Sándor K. Jakab
58185583500
Publications - 13
Optimal design of agro-residue filled poly(lactic acid) biocomposites using an integrated CRITIC-CoCoSo multi-criteria decision-making approach
Publication Name: Scientific Reports
Publication Date: 2025-12-01
Volume: 15
Issue: 1
Page Range: Unknown
Description:
In recent years, there has been a rise in environmental awareness, leading to increased efforts to develop eco-friendly materials as alternatives to petroleum-based polymers. This study examined the performance optimization of poly(lactic acid) (PLA) biocomposites filled with agricultural byproducts at concentrations ranging from 0 to 20% by weight, highlighting their potential as substitutes for commodity plastics. The agro-residues used as fillers were flax seed meal and rapeseed straw. A hybrid decision-making algorithm was proposed, utilizing the “criteria importance through inter-criteria correlation” (CRITIC) alongside the “combined compromise solution” (CoCoSo), aimed at identifying the optimal alternative among the evaluated samples. The algorithm considered several attributes, including mechanical traits evaluated via tensile, flexural, and impact tests, hardness, water absorption, biodegradation, and production cost. The findings revealed that the strength properties, including tensile, flexural, impact, and water absorption, were most advantageous for neat PLA. In contrast, the highest modulus values were recorded for the biocomposite filled with 20 wt% rapeseed straw. The biocomposites exhibit increased hardness as agro-waste content rose, with the highest hardness observed in the biocomposite filled with 20 wt% flax seed meal. The study on biodegradation indicates that a higher content of agro-waste promotes disintegration, with flax seed meal emerging as the most effective additive in this context. The findings show that adding various agricultural byproducts in varying amounts affects the evaluated properties differently. Hence, the hybrid CRITIC-CoCoSo optimization approach is utilized to choose the optimal biocomposite. The findings show that the biocomposite with 20 wt% rapeseed straw demonstrated optimal physico-mechanical and biodegradation properties, making it a promising eco-friendly alternative for future applications.
Open Access: Yes
Automotive Application of Chemically Foamed rPET
Publication Name: Polymers
Publication Date: 2025-05-01
Volume: 17
Issue: 9
Page Range: Unknown
Description:
This study investigated the automotive applicability of parts produced from a newly developed foamed recycled polyethylene terephthalate (rPET). The injection molded part contained a combination of both endothermic and exothermic foaming agents and phosphorus (Exolit OP 1240) (OP)- and melamine polyphosphate (MPP)-based flame retardant agents. The parts were produced using a breathing mold technique to achieve a suitable level of foaming. The aim was to produce lighter parts made of recycled material that also complied with the fire safety automotive industry standards. Computer tomographic scans revealed the foam structure formed successfully, which contributed to an improved strength-to-weight ratio. The scans further showcased that larger cells tended to form in the thicker areas within the part, while smaller cells generally formed in the thinner areas. Finite element simulations showed that the large cell formation in the thicker parts had no effect on the part’s load bearing property, and there were not stress concentration points after the boundary conditions were defined. The sample produced from the material was determined to be a possible replacement of small-sized automotive components.
Open Access: Yes
Synergistic effects of annealing heat treatment and lignocellulose fiber incorporation on the thermal, mechanical, and water absorption properties of poly(lactic acid)-based biocomposites
Publication Name: Polymer Composites
Publication Date: 2025-10-10
Volume: 46
Issue: 14
Page Range: 12790-12804
Description:
This study investigates the effect of annealing heat treatment on polymer composites composed entirely of biodegradable components. Poly(lactic acid) (PLA) was used as the matrix material paired with three different types of commercial lignocellulose fibers of varying sizes. Composites containing 10 wt.% fibers were processed through extrusion followed by injection molding. The amorphous (unannealed) and semi-crystalline (annealed) samples were characterized for their morphological, thermal, mechanical, and water absorption properties. Scanning electron microscopic analysis revealed a homogenous distribution of cellulose fibers within the PLA matrix, even though the composite with the smallest fiber size exhibited slight agglomeration. Differential scanning calorimetric measurements indicated that the annealing heat treatment successfully induced crystallization, with the filler particles capable of increasing the extent of crystallinity formed during the annealing heat treatment from 28% to 36%. Based on the tensile tests, as a result of annealing heat treatment, the composites' strength increased from 48–50 to 53–56 MPa, while their Young's modulus increased from 3.1 GPa to 3.3-3.5 GPa. The Charpy impact tests also revealed an enhanced toughness for the samples exposed to the annealing heat treatment. In terms of water absorption, annealing enhanced the hydrophobic nature of PLA. In addition, the semi-crystalline structure formed during the heat treatment also inhibited the highly hydrophilic cellulose fibers from absorbing as much moisture as they did when incorporated inside amorphous PLA; cellulose fibers embedded in the semi-crystalline PLA matrix consequently exhibited less moisture absorption than the ones in amorphous PLA. Highlights: Through annealing, crystallinity was developed in PLA/lignocellulose composites. Lignocellulose fibers facilitated crystallization by acting as a nucleating agent. Crystallized biocomposites exhibited superior mechanical properties Crystalline segments hindered the water absorption of embedded lignocellulose.
Open Access: Yes
DOI: 10.1002/pc.29898
Use of Hybrid Flame Retardants in Chemically Foamed rPET Blends
Publication Name: Crystals
Publication Date: 2025-01-01
Volume: 15
Issue: 1
Page Range: Unknown
Description:
The foamed structure of recycled polyethylene-terephthalate (rPET) is a promising solution for industrial applications; however, the remedy for its inherent melt-dripping property is still a challenging topic. In our research, we were able to improve the flame retardancy of the endothermic–exothermic hybrid rPET foam by adding a different mixture of flame retardants to the formula. Three different kinds of halogen-free flame retardant agents were used: ammonium polyphosphate-based Exolit AP 422 (AP), organic aluminum phosphate in the form of Exolit OP 1240 (OP), and Budit 342 containing melamine polyphosphate (MPP). The hybrid flame retardant mixture, by combining the swelling and charring mechanism, increased the flame retardancy of the samples. The sample made with 15 phr OP and 5 phr MPP displayed outstanding performance, where five samples were capable of self-extinguishing in 5 s, while only slightly decreasing the tensile and flexural strength properties and simultaneously increasing the Young and flexural modulus compared to the reference sample. The addition of MPP reduced the porosity in many cases, while preventing cell coalescence. Our results prove that the hybrid flame retardant agent frameworks efficiently increase the flame retardancy of rPET foams, facilitating their application in industrial sectors such as the aerospace, packaging, renewable energy, and automotive industries to realize sustainability goals. The utilization of halogen-free flame retardants is beneficial for better air quality, reducing toxic gas and smoke emissions.
Open Access: Yes
Effect of filament humidity on the properties of material extrusion 3D-printed acrylonitrile butadiene styrene/hexagonal boron nitride composites
Publication Name: Emergent Materials
Publication Date: 2025-01-01
Volume: Unknown
Issue: Unknown
Page Range: Unknown
Description:
This study investigates the effect of filament moisture content on material extrusion (MEX) 3D-printed composites using acrylonitrile butadiene styrene (ABS) as the polymer matrix and 0–10 vol% hexagonal boron nitride (BN) as reinforcement. ABS/BN composites were prepared through batchwise compounding and extruded into MEX-suitable filaments. The filaments were conditioned at 30 °C and 10% or 90% relative humidity (RH) before/during direct feeding into the 3D printer. Specimens were fabricated with raster angles parallel (0°) and perpendicular (90°) to their length. Micro- and macrostructural analyses using scanning electron microscopy and computed tomography revealed intensive void formation, especially in BN-filled composites 3D-printed from humid filaments. This was attributed to BN acting as a physical barrier, hindering the outgassing of evaporated water during 3D printing. Mechanical properties were evaluated using tensile and Charpy impact tests. Based on the tensile test results, neat ABS was the least sensitive to filament moisture, with tensile strength at 0° raster angle dropping from 40.5 MPa to 36.7 MPa as storage RH was increased from 10 to 90%. For composites with 10 vol% BN loading, tensile strength dropped from 34.1 MPa to 22.3 MPa. Charpy impact strength exhibited similar reductions, ascribed to the porous structure of the BN-filled composites caused by the evaporated moisture. Thermal conductivity was also examined, showing slightly superior performance for samples 3D-printed from filaments stored in less humid conditions. For unfilled ABS, the conductivity slightly decreased from 0.188 to 0.185 W/mK, while for 10 vol% BN-filled composite, it dropped from 0.778 to 0.617 W/mK.
Open Access: Yes
Influence of environmental humidity during filament storage on the structural and mechanical properties of material extrusion 3D-printed poly(lactic acid) parts
Publication Name: Results in Engineering
Publication Date: 2024-12-01
Volume: 24
Issue: Unknown
Page Range: Unknown
Description:
Material extrusion (MEX) is one of the most widely used additive manufacturing techniques these days. This study investigates how the properties of MEX 3D-printed objects depend on the relative humidity (RH) conditions in which filaments are stored before and during the manufacturing process. Poly(lactic acid) (PLA) filament was drawn directly from a humidity-controlled chamber into the MEX 3D printer's nozzle. For each set of samples, the filaments were conditioned under different RH conditions, ranging from 10 % to 90 %. The macrostructure of the fabricated products was characterized using computed tomography, revealing increased porosity at higher RH values (from 0.84 % to 4.42 %). The increased porosity at higher storage RH is attributed to under-extrusion and volatile entrapment due to excess moisture. With growing storage RH, the melt flow rate of PLA also gradually increased, indicating a plasticizing effect of humidity on the biopolymer. Gel permeation chromatography and differential scanning calorimetry analyses were conducted to determine whether hydrolytic chain scission took place when PLA was processed in the presence of excessive moisture. Neither measurement indicated any considerable alteration in molecular integrity and crystalline structure as a function of storage RH. Mechanical tests, however, revealed a reduced load-bearing capacity of the manufactured PLA specimens. Flexural strength decreased from 103.0 to 99.6 MPa, and the impact strength dropped from 18.2 to 16.2 kJ/m2, which is ascribed to the increasing size of pores inside the specimens with increasing storage RH. These findings should be taken into account when designing and processing PLA products by MEX-based additive manufacturing.
Open Access: Yes
Selection of straw waste reinforced sustainable polymer composite using a multi-criteria decision-making approach
Publication Name: Biomass Conversion and Biorefinery
Publication Date: 2024-09-01
Volume: 14
Issue: 17
Page Range: 21007-21017
Description:
The valorization of straw waste as a sustainable and eco-friendly resource in polymer composites is critical for resource recycling and environmental preservation. Therefore, many research works are being carried out regarding the development of wheat straw-based polymer composites to identify the reinforcing potential of these sustainable resources. In this study, three different sizes of wheat straw fibers (60–120 mesh, 35–60 mesh, and 18–35 mesh) were used, and their different ratios (0, 2.5, 5, 10, and 20% by weight) were systematically investigated for the physical and mechanical properties of polypropylene-based sustainable composites. The results indicated that the evaluated composites’ properties are strongly dependent on the quantity and size of the utilized wheat straw. Therefore, a preference selection index was applied to rank the developed sustainable polymer composites to select the best composition. Various properties of the composite materials were considered as criteria for ranking the alternatives, namely tensile strength and modulus, flexural stress at conventional deflection and flexural modulus, impact strength, density, water absorption, material cost, and carbon footprint. The decision-making analysis suggests the alternative with wheat straw content of 20 wt.% (35–60 mesh size) dominating the performance by maximizing the beneficial criteria and minimizing the non-beneficial criteria, making it the most suitable alternative. This study will significantly help formulation designers to deal with the amount and size issues when developing polymeric composites.
Open Access: Yes
Agricultural by-product filled poly(lactic acid) biocomposites with enhanced biodegradability: The effect of flax seed meal and rapeseed straw
Publication Name: Composites Part C Open Access
Publication Date: 2024-07-01
Volume: 14
Issue: Unknown
Page Range: Unknown
Description:
The purpose of this research was to develop “green” materials by combining poly(lactic acid) (PLA) with two agricultural by-products, namely flax seed meal (FSM) and rapeseed straw (RSS). The natural fillers (0–20 wt.%) were mixed with PLA through extrusion and then injection molded into specimens. The samples were analyzed for their thermal, morphological, mechanical, and physical features and biodegradability. Thermal properties and crystallinity were analyzed using Differential Scanning Calorimetry (DSC), while the morphology was investigated by Scanning Electron Microscopy (SEM). Mechanical properties were characterized through tensile, flexural, and impact measurements, while surface hardness was evaluated by Shore D tests. Water absorption and biodegradability of the samples were also examined. DSC measurements revealed a nucleating effect of both bio-fillers. Based on the tensile tests, major improvement in stiffness was found with the biocomposites having up to ∼16 % higher Young's modulus than neat PLA (2.5 GPa). It came, however, at the cost of tensile strength, which decreased from 56 to 51 MPa even in the presence of the lowest amount (2.5 wt.%) of FSM. Loss in strength was due to the limited adhesion between the components, as also supported by SEM images. The hardness slightly (1–2 %) improved in the presence of even 2.5 wt.% bio-filler and it remained at that level at higher filler loading as well. Laboratory-scale composting revealed that both fillers facilitated biodegradation with FSM being superior. In the presence of 10–20 wt.% FSM, the rate of decomposition was found to be twice as fast compared to neat PLA.
Open Access: Yes
The Effect of Wood Flour Incorporation on the Properties of Injection Molded Poly(Lactic Acid) Products †
Publication Name: Engineering Proceedings
Publication Date: 2024-01-01
Volume: 79
Issue: 1
Page Range: Unknown
Description:
Wood flour-paired poly(lactic acid) (PLA)-based biocomposites were fabricated with filler contents of 0, 2.5, 5, 10, and 20 wt.%. The samples were processed through extrusion followed by injection molding. The injection-molded specimens were subjected to tensile tests, impact tests, and water absorption tests. Based on the results, increasing the amount of lignocellulose fibers effectively improved the modulus of PLA from 2.8 to 3.6 GPa at 20 wt.% wood flour loading; however, this came at the cost of strength, which dropped from 55.0 to 48.8 MPa. Additionally, the incorporation of lignocellulose increased the hydrophilicity of the composites, resulting in a threefold increase in water absorption at 10 wt.% filler content. These results provide insight into the effects of embedding lignocellulose fibers into PLA.
Open Access: Yes
Foam Injection Molding of Poly(Lactic Acid) with Azodicarbonamide-Based Chemical Blowing Agent †
Publication Name: Engineering Proceedings
Publication Date: 2024-01-01
Volume: 79
Issue: 1
Page Range: Unknown
Description:
In this study, poly(lactic acid) (PLA)-based biopolymer foams were prepared through injection molding using the high-pressure foam injection molding method, also referred to as “breathing mold” technique, with the addition of various amounts (0, 1, 2, and 4 wt.%) of azodicarbonamide-based chemical blowing agent (CBA). The prepared samples were analyzed for their macrostructure using computed tomography (CT) while the mechanical properties were determined by flexural and Charpy impact tests. CT analysis revealed a finer foam cell structure and decreasing shell thickness with increasing CBA content. Regarding the mechanical properties, the specific flexural strength and flexural modulus of PLA were improved as a result of foaming; however, this improvement came at the cost of a slight deterioration in impact strength.
Open Access: Yes
Comparison of Mechanical Properties of PLA-Based Biocomposites Filled with Different Agricultural By-Products
Publication Name: Advances in Transdisciplinary Engineering
Publication Date: 2024-01-01
Volume: 59
Issue: Unknown
Page Range: 486-493
Description:
In this study, biopolymer composites were developed using poly(lactic acid) (PLA) as a polymer matrix. Various agricultural by-products, including flax seed meal, rapeseed straw, and mustard seed meal, were added as a reinforcement. The research aimed to provide insight into the valorization of cheap, readily available residues generated in the agricultural industry and assess the mechanical properties of composites prepared using them. The experimental fabrication was conducted by compounding PLA with agro-waste particles in 10 and 20 wt% concentrations. These components were melt mixed with a twin-screw extruder and injection molded into standardized forms. The resulting fabricated composites were tested for tensile and flexural mechanical properties and hardness. Through scanning electron microscopy, images of the natural particles were taken to better understand their structure, geometry, and possible ways of interaction between them and the PLA matrix. The results of quasi-static mechanical tests suggest that using agricultural by-products can effectively improve Young's modulus and flexural modulus of PLA but at the cost of tensile and flexural strength, which decreased with the by-products' introduction. Of the three agro-waste options, rapeseed straw emerged as the superior choice because it only marginally reduced the mechanical strength of the PLA and enhanced its stiffness the most. Hardness was the least affected property, test results showed that the added fillers did not substantially change the polymer matrix's hardness.
Open Access: Yes
DOI: 10.3233/ATDE240584
Effect of Maleated Compatibilizer on the Mechanical Properties of PLA/Mustard Waste Biocomposites
Publication Name: Chemical Engineering Transactions
Publication Date: 2024-01-01
Volume: 114
Issue: Unknown
Page Range: 775-780
Description:
Natural fiber polymer composites of biodegradable poly(lactic acid) (PLA) and mustard waste were fabricated with the addition of various amounts (0.25-2.00 wt.%) of maleic anhydride grafted PLA (PLA-g-MA), which was used as a coupling agent to improve interfacial adhesion between the components and thereby enhance the mechanical features of the biocomposite. PLA-g-MA was synthesized in-house by reactive melt grafting using dicumyl peroxide as a free grafting initiator. Preparation of the biocomposite samples was carried out using a twin screw extruder and an injection molding machine. The effect of PLA-g-MA concentration on the samples’ mechanical traits and surface hardness was investigated. Mechanical properties were determined using uniaxial tensile tests, flexural tests, and Charpy impact tests; additionally, the surface hardness was tested with a Shore D indenter. The tensile tests revealed that even the lowest amount (0.25 wt.%) of PLA-g-MA was sufficient to effectively improve the interfacial adhesion between PLA and mustard waste, as manifested in an increased tensile strength (34 to 39 MPa). Similarly, the flexural and the Charpy impact strength also exceeded that of neat PLA/mustard waste biocomposite by 31 % and 45 %, respectively. The addition of compatibilizer in higher concentrations than 0.25 wt.% did not improve the mechanical properties further, ascribed to the excess PLA-g-MA plasticizing the composite. Based on Shore D testing, the compatibilization did not affect the surface hardness of the biocomposites significantly.
Open Access: Yes
DOI: 10.3303/CET24114130
Effect of Injection Molding Parameters on the Chemical Foaming of Acrylonitrile Butadiene Styrene (ABS) Using Breathing Mold Technology
Publication Name: Chemical Engineering Transactions
Publication Date: 2023-01-01
Volume: 107
Issue: Unknown
Page Range: 247-252
Description:
Manufacturers have to adapt very quickly to the accelerating world and use specialized machines for production to meet the demands. This also means that those machines are not used as often as their mass-producing counterparts and sometimes become obsolete. In the case of foaming with injection molding, a complicated system has to be built around the machine and has to be structured in a specific way, which is not always cost-efficient. In this paper, two methods of chemical foaming of Acrylonitrile Butadiene Styrene (ABS) were performed on a regular injection molding machine. Chemical Blowing Agent (CBA) and Expandable Microsphere (EMS) were used with breathing mold technology. Injection molding parameters were modified, and specimens were produced for mechanical and morphological examinations. Properly selected parameters for foaming play an important role in retaining the mechanical strength of the product. With low switch-over volume and using the core-back method, it is possible to foam ABS using a Chemical Blowing Agent.
Open Access: Yes
DOI: 10.3303/CET23107042
