All issues / Volume 14 (2020) / Issue 8 (August)
This is an editorial article. It has no abstract.
A novel bio-based flame retardant (Phytic acid – trometamol, PA-THAM) was prepared via salt formation reaction between phytic acid and trometamol. The chemical structure and thermal stability of this novel phytate were characterized by Nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). Afterward, the effect of PA-THAM on the flammability of PLA was investigated. On the basis of the results, 3 wt% incorporation of PA-THAM in PLA exhibited better results than pure PLA in flame combustion tests, for example, LOI value increased from 19.9 to 25.8% and ratings in UL-94 varied from No Rating to V-0 rating. This ignitionresistance performance was analyzed investigating the relationship between properties and structure. The results elucidated that the incorporation of PA-THAM significantly reduced the molten viscosity of biocomposite, which facilitated the ‘heat transfer’ effect to rapidly decrease the surface temperature. In comparison with neat PLA, the same load of PA-THAM in PLA had little effect on the mechanical properties of PLA-based biocomposite, which indicated that the optimum load of PA-THAM maintained the balance of fire retardancy and mechanical properties of the PLA biocomposite.
The present study deals with the incorporation of different ratios of alkali-treated coir fibres (CF) and pineapple leaf fibres (PALF) in polylactic acid (PLA) hybrid composites. Developed hybrid composites are characterized in terms of mechanical, morphological, thermal and physical properties. Mechanical characterization revealed that alkali-treated C3P7 hybrid composites (CF:PALF = 3:7) showed highest tensile strength (30.29 MPa) and young’s modulus (5.16 GPa) among all hybrids composites, whereas C1P1 (CF:PALF = 1:1) showed highest impact properties. Scanning electron microscopy (SEM) justified the consequence of alkali treatment on fibre-matrix adhesion. Thermal analysis revealed that C1P1 and C7P3 (CF:PALF = 7:3) having a higher thermal stability and char content due to the higher content of lignin in CF. Remarkably, the coefficient of thermal expansion (CTE) of treated hybrid composites displayed lesser values than untreated hybrid composites. The physical tests revealed that C3P7 showed highest water absorption (WA) and thickness swelling (TS) though after treatment the WA and TS values get reduced. Overall results indicated that treated CF/PALF/PLA hybrid composites possess enhanced mechanical, thermal and physical properties with lowered CTE over untreated CF/PALF/PLA hybrid composites. The success of these findings results sustainable and degradable hybrid composites for different outdoor and food packaging-based applications.
Effect of viscoelastic and surface properties on tack, peel adhesion and shear strength of polymer blends applied as hot melt pressure sensitive adhesive models comprising tackifying agents of various chemical nature
T. Abboud, A. Wutzler, H-J. Radusch
Vol. 14., No.8., Pages 731-740, 2020
Vol. 14., No.8., Pages 731-740, 2020
Viscoelastic and surface properties of polymer blends prepared as models of hot melt pressure sensitive adhesives (HMPSA) were investigated and the correlation to tack, peel, and shear adhesion properties was discussed. Three different types of tackifiers, which present a softening point of ca. 100 °C as well as different compatibility degree with the midblock and the end-block of poly(styrene-block-isoprene-block-styrene) (SIS), were employed. A good association degree between the midblock and the tackifiers was observed. Surface energy was used to evaluate the blend compatibility trend. The blends presented lower surface energy than the pure materials due to non-polar and acid-base interactions. This is a feature of compatible blends. PSA character was observed based on the obtained results of tack and peel for the blends and it is a consequence of the adequate degree of compatibility of the tackifiers and the midblock. The compatibility of the tackifiers and the end-block influenced shear adhesion. Rosin ester resin showed a better association with the styrenic domains. The second maximum of the loss modulus (G″) curve for a blend containing rosin resin shifted to lower temperatures in comparison to blends containing the other investigated resins. The lowest holding power values were measured for the blends containing rosin ester resin. The styrene domains were pronouncedly disturbed by this resin.
In this paper, 12-hydroxystearic acid was used to modify the surface nano-hydroxyapatite(n-HA) by co-precipitation method or blending method. Fourier transformation infrared (FTIR), X-ray diffraction (XRD), intuitionistic dispersion, transmission electron microscope (TEM) and thermal gravimetric analysis (TGA) showed that the blending method confirmed 12-hydroxystearic acid was successfully grafted on the surface of n-HA, which endowed n-HA with better dispersion in hydrophobic solvents, and the dispersion was improved with the addition amount of 12-hydroxystearic acid. Correspondingly, it exhibited better improvement for poly (lactic-o-glycolide)(PLGA), owing to better interface adhesion in PLGA matrix and promotion crystallization by investigating the tensile strength, fracture morphology, polarized optical microscopy (POM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) of the composites. Especially, the tensile strength was 23.81% higher than that of pure PLGA when 5 wt% n-HA was added, suggesting the obtained n-HA was promising to improve the mechanical strength of PLGA. Moreover, in vitro cell culture, experimental results indicated that n-HA/PLGA composites displayed better cell biocompatibility. Taken together, these results demonstrated that the introduction of 12-hydroxystearic acid by blending method was a novel method to modify the surface of n-HA, which has a great potential to obtain ideal n-HA/PLGA composite as bone materials.
A series of novel quaternary copolymerized thermoplastic polyimides were successfully prepared with asymmetric diahydride: 3,4′-oxydiphthalic anhydride (a-ODPA) and symmetric anhydride: 4,4′-oxydiphthalicanhydride (s-ODPA), 9,9′-bis(4-aminophenyl)fluorene (BAFL) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) as diamine. The synergistic effect of non-coplanar structure, fluorenyl cardo groups, methyl groups and flexible groups on the solubility, heat resistance and thermoplasticity of polyimide was discussed. The experimental results showed that the addition of BAFL greatly improved the heat resistance of polyimide. The glass transition temperature (Tg) of PI-A~PI-E with different ratios were 235.3–305.5 °C. Compared with control group PI-F, PI-A~PI-E were completely soluble within 3 h in DMF, DMAc, NMP, showing that they had excellent solubility, and what’s more, under the synergistic effect, the thermoplasticity of PI-A~PI-E was also greatly improved.
Poly(lactic acid) (PLA) and thermoplastic starch (TPS) blends with two different glycerol contents were prepared by injection molding. Mechanical properties were characterized by tensile and impact testing, structure by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) as well as Raman spectroscopy, and water absorption was determined as a function of time. Compression-molded specimens were used as reference. The properties of the blends cover a wide range, stiffness changes from 3.3 to around 1.0 GPa, while strength from 54 to 22 MPa as TPS content increases from 0 to50 wt%. Heterogeneous structure forms in the blends because of the weak interaction of the components. Processing conditions do not change bulk properties. Weak interactions and the large difference in the viscosity of the components lead to the formation of a skin on the surface of the specimens. The skin consists mainly of PLA, while the core contains a larger amount of TPS. The thickness of the skin depends on processing technology and conditions; it is about 18 μm for the injectionmolded, while 4.5 μm for the compression-molded parts at 50 wt% TPS content. The development of the skin layer can be advantageous in some applications because it slows down water absorption considerably.
A triazine-based functional monomer (AET) was synthesized via a nucleophilic substitution reaction between cyanuric chloride and 3-aminophenylacetylene. The comprehensive properties were superior, including simple synthesis conditions, moderate curing conditions, excellent thermal properties, and good mechanical properties of laminated composites comprised of AET and quartz fiber. The curing reaction showed high reactivity and low temperature, an activation energy of 106.33 kJ・mol–1 and cure exothermic peak between 140 and 250 °C with an enthalpy of 780 J・g–1. The decomposition temperature at 5% mass loss was 521 °C, the char yield at 800 °C was 78% and the glass transition temperature was 470 °C. Moreover, QF/P-AET laminated composite possessed good mechanical properties. The flexural strength was 364.94 Mpa and the interlaminar shear strength was 30.4 MPa at room temperature (RT); especially at 300 and 500 °C, the composite still displayed a high mechanical strength retention of up to 66 and 88, and 45 and 42%, respectively which is unachievable for cyanate and aryl acetylene resins. All above attracting properties make AET a good candidate as a matrix for high performance polymeric composite materials.