The objective of this study is to investigate the microstructure, water permeability and the adhesion of waterborne coating on the flattened bamboo. The flattened bamboo was obtained by softening bamboo culm at 180 °C followed by compression. The microstructure and chemical component of flattened bamboo were investigated by scanning electron microscopy, Fourier transforms infrared spectroscopy, and X-ray diffraction. The adhesion and interface structure of waterborne coating onto flattened bamboo surface were also examined. The result indicated that the parenchyma cells in flattened bamboo were compressed, and starch in the parenchyma cell was extracted during the softening and flattening process in which the main chemical component did not change significantly. The water permeability of both flattened bamboo and bamboo culm is dependent on the direction: longitudinal direction > tangential direction > radial direction. However, the water permeability in all three directions in flattened bamboo was higher than those in the untreated bamboo. In addition, alkali dye solution was found to more easily permeate through the flattened bamboo when compared to acid dye solution, and the permeability varied depending on alkali dye or acid dye concentration. The adhesion of water-based polyurethane coating on the flattened bamboo can reach the second level. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

In this paper, a triple-layer hybrid optical orthogonal frequency division multiplexing (THO-OFDM) for intensity modulation with direct detection (IM/DD) systems with a high spectral efficiency is proposed. We combine N-point asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM), N /2-point ACO-OFDM, and N /2-point pulse amplitude modulated discrete multitoned (PAM-DMT) in a single frame for simultaneous transmission. The time-and frequency-domain demodulation methods are introduced by fully exploiting the special structure of the proposed THO-OFDM. Theoretical analysis show that, the proposed THO-OFDM can reach the spectral efficiency limit of the conventional layered ACO-OFDM (LACO-OFDM). Simulation results demonstrate that, the time-domain receiver offers improved bit error rate (BER) performance compared with the frequency-domain with ∼40% reduced computation complexity when using 512 subcarriers. Furthermore, we show a 3 dB improvement in the peak-to-average power ratio (PAPR) compared with LACO-OFDM for the same three layers.

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