As a high-performance material for preparing composite materials, polyimide fibers suffer from many potential drawbacks, including poor bonding with other substrates, which results in composite materials with poor mechanical properties. Therefore, this study proposed a simple and rapid technique for obtaining loose, porous polyimide fiber papers by implementing a wet method using equal amounts of polyimide fiber and polyimide fiber paper as reinforcements, respectively. The polyimide resin-based composite materials were prepared by hand lay-up and hot pressing. The results showed that the paper-based reinforcement exhibited high porosity and the fibers were arranged with a uniform pore size distribution. The tensile properties, bending performance, and interlaminar shear performance of the paper-based composite improved by 130%, 108%, and 34.5%, respectively, compared to those of the fiberbased counterpart. The factors affecting the mechanical properties of the composites were analyzed based on the fiber length, fiber beating or lack thereof, and the basis weight of the paper. The increased uniformity of the polyimide fiber paper changed the ordering of the fibers and resolved drawbacks such as difficult dispersion, uneven pore size distribution, and poor mechanical properties related to single fibers in the resin-based composite material.

In this study, rice straw (RS) was liquefied by ethylene carbonate (EC) using H₂SO₄ as a catalyst. The effects of various process conditions on the liquefaction characteristics were investigated by FT-IR and residue content analysis. The results show that cellulose and lignin are degraded during the liquefaction process and large amounts of groups are generated. In addition, it is difficult to effectively liquefy RS by using EC alone as the liquefying agent without other additives. Compared to water addition on liquefaction, the residue content can be significantly reduced up to 30% by adding H₂O₂. It has also been proved that the liquor ratio (RS/EC, w/v) of 1∶5 with H₂O₂ as an additive at 145℃ for liquefaction time of 60 min in the presence of H₂SO₄ can accelerate the liquefaction process and high liquefaction yield can be obtained.