams in which an additional granulator system is required [9,10,18]. ...
... These results suggest that the saturation condition should be properly selected to control the extent of hydrolysis to produce EPLA beads with the desired cellular morphology and expansion ratio. By compounding PLA with a hydrolysis stabilizer via reactive extrusion, Bonten et al. [26] found that the hydrolysis of PLA during autoclave foaming can be markedly suppressed without compromising the foamability of EPLA beads. ...
... These results suggest that the saturation condition should be properly selected to control the extent of hydrolysis to produce EPLA beads with the desired cellular morphology and expansion ratio. By compounding PLA with a hydrolysis stabilizer via reactive extrusion, Bonten et al. [26] found that the hydrolysis of PLA during autoclave foaming can be markedly suppressed without compromising the foamability of EPLA beads. EPLA beads can also be prepared through extrusion foaming. ...
The diverse physical appearances and wide density range of polymer bead foams offer immense potential in various applications and future advancements. The multiscale and multilevel structural features of bead foams involve many fundamental scientific topics. This review presents a comprehensive overview of recent progress in the preparation and molding techniques of bead foams. Firstly, it gives a comparative analysis on the bead foam characteristics of distinct polymers. Then, a summary and comparison of molding techniques employed for fabricating bead foam parts are provided. Beyond traditional methods like steam-chest molding (SCM) and adhesive-assisted molding (AAM), emerging techniques like in-mold foaming and molding (IMFM) and microwave selective sintering (MSS) are highlighted. Lastly, the bonding mechanisms behind these diverse molding methods are discussed.
... According to the pH-value change curve, within the first two months, the pH values of both PCL and CA8/2 strapping bands decreased below 7.35. It is possible that the degraded PLLA produces small lactate molecules, which make the pH values below the normal range of the human body [37,38]; From 3-14 months, the pH value of CA8/2 was between 7.35 and 7.45. The pH value of PCL strapping bands was slightly higher than 7.45 at the 14th month; From 14 to 18 months, the pH values of the solution of PCL and CA8/2 strapping bands reached 7.33 and 7.26, respectively, It is possible that the dissolution of some acidic oligomers produced by PCL degradation in PBS makes the pH value lower than the normal range of the human body [39,40]. ...
Early fracture fixation is the critical factor in fracture healing. Common internal fracture implants are made of metallic materials, which often affects the imaging quality of CT and MRI. Most patients will choose secondary surgery to remove the internal fixation implants, which causes secondary damage to them. The development of new degradable internal fracture implants has attracted more and more attention from orthopedic surgeons and researchers. Based on these problems, we improved the various properties of medical grade polycaprolactone (PCL) by adding poly(L-lactide) (PLLA). We produced PCL/PLLA strapping bands with different mass ratios by injection molding. We compared the mechanical properties, degradation properties, cell biocompatibility, bone marrow mesenchymal stem cells (BMSCs) adhesion, proliferation, osteogenic differentiation and fracture fixation effect of these strapping bands. The results showed that the tensile strength and yield force of the strapping bands increased with the increase of the content of PLLA. The addition of PLLA could significantly improve the mechanical strength in the early stage and accelerate the degradation rate of the strapping band. PCL/PLLA (80/20) strapping band had no significant cytotoxicity toward rBMSCs and could promote osteogenic differentiation of rBMSCs. The strapping band could ensure femoral fracture healing of beagles in 3 months and didn’t cause damage to the surrounding tissues and main organs. This study will provide some new insights into the biodegradable products of PCL/PLLA blends for internal fixation of fracture.
Graphical Abstract
... This behavior may be disadvantageous when the processing of polymers with melt temperatures at these temperatures is considered. Processing PLA at temperatures of 200 • C in air may lead to thermal oxidation with degradation, due to random chain scission [46][47][48]. ...
... However, the overlap in standard deviations for 170 • C with 1.5 MPa and 2.5 MPa prevent the determination of significant differences. The reduction in both bending modulus and strength with an increasing temperature might be related to the oxidization and degradation of the matrix polymer in air [44,[46][47][48]. This leads to drastically reduced bending moduli, at 2.1 GPa-60% of the raw material-and bending strengths as low as 20 MPa. ...
... Similar effects have been reported in the literature and may be connected to limited fiber-matrix adhesion [36][37][38]. temperature might be related to the oxidization and degradation of the matrix polymer in air [44,[46][47][48]. This leads to drastically reduced bending moduli, at 2.1 GPa-60% of the raw material-and bending strengths as low as 20 MPa. ...
This study investigates the influence of a hot press process on the properties of hemp fiber-reinforced organo sheets. Plain-woven fabric made from hemp staple fiber yarns is used as textile reinforcement, together with a recycled poly-lactic acid (PLA) matrix. Process pressure and temperature are considered with three factor levels for each parameter. The parameter influence is examined based on the B-factor model, which considers the temperature-dependent viscosity of the polymer, as well as the process pressure for the calculation of a dimensionless value. Increasing these parameters theoretically promotes improvements in impregnation. This study found that the considered recycled polymer only allows a narrow corridor to achieve adequate impregnation quality alongside optimal bending properties. Temperatures below 170 °C impede impregnation due to the high melt viscosity, while temperature increases to 185 °C show the first signs of thermal degradation, with reduced bending modulus and strength. A comparison with hemp fiber-reinforced virgin polypropylene, manufactured with identical process parameters, showed that this reduction can be mainly attributed to polymer degradation rather than reduction in fiber properties. The process pressure should be at least 1.5 MPa to allow for sufficient compaction of the textile stack, thus reducing theoretical pore volume content to a minimum.
... As shown in Figure 2, the preparation method of bead foams mainly includes autoclave foaming and extrusion foaming. Autoclave foaming is a batch process, during which polymer pellets are saturated with high pressure gas under temperatures lower than their melting point, and foaming occurs upon rapid depressurization [4,28]. Extrusion foaming is a continuous process to prepare bead foams, which requires additional granulator system [11,12,20]. ...
... These results suggest that the saturation condition should be properly selected to control the extent of hydrolysis to produce EPLA beads with desirable cellular morphology and expansion ratio. By compounding PLA with a hydrolysis stabilizer via reactive extrusion, Bonten et al. [28] found that the hydrolysis of PLA during autoclave foaming could be markedly suppressed without compromising the foamability of EPLA beads. ...
The diverse physical appearances and wide density range of polymer bead foams offer immense potential across various applications and future advancements. The multi-scale and multi-level structural features of bead foams involve many fundamental scientific topics. This review presents a comprehensive overview of recent progress in bead foams preparation and molding techniques. Initially, a comparative analysis is conducted among bead foam characteristics of distinct polymers, based on their unique properties. Subsequently, a summary and comparison of molding processes employed for fabricating bead foam parts are provided. Beyond traditional methods like steam-chest molding (SCM) and adhesive-assisted molding (AAM), emerging techniques like in-mold foaming and molding (IMFM) and microwave selective sintering (MSS) are highlighted. Lastly, the bonding mechanisms behind the diverse molding methods are discussed.
... Degradation of PLA describes any mechanism that results in shortening of the polymer chains and reduction in the molecular weight [37], caused by different factors such as heat, mechanical stress, oxygen, moisture, etc. [33,38,39]. Since melt processing is dominated by the above-mentioned four fundamental parameters (moisture, temperature, residence time, and shear), the total degradation of PLA during melt processing is a combination of thermal, hydrolytic, and thermomechanical degradation: ...
... Nofar et al. [72] used the time to reach a 10% viscosity drop to compare how fast PLA and PBAT degraded. Other researchers [20,37,56,73] used the same test method to successfully study degradation through time, making oscillatory time sweep measurements an interesting method to study thermal, oxidative, and hydrolytic degradation. A disadvantage is that the mechanical stresses on the polymer chains are small in comparison to actual melt processing techniques such as All previously described viscosity-or MFI-measurements use a sample that is collected after processing on an injection molding machine or a single-or twin-screw extruder, which means that the sample is already degraded. ...
... Nofar et al. [72] used the time to reach a 10% viscosity drop to compare how fast PLA and PBAT degraded. Other researchers [20,37,56,73] used the same test method to successfully study degradation through time, making oscillatory time sweep measurements an interesting method to study thermal, oxidative, and hydrolytic degradation. A disadvantage is that the mechanical stresses on the polymer chains are small in comparison to actual melt processing techniques such as extrusion and injection molding; therefore, studying thermomechanical degradation on a parallel plate rheometer is not ideal. ...
This review paper presents an overview of the state of the art on process-induced degradation of poly(lactic acid) (PLA) and the relative importance of different processing variables. The sensitivity of PLA to degradation, especially during melt processing, is considered a significant challenge as it may result in deterioration of its properties. The focus of this review is on degradation during melt processing techniques such as injection molding and extrusion, and therefore it does not deal with biodegradation. Firstly, the general processing and fundamental variables that determine the degradation are discussed. Secondly, the material properties (for example rheological, thermal, and mechanical) are presented that can be used to monitor and quantify the degradation. Thirdly, the effects of different processing variables on the extent of degradation are reviewed. Fourthly, additives are discussed for melt stabilization of PLA. Although current literature reports the degradation reactions and clearly indicates the effect of degradation on PLA's properties, there are still knowledge gaps in how to select and predict the processing conditions that minimize process-induced degradation to save raw materials and time during production.
... Nowadays, various microcellular foaming techniques have been developed, including batch foaming (like autoclave foaming and molded foaming), extrusion foaming and foam injection molding [3]. Notably, bead foaming is a member of the autoclave foaming process [4], which is the first commercialized foaming technology and the most commonly used foaming method in our daily bead foam products (like expanded polypropylene (EPP) [5], expanded polystyrene (EPS) [6], expanded polylactide (EPLA) [7], expanded thermoplastic polyurethane (ETPU) [8] and expanded polycarbonate (EPC) [9]). Because the biggest advantage of bead foaming is that it can produce complex 3D components and has excellent structural controllability [10]. ...
... Steam-chest mold is widely used in the industrialized manufacture of EPP, EPS, EPLA and ETPU foams [5][6][7][8], by which the expanded bead foams can be molded into different products with 3D complex shapes for packaging, thermal insulation, etc. In general, the diffusion of polymer chains will happen during the steam-chest molding process (because the high-temperature steam can work as heating medium), which can drive the entanglement of chains and even crystallization [32], and then form strong inter-bead bonding across the skin regions. ...
Expanded polypropylene (EPP) foam, is widely used in the field of packaging, automotive and toys, etc., and its preparation process is mainly obtained by semi-continuous autoclave bead foaming. Because foamed beads can be fabricated into complex 3D components and have excellent structural controllability. In contrast, a novel method for continuous production of expanded PP foamed beads is developed via supercritical CO2 (scCO2) extrusion foaming coupling with a wind cutting device, then the real-time cell growth and pelletizing processes of the extruded bead foams are revealed by using a high-definition camera for the first time. Interestingly, the processes of solubilization, compounding, pelletizing and foaming can happen in a one-step process through the above method, which can greatly shorten the production time, save energy consumption, and promote structural diversification. Besides, the transformation of foamed beads, like spherical, cylindrical and dumbbell-shaped, can be achieved by adjusting the pelletizing speeds based on the Barus effect. Furthermore, the steam-chest molding of the extruded foamed beads into foamed product shows that it is possible to sinter the beads at a low steam pressure (2.0 bar). In addition, the as-prepared foamed products can withstand constantly treading by an adult, and the surface of the foamed product rises only ~7.5 °C after prolonged heating, illustrating the outstanding mechanical and thermal insulation properties. Finally, it can be imagined that the related technical route has important scientific significance for the development of other polymeric bead foaming systems.
