All issues / Volume 15 (2021) / Issue 12 (December)
This is an editorial article. It has no abstract.
Molecular orientation can determine the final properties in polymer parts during processing: in optoelectronic devices, the emission efficiency is strongly dependent on the orientation of the emitter materials; mechanical performances in polymer parts depend on the orientation and dimension of crystalline structures. A simpler and faster method to obtain the quantitative orientation of crystalline structures, based on atomic force microscopy, is introduced as a powerful alternative to the techniques mentioned above. This method is based on the acquisition of topographical maps along with the sample thickness and applying the directionality analysis to each map to obtain the distribution of orientation on the map. Such a distribution was analyzed following two approaches: the first one is based on Herman’s analysis; it is quite similar to the one adopted for calculating the Herman’s factor from the wide-angle X-ray scattering. The second one is simpler; it is based on the standard deviation of the distribution. Both approaches allowed the determination of an orientation parameter: the orientation parameter was close to 1 in the regions where a high number of oriented fibrils were found, vice versa, the orientation parameter was close to zero where spherulites were found. The orientation parameter was found highly consistent with Herman’s factor for injection molded samples obtained with different mold temperatures, thus with different distributions of orientation and morphology.
Epoxy acrylate (EA) resin, due to its thermo-mechanical properties, performs excellent shaper memory properties. 3D printing opens new opportunities to fabricated shape memory polymer (SMP), which contributed to a rising variety of applications, also requires 3D-printable capability with more advanced shape-memory function and mechanical performance of the material. In this paper, a new strategy was developed to fabricate high strain EA-based SMP through digital light processing (DLP) 3D printing, which took advantage of free radical copolymerization of epoxy acrylate-based oligomer and monomers. The 3D-printed SMP showed high strain at break (up to 90%), thermal stability, as well as excellent shape memory performance. In addition, the shape memory-based self-driven electronics was fabricated by combining shape memory polymer with light-absorbing and conductive ink. The device could change its configuration in response to light and temperature, which has great potential application for soft robotics, flexible electronics, and intelligent control devices.
Thermoplastic natural rubber (TPNR) nanocomposites based on epoxidized natural rubber (ENR) and polypropylene (PP) blends filled with 2.5 wt% nano-silica (SiO2) were prepared using a two-step compounding process to improve the dispersion of SiO2 in TPNR. The effects of the compounding techniques, i.e., solid pre-compounding and latex pre-compounding processes of SiO2 and ENR, and surface modification of SiO2 on the morphological, mechanical, and thermal properties together with the crystallization behavior of PP phase in ENR/PP blends were demonstrated. Scanning electron microscope (SEM) results showed that latex pre-compounding of SiO2 and ENR gave finer dispersion and distribution of SiO2 particles in the TPNR matrix as compared with the solid pre-compounding technique. Also, the superior mechanical properties and thermal stability of the blends were achieved by using the latex pre-compounding technique. Moreover, surface modification of SiO2 by organosilane was found to enhance crystallization rate and the degree of crystallinity of PP phase in the TPNR, leading to an improvement in the strength and mechanical properties of the ENR/PP blends. These results agree well with the morphological properties that presented a good dispersion and distribution of silane-modified SiO2 particles in the TPNR matrix.
In the past, polymer materials have been used in electronic devices; however, the major drawback with polymers is their low thermal conductivity, i.e., 0.1–0.5 W/(m・K). Hence, researchers came up with the idea of incorporating conductive fillers into the polymer matrix in order to increase their thermal conductivity. Different conductive materials classified as carbon, metallic, and ceramic-based fillers have been used for this task. However, the drawback with carbon and metalbased fillers is that they reduce the intrinsic insulating properties of polymer materials. Recently, boron nitride (BN), a ceramic-based filler was selected as the conductive filler of choice due to its combined excellent thermal conductivity and electrical insulation as well as high breakdown strength. Due to differences in polarities, boron nitride and polymer matrices form a weak interfacial bond. Therefore, the weak interfacial bond is commonly improved by surface chemical modification of the boron nitride fillers. Furthermore, most of the theoretical models are used to predict the thermal conductivities of boron nitride-polymers composites fitted well with experimental data. This proved that the models could be used to predict the properties of boron nitride composites before their experimental data. The review paper discusses the effect of boron nitride orientation, nanostructures, modification, and its synergy with other conductive fillers on the thermal conductivity and mechanical properties of the polymer matrices.
Spiroorthocarbonates (SOCs) exhibit good shrinkage resistance with ring-opening polymerization initiated by a cationic photoinitiator, with potential application in reducing the volume shrinkage by C=C double bond polymerization on three-dimensional (3D) printing. However, SOCs as an additive dealing with volume shrinkage in 3D printing are rarely reported. Moreover, little progress has been made in the kinetics study on its ring-opening polymerization. In this study, we presented an effective strategy to reduce 3D printing volume shrinkage based on SOCs chemistry and systematically studied the ring-opening photopolymerization kinetics. 3,9-diethyl-3,9-bis(allyloxymethyl)-1,5,7,11-tetraoxastetraoxaspiro undecane (DB-TOSU), one kind of SOCs, was adopted as an expanding monomer. Initiated by cationic photoinitiator with sensitizer under 405 nm LED light, the maximum conversion of DB-TOSU is up to 84%. As a volume-control agent for 3D printing, volume shrinkage reduction is 71.2% when adding DB-TOSU into 3D printing resin based on SOCs chemistry. Moreover, the toughness of resin was enhanced. In the 3D printing application test, DB-TOSU displayed a good application prospect owing to its good compatibility with the printing resin and printing accuracy after volume expansion.
Preparing an epoxy resin with biomass resources as an alternative for bisphenol A is significant for sustainable and renewable development under great pressure of limited fossil resources and urgent environmental issues. Herein, we synthesized an epoxy oligomer P-DBP-EP-n derived from biomass magnolol through an efficient one-step glycidylation. P-DBP-EP-n exhibited a low viscosity of 11.7 Pa・s at room temperature, endowing it with excellent processability as diglycidyl ether of bisphenol A (DGEBA) and magnolol-based epoxy monomer EDBP. Then P-DBP-EP-n was cured with a diamine curing agent, 4,4′-diaminodiphenyl methane (DDM), and following thermal addition polymerization of allyl units. Compared with DGEBA/DDM and EDBP/DDM, P-DBP-EP-n/DDM possessed a higher glass transition temperature (Tg) (304 to 167 and 226 °C), implying distinguished heat resistance. Furthermore, the tensile properties and notched impacted strength of P-DBP-EP-n/DDM were better than EDBP/DDM (20.7 to 19.4 MPa, 2.0 to 1.6 GPa, and 2.5 to 2.0 kJ/m2). The initial degradation temperature and char residue of P-DBP-EP-n/DDM were 421 °C and 35.2%, with a 13.5 and 101% increase compared with those of DGEBA/DDM, respectively. Additionally, P-DBP-EP-n/DDM displayed outstanding flame retardancy with V-0 rate for the vertical burning test and limiting oxygen index value of 47.7%, which was almost twice as much as that of DGEBA/DDM. This study offers a promising and feasible pathway to obtain a fully bio-based epoxy resin substituted for petroleum-based DGEBA with distinguished processability, heat resistance, and flame retardancy. Comprehensive properties of the bio-based thermosets are expected to be further regulated by the thermal addition polymerization of allyl units.
This research investigates various proportions of a compatibilizer, joncryl®, in a newly developed blend of rPET/PA11 having 80 wt% rPET and 20 wt% PA11. The proposed blend exhibits unique and outstanding mechanical properties. A few of the significant benefits of carrying out this research work include recycling the highest amount of rPET, saving natural recourses, and encountering the environmental issues associated with the wastage of polymers. Five different proportions of joncryl® (0,1,2,3 and 4 phr) were introduced to the blend of rPET/PA11 through a twin-screw extruder and injection moulding machine. The blend interface studied by scanning electron microscope (SEM) indicated that joncryl® boosted the chain extension. The results of tensile strength, Young's modulus and flexural strength displayed the boost up in properties at all proportions; however, the properties at 2 phr of joncryl® were unique and exclusive. The tensile strength of blend at 2 phr (joncryl®) is remarkably increased from 26.8 MPa to 46.24 MPa with a uniquely increased strain% from 3.56% to 196%. Young's modulus is also significantly improved. The impact strength rose from 147.12 to 667.68 J/m