The recycling of filaments used in three-dimensional (3D) printing systems not only mitigates the environmental issues associated with conventional 3D printing approaches but also simultaneously reduces manufacturing costs. This study investigates the effects of successive recycling of polylactic acid (PLA) filaments, which were used in the printing process, on the mechanical properties of recycled filaments and printed objects. The mechanical strengths of the printed PLA and the adhesion strengths between 3D-printed beads were evaluated via the tensile testing of the horizontally and vertically fabricated specimens. Gel permeation chromatography analysis revealed a reduction in the molecular weight of the polymer as a result of recycling, leading to a decrease in the mechanical strength of the 3D-printed product. Additionally, scanning electron microscopy images of the cutting plane showed that the fabricated beads were broken in the case of the horizontally fabricated specimen, whereas in the case of the vertically fabricated samples, the adhesion between the beads was weak. These findings indicate that the mechanical strength in the in-plane and out-of-plane directions must be improved by increasing the mechanical strength of the bead itself as well as the adhesion strength of the beads.

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The purpose of this study is to investigate the relationships between moral sensitivity for topics related to science and preference for science, and belief about learning science. 129 middle school students were involved in this study and completed questionnaires to measure moral sensitivity for topics related to science, preference for science, and belief about learning science. Students' responses were analysed to show the distribution of variables and the correlation between variables by gender and grade. As a result, moral sensitivity was not affected by respondents' grades and genders, but was affected by different topics. Preference for science was not affected by respondents' grades and genders, while belief about learning science was not affected by respondents' genders but affected by lower grade. There were correlations between students' moral sensitivity and preference in case of female students and higher grades, as well as relationship between moral sensitivity and belief about learning science. This result infers that students who have higher moral sensitivity can prefer science and show more positive belief about learning science. Also, it can implicate that affective domain including interest or belief can play an important role in the context of science education focusing on moral aspect or ethics, and that teachers should be aware of personal differences in case of teaching moral aspect of science.

Ⅰ. 서론과학의The purpose of this study is to explore the relationship between motivational belief about learning science, self-directed learning ability and conceptual understanding of matter change with a quantitative method, assuming that motivational belief and self-directed learning ability might affect conceptual understanding.To do this, the authors investigated middle school students' motivational belief about learning science, self-directed learning ability, and conceptual understanding of matter change using measurement tools based on previous studies, and then analysed the casual relationship between three variables using PLS structural equation model. As a result, three latent variables in this study could be evaluated as appropriated in reliability and validity. And also, self-directed learning ability could affect both the motivational belief and conceptual understanding, while motivational belief could affect only self-directed learning ability but not conceptual understanding. Through this study the authors confirmed that in the context of science learning self-directed learning ability can directly affect conceptual understanding but motivational belief can affect indirectly. This study is significant in that the causal relationship between different variables in science learning could be confirmed in a quantitate manner, and also in that it can suggest PLS structural equation method as a new research methodology in science education research area. Lederman, 1992;Ryan & Aikenhead, 1992;Pomeroy, 1993;Hammer, 1994a;Hammer, 1994b;Redish et al., 1998;Tsai, 1998;Im, 2001). Table 3와 같다. Table 3. The structure of survey tool for motivational belief in learning science Keywords