Reaction Mechanism and Mechanical Property Improvement of Poly(Lactic Acid) Reactive Blending with Epoxy Resin

Effect of Plasma Treatment on Bamboo Fiber-Reinforced Epoxy Composites

Bamboo cellulose fiber (BF)-reinforced epoxy (EP) composites were fabricated with BF subjected to plasma treatment using argon (Ar), oxygen (O2), and nitrogen (N2) gases. Optimal mechanical properties of the EP/BF composites were achieved with BFs subjected to 30 min of plasma treatment using Ar. This is because Ar gas improved the plasma electron density, surface polarity, and BF roughness. Flexural strength and flexural modulus increased with O2 plasma treatment. Scanning electron microscopy images showed that the etching of the fiber surface with Ar gas improved interfacial adhesion. The water contact angle and surface tension of the EP/BF composite improved after 10 min of Ar treatment, owing to the compatibility between the BFs and the EP matrix. The Fourier transform infrared spectroscopy results confirmed a reduction in lignin after treatment and the formation of new peaks at 1736 cm-1, which indicated a reaction between epoxy groups of the EP and carbon in the BF backbone. This reaction improved the compatibility, mechanical properties, and water resistance of the composites.

Influence of a Biofiller, Polylactide, on the General Characteristics of Epoxy-Based Materials

The aim of this work was to obtain epoxy-based composite structures with good mechanical performance, high aging resistance, and an improved degradability profile. For this purpose, powdered polylactide in the amount of 5, 10, 20, 30, and 40 phr was introduced into the epoxy resin, and the composites were fabricated by a simple method, which is similar to that used on an industrial scale in the fabrication of these products. The first analysis concerned the study of the effect of PLA addition to epoxy resin-based composites on their mechanical properties. One-directional tensile tests of samples were performed for three directions (0, 90, and 45 degrees referring to the plate edges). Another aspect of this research was the assessment of the resistance of these composites to long-term exposure to solar radiation and elevated temperature. Based on the obtained results, it was observed that the samples containing 20 or 40 phr of polylactide were characterized by the lowest resistance to the solar aging process. It was therefore concluded that the optimal amount of polylactide in the epoxy resin composite should not be greater than 10 phr to maintain its mechanical behavior and high aging resistance. In the available literature, there are many examples in which scientists have proposed the use of various biofillers (e.g., lignin, starch, rice husk, coconut shell powder) in epoxy composites; however, the impact of polylactide on the general characteristics of the epoxy resin has not been described so far. Therefore, this work perfectly fills the gaps in the literature and may contribute to a more widespread use of additives of natural origin, which may constitute an excellent alternative to commonly used non-renewable compounds.

Bamboo Pulp Toughening Poly (Lactic Acid) Composite Using Reactive Epoxy Resin

A novel poly (lactic acid) (PLA) composite with excellent mechanical properties, toughness, thermal stability, and water resistance was developed using a reactive melt-blending technique. PLA was melt mixed with epoxy resin (EPOXY) and bamboo pulp (PULP) to improve its reaction and mechanical properties. FTIR analysis confirmed the successful reaction of the PLA/EPOXY/PULP composites; the epoxy groups of EPOXY reacted with the -COOH groups of PLA and the -OH groups of PULP. The PLA/EPOXY/PULP5 composite showed a high tensile strength (67 MPa) and high toughness of 762 folding cycles, whereas the highest tensile strength was 77 MPa in the PLA/EPOXY5/PULP20 sample. SEM images presented a gap between the PLA and PULP; gap size decreased with the addition of EPOXY. The Tg of the PLA decreased with the EPOXY plasticizer effect, whereas the Tm did not significantly change. PULP induced crystallinity and increased Vicat softening of the PLA/PULP and PLA/EPOXY/PULP composites. The EPOXY reaction of the PLA/PULP composites improved their tensile properties, toughness, thermal stability, and water resistance.

Reactive Blending of Modified Thermoplastic Starch Chlorhexidine Gluconate and Poly(butylene succinate) Blending with Epoxy Compatibilizer

Biodegradable starch-based polymers were developed by melt-blending modified thermoplastic starch (MTPS) with poly(butylene succinate) (PBS) blended with epoxy resin (Er). A modified thermoplastic starch blend with chlorhexidine gluconate (MTPSCh) was prepared by melt-blending cassava starch with glycerol and chlorhexidine gluconate (CHG) 1.0% wt. The Er was melt-blended with PBS (PBSE) at concentrations of 0.50%, 1.0%, 2.5%, and 5.0% (wt%/wt%). The mechanical properties, water resistance, and morphology of the MTPSCh/PBSE blends were investigated. The MTPSCh/PBSE2.5% blend showed an improvement in tensile strength (8.1 MPa) and elongation at break (86%) compared to the TPSCh/PBS blend (2.6 MPa and 53%, respectively). In addition, water contact angle measurements indicated an increase in the hydrophobicity of the MTPSCh/PBSE blends. Thermogravimetric analysis showed an improvement in thermal stability when PBS was added to the MTPSCh blends. Fourier transform infrared spectroscopy data confirmed a new reaction between the amino groups of CHG in MTPSCh and the epoxy groups of Er in PBSE, which improved the interfacial adhesion of the MTPSCh/PBSE blends. This reaction improved the mechanical properties, water resistance, morphology, and thermal stability of the TPSCh/PBSE blends.

Improving the Heat Resistance and Flame Retardancy of Epoxy Resin Composites by Novel Multifunctional Cyclophosphazene Derivatives

A novel multiple-ring molecule containing P and N, called HCCP-SA, was successfully prepared by the nucleophilic substitution reaction of salicylamide (SA) and hexachlorocyclotriphosphazene (HCCP). Particularly, HCCP-SA possessed the dual functions of heat resistance and flame retardancy. The molecular structure of HCCP-SA was identified by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. HCCP-SA was bonded into the molecular chain of epoxy resin by the ring-opening curing reaction of epoxy resin, aiming to form a heat-resistant and flame-retardant composite (E-HS-x). In particular, the best-prepared E-HS-x composite with a 20 phr content of HCCP-SA (E-HS-20) presented excellent thermal stability, with an initial decomposition temperature of 267.94 °C and a max weight loss speed of only 0.95 mg·min^-1. Moreover, E-HS-20 exhibited remarkable flame retardancy with a limiting oxygen index value of 27.1% and a V-2 rating in the UL94 flame retardancy test. The best-prepared E-HS-20 composite would be a suitable and potential candidate for heat-resistant and flame-retardant polymer materials.

Optimization of 3D Printing Technology for Fabrication of Dental Crown Prototype Using Plastic Powder and Zirconia Materials

This research was aimed at developing a dental prototype from 3D printing technology using a synthetic filament of polylactic acid (PLA) and zirconium dioxide (ZrO₂) with glycerol and silane coupling agent as a binder. A face-centered central composite design was used to study the effects of the filament extrusion parameters and the 3D printing parameters. Tensile and compressive testing was conducted to determine the stress-strain relationship of the filaments. The yield strength, elongation percentage and Young's modulus were also calculated. Results showed the melting temperature of 193 °C, ZrO₂ ratio of 17 wt.% and 25 rpm screw speed contributed to the highest ultimate tensile strength of the synthetic filament. A Nozzle temperature of 210 °C and an infill density of 100% had the most effect on the ultimate compressive strength whilst the printing speed had no significant effects. Differential scanning calorimetry (DSC) was used to study the thermal properties and percentage of crystallinity of PLA filaments. The addition of glycerol and a silane coupling agent increased the tensile strength and filament size. The ZrO₂ particles induced the crystallization of the PLA matrix. A higher crystallization was also obtained from the annealing treatment resulting in the greater thermal resistance performance of the dental crown prototype.

Tailoring the composition of biocopolyester blends for dimensionally accurate extrusion-based printing, annealing and steam sterilization

Fused filament fabrication (FFF) represents a straightforward additive manufacturing technique applied in the medical sector for personalized patient treatment. However, frequently processed biopolymers lack sufficient thermal stability to be used as auxiliary devices such as surgical guides. The aim of this study was to evaluate the dimensional accuracy of experimental biocopolyester blends with improved thermal characteristics after printing, annealing and sterilization. A total of 160 square specimens and 40 surgical guides for oral implant placement were printed. One subgroup of each material (n = 10) underwent thermal annealing before both subgroups were subjected to steam sterilization (134 °C; 5 min). Specimens were digitized and the deviation from the original file was calculated. The thermal behavior was analyzed using differential scanning calorimetry and thermogravimetric analysis. A one-way ANOVA and t-tests were applied for statistical analyses (p < 0.05). All biocopolyester blends showed warpage during steam sterilization. However, the material modification with mineral fillers (21-32 wt%) and nucleating agents in combination with thermal annealing showed a significantly reduced warpage of printed square specimens. Geometry of the printing object seemed to affect dimensional accuracy, as printed surgical guides showed less distortion between the groups. In summary, biocopolyesters did benefit from fillers and annealing to improve their dimensional stability.

A Study on Temperature Distribution within HVDC Bushing Influenced by Accelerator Content during the Curing Process

Power transmission technology plays an important role in energy sustainability. Bushing is an indispensable type of equipment in power transmission. In production, the accelerator changes the temperature distribution during the curing process, influencing the formation of defects and thus the safety output of renewable energy. In this study, uncured epoxy resin samples with different accelerator contents were prepared and measured by differential scanning calorimetry (DSC). The obtained heat flow curves were analyzed for curing kinetics. Then, the curing process of large length–diameter ratio bushings was simulated by using the finite element method combined with a curing kinetics model, transient Fourier heat transfer model, and stress–strain model. The study reveals that the curing system can be established by the Sestak–Berggren autocatalytic model with different accelerator contents. The overall curing degree and the maximum radial temperature difference of the capacitor core tend to increase and then decrease with the accelerator content. This is mainly attributable to the rapid exotherm excluding the participation of some molecular chains in the reaction, resulting in permanent under-curing. As the accelerator content increases, the strain peak decreases and then increases. This paper provides guidance for the comprehensive evaluation and manufacturing of the low-defect capacitor cores of large-size high voltage direct current (HVDC) bushings.

Modified Poly(Lactic Acid) Epoxy Resin Using Chitosan for Reactive Blending with Epoxidized Natural Rubber: Analysis of Annealing Time

Poly(lactic acid) was melt-blended with epoxy resin without hardener and chitosan (CTS) to prepare modified PLA (PLAEC). Epoxy resin 5% and CTS 1–20% (wt/wt) were incorporated into PLA during melt mixing. PLAEC was melt-blended with an epoxidized natural rubber (ENR) 80/20 wt. The PLAEC CTS 1% blended with ENR (PLAEC1/ENR) showed a high tensile strength (30 MPa) and elongation at break (7%). The annealing process at 80 °C for 0–15 min maintained a tensile strength of approximately 30 MPa. SEM images of the PLAE/ENR blend showed phase inversion from co-continuous to ENR particle dispersion in the PLA matrix with the addition of CTS, whereas the annealing time reduced the hole sizes of the extracted ENR phase due to the shrinkage of PLA by crystallization. Thermal properties were observed by DSC and a Vicat softening test. The annealing process increased the crystallinity and Vicat softening temperature of the PLAEC1/ENR blend. Reactions of −COOH/epoxy groups and epoxy/−NH₂ groups occurred during PLAE and PLAEC preparation, respectively. FTIR confirmed the reaction between the −NH₂ groups of CTS in PLAEC and the epoxy groups of ENR. This reaction increased the mechanical properties, while the annealing process improved the morphology and thermal properties of the blend.

Mechanically Robust and Flame-Retardant Polylactide Composites Based on In Situ Formation of Crosslinked Network Structure by DCP and TAIC

The addition of intumescent flame retardant to PLA can greatly improve the flame retardancy of the material and inhibit the dripping, but the major drawback is the adverse impact of the mechanical properties of the material. In this study, we found that the flame retardant and mechanical properties of the materials can be improved simultaneously by constructing a cross-linked structure. Firstly, a cross-linking flame-retardant PLA structure was designed by adding 0.9 wt% DCP and 0.3 wt% TAIC. After that, different characterization methods including torque, melt flow rate, molecular weight and gel content were used to clarify the formation of crosslinking structures. Results showed that the torque of 0.9DCP/0.3TAIC/FRPLA increased by 307% and the melt flow rate decreased by 77.8%. The gel content of 0.9DCP/0.3TAIC/FRPLA was 30.8%, indicating the formation of cross-linked structures. Then, the mechanical properties and flame retardant performance were studied. Results showed that, compared with FRPLA, the tensile strength, elongation at break and impact strength of 0.9DCP/0.3TAIC/FRPLA increased by 34.8%, 82.6% and 42.9%, respectively. The flame retardancy test results showed that 0.9DCP/0.3TAIC/FRPLA had a very high LOI (the limiting oxygen index) value of 39.2% and passed the UL94 V-0 level without dripping. Finally, the crosslinking reaction mechanism, flame retardant mechanism and the reasons for the improvement of mechanical properties were studied and described.

Improving the curing and flame retardancy of epoxy resin composites by multifunctional Si-containing cyclophosphazene derivatives

Novel star-like molecules containing P, N and Si with dual functions of flame retardance and curing promotion (abridged as HCCP–KH540) were successfully synthesized through the nucleophilic substitution reaction of hexachlorocyclotriphosphazene (HCCP) and 3-aminopropyltrimethoxysilane (KH540). HCCP–KH540 was incorporated with the matrix of epoxy resin (EP) to form a flame retardant composite abridged as E-HK. The activation energy of the curing reaction of the E-HK composite was reduced but the curing reaction rate was accelerated by HCCP–KH540. The E-HK composite with 30 phr content of HCCP–KH540 exhibited excellent flame retardancy with limiting oxygen index of 29.6% and V-1 rating in the vertical burning test as well as excellent thermal stability with a char yield of 23.77% at 700 °C, compared with only 8.64% for pure EP.

Novel star-like molecules containing P, N and Si with dual functions of flame retardance and curing promotion were synthesized through the nucleophilic substitution reaction of hexachlorocyclotriphosphazene and 3-aminopropyltrimethoxysilane.

Thermoplastic cassava starch blend with polyethylene-grafted-maleic anhydride and gelatin core-shell structure compatibilizer

Thermoplastic starch (TPS) was prepared from cassava starch blended with glycerol (70:30 w/w). Gelatin (Gel) was incorporated into the TPS in water. The TPS/Gel was melt-blended with polyethylene-grafted-maleic anhydride (PEMAH). Maximum tensile strength of the TPS/PEMAH/Gel10 (29.3 MPa) increased significantly compared to the TPS/PEMAH blend (6.3 MPa), while elongation at break was 70%. The morphology of the TPS/PEMAH showed co-continuous morphology, while phase inversion occurred with the addition of Gel. The Gel was dispersed in the TPS matrix and covered the PEMAH. The TPS/PEMAH/Gel was nanoparticles (200 nm) in the TPS matrix. It showed two melting temperatures for PEMAH due to two structures with different crystal sizes. Melt viscosity of the TPS/PEMAH was enhanced with increasing Gel as the reaction induced chain extension. FTIR and rheology measurements confirmed the reaction between -NH groups of Gel and MAH groups of PEMAH. This reaction improved interfacial adhesion, morphology, and the mechanical properties of the blends.

Corn starch reactive blending with latex from natural rubber using Na+ ions augmented carboxymethyl cellulose as a crosslinking agent

A mixture of corn starch and glycerol plasticizer (CSG) was blended with latex natural rubber (LNR) and carboxymethyl cellulose (CMC). The addition of 10 phr of CMC improved the Young's modulus (6.7 MPa), tensile strength (8 MPa), and elongation at break (80%) of the CSG/LNR blend. The morphology of the CSG/LNR/CMC blends showed a uniform distribution of LNR particles (1-3 µm) in the CSG matrix. The addition of CMC enhanced the swelling ability and water droplet contact angle of the blends owing to the swelling properties, interfacial crosslinking, and amphiphilic structure of CMC. Fourier transform infrared spectroscopy confirmed the reaction between the C=C bond of LNR and the carboxyl groups (-COO-) of CMC, in which the Na+ ions in CMC acted as a catalyst. Notably, the mechanical properties of the CSG/LNR/CMC blend were improved owing to the miscibility of CSG/CMC and the CMC/LNR interfacial reaction. The CSG/LNR/CMC biodegradable polymer with high mechanical properties and interfacial tension can be used for packaging, agriculture, and medical applications.