Abstract
Hemp paper made from Manila hemp pulp was processed by a traditional Japanese hand-crumpling technique. The applicability of the hemp paper to clothing was examined. Hand-crumpling decreased the dry tensile index of the hemp paper but increased the seam strength index of the sewn hemp paper. A scanning electron microscope was used to observe a piece of hemp paper; the results showed that pulp fibers that were not hand-crumpled suffered brittle fracture without being elongated, while pulp fibers of hand-crumpled hemp paper were elongated and broken by ductile fracture. This implies that hand-crumpling inhibits cracks generated in the stitch from propagating and produces a high stitch strength index. The air permeability and water absorbency of the hemp paper were considerably increased by hand-crumpling. Hand-crumpling considerably improves the softness of Manila hemp paper and enhances its applicability as clothing material.
In ancient times (eighth and ninth centuries CE), the Japanese used hemp paper for historical documents. Analysis by the Imperial Household Inventory of Precious National Treasures of the registry of tributes of Todai-ji temple—stored in the Shosoin repository—revealed that the paper of ancient documents was made from hemp. 1 The complete papermaking method was implemented by the kamiyain (i.e. authorized public papermaking house) of the zushoryo (i.e. national government office in charge of storing archives describing the national history, supplies of paper, brushes, and inks for official use, Imperial household ritual events, etc.) and is specified in the Engi-shiki (i.e. Procedures of the Engi Era) as part of ritsuryo (i.e. national laws during the Heian period).2,3 Washi paper is highly tough and has a very long service life, compared with paper made in the Western way. In practice, old documents made of Washi paper prepared more than 1000 years ago are preserved in Shosoin.
Wood pulp, raw material for ordinary paper (paper made in the Western way), contains a large amount of lignin. For this reason, ordinary paper is ready to yellow and is lower in strength. On the other hand, the material itself for Washi paper characteristically contains less lignin and, therefore, the delignification is unnecessary, which probably damages the fibers of the paper. It is speculated that the Washi paper has high polymerization degrees of its fibers, is tough, and has a long service life, although a sheet of Washi paper is thin, due to the application of no delignification.
Izumo washi, which was a traditional handmade paper produced in the Izumo province, is described in Shakyo Kanshige, which is a document stored in the Shosoin repository. According to this document, izumo washi paper was as highly valued as those produced in areas such as Mimasaka, Koshinokuni, Harima, and Mino because it was tough, smooth for writing, and of uniform quality. 4 A professional team led by Mr Eishiro Abe, who has been designated as a living national treasure, investigated papers stored in the Shosoin repository and succeeded in reproducing the same paper by the technique for making izumo washi. Mr Abe has investigated new possible applications of washi paper, including experimental modern clothing made from hand-crumpled paper. 5 These textiles were developed by coating the surfaces of the washi paper with konjac paste and crumpling them by hand. 6
By hand-crumpling, innumerable fine wrinkles can be formed on the paper. By mechanical crumpling, such formation cannot be achieved. Mechanically crumpled paper has no feel of warmth and elegance peculiar to the hand-crumpled paper. The coating with Konjac paste can inhibit the fluffing of fibers on the paper surface and maintain the cohesion between the fibers at a high level, which brings out advantages such as the enhancement of water resistance and the like. Mr Issei Miyake, a prestigious Japanese fashion designer, recently presented paper blousons that enjoyed strong reviews for the modern use of a traditional material.7,8
The authors realized the importance of paper clothes and examined the applicability of washi paper to clothing materials having novel functions.9,10 The present study focused on hemp paper used by ancient Japan and examined its applicability to clothes when softened by a traditional hand-crumpling technique. Generally, hemp paper is made from hemp or ramie. However, obtaining these materials in Japan is difficult. Thus, Manila hemp was used as a raw material in this study since it is favorable for industrial production, and its fibers have the same morphological features and same texture as those of finished washi paper. 11 Paper made from Manila hemp pulp compounded with vinylon 12 was also investigated with the aim of developing a papermaking process using a drum drier at 120℃. The authors attempted to develop non-petroleum-type clothing materials making use of traditional Washi paper techniques from Japan.
Experimental details
Test sample
Manila hemp pulp
Manila hemp pulp (BPS-G grade) was obtained (CPMC Co., Canlubang, Philippines). This pulp was prepared by removing the texture from Manila hemp; only the fibers were collected and bleached. The obtained Manila hemp pulp was beaten until the Canadian Standard Freeness reached 550 ml CSF. This pulp was used as raw material for the paper. The pulp had a fiber length of 2–8 mm (average length: ∼5 mm).
Vinylon
Vinylon (SML type) from Unitika Ltd was used. Vinylon has a low melting point and is thermally adhesive at 70℃; it has a size of 1.1 dtex. The fibers were cut into short strips of 3 mm.
Binder
In order to enhance the adhesion of the Manila hemp pulp, an emulsion (Seiko PMC Corp., WS4024) of polyamide/epichlorohydrin copolymer with a molecular weight of ∼1 million was added to the raw material liquid for the papermaking process. With this binder, azetidinium rings contained in the molecular structure are opened and covalently bound to the hydroxyl groups of cellulose molecules to form a cross-linked structure. A previous study showed that the addition of 0.75 wt% binder to the paper increased the wet paper strength; the paper could endure being washing for 20 cycles. 10 Thus, 0.75 wt% binder was added in the present study.
Preparation of hemp paper
Papermaking process
A paper machine (Kawanoe Zoki Co., Ltd) comprising an inclined tanmo paper machine and former was used for testing. This machine has an inline system comprising three steps, that is, a wire part, press part, and drier part. Twenty kilograms of raw material for papermaking was charged through a hopper and paper sheets were prepared. The wet paper was then compressed with press rollers from above and below to squeeze the water out of the wet paper. The wet paper was heated with a Yankee dryer to evaporate the water. Manila hemp paper was wound under the condition that the take-up speed was 10–15 m/min; the maximum weight of the paper became 100 g/m2. The raw materials for papermaking were hemp pulp only and hemp pulp compounded with 3% vinylon. Vinylon was compounded to facilitate high-speed papermaking.
Coating with konjac
Refined konjac flour manufactured by the Japan Konjac Association Incorporated Foundation was used. Firstly, 0.5 wt% konjac flour was added to distilled water, stirred for 30 min, and left to stand for 40 min. Then, 0.02% Ca(OH)2 was added to prepare an aqueous solution of konjac paste directly prior to coating. A bar coater (No. 10, Yasuda Seiki Seisakusho, Ltd) was used to coat the top surface of the hemp paper with 2.64 g/m2 of the aqueous solution of konjac paste. The coated hemp paper was suspended and air-dried for 6 h. The bottom surface of the hemp paper was then coated and air-dried in the same manner as the top surface.
Hand-crumpling
Following the traditional hand-crumpling method, fine crumpling (Figure 1(a)), rod-crumpling (Figure 1(b)), and uncrumpling (Figure 1(c)) were carried out. The term of fine crumpling (Ko-momi) means an operation for forming fine wrinkles on paper, in which the paper is sandwiched between the thumb and the forefinger of each of one’s hands and in this state, the hands are moved finely and relatively. The term rod-crumpling (Boh-shibori) means an operation for forming relatively large winkles in a wide area of the paper, in which the paper is wound around a wooden rod and downwardly pressed against a base. In rod-crumpling, the directions of wrinkles can be made different by changing the winding direction of the paper around the rod. The term uncrumpling (Shiwa-nobashi) means an operation for smoothening wrinkles on the paper, in which the crumpled paper is extended, and the surface of the paper is rubbed with one’s hands. This operation is necessary for the formation of innumerable fine wrinkles on the paper. The hand-crumpling process is performed by repeating a series of the above-described operations many times.
Softening process of Manila hemp paper by the traditional hand-crumpling technique: (a) fine crumpling (ko-momi); (b) rod-crumpling (boh-shibori); (c) uncrumpling (shiwa-nobashi).
By such hand-crumpling process as described above, innumerable fine “wrinkles” can be formed on the paper. Thereby, the paper can be provided with taut hand-feeling. With the hand-crumpling, a feel of warmth and elegance can be expressed by the paper, as it is different from mechanically crumpled paper.
Four workers hand-crumpled each hemp paper sample to minimize differences in crumpling by different workers. The above hand-crumpling steps were carried out for 5 min by one crumpling worker. In other words, the hand-crumpling process for each sample was completed in 20 min by the four crumpling workers. The hand-crumpling was carried out as non-directionally and uniformly as possible.
Measurement method
Change in size and shape by hand-crumpling
A hemp paper sample with a length of 350 mm and width of 240 mm was prepared as a test piece. The length of the test piece was measured before and after hand-crumpling. The crumpling–shrink ratio of the hemp paper was calculated using Equation (1). The weight of the same test piece was measured before and after hand-crumpling. The decrease in the weight ratio was calculated using Equation (2). The thickness of the same test piece was measured at a load of 23.5 kPa with a dial gauge (minimum measurable thickness = 0.01 mm). The thicknesses at 10 randomly selected points of one test piece were measured, and the average value was calculated. The increase in thickness ratio was calculated using Equation (3).
Mechanical properties
The tensile strength of a test piece was tested under dry conditions in compliance with JIS-P8113. The test piece was cut to a width of 15.0 ± 0.1 mm and length of 250 ± 1 mm. The maximum load at failure of the test piece was measured with a tensile tester at a chuck interval of 180 ± 1.0 mm and tension speed of 20 mm/min. The measured value was normalized to a value for a width of 1 m. The tensile index was calculated by dividing the converted value by the basis weight of the hemp paper. The elongation when the test sample broke owing to tension was measured, and the tensile elongation ratio was calculated. In both tests, the measurement was carried out in the longitudinal direction only. In addition, the test piece was swollen with water for 1 h. The test piece was tested under wet conditions in the same manner as described above.
The Clark stiffness of the hemp paper was measured in compliance with JIS-P8143. A test piece with a width of 30 mm and length of 80 mm was sandwiched between two rollers that can be rotated in the clockwise and counterclockwise directions. The critical length of the test piece was measured; the critical length is the length of the test piece when it bends at an angle (critical turning angle) of 90°, caused by its empty weight, with the rotation of the rollers. The Clark stiffness is calculated by raising the critical length to the third power and dividing by 100; this value represents the bending resistance of a test piece owing to its empty weight—that is, the hardness of paper.
Seam strength index
Two test pieces cut in rectangles with a width of 25.0 ± 0.1 mm and length of 140 ± 1 mm were overlaid on each other and machine-sewed in a straight line (stitch type: 301) with 60-count polyester machine-sewing yarn (Yokota Co., Ltd, Daruma Lofty). The seam allowance was 10 mm, and the stitch length was 1.5 mm. The two test pieces were pulled apart and subjected to tension at a constant rate by an elongation-type tensile tester at a clamp interval of 76 mm and tension speed of 300 mm/min (see Figure 2). The maximum load at failure of the test piece was measured, normalized to a value per meter of width, and divided by the basis weight of the hemp paper. This value was defined as the seam strength index.
Testing method of seam strength for sewn papers.
Observation under a scanning electron microscope
A carbon tape for vapor deposition was pasted on a stage for electron microscopy, and a sample was fixed onto the tape. After the fixed sample was dried at room temperature for 24 h, gold was vapor-deposited on the sample using an ion sputterer (E-1010, Hitachi High-Technologies Corp.). An S-3000N scanning electron microscope (SEM; Hitachi Science Systems Co., Ltd) was then used to observe the surface of the papers. The SEM was operated at an accelerating voltage of 20 kV.
Gurley air resistance
The air resistance of the hemp paper was measured using a Gurley testing machine in compliance with JIS-P8117. Firstly, 300 ml of air that was compressed by the weight of an inner cylinder was passed through a 50 mm × 50 mm test piece fixed to a tightening plate with a circular hole having a diameter of 28.6 ± 0.1 mm (air permeation area: 642 mm2). The time period required for 100 ml of the compressed air to pass through the hole was represented by t [s]. A shorter t meant a higher air permeability for the hemp paper.
Water absorption property
The rising height (mm) of distilled water from 2.5 min after the start of rising to 30 min after capillary action was measured according to the Byreck method. A greater rising height meant greater water absorption.
Results and discussion
Effect of hand-crumpling and coating with konjac paste on the mechanical properties of hemp paper
Effects of hand-crumpling process on the size and weight of Manila hemp paper
The hemp paper samples were subjected to the tensile test under wet and dry conditions. Figure 3(a) shows the tensile indexes under the dry condition. Figure 3(b) shows the tensile indexes under the wet condition. Hand-crumpling decreased the tensile indexes under the dry condition by about 45–55 N-m/g. This may be because hand-crumpling caused less agglutination of Manila hemp pulp fibers; that is, the bonds between the fibers were weakened.
Effects of hand-crumpling and coating with konjac paste on tensile index of Manila hemp paper: (a) dry condition; (b) wet condition.
The effect of coating the hemp paper with konjac paste on the tensile index was examined. Almost no difference in tensile index due to coating with konjac paste was found. Hemp paper samples made from Manila hemp pulp compounded with 3.0% vinylon and hand-crumpled showed an increase in the tensile index under the dry condition of about 5 N-m/g.
The tensile indexes under the wet condition were about 20–30 N-m/g. Coating with konjac paste and compounding with vinylon caused no significant difference in the tensile index. The tensile elongation of the hemp paper was also examined. Figures 4(a) and (b) show the tensile elongations under the dry and wet conditions, respectively. Hand-crumpling increased the tensile elongation under the dry condition by 7.0–8.0 points. Coating with konjac paste and compounding with vinylon barely affected the tensile elongation of the hemp paper.
Effects of hand-crumpling and coating with konjac paste on tensile elongation of Manila hemp paper: (a) dry condition; (b) wet condition.
Hand-crumpling increased the tensile elongation of the samples by 1.0–2.0 points under the wet condition. Coating with konjac paste was found to have no effect on the tensile elongation. Compounding with vinylon caused the tensile elongation of the hemp paper to increase by 1.0–2.0 points compared with hemp paper made from Manila hemp pulp only.
The above results show that hand-crumpling caused the hemp paper to easily elongate and have higher softness. The effects of hand-crumpling on the softness were quantified using the Clark stiffness. The Clark stiffness represents the deformation of hemp paper in the bending direction. Figure 5 shows the effects of coating with konjac paste and hand-crumpling on the Clark stiffness of the hemp paper. Hand-crumpling caused the stiffness to decrease by 25.0—that is, hand-crumpling made the hemp paper softer.
Effects of hand-crumpling and coating with konjac paste on the Clark stiffness of Manila hemp paper.
Effects of hand-crumpling on the seam strength index of hemp paper
The above results show that hand-crumpling effectively enhanced the softness of hemp paper. This is advantageous to the use of hemp paper as clothing material. The hand-crumpled hemp paper was then examined with regard to its potential as clothing material. Firstly, it was examined whether or not the hemp paper is durable to machine sewing. The hemp paper was cut into rectangles and machine-sewed. The seam strength index of the hemp paper was measured (see Figure 6).
Effects of hand-crumpling and coating with konjac paste on the seam strength index of Manila hemp paper.
The seam strength indexes of the hand-crumpled samples were higher than those not hand-crumpled by about 7–10 N-m/g. That is, the hemp paper softened by hand-crumpling exhibited a clearly decreased tensile index but enhanced seam strength index. This indicates that hand-crumpling of the hemp paper is advantageous for sewing. Coating with konjac paste hardly affected the seam strength indexes. Compounding with vinylon caused the seam strength index to increase by about 1 N-m/g compared with the hemp paper made from Manila hemp pulp only.
Hand-crumpling caused the tensile indexes to decrease by about 45–55 N-m/g but the seam strength index to increase by about 7–10 N-m/g. The following experiment was carried out: a test piece was perforated without thread being passed through the perforations and subjected to a tensile test under the same conditions as those for the seam strength index; the schematic is shown on the left-hand side of Figure 7. The fractured surfaces of the test piece after breaking were observed with the SEM. The results suggest the following: bonds between pulp fibers of samples that were not hand-crumpled were difficult to be relaxed, so the pulp broke without being elongated (i.e. brittle fracture (Figure 7(a))); bonds between pulp fibers of hand-crumpled samples were readily relaxed, so the pulp fibers broke after being elongated (i.e. ductile fracture (see Figure 7(b))). The fractured parts of the test pieces showed that fiber extraction occurred differently depending on whether or not hand-crumpling was carried out. Cracks were assumed to be inhibited from propagating from the seams of the hand-crumpled test pieces, which resulted in the high seam strength index of the hemp paper.
Scanning electron micrograph of Manila hemp paper test piece sewn with needle not threaded after tensile test (×70): (a) without crumpling; (b) with crumpling. A schematic diagram of the test piece prior to the tensile test is on the left-hand side.
Effects of hand-crumpling on air permeability and water absorption
Air permeability and water absorption are important properties that affect the wearing comfort of clothes. The Gurley air resistance of hemp paper was measured to examine the air permeability (see Figure 8). All of the hand-crumpled samples exhibited low Gurley air resistances, that is, about 4–6 s. Samples that were not hand-crumpled and coated with konjac paste showed high Gurley air resistances of 120–140 s. In other words, hand-crumpling enhanced the air permeability by 100 s.
Effects of hand-crumpling and coating with konjac paste on air resistance (Gurely) of Manila hemp paper.
Coating with konjac paste and compounding with vinylon had almost no effect on the air resistance of the hand-crumpled samples; the air resistance was low for all of the hand-crumpled samples. In other words, hand-crumpling caused the air resistance to considerably decrease in all cases and thus enhanced the air permeability. This may be because hand-crumpling caused the fibers to disentangle and form sufficient gaps for air to pass through. These results showed that hemp paper with high air permeability can be produced by hand-crumpling.
The water absorption of hemp paper was then tested. Figure 9 shows the time-dependent water absorption heights of hemp paper made from hemp pulp only. The water absorption heights of the hand-crumpled hemp paper were greater than those of the hemp paper that was not hand-crumpled. The water absorption heights of the hemp paper coated with konjac paste were smaller than those of the uncoated hemp paper. The water absorption heights measured 30 min after the start of measurement were compared. The water absorption height of the hand-crumpled hemp paper that was not coated with konjac paste was greatest at about 120 mm. In other words, water absorption was reduced by the coating with konjac paste. This shows that the water absorption height of the hemp paper was more affected by hand-crumpling than by the coating with konjac paste. This may be because hemp paper softened by hand-crumpling loosened agglutination of fibers, so the fibers became separate from each other; this allowed capillary action to occur more easily, and the water absorption property was enhanced.
Time dependence of water absorption of paper made purely from Manila hemp pulp.
Effects of hand-crumpling on sewing of hemp paper
Clothes were prepared by using hand-crumpled hemp paper coated with konjac paste. Figure 10 shows a sewn vest. Figures 10(a)–(d) show magnified photographs of the buttonholes, buttons, machine-sewn portion, and dart portion, respectively. Hand-crumpled hemp paper could easily be used to fabricate the machine-sewn and buttonhole portions.
Image of vest made with hand-crumpled Manila hemp paper and magnified drawings of parts of the vest: (a) buttonholes; (b) buttons; (c) machine-sewn portions; (d) dart portions.
Hemp paper that was not hand-crumpled was difficult to feed into the machine, which disabled the machine sewing. In addition, the sewing of the buttonholes was impossible. This may be because hemp paper that was not hand-crumpled has no concavity and convexity at the surface; thus, the hemp paper could not engage with the teeth of the cloth-feeding gear of the sewing machine and could not move in the advancing direction. Accordingly, hand-crumpling the hemp paper and forming a concave and convex surface is very important to allow the use of a sewing machine.
The hemp paper produced in this study was subjected to repeated washing. All of the hemp paper samples to which the binder was added were durable and did not break after being washed for 20 cycles, irrespective of hand-crumpling.
For comparison, measurement was made on the mechanical properties of a spun-bonded nonwoven polyester fabric with a real fiber weight of 60 g/m2, used for disposable medical gowns. As a result, the tensile index was almost equal to that of the hemp paper hand-crumpled in this study, and the tensile elongation was about two to three times that of the hemp paper. However, the nonwoven fabric barely exhibited water absorption property, and the air permeability was inferior to that of the hemp paper. The results suggest that the hemp paper produced in this study is usable as a semi-disposable type clothing material.
Conclusions
Hemp paper made from Manila hemp pulp was hand-crumpled based on a traditional Japanese technique. The hand-crumpled hemp paper was examined with regard to its applicability as clothing material. The following results were obtained.
Hand-crumpling dry hemp paper caused the tensile indexes to decrease by about 45–55 N-m/g, the tensile elongation to increase by 7.0–8.0 points, and the stiffness to lower by about 25.0. The results quantitatively showed that hand-crumpling effectively softens hemp paper. Dry hemp paper made from Manila hemp pulp compounded with 3.0% vinylon had a higher tensile index by about 5 N-m/g than hemp paper made from hemp pulp only. Hand-crumpling increased the seam strength index of the hemp paper by about 7–10 N-m/g. The cause was examined by observing a fractured part of the hemp paper after the tensile test. Pulp fibers of hemp paper that was not hand-crumpled underwent brittle fracture without being elongated. Pulp fibers of hand-crumpled hemp paper underwent ductile fracture while being elongated. The results suggest that hand-crumpling stopped cracks generated at the seam from easily propagating, which resulted in a high seam strength index. Hand-crumpling had a large effect on the air permeability and caused the air resistance to decrease to about 4–6 s. This result shows that the air permeability of hemp paper can be enhanced by hand-crumpling. With crumpling, coating has less effect on air resistance. Without crumpling, air resistance increased a little after coating. Hand-crumpled hemp paper had higher water absorption than hemp paper that was not hand-crumpled. The water absorption height of hemp paper not coated with konjac paste reached about 120 mm 30 min after the start of the measurement. Coating with konjac paste caused the water absorption to decrease; however, the decrease was small. The results show that the water absorption of hemp paper is largely affected by hand-crumpling. Thus, hand-crumpling of hemp paper can intensively increase its softness and enhance its applicability as clothing material.
Footnotes
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Acknowledgment
We thank Ms Wakako Tanabe (Group Leader for the Promotion of Compulsory Education) of the Compulsory Education Division, Shimane Prefectural Government, for her kind advice on English proofing.