In-situ self-crosslinking strategy for super-tough polylactic acid/ bio-based polyurethane blends.

As a bio-based degradable plastic, polylactic acid (PLA) is highly commercialized, but its inherent brittleness limits its widespread use. In-situ polymerization techniques are effective in improving the toughness of PLA. However, the enhancement of the toughening effect in polyurethanes (PUs) through in-situ self-crosslinking still requires improvement and heavily relies on petroleum-derived feedstocks in certain approaches. In this paper, 1,3-polypropanediol (PO3G) of bio-based origin rather than conventional polyols like polyethylene glycol (PEG) and poly propylene glycol (PPG) was used. PLA/PO3G-PU blends were prepared via an in-situ self-crosslinking strategy. With a notch impact and tensile strength of 55.95 kJ/m2 and 47.77 MPa (a retention rate of 68.9 % compared with pure PLA), respectively, PLA/PO3G-PU blends achieved a better balance between stiffness and toughness. This work provides a new option for PLA to achieve a stiffness-toughness balance and get rid of dependence on petrochemical resources.

Finite Element Solution for Dynamic Mechanical Parameter Influence on Underwater Sound Absorption of Polyurethane-Based Composite.

Underwater noise pollution, mainly emitted by shipping and ocean infrastructure development of human activities, has produced severe environmental impacts on marine species and seabed habitats. In recent years, a polyurethane-based (PU-based) composite with excellent damping performance has been increasingly utilized as underwater sound absorption material by attaching it to equipment surfaces. As one of the key parameters of damping materials, dynamic mechanical parameters are of vital importance to evaluating the viscoelastic damping property and thus influencing the sound absorption performance. Nevertheless, lots of researchers have not checked thoroughly the relationship and the mechanism of the material dynamic mechanical parameters and its sound absorption performance. In this work, a finite element model was fabricated and verified effectively using acoustic pulse tube tests to investigate the aforementioned issues. The influence of the dynamic mechanical parameters on underwater sound absorption performance was systematically studied with the frequency domain to reveal the mechanism and the relationship between damping properties and the sound absorption of the PU-based composite. The results indicate that the internal friction of the molecular segments and the structure stiffness were the two main contributors of the PU-based composite's consumption of sound energy, and the sound absorption peak and the sound absorption coefficient could be clearly changed by adjusting the dynamic mechanical parameters of the composite. This study will provide helpful guidance to develop the fabrication and engineering applications of the PU-based composite with outstanding underwater sound absorption performance.

Development of nitrile rubber/eucommia ulmoides gum composites for controllable dynamic damping and sound absorption performance.

Aiming at enhancing the damping and sound absorption performances of nitrile rubber (NBR) incorporated Eucommia ulmoides gum (EUG), a series of NBR/EUG composites were successfully fabricated using an open mixing mill. The co-vulcanization behaviors, fracture surface morphology observations, mechanical and thermal properties and damping and sound absorption performances of NBR/EUG composites were investigated systematically. It was shown that the crystalline area and the amorphous area in NBR/EUG composites displayed a sea-island phase distribution and most of the EUG crystals were ß-form crystals. Compared to that of neat NBR, the tensile strength and storage modulus of NBR/EUG composites increased dramatically with the increasing EUG content, owing to the gradually increasing number of crystals in the NBR/EUG composites. In addition, the incorporation of EUG into the NBR matrix distinctly improved the sound absorption performance of NBR/EUG composites. This work is expected to provide a new insight into the fabrication of other composite materials with controllable damping and sound absorption properties.

Bio-Based Polyurethane and Its Composites towards High Damping Properties.

The operation of mechanical equipment inevitably generates vibrations and noise, which are harmful to not only the human body but also to the equipment in use. Damping materials, which can convert mechanical energy into thermal energy, possess excellent damping properties in the glass transition region and can alleviate the problems caused by vibration and noise. However, these materials mainly rely on petroleum-based resources, and their glass transition temperatures (Tg) are lower than room temperature. Therefore, bio-based materials with high damping properties at room temperature must be designed for sustainable development. Herein, we demonstrate the fabrication of bio-based millable polyurethane (BMPU)/hindered phenol composites that could overcome the challenges of sustainable development and exhibit high damping properties at room temperature. BMPUs with a high Tg were prepared from modified poly (lactic acid)-based polyols, the unsaturated chain extender trimethylolpropane diallylether, and 4,4'-diphenylmethane diisocyanate, and 3,9-Bis-{1,1-dimethyl-2[ß-(3-tert-butyl-4-hydroxy-5-methylphenyl-)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro [5,5]-undecane (AO-80) was added to prepare BMPU/AO-80 composites. Finally, the properties of the BMPUs and BMPU/AO-80 composites were systematically evaluated. After adding 30 phr of AO-80, the Tg and maximum loss factor (tan δmax) of BMPU/AO-80 composites increased from 7.8 °C to 13.5 °C and from 1.4 to 2.0, respectively. The tan δmax showed an improvement of 43%. Compared with other polyurethanes, the prepared BMPU/AO-80 composites exhibited higher damping properties at room temperature. This study proposes a new strategy to reduce society's current dependence on fossil resources and design materials featuring high damping properties from sustainable raw materials.

Facile Fabrication of PBS/CNTs Nanocomposite Foam for Electromagnetic Interference Shielding.

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending poly (butylene succinate) (PBS) with carbon nanotubes (CNTs) followed by foaming with supercritical CO2 . The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Increasing the CNT content from 0 to 4 wt % leads to an increase of approximately 3 orders of magnitude in storage modulus and nearly 9 orders of magnitude in enhancement of electrical properties. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm3 /g. This study provides a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.

Fabrication of Millable Polyurethane Elastomer/Eucommia Ulmoides Rubber Composites with Superior Sound Absorption Performance.

Sound absorbing materials combining millable polyurethane elastomer (MPU) and eucommia ulmoides rubber (EUG) were successfully fabricated via a physical blending process of EUG and MPU. The microstructure, crystallization performances, damping, mechanical and sound absorption properties of the prepared MPU/EUG composites were investigated systematically. The microstructure surface of various MPU/EUG composites became rough and cracked by the gradual incorporation of EUG, resulting in a deteriorated compatibility between EUG and MPU. With the increase of EUG content, the storage modulus (E') of various MPU/EUG composites increased in a temperature range of -50 °C to 40 °C and their loss factor (tanδ) decreased significantly, including a reduction of the tanδ of MPU/EUG (70/30) composites from 0.79 to 0.64. Specifically, the addition of EUG sharply improved the sound absorption performances of various MPU/EUG composites in a frequency range of 4.5 kHz-8 kHz. Compared with that of pure MPU, the sound absorption coefficient of the MPU/EUG (70/30) composite increased 52.2% at a pressure of 0.1 MPa and 16.8% at a pressure of 4 MPa, indicating its outstanding sound absorption properties.

Fabrication of branching poly (butylene succinate)/cellulose nanocrystal foams with exceptional thermal insulation.

Branching poly (butylene succinate) (BPBS) nanocomposite foams incorporated with cellulose nanocrystals (CNCs) were prepared by supercritical CO2. Surface modification of CNCs by acetylation was achieved through replacing hydrophilic hydroxyl groups with hydrophobic acetyl groups, which improved the dispersibility of CNCs significantly. The crystallite sizes of CNCs and acetylated CNCs were calculated by Scherrer's formula as 25 and 19 nm, respectively. The initial crystallization temperature of diverse poly (butylene succinate) (PBS) specimens, a crucial factor for regulating cell nucleation type, increased remarkably by 11.8 °C as well as their storage modulus increased by 2 orders of magnitudes, due to branching reaction and bio-filler addition. BPBS/CNCs foam possessed a high volume expansion ratio as 37.1 times and displayed an exceptional thermal conductivity as 0.021 W(m K)-1. This study provided a promising potential strategy to develop exceptional thermal-insulation polymer foams for composite structures, energy conservation and environment protection.

Fabrication of biodegradable poly (lactic acid)/carbon nanotube nanocomposite foams: Significant improvement on rheological property and foamability.

Recently, biodegradable macromolecules have been highly desired as a promising alternative for traditional oil-based plastics to work out the eco crisis and biological health problems triggered by microplastics. Herein, we presented a simple, effective, environmentally friendly and CO2-based foaming methodology for fabricating ultra-low-density poly (lactic acid)/carbon nanotube (PLA/CNTs) nanocomposite foam. By the gradual incorporation of CNTs, three kinds of networks generated in PLA/CNTs nanocomposites and had a distinct reinforcement influence on their melt viscoelasticity, which testified by transmission electron microscope, electrical conductivity and rheological property measurements, severally. Specifically, the storage modulus of PLA/CNTs nanocomposites were 3 orders of magnitude higher in contrast to pure PLA. Interestingly, relative to that under regular differential scanning calorimetry (DSC), a double melting peak phenomenon appeared in the high-pressure DSC curves of diverse PLA specimens. Biodegradable PLA/CNTs nanocomposite foam was successfully fabricated with a super-high volume expansion ratio (VER) of 49.6 times, which could offer a promising strategy for developing other thermoplastic polyester foams with ultra-high VER to obtain some unique functional attributes.