The authors are motivated to develop a series of hydrochromic copolymers with fast response, reversibility, repeatability, and visual transparency transition. The hydrochromic block copolymers are based on the rational ratio of hydrophilic segments of poloxamer block and hydrophobic segments of ethyl cellulose according to the preparation method of polyurethane. By tuning the ratio of hydrophilic segments or adding hygroscopic salts, the hydrochromic polymer is endowed with the ability to visualize the transparency in response to the relative humidity. Especially, the response time of the polymer is extremely shortened, up to 1 s for the optimized sample. Within the moisture stimulation, the hygroscopic swelling increases the film thickness, leading to a reversible transparency switching from a highly transparent state (82%) to an opaque white state (20.5%).

Currently, about 20 universities in China offer undergraduate courses related to pulp and paper. This large number is congruent with the rapid development of the Chinese pulp and paper industry in the past several decades. In the context of ever-increasing internationalization and global cooperation, English-assisted teaching in Chinese universities has much potential. The wide-spread implementation of English-assisted teaching would promote the career development of students and help foster the advancement of the Chinese pulp and paper industry.