The processing routes from spruce,

The processing routes from spruce, to either holocellulose fibers or Kraft fibers and final high-density paper structures are depicted schematically in Figure 1. Holocellulose fibers were obtained through a mild PAA delignification process, see experimental section. To keep the pH and PAA concentration stable throughout the reaction, multiple rounds of treatment were undertaken until individual fibers were disintegrated. No mechanical stirring was used in order to minimize fiber damage. Neither holocellulose nor Kraft fibers were subjected to beating in order to minimize fiber damage.