Photonic generation of frequency-doubling Nyquist pulses using external modulation.

In this paper, an approach to generate frequency-doubling sinc-shaped optical Nyquist pulses based on external modulation is proposed and demonstrated. First, four flat optical frequency comb (OFC) lines are obtained after optical carrier suppression modulation in a dual-electrode Mach-Zehnder modulator. Then an optical interleaver is introduced to split the phase-locked OFC into two paths, of which one is transmitted to a dual-parallel Mach-Zehnder modulator for quadrupling RF modulation and another is applied to the remodulated signal to acquire comb lines with equal intervals. Thus, a phase-locked 12-line flat OFC with equal frequency intervals and corresponding Nyquist pulses is finally obtained, and Nyquist pulses at 2.5 GHz, 5 GHz, 10 GHz, and 15 GHz are achieved.

Improving the degree of polymerization of cellulose nanofibers by largely preserving native structure of wood fibers.

The degree of polymerization (DP) of cellulose plays an essential role in unlocking the superior mechanical potential of wood cellulose nanofibrils (CNFs). However, severe degradation of cellulose chains during the chemical pulping is a big challenge to obtain CNFs with high DP. In this work, we tend to improve the DP of wood CNFs by significantly preserving the native structure of wood fibers in an industrial method. Wood sticks are first pretreated with hydrothermal treatment to partially remove hemicellulose, thus leading to an increased porous structure that facilitates the penetration of cooking liquid and lignin removal during delignification, and dilute-alkali-sulfate pulping is then employed to obtain wood fibers with highest viscosity average DP (DPV) of nearly 2400. After that, the as-prepared wood fibers with high DP are separated into CNFs with highest average DPV of 1333. Finally, we demonstrate the potential application of wood CNFs with improved DPV in the fabrication of strong and tough isotropic films and macrofibers.

Wood-inspired strategy to toughen transparent cellulose nanofibril films.

The simultaneous attainment of high strength and high toughness of transparent cellulose nanofibril (CNF) film can expedite its uses in advanced applications. In this work, a wood-inspired strategy is proposed to address the conflict between strength and toughness by using natural derived lignosulfonic acid (LA) as a reinforcing additive. Only 1 wt% LA addition can double the toughness (11.0±1.3 MJ/m3) of pure CNF film. Consequently, the as-prepared CNF/LA-1 nanocomposite film not only exhibits superior mechanical properties (23.6±1.3 MJ/m3 toughness, 249±6 MPa strength, and 15.4±1.4 % strain), but also maintains an excellent optical transparency of 91.2 % (550 nm). Furthermore, the mechanism for simultaneously enhancing strength and toughness is essentially attributed to the improved hydrogen bonding between CNF-OH and LA-SO3H and effective energy dissipation system. This work provides a green and effective approach to prepare strong yet tough and transparent biodegradable CNF film for high-end applications.

Favorable combination of foldability and toughness of transparent cellulose nanofibril films by a PET fiber-reinforced strategy.

Transparent cellulose nanofibril (CNF) films have been considered a promising sustainable alternative for nonrenewable and nonbiodegradable petroleum-based plastic films. However, their relatively low toughness and poor folding endurance are two remaining challenges for commercial application. In this work, inspired by fiber-reinforced polymer, a transparent CNF film with favorable combination of toughness and folding endurance is demonstrated by a facile and scalable polyethylene terephthalate (PET) fiber-reinforced strategy. The as-prepared PET fiber-reinforced CNF film not only exhibits a maximum average toughness of 13.7 ± 2.4 MJ/m3 that is nearly 4 times stronger than that of pure CNF film (3.7 ± 1.1 MJ/m3), but also presents superior bending flexibility with a folding endurance of over 104 times that is an order of magnitude higher than that of pure CNF film (~4 × 103 times). Moreover, its underlying principle for the enhanced toughness and foldability is explored. This work provides a facile strategy to prepare tough yet foldable CNF film and could promote its industrial uses in the fields of energy storage devices, packaging, and electronic devices.