Research on the Basic Performance and Fiber Appearance Characteristics of Grass Paper from Stellera chamaejasme in Different Origins on the Qinghai–Tibet Plateau

Abstract

As one of the important carriers of Tibetan ethnic minority culture inheritance on the Qinghai–Tibet Plateau, the basic properties and fiber morphology of grass paper from Stellera chamaejasme have a significant impact on its paper quality. The basic properties of grass paper from Stellera chamaejasme from six different production areas on the Qinghai–Tibet Plateau were systematically tested and analyzed according to relevant national standards, and the fiber morphology characteristics were experimentally observed. The results showed that the grammage, thickness, density, bulk, brightness, gloss, folding resistance, and tensile strength performance indicators of grass paper from Stellera chamaejasme on the Qinghai–Tibet Plateau were generally good; the basic properties of grass paper from Stellera chamaejasme in different origins vary to some extent; and the fibers of grass paper from Stellera chamaejasme are mostly yellow in color, with slender fibers and small, uneven widths. The ends of the fibers are sharp, and the fibers are arranged in a staggered manner. There is a phenomenon of fiber aggregation, showing a clear flat band structure with a clear mesh structure. The surface has many rough horizontal knots, visible cell cavities, mixed cells, and obvious longitudinal wavy folds. Therefore, the basic performance of grass paper from Stellera chamaejasme is excellent, which is consistent with the historical description of the excellent quality of Tibetan paper, and is closely related to its fiber morphology characteristics.

1. Introduction

The grass paper from Stellera chamaejasme is one of the main types of traditional Tibetan paper. It is widely used in all aspects of Tibetan production and life. It is a traditional handmade paper that has been produced and used in Tibetan areas for a long time, and has played an important role in the economic, social, and cultural development of Tibetan areas. As one of the important carriers of Tibetan cultural heritage, Tibetan paper, represented by Stellera chamaejasme, has attracted extensive attention due to its excellent characteristics [1].

Tibetan traditional manual papermaking has a long history. According to the records of ancient Chinese Han and Tibetan history books, the papermaking method in the Central Plains was introduced to Tubo in the Tang Dynasty [2,3]. Due to the differences in natural conditions and plant resources between the Central Plains and Tibet, it is impossible to cultivate hemp, rattan, papyrus, and other commonly used papermaking materials in the Central Plains. Princess Wencheng brought papermaking craftsmen into Tibet to help Tibetans find new plant materials such as Daphne odora, laurel, lampstand tree, wild tea grass, and Stellera chamaejasme, which are used to manufacture Tibetan paper [4]. Therefore, the raw materials used in grass paper from Stellera chamaejasme are common Stellera chamaejasme in Tibet. Stellera chamaejasme L., the scientific name of the Wolf poisonous weed, is also known as heartbroken grass, mugwort flower, big bowl flower, and steamed bread flower in folklore. It is a perennial herb belonging to Stellera chamaejasme in the Daphne family, and is also one of the main toxic plants in grasslands in China [5,6]. It is an associated species of the grassland plant community. It is widely distributed on the degraded grassland of dry grassland, sandy grassland and typical grassland in Northeast, North China, Southwest, Northwest China, Ningxia, Gansu, Qinghai, Tibet, Inner Mongolia, and other places in China, as well as in the sunny parts of high mountains. It has become a major constructive species on the severely degraded grasslands [7,8,9].

Domestic scholars’ research on the scientific detection of Tibetan paper started late. In recent years, some scholars have studied the durability, bacteriostasis, anti-aging, light stability, and fiber structure of Tibetan paper, and also made new discoveries [10,11,12,13,14,15,16]. However, these studies mainly focus on the single origin of Tibetan paper, or on the performance indicators of Tibetan paper. The purpose of this research contribution is to systematically and comprehensively study the basic properties of grass paper from Stellera chamaejasme from different origins in the Qinghai Tibet Plateau, analyze its fiber morphology characteristics, scientific papermaking process, and verify the rationality of previous descriptions. This will provide a reliable basis for the protection, restoration, and reproduction of Tibetan paper relics or products, and also lay a solid research foundation for the further development and utilization of grass paper from Stellera chamaejasme.

2. Materials and Research Methods

2.1. Overview of the Study Area

The Qinghai–Tibet Plateau is the largest plateau in China and has the highest altitude in the world. It is known as the “roof of the world” and the “third pole”. It has a vast territory and high terrain. From the south to the north, there are four huge mountains extending from the west to the east, namely, the Altun Qilian Mountains, the Kunlun bayankara mountains, the karakunlun Tanggula mountains, and the Himalayas. Tibet is the main part of the Qinghai–Tibet Plateau, accounting for about half of the total area of the Qinghai–Tibet Plateau, with an average altitude of more than 4000 m. The climate of the Tibetan Plateau is cold, and the annual average temperature is below 5 °C, and the temperatures of the northern Tibetan Plateau and the upper part of the mountains are below 0 °C; there is less precipitation and distinct dry and wet seasons. April to September is the rainy season, and about 90% of the precipitation is concentrated in the rainy season, while October to March is the dry season. The Qinghai–Tibet Plateau has a unique natural environment, a complex ecological environment, and is rich in natural resources such as light, water, grassland, forest, minerals, and wild plants, which provide favorable conditions for the development of industry, agriculture, forestry, animal husbandry, and fishery on the plateau, as well as a good natural paper making environment for the paper industry in Tibet.

2.2. Experimental Materials and Treatment

Six uniform and paperless grass paper samples from Stellera chamaejasme (numbered S1–S6) were selected from six different places of origin in the Qinghai Tibetan region, Yunnan Tibetan region, Sichuan Tibetan region, and Tibet (

Table 1. Grass paper from Stellera chamaejasme in Qinghai–Tibet Plateau.

Sample No.	Paper Type	Plant Raw Materials	Paper Description	Paper Size (CM)	Origin/Manufacturer	Cooking Process
S1	Xiangda Tibetan paper	Stellera chamaejasme L.	Dark yellow, smooth paper	21 × 15	Nangqian County, China	Steam and cook once in the earth alkali or industrial alkali
S2	Qiangduo Tibetan paper	Stellera chamaejasme L.	Yellow, wrinkled, fiber bundle	73 × 28	Shangri-La, China	Steam and cook once in the stove ash or wood ash
S3	Dege Tibetan paper	Stellera chamaejasme L.	White, uniform texture, fiber bundle	71 × 55	Dege County, China	Steam and cook once in the stove ash or industrial alkali
S4	Potala Palace Tibetan paper	Stellera chamaejasme L.	Ivory white is gray, thinner, with black impurities	74 × 55	Lhasa, China	Steam and cook once in the earth alkali or industrial alkali
S5	Jingdong Tibetan paper	Stellera chamaejasme L.	White gray, fiber bundles are clearly visible	72 × 56	Lang County, China	Steam and cook once in the wood ash or earth alkali or industrial alkali
S6	Xuela Tibetan paper	Stellera chamaejasme L.	Gray, thinner	76 × 49	Nimu County, China	Steam and cook once in the earth alkali or industrial alkali

). The paper samples were treated at constant temperature and humidity according to the requirements of the national standard GB/T 10739-2002.

2.3. Experimental Method

2.3.1. Measurement of Foundation Performance

The paper grammage is measured by using the YQ-Z-12 paper quadrant scale of the Sichuan Changjiang paper instrument factory in accordance with the national standard GB/T 451.2-2002 determination of paper and board weight. The specific method is as follows: use a sampler to take a circular sample with an area of 0.01 m², and take 10 samples for each kind of paper sample; and weigh with a scale with a division value of 0.001 g (sample mass below 5 g) or 0.01 g (sample mass above 5 g) and record. The thickness shall be measured according to the national standard GB/T 451.3-2002 determination of the thickness of paper and paperboard using the American Thwing-Albert instrument company (West Berlin, NJ, USA) progage electronic thickness gauge. The specific method is as follows: use a sampler to take circular samples with an area of 0.01 m², and take 10 samples for each paper sample; use the electronic thickness gauge, adjust the zero point of the instrument, and put the sample on the measuring surface; and when measuring, move the other measuring surface to the sample at a speed of less than 3 mm/s. After the indicated value is stable, complete the reading within 5 s, record the experimental data, and avoid other pressure shocks during the experiment.

Brightness is measured by the XT-48B/BN whiteness tester of Hangzhou yante Technology Co., Ltd. (Hangzhou, China) in accordance with the national standard GB/T 7974-2013 determination of blue diffuse reflectance factor D65 brightness of paper, board, and pulp. Gloss is measured according to the international standard GB/T 8941-2013 determination of specular glossiness of paper and paperboard. The Japanese Tokyo Denshoku (Tokyo, Japan) TC-108DP/A multi angle glossometer is used to select the incident angles of 45°, 60°, 75°, and 85°. These four angles were selected in the gloss experiment of handmade paper because they can simulate different observation conditions. An angle of 45° is close to daily oblique observation, 85° is close to vertical observation, and 60° and 75° are common angles in the middle. At the same time, this meets the relevant measurement standards. An angle of 60° is a general angle, 85° is suitable for measuring high gloss, 45° is suitable for measuring low gloss, and 75° can be used as a supplement. By measuring from different angles, the gloss performance of handmade paper at different angles can be compared, and its optical properties and quality can be evaluated more comprehensively and accurately.

According to the national standard GB/T 457-2008 determination of folding resistance, the folding resistance is tested by the U.S. Tinius Olsen (Horsham, PA, USA) MIT#1VS fold intensity tester using the MIT method. In this paper, the folding index is used to express the folding strength of paper samples. According to the national standard GB/T 12914-2008 determination of tensile strength of paper and board, the tensile strength was tested by the constant speed tensile method and the kzw-300 micro control tensile testing machine of Changchun paper testing machine Co., Ltd. (Changchun, China) In this paper, the tensile index is used to describe the tensile strength of paper samples.

The sample grammage calculation Formula (1), density calculation Formula (2), bulk calculation Formula (3), folding index calculation Formula (4), tensile strength calculation Formula (5), and tensile index calculation Formula (6) are as follows:

$$\mathrm{G}={\displaystyle \frac{\mathrm{M}}{\mathrm{S}}}$$

(1)

where G is grammage (g/m²); M is the total mass of 10 0.01 m² samples (g); and S is the total area of the sample (m²).

$$\mathrm{D}={\displaystyle \frac{\mathrm{G}}{\mathrm{T}\times 1000}}$$

(2)

where D is density (g/cm³); G is grammage (g/m²); T is the thickness (mm); and the constant 1000 is a unit conversion factor.

$$\mathrm{V}={\displaystyle \frac{\mathrm{T}\times 1000}{\mathrm{G}}}$$

(3)

where V is the bulk of the paper (cm³/g); G is the grammage of paper (g/m²); T is the thickness of the paper (mm); and the constant 1000 is a unit conversion factor.

$$\mathrm{I}={\displaystyle \frac{\overline{\mathrm{L}}}{\mathrm{G}}}$$

(4)

where I is the folding index; $\overline{\mathrm{L}}$ is the average value of folding resistance (logarithm); and G is the grammage of the sample (g/m²).

$$\mathrm{S}={\displaystyle \frac{\overline{\mathrm{F}}}{\mathrm{W}\mathrm{i}}}$$

(5)

where s is tensile strength (kN/m); $\overline{\mathrm{F}}$ is the average value of the maximum tension (N); and Wi is the width of the specimen (mm).

$$\mathrm{I}={\displaystyle \frac{\mathrm{S}}{\mathrm{G}}}\times {10}^3$$

(6)

where I is tensile index (N· m/g); S is tensile strength (kN/m); G is the average grammage value of the sample (g/m²); and the constant 10³ is a unit conversion factor.

2.3.2. Measurement of Fiber Morphology

The fiber morphology of the samples was observed by the KEYENCE (Osaka, Japan) vhx-600k ultra depth of field 3D video microscope, xsp-2ca biological microscope (Shanghai, China), and JEOL (Tokyo, Japan) jsm-6610lv scanning electron microscope. The preparation of the Herzberg stain is as follows: add 25 mL distilled water to 50 g dry ZnCl₂ to prepare saturated solution, dissolve 0.25 g iodine and 5.75 g potassium iodide in 12.5 ml distilled water, mix the two solutions, stand for 12–24 h, take the clear solution into the dark bottle, and add 0.01 g iodine. The preparation of fiber suspension is as follows: the paper is moistened and torn with water, rolled into about 0.1 g ultra dry pellets, and vibrated with distilled water. Use a dropper to take the suspension to drip on the slide for drying, add gelatin to disperse, cool it, dye it with dye for 1 min, and cover the slide to absorb the remaining liquid for standby purposes.

3. Results and Analysis

3.1. Basic Properties of Grass Paper from Stellera chamaejasme in Different Origins

See

Table 2. The grammage, thickness, density, and bulk of grass paper from Stellera chamaejasme.

Sample No.	Grammage (g/m2)	Thickness (mm)	Density (g/cm3)	Bulk (c m3/g)
S1	80.87	0.111	0.729	1.373
S2	142.97	0.269	0.531	1.882
S3	60.00	0.194	0.309	3.233
S4	56.49	0.190	0.297	3.363
S5	72.41	0.344	0.210	4.751
S6	60.00	0.179	0.335	2.983

for the test results of the grammage, thickness, density, and bulk of each sample of grass paper from Stellera chamaejasme. The stability of paper grammage is directly related to the quality of paper. Its height and uniformity (including horizontal and vertical uniformity) affect the physical, mechanical, optical, printing, and electrical properties of paper, and determine the physical properties of paper such as tensile strength, folding strength, tightness, and thickness [17,18,19]. The measurement results of grammage showed that the grammage of grass paper from Stellera chamaejasme in Tibet was mostly low, indicating that it was light in weight; there are some differences in the grammage of grass paper from Stellera chamaejasme in different origins, but most of them have little difference, and even have the same grammage. For example, the grammage of samples S3 and S6 are the same, both of which are 60.00 g/m²; the grammage of sample S2 was higher than that of other samples; and the grammage order of each sample is as follows: S2 > S1 > S5 > S3 ≥ S6 > S4.

Thickness and grammage are closely related. In general, the paper thickness is large, and its grammage is correspondingly high, but this is not absolute. Although some papers are thin, their grammage is greater than or equal to that of thicker papers [20]. The thickness measurement results showed that most of the grass paper from Stellera chamaejasme in Tibet was not thick; the order of thickness of each sample is as follows: S5 > S2 > S3 > S4 > S6 > S1. The relationship between thickness and grammage is not static, and is caused by the influence of tightness. The density of handmade paper depends on the type of raw fiber, beating degree, dehydration during papermaking, wet pressing degree, and calendering degree. The density of each sample is small, and the order is as follows: S1 > S2 > S6 > S3 > S4 > S5. The bulk of paper is generally closely related to its tensile strength, ink absorption, and opacity. The order of bulk is as follows: S5 > S4 > S3 > S6 > S2 > S1.

The brightness test results of each sample are shown in

Table 3. The brightness of grass paper from Stellera chamaejasme.

Sample No.	Brightness (%ISO)
	Surface A	Surface B
S1	21.43	21.42
S2	20.06	20.24
S3	52.64	52.95
S4	38.93	39.00
S5	45.57	45.87
S6	45.98	46.03

. The results showed that the brightness of grass paper from Stellera chamaejasme in Tibet was low; there is little difference in brightness between side A and side B of the same paper from different origins. Gloss, as a characteristic of paper surface, depends on the ability of specular reflection light on paper surface. The gloss test results of each sample under different incident angles are shown in

Table 4. The gloss test results of grass paper from Stellera chamaejasme.

Sample No.	45° Brightness (%)		60° Brightness (%)		75° Brightness (%)		85° Brightness (%)
	Surface A	Surface B	Surface A	Surface B	Surface A	Surface B	Surface A	Surface B
S1	4.1	4.0	4.4	4.4	4.1	4.1	3.0	2.8
S2	5.7	6.0	2.6	2.5	1.2	0.9	0.8	0.1
S3	4.3	4.7	5.2	5.6	3.4	4.3	1.2	1.7
S4	3.7	3.8	6.0	5.3	4.8	4.1	0.9	0.6
S5	4.2	4.1	5.8	5.7	4.2	4.2	0.7	1.0
S6	3.7	3.7	5.1	5.2	4.6	4.2	1.4	0.8

. The results showed that the gloss of grass paper from Stellera chamaejasme was not high under the irradiation of 45°, 60°, 75° and 85°, respectively, which was suitable for printing and reading; the gloss test results of surface A and surface B of each sample are almost the same.

Folding resistance is one of the basic mechanical properties of paper. It should be noted that due to the use of manual papermaking, the thickness of traditional handmade paper from different origins will be different, and even the thickness of different handmade paper from the same origin will be different. In order to compare the paper samples with different thickness under the same amount, it is necessary to use the folding index to quantify and process the data. The bending resistance test results of each sample in the transverse and longitudinal directions are shown in

Table 5. The folding resistance of grass paper from Stellera chamaejasme.

Sample No.	Folding Resistance Average		Folding Resistance Index
	Transverse	Longitudinal	Transverse	Longitudinal
S1	116	132	1.43	1.63
S2	148	249	1.04	1.74
S3	18	44	0.30	0.73
S4	70	82	1.24	1.45
S5	30	68	0.41	0.94
S6	25	37	0.42	0.62

. The results showed that the folding properties of grass paper from Stellera chamaejasme in different habitats were quite different. The folding indexes of samples S1, S2, and S4 were larger in the transverse and longitudinal directions, indicating that the folding properties of these three samples were better, while the folding indexes of samples S3, S5, and S6 were smaller in the transverse and longitudinal directions, indicating that their folding properties were lower than those of the other three samples; the longitudinal folding index of each sample is greater than its transverse folding index, indicating that the longitudinal folding performance of each sample is better than its transverse folding performance; and the longitudinal folding resistance of each sample is ranked from high to low as follows: S2 > S1 > S4 > S5 > S3 > S6.

Tensile strength is widely used to characterize the mechanical properties of paper, and is one of the most important parameters in judging the strength of paper materials. The tensile strength test results of each sample are shown in

Table 6. The tensile strength of grass paper from Stellera chamaejasme.

Sample No.	Tensile Strength (kN·m)		Tensile Index (N·m/g)
	Transverse	Longitudinal	Transverse	Longitudinal
S1	4.54	6.21	56.14	76.79
S2	1.05	1.22	7.34	8.53
S3	1.39	3.42	23.17	57.00
S4	1.65	1.83	24.42	27.08
S5	1.72	1.81	23.75	25.00
S6	2.22	2.99	29.72	40.03

. The results showed that the tensile strength of grass paper from Stellera chamaejasme in Tibet was generally good, and the tensile indexes of samples S1, S3, S4, S5, and S6 in the transverse and longitudinal directions were higher, indicating that their tensile properties were also better, and the tensile indexes of sample S2 in the transverse and longitudinal directions were significantly lower than those of the other five samples, indicating that their tensile properties were low; the longitudinal tensile index of each sample was greater than its transverse tensile index, indicating that the longitudinal tensile property of each sample was better than its transverse tensile property; the longitudinal tensile properties of each sample were ranked from high to low as follows: S1 > S3 > S6 > S4 > S5 > S2.

3.2. Fiber Morphology of Grass Paper from Stellera chamaejasme in Different Origins

Paper is a special material made of plant fiber and non-plant fiber (mainly plant fiber) as raw materials, adding non fiber materials such as rubber, filler, and additives, and then processed into pulp through papermaking, drying, pressing, and other processes [21,22]. When observed under the objective lens magnification of the super depth-of-field three-dimensional video microscope at 200 times, it was found that grass paper fiber from Stellera chamaejasme were staggered, with disorderly arrangement directions, and the directionality was obviously inferior to that of machine-made paper, with obvious beating marks and fiber flocculation (Figure 1); the fiber of grass paper from Stellera chamaejasme sample is slender. Compared with the average fiber width the Stellera chamaejasme root and leaf stem [23] (about 8.2–13.6 μm), the average fiber width after paper formation shows little change (

Table 7. The fiber width of grass paper from Stellera chamaejasme.

Sample No.	Fiber Width (um)
	1	2	3	4	5	6	7	8	9	10	Average Value
S1	34.44	29.71	16.45	24.34	28.94	14.34	22.41	15.83	34.28	16.45	23.72
S2	8.23	9.85	7.47	6.76	9.85	9.42	9.02	10.69	6.12	9.47	8.69
S3	10.30	9.56	10.30	16.51	10.30	11.51	12.25	11.67	15.45	16.94	12.48
S4	9.56	13.92	9.42	10.34	14.63	10.9	11.63	7.47	13.59	14.57	11.60
S5	10.69	8.55	11.67	11.67	6.9	6.76	6.96	5.15	7.71	7.47	8.35
S6	13.42	14.38	13.69	12.58	13.52	12.87	11.51	12.47	11.67	12.10	12.82

), the fiber morphology tends to be consistent, the fibers are closely intertwined, and the paper strength is good; the fiber width of sample S1 is much wider than the average fiber width of the Stellera chamaejasme root and leaf stem, which may be due to the reduction of the content of lignin and the weakening of the binding force between fiber bundles after treatment under the action of alkali and high temperature during cooking. During comprehensive treatment, the degradation reaction of cellulose, hemicellulose, and lignin occurs in the fiber due to similar mechanical fracture, thermal degradation, and hydrogen bond destruction, and the separation of each component, resulting in obvious changes in the fiber structure [24,25].

The sample fibers were observed under the 10 × 10 magnification of the objective lens of the biological microscope. It was found that the fibers of grass paper from Stellera chamaejasme were mostly yellow, slender, small, and uneven in width, with more transverse knots on the surface. Cell cavities were visible, both ends of the fibers were pointed, and the number of hybrid cells was different. There were fewer hybrid cells in samples S1, S3, and S5, and more hybrid cells in samples S2, S4, and S6 (Figure 2). Part of the fracture area of the fiber may be due to the hammer marks of artificial papermaking. Sample S1 has obvious short fibers, which may be due to the addition of other sizes in the papermaking process, or the relatively high beating degree. Further observation of the sample using a scanning electron microscope showed that grass paper fiber from Stellera chamaejasme showed an obvious flat-banded structure, and most of them were full and straight, with a clear network structure, closely staggered, a rough surface, and obvious longitudinal wavy folds (Figure 3).

4. Discussion

As an important material in the writing and printing process, the basic properties of paper affect the quality of its writing and printing products [26]. The grass paper has excellent performance, which allows the ink to transfer completely, and the images and texts reproduced on the paper are clearer and fuller so that the writing and printing effect is satisfactory [27]. The paper grammage and thickness of grass paper from Stellera chamaejasme will vary according to the origin, papermaking process, and use. Grass paper from Stellera chamaejasme has smaller compactness and larger bulk. It can be inferred that its absorption rate is faster, the absorption time is shorter, the opacity is increased, and the imprint is easy to dry, making it less likely to cause dirt on the back. Grass paper from Stellera chamaejasme has low brightness, and there is little difference between the brightness of side A and side B, so it is a good reading surface. The gloss of grass paper from Stellera chamaejasme is not high, and the gloss test results of surface A and surface B of each sample are almost the same, making it suitable for reading and printing. The brightness and gloss of grass paper from Stellera chamaejasme in different regions are different, which are closely related to the whiteness of pulp from different regions, the amount of soil alkali (or saline alkali or plant ash) added in cooking, and the lignin content in the pulp.

The tensile strength and folding resistance of grass paper from Stellera chamaejasme are generally good, and the longitudinal strength performance is better than its transverse strength performance. The folding properties of grass paper from Stellera chamaejasme in different origins are quite different, which is due to the comprehensive influence of the average fiber length, fiber strength, fiber flexibility, and the bonding strength, grammage, thickness, density, and moisture content between fibers. The tensile strength of different papers from the same origin or different sides of the same paper has certain differences, which is mainly related to the comprehensive effects of paper grammage, raw fiber strength, paper fiber arrangement direction, fiber length width ratio, fiber adhesion, and beating degree. From the perspective of paper grammage, paper with a larger grammage has a higher fiber content per unit area, and is theoretically able to withstand greater tensile strength, and typically has higher tensile strength. On the contrary, with a small quantity and fewer fibers, the tensile strength is relatively low. The strength of raw material fibers is also crucial. If the fibers of the raw material are strong and tough, the tensile strength of the paper made from cotton fibers will inevitably be considerable. Compared to grass fiber paper, paper made from cotton fibers has better tensile performance. The arrangement direction of paper fibers also has a significant impact. When fibers are arranged parallel to the direction of force on the paper, they can more effectively disperse tension and enhance tensile strength; the disorderly arrangement of fibers can easily lead to stress concentration points and reduced tensile strength. In terms of fiber aspect ratio, the network formed by interweaving long and wide fibers is more stable, and the bonding force between the fibers is stronger, thereby improving the tensile strength of paper. The degree of beating is related to the degree of fiber separation and pulverization. If the degree of beating is appropriate, the fiber separation and pulverization will be sufficient, increasing the contact area between fibers, enhancing the bonding force, and improving the tensile strength.

Fiber length, width, and strength are the three basic properties of papermaking fibers, which are closely related to the properties of paper [28]. Fiber length and width reflect the basic characteristics of fiber morphology, and have a great impact on the physical properties and printing performance of paper. Through the observation of the morphological characteristics of grass paper from Stellera chamaejasme in different habitats, some common problems affecting the basic properties of grass paper from Stellera chamaejasme were found, such as fiber flocculation, miscellaneous cells, rough surfaces, and so on. Fiber flocculation is the main factor affecting paper evenness [29]. The flocculation of grass paper fiber from Stellera chamaejasme is related to its size concentration, because the size concentration directly affects the flocculation. The pulp fibers with a high concentration have a high probability of collision with each other, which will cause strong flocculation. Most of the heterogenous cells (i.e., non-fibrous cells) have thin walls, large cavities, short lengths, and no strength. When pulping, it will absorb a large amount of cooking liquid, and since it is difficult to filter water when washing the pulp, this will reduce the strength and opacity of the paper [30]. One reason for the rough surface of grass paper fiber from Stellera chamaejasme may be that there are more long fibers. Because of its high molecular weight, long fibers improve the roughness of paper, and are more rough than short fibers. The rough fibers make the paper more rough. Therefore, in papermaking, the relative proportion of short fibers can be increased by increasing the beating degree, and the average molecular weight can be reduced to reduce the roughness of grass paper from Stellera chamaejasme.

5. Conclusions

The grass paper from Stellera chamaejasme in the Qinghai–Tibet Plateau is generally low in grammage, light in weight, thin in most cases, low in density, low in brightness and gloss, and generally good in strength performance indicators such as folding resistance and tensile strength. This shows that the basic performance of grass paper from Stellera chamaejasme from the Qinghai–Tibet Plateau is generally good, which is consistent with the historical description of the better quality of Tibetan paper. Affected by the factors such as pulp raw materials, papermaking process, and paper use, the basic properties of grass paper from Stellera chamaejasme, such as grammage, thickness, density, bulk, folding resistance, and tensile strength, will vary due to different origins. The grass paper fiber from Stellera chamaejasme after paper formation are generally yellow, with slender fibers, sharp ends, small and uneven widths, staggered fibers, disorderly arrangement directions, fiber flocculation, more transverse knots on the surface, and obvious flat ribbon structures; most of them are full and straight, with clear reticular structures, visible cell cavities, are staggered closely, have rough surfaces, mixed cells, and obvious longitudinal wavy folds.