Development and evaluation of a guayule debarker

Guayule (Parthenium argentatum Gray) stores its rubber primarily within the cells of its bark, which constitutes only 30% of the dry weight of the whole shrub. Debarking guayule soon after harvesting at the crop site would substantially improve the efficiency of latex extraction technology by reducing transport costs to the processing plant and increasing the processing capacity of the latex extraction plant. The objective of this study was to design, fabricate and evaluate an efficient debarking machine for guayule. The bark removal unit consists of a pair of grooved rubber rollers rotating in opposite directions at different speeds, drawing and crushing the cut stems without chipping the core. The clearance between the rollers is adjustable and can handle different stem sizes ranging from 6 to 45 mm. The speed difference between the rollers creates a shearing action, required for peeling the bark. The separation unit consists of a fan attached to metal tubing, a discrimination chamber for grading processed material and a water trough where lighter material is removed by flotation. The debarking system was tested to determine bark removal performance as well as separation of bark from other processed plant material. A debarking efficiency of up to 95% and maximum separation efficiency of 75% were found from the evaluation. The prototype debarking machine produced a throughput capacity of up to 450 kg/h which can be increased by converting it to a full-size field machine.     

Properties of thermoplastic composites with cotton and guayule biomass residues as fiber fillers

This study was conducted to evaluate the suitability of using residual plant fibers from agricultural waste streams as reinforcement in thermoplastic composites. Three groups of plant fibers evaluated included cotton burrs, sticks and linters from cotton gin waste (CGW), guayule whole plant, and guayule bagasse. The plant fibers were characterized for physical (bulk density and particle size distribution) and chemical properties (ash, lignin and cellulose contents). A laboratory experiment was designed with five fiber filler treatments, namely control (oak wood fiber as the filler - OWF), cotton burr and sticks (CBS), CBS with 2% (by weight) second cut linters (CBL), CBS with 30% (by weight) guayule whole plant (CGP), and CBS with 30% (by weight) guayule bagasse (CGB). The composite samples were manufactured with 50% of fiber filler, 40% of virgin high-density polyethylene (HDPE), and 10% other additives by weight. The samples were extruded to approximately 32 × 7 mm cross-sectional profiles, and tested for physico-mechanical properties. The CBS and CBL had considerably lower bulk density than the other fibers. Cotton linters had the highest α-cellulose (66.6%), and lowest hemicellulose (15.8%) and lignin (10.5%) of all fibers tested. Guayule whole plant had the lowest α-cellulose and highest ash content. Both CBS and guayule bagasse contained α-cellulose comparable to OWF, but slightly lower hemicellulose. Evaluation of composite samples made from the five fiber treatments indicated that fibers from cotton gin byproducts and guayule byproducts reduced the specific gravity of the composites significantly. However, the CBS and CBL samples exhibited high water absorption and thickness swelling, but the addition of guayule bagasse reduced both properties to similar levels as the wood fiber. The CGP exhibited significantly lower coefficient of thermal expansion. Composite samples with the five different fiber fillers showed similar hardness and nail holding capacity, yet oak fibers imparted superior strength and modulus under flexure and compression with the exception of the compressive modulus of CGB composites. In general, both cotton ginning and guayule processing byproducts hold great potential as fiber fillers in thermoplastic composites.     

Guayule as a feedstock for lignocellulosic biorefineries using ammonia fiber expansion (AFEX) pretreatment

Natural rubber latex extraction from guayule leaves behind greater than 90% (by weight) of agricultural residue as a feedstock suitable for conversion to biofuels via a thermochemical or biochemical route. Untreated guayule shrub and bagasse (after latex extraction) has shown to be very recalcitrant to enzymatic hydrolysis, necessitating application of a chemical pretreatment to enhance cellulase accessibility. The objective of this work was to carry out detailed compositional analysis, ammonia fiber expansion (AFEX¹) pretreatment, enzymatic hydrolysis and ethanol fermentation for various guayule-derived biomass fractions. Plant feedstocks tested were derived from two sources; (a) a mature 2007 AZ-2 whole guayule shrub plant obtained from USDA/ARS² research fields, and (b) the guayule latex-extracted commercial grade bagasse (62505) from Yulex Corporation. Compositional analysis and enzymatic hydrolysis were carried out using standard NREL³ protocols (www.nrel.gov/biomass/analytical_procedures.html). AFEX pretreatment was carried out using concentrated ammonium hydroxide at elevated temperatures for desired residence times in a pressurized reactor. Yeast fermentations on biomass hydrolyzates were carried out micro-aerobically using Saccharomyces cerevisiae (424A strain) in shake flasks.AFEX pretreatment was found to substantially improve overall enzymatic digestibility by 4-20 fold for both untreated guayule shrub and latex-extracted bagasse. Maximum glucan and xylan conversion achieved for the latex-extracted bagasse was 40% and 50%, respectively. The yeast was readily able to ferment both glucose and xylose to ethanol from the guayule bagasse hydrolyzate with or without external nutrient supplementation (i.e., yeast extract and tryptone). Our results highlight the possible utilization of guayule as a feedstock for lignocellulosic refineries co-producing natural rubber latex and biofuels. However, further process improvements (e.g., lignin/resin extraction and cellulose decrystallization using a modified AFEX process) are necessary to increase the effectiveness of ammonia-based pretreatments for further enhancing enzymatic digestibility of guayule-derived hardwood biomass.     

The formation of rubber particles in developing cortical parenchyma of Parthenium argentatum plants exposed to the low temperatures of fall and winter of the Chihuahuan Desert

In this paper we have examined rubber particle formation in cortical parenchyma cells of guayule (Parthenium argentatum Gray) plants exposed to the low temperature of the fall and winter of the Chihuahuan Desert that stimulates rubber formation.Plants were transplanted to field plots in May in Ft. Stockton, TX. In September most of the cortical parenchyma in cross-sections 3 cm from the stem tips and from the base of the stems were mature, containing a central vacuole, tonoplast and a parietal cytosol with chloroplasts, mitochondria, peroxisomes and a few rubber particles. In 8-month-old plants examined in January many of the cortical parenchyma cells 3 cm from the stem tip were immature and completely filled with cytosol containing a high population of rubber particles. At this stage of development there was a thickened secondary cell wall but no central vacuole, tonoplast or parietal cytosol and all the rubber particles were formed in the central cytosol. In the cortical parenchyma in early stages of central vacuole development, by the coalescing of microvacuoles, the rubber particles were located in the developing central vacuole and in the cytosol being appressed toward the cell wall. In 8-month-old plants in January, the cortical parenchyma at the base of the stems was more mature than cells near the stem tips. These cells showed a later stage of development of a central vacuole from microvacuole fusing and contained a high population of mixed sizes of rubber particles and a thin layer of parietal cytosol containing chloroplasts, mitochondria and rubber particles with a partly developed tonoplast. There was clear evidence of the fusion of small rubber particles with other rubber particles that may represent a mechanism for the growth of rubber particles.     

Antioxidant activity and phenolic content of chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark extracts

Chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark, waste products of the food and wood industries, respectively, were analysed as potential sources of antioxidant compounds. The extraction yield, the antioxidant activity and total phenols content of the extracts were greater in chestnut shell than in eucalyptus bark for most of the extraction conditions essayed. Extraction of chestnut shell with a 2.5% Na₂SO₃ aqueous solution led to the highest extraction yield, 25.6%, total phenols, 13.4 g gallic acid equivalent/100 g oven-dried shell, and FRAP antioxidant activity, 80.7 mmol ascorbic acid equivalent/100 g oven-dried shell. Extraction with methanol:water (50:50, v/v) provided the best results for eucalyptus bark. The antioxidant activity and the total phenols content of the extracts had a positive linear correlation. FTIR spectroscopy confirmed the higher content of phenolic compounds in chestnut shell extracts compared to eucalyptus bark extracts. Chestnut shell extracts were characterized by the presence of high molecular weight species whereas lower molecular weight species were predominant in eucalyptus bark extracts.     

Studies on Ipomea carnea and Cannabis sativa as an alternative pulp blend for softwood: An optimization of kraft delignification process

Ipomea carnea Jacq, a common weed known as ‘Beshram’ was introduced in India, as an ornamental plant. Surprisingly, except fiber length, other morphological characteristics like, cell wall thickness, lumen diameter, flexibility coefficient and wall fraction of I. carnea resemble with softwoods like, Pinus kesiya, and Picca abies. Cannabis sativa L., a common weed known as soft hemp consists of both bast fiber as well as core fiber. The unique morphological characteristics of I. carnea like, cell wall thickness and flexibility coefficient, which resembles with softwoods along with long fibers of C. sativa, in which I. carnea deficits in a proper blend ratio, can be used in a better way for the development of high quality value added paper. The optimum kraft cooking conditions for I. carnea and C. sativa were: active alkali 16%, sulfidity 20%, temperature 165 °C, time (at temperature) 120 min and wood to liquor ratio of 1:4 for I. carnea and 1:3.5 for C. sativa. The screened pulp yield of I. carnea and C. sativa were found to be 49.3 and 54.3% at Kappa number of 29, respectively. An anthraquinone (AQ) dose of 0.1% increases the pulp yield to the tune of around 0.6% as well reduce the Kappa number to the tune of 22%. CEHH bleaching of C. sativa produces pulp brightness of 82% (Elrepho) at total chlorine demand of 5.07%. On contrary to this the I. carnea kraft pulp at same chlorine demand produce a pulp with improved brightness of 85.4% (Elrepho).     

Feeding behavior of a potential insect pest, Lygus hesperus, on four new industrial crops for the arid southwestern USA

Camelina (Camelina sativa), guayule (Parthenium argentatum), lesquerella (Physaria fendleri), and vernonia (Centrapalus pauciflorus [formerly Vernonia galamensis]) are either under limited commercial production or being developed for production in the southwestern USA. Insect pests are a potential economic threat to all these new crops, with Lygus hesperus, the western tarnished plant bug, among the most prominent due to its regional abundance and propensity to feed on reproductive plant tissue. The objectives of this study were to establish baseline data on the feeding behavior and potential impact of L. hesperus on camelina, guayule, lesquerella and vernonia. Behavioral observations of adult females and males, and nymphs of this insect were made in the laboratory. Insects spent ≈35% of their time either probing (=tasting) or feeding on various reproductive and vegetative tissues of guayule, lesquerella or vernonia, but only 20% on camelina. When insects did probe and feed they preferred reproductive tissues, primarily flowers and siliques/achenes, and there were differences in these behaviors relative to crop but not generally to insect stage or sex. Insects probed and fed more on flower tissue of guayule and vernonia compared with camelina and lesquerella, and more on siliques of lesquerella compared with achenes of vernonia. When probing and feeding on vegetative tissue, there was generally a preference for stems compared with leaves in all crops except guayule. Results show that L. hesperus will readily feed on the economically important tissues of all crops, and although research has shown that this feeding did not consistently affect lesquerella yield, further work will be needed to determine if such feeding poses a risk to commercial production of camelina, guayule or vernonia.     

Plant population,planting date,and germplasm effects on guayule latex,rubber, and resin yields

Guayule (Parthenium argentatum Gray) is a perennial shrub native to the Chihuahuan Desert. While guayule traditionally has been cultivated for rubber, more recently it is being cultivated for its hypoallergenic latex. Other uses including termite resistant wood products and an energy source have also been identified. However, the effects of various agronomic practices, such as planting and harvesting dates, plant spacing, cutting height and frequency, irrigation frequency, and herbicide application, on latex concentration and yield of newly developed germplasm have not been reported. The objectives of this study were to determine the yield and concentration of latex, rubber, and resin of four guayule lines planted at two populations and two planting dates. Four guayule lines (AZ-1, AZ-3, AZ-5, and 11591) were transplanted at two dates (28 November 2000 and 7 June 2001) and two plant populations (27,000 and 54,000 plants ha^?1). Treatments were replicated four times. Each treatment plot was subdivided into six subplots for harvesting at 6-month intervals beginning 1 year after transplanting. Results showed that transplanting date did not affect plant size or latex concentration or yield consistently. Instead, it appeared that the time of harvest (fall vs. spring) was more important. The sixth (last harvest) in the fall planting date and the fifth harvest date in the spring planting date were the optimum for plant biomass and latex, rubber, and resin concentrations and yields. The lines AZ-1 and AZ-3 were larger, whereas AZ-5 had higher latex and rubber concentrations than the control, 11591. The greater plant population (54,000 plants ha^?1) had higher biomass, rubber, and resin yields than the lower population (27,000 plants ha^?1) at the early harvest dates, but not at the later harvest dates (5 and 6). More studies must to be conducted to determine the optimum plant population and transplanting date for other newly developed guayule germplasm lines.     

Essential oil composition of Hypericum perfoliatum L. and Hypericum tomentosum L. growing wild in Tunisia

The essential oils obtained by hydrodistillation from the aerial parts of Tunisian native Hypericum perfoliatum L. (sect. Drosocarpium Spach.) and Hypericum tomentosum (sect. Adenosepalum Spach.) were analyzed by GC and GC–MS. Thirty-two compounds were identified in the essential oils of H. perfoliatum with α-pinene (13.1%), allo-aromadendrene (11.4%), germacrene-D (10.6%), n-octane (7.3%), α-selinene (6.5%) and β-selinene (5.5%) as main constituents. Sixty-seven components were identified in the oil of H. tomentosum with menthone (17.0%), n-octane (9.9%), β-caryophyllene (5.3%), α-pinene (5.2%), lauric acid (4.1%) and β-pinene (3.7%) as the most abundant components. Both oils were characterized by the presence of many components which could have numerous applications in food, pharmaceutical and perfume industries.     

Nutrients,Antioxidant Capacity and Safety of Hot Water Extract from Sugar Maple (<Emphasis Type="Italic">Acer saccharum</Emphasis> M.) and Red Maple (<Emphasis Type="Italic">Acer rubrum</Emphasis> L.) Bark

Sugar maple (Acer saccharum M.) and red maple (Acer rubrum L.) barks were treated with hot water to extract nutrients in order to explore, for the first time, its potential as safe dietary antioxidants. The organic and inorganic nutrients of these extracts, as well as their safety on human PLB-985 cells differentiated into neutrophils-like cells, were determined. Proximate analysis showed that both bark extracts were low in moisture and fat. Sugar maple bark extract (SM-BX) showed crude protein and ash content higher than those found in red maple bark extract (RM-BX). In addition, SM-BX had total sugars higher than those evaluated in RM-BX, while complex sugars (oligo- and/or poly-saccharides) were similarly abundant in both bark extracts. Furthermore, SM-BX demonstrated a wide array of vital minerals (K, Ca, Mg, P, Na, Fe and Cu) in quantity larger than that evaluated in RM-BX, whereas RM-BX have Zn and Mn levels higher than those found in SM-BX. Phytochemical analyses showed that RM-BX exhibited total phenolic and flavonoid contents higher than those measured in SM-BX. Consequently, RM-BX presented an antioxidant activity higher than that of SM-BX: 2.85-fold ABTS radical cation scavenging capacity and 1.9-fold oxygen radical absorbance capacity. Finally, RM-BX and SM-BX were greatly safe since, at concentration up to 100 μg/ml, they did not modify the viability of neutrophils as determined by flow-cytometry assay using Annexin V-FITC/Propidum Iodide as markers. In conclusion, our in vitro studies indicate that both red and sugar maple bark extracts have a real potential as food additives.     

Quality of guayule seeds separated by physical attributes

Guayule (Parthenium argentatum Gray) is being developed as a new commercial crop to be grown in arid and semiarid regions. Guayule stands are presently established using transplants; however, establishment by direct-seeding would reduce costs and make production more economical. A major difficulty in field establishment by direct-seeding is the variation in the quality of guayule seeds. Guayule seeds vary greatly in color, size, and weight, which are the attributes believed to be associated with the observed germination differences among and within seed lots. To determine the importance of these attributes, guayule seeds from different seed lots were separated by size (diameter) and color, each separation class was weighed and then seed quality determined by germination percentage and rate. X-ray analysis was used to distinguish filled from unfilled seeds, and this was related to the germination results. In six guayule breeding lines (N565, 11591, AZ-2, AZ-3, AZ-4, and AZ-5), the highest quality seeds were darker (opaque-black and gray), small to medium in diameter (1.4–1.6 mm), and were heavier (a greater proportion of filled seeds). Color appeared to be a more efficient separator for seed quality than seed size; however, separation by size may be acceptable on a large scale and still provide higher quality and more uniform seed lots.     

Milkweed seedmeal: a control for Meloidogyne chitwoodi on potatoes

Milkweed (Asclepias) is a new crop being produced for its fiber in pillows and comforters. Cardiac glycosides (cardenolides), are endemic in milkweed and may hinder utilization of its seed as an animal feed. In an ongoing effort to develop new coproducts for milkweed fiber, we found that the defatted seedmeal is an effective nematicide and pesticide for army worms. A procedure for separating the cardenolides from milkweed seedmeal has also been developed.     

Fortification of sulfited tannin from the bark of Acacia mangium with phenol–formaldehyde for use as plywood adhesive

The Acacia mangium tree contains 10% bark (v/v), of which about 20% are extractives. Extraction of this bark using a combination of water and sulfite medium can produce between 15% and 25% tannin materials (dry weight). In this work, several extraction conditions such as bark size, plantation site, extraction time and extraction medium were studied. The results showed that by using either hot water or a sulfite medium, a reasonable amount of tannin yield can be obtained. Bark size of less than 1-mm mesh size gave relatively high tannin yield irrespectively of the extraction medium used. Using a 600:100:2:0.5 (w/w) ratio of water:bark:sodium sulfite:sodium carbonate, and reacted at 75 °C for 3 h improved the tannin yield by at least 30%. The extracts were reasonably reactive towards formaldehyde as shown by their high Stiasny number; water extract, 60–70% and aqueous sulfite–carbonate extracts, 85–90%. The gluing results showed that the shear strength of the plywood can meet the requirements of the European Standards EN 314-1 and EN 314-2:1993. Incorporation of low molecular weight PF resin (10 parts) and PF (10 parts) improved the shear strength from 0.96 MPa to 1.43 MPa after a 72 h boiling test. This study showed that A. mangium tannin blended with commercial plywood phenol–formaldehyde resin, low molecular weight PF and paraformaldehyde as a cross-linker can be used to bond Kedondong (Canarium spp.) wood veneers suitable for both interior and exterior grade plywood.     

Modification of natural bamboo fibers for textile applications

Natural bamboo fibers have excellent properties suggesting that there is a good potential for them to be used in textiles; however, they have not received the attention that they deserve owing to their coarse and stiff quality. Therefore, a chemical method for extraction and modification of natural bamboo fibers for textile end uses were developed and optimized in this paper. The quality of natural bamboo fibers were characterized by their chemical composition, linear density, and tenacity. Experimental results show that the modified bamboo fibers are finer, with significant lower content of noncellulosic substances. The processing parameters are optimized as: 20 g/l NaOH, 3 g/l Na₅P₃O₁₀, 5 g/l Na₂SO₃, 3 g/l penetrating agent, with a fiber to liquid ratio of 1:10, at 100 °C for 2 h, and the bamboo fiber thus produced has cellulose amount of 73.25 %, fineness of 3.26 tex, average length of 44.5 mm, breaking elongation of 2.8 % and tenacity of 2.41 cN/dtex. The result of this study may offer a possibility of developing natural bamboo fibers into practical applications in textiles.     

The effect of extraction process on polyphenol content, triterpene composition and bioactivity of yellow birch (Betula alleghaniensis Britton) extracts

Crude ethanol extracts from different tissues of Betula alleghaniensis: wood, inner and outer bark, foliage, and twigs were evaluated for their nitric oxide (NO)-radical scavenging activities and inhibitory effects on the production of NO in LPS/INFγ-stimulated RAW 264.7 macrophages. As a renewed interest in plant-derived drugs has led to an increased need for efficient extraction methods, ultrasonic-assisted extraction (UAE) was investigated and compared with conventional maceration. The lower energy consumption by the UAE process compared to maceration determined in our study qualifies also this extraction as an environmentally friendly process. Our results indicate that the foliage extract has the most potent radical scavenging capacity while wood and twigs extracts exert the highest inhibitory effects on the production of NO in LPS/INFγ-stimulated RAW 264.7 macrophages. Extracts obtained by UAE present lower cytotoxic activity on RAW cells. Our results also demonstrate that ultrasounds help to selectively extract the bioactive molecules from foliage, twigs and wood, which inhibit the production of NO by macrophages. The highest total phenol content has been determined for the inner bark extracts and the flavonoids are the major phenolics present in foliage extracts. Poor correlations determined between the total phenols and radical scavenging capacity of the extracts indicates to the synergistic or antagonist effects of molecules present, various polyphenols and triterpenes being identified in the extracts studied in this research.     

Preparation and antibacterial property of the mulberry based textiles

The mulberry based textile products were prepared by means of degumming, dyeing, spinning and weaving using mulberry bark as raw materials. The structure of the mulberry based textiles was characterized by scanning electron microscope (SEM). The antibacterial property of the mulberry fibers was evaluated by means of antibacterial testing, and the antibacterial composition in the mulberry based textiles was investigated by FTIR and ¹³C-NMR. The results show that the mulberry based fibers, dyed fibers, yarns and fabrics with high quality can be prepared successfully by the above processes. The mulberry based textiles have excellent antibacterial property. The inhibitory rate of raw mulberry bark on Escherichia coli and Staphylococcus aureus is (67.2±3.1)% and (53.8±4.6)% respectively, and the inhibitory rate of mulberry fiber on Escherichia coli and Staphylococcus aureus is both above 80%. The inhibitory rate of the mulberry/cotton blended yarn on Escherichia coli and Staphylococcus aureus ranges from (51.7±5.1)% to (72.4±4.1)%, which has similar inhibitory rate with the mulberry/cotton blended fabric. The results of Fourier Transform-Infrared (FTIR) and ¹³C-nuclear magnetic resonance (¹³C-NMR) show that the typical functional group (hydroxyl, carbonyl, double bond and epoxy bond) exist in the composition of the mulberry fiber, which indicates that the flavones and phenolic compounds including in the mulberry fiber.     

Easy Preparation of Dietary Fiber with the High Water-Holding Capacity from Food Sources

Dietary fibers were prepared as alkali- and acid-insoluble fractions with chemical phosphorylation from Tossa jute (Corchorus olitorius), defatted soybean (Glycine max), and Shiitake (Lentinula edodes). The dietary fiber fractions treated with alkaline solution containing sodium metaphosphate had the lower protein content and higher total dietary fiber content than those of the preparations without phosphorylation. Alkaline extraction followed by phosphorylation led to a 1.5-fold increase in the water holding capacity of dietary fiber compared with no phosphorylation, whereas the binding capacity to bile acids of dietary fiber was almost the same. The alkali- and acid-insoluble extraction with phosphorylation provided an efficient preparation of water-insoluble dietary fiber with high-water holding capacity from various food sources.     

Preparation,composition, structure and properties of the <Emphasis Type="Italic">Kosteletzkya virginica</Emphasis> bast fiber

In this paper, the bast of the Kosteletzkya virginica are degummed and separated into fine fibers, the chemical composition, morphology, microstructure and mechanical properties of the Kosteletzkya virginica bast fibers are characterized by means of SEM, ART-FTIR, DSC-TGA, XRD and Instron tensile tester. The results show that the surface of the Kosteletzkya virginica bast fibers is smooth, and there are many visible grooves along the vertical section. Typical cellulose I in the Kosteletzkya virginica bast fibers is confirmed by FTIR and XRD analysis. The crystallinity of the Kosteletzkya virginica bast fibers is higher than that of the cotton fibers and lower than that of the castor-oil plant bast fibers. The beginning and maximum decomposition temperature of the Kosteletzkya virginica bast fibers are 252 and 347 °C respectively, which indicate that the Kosteletzkya virginica bast fibers have an appropriate thermal stability. The Kosteletzkya virginica bast fibers have a better mechanical properties and excellent hygroscopicity. All the results show that the Kosteletzkya virginica bast fiber is one of an ideal candidate for the new textile material.     

Improving the use of kenaf for kraft pulping by using mixtures of bast and core fibers

Kenaf (Hibiscus cannabinus L.) is a herbaceous annual plant amenable to use as a papermaking raw material. Kraft and soda pulping of kenaf have so far been done exclusively on the bark fraction (about 34–38% of the stem) or whole stem of the plant. Using kenaf bark exploits the higher quality of its bast fibers but reduces the typically high crop yields of this plant. In any case, core kraft pulp has acceptable properties some of which (e.g. tensile index, burst index) can even surpass those of bark pulp. Pulp made from both fractions has been found to exhibit better bonding properties than bark pulp. However, too high a proportion of core fibers can result in difficult drainage, a low tear strength or poor air permeability. These problems restrict the proportion of core that can be mixed with bast fibers, hinders separation of the two fractions and raises operational costs.The primary purpose of this study was to examine the influence of the core–bark ratio on the properties of mixed kenaf pulp. We used unrefined core pulp and refined bark pulp. Based on the results for kraft sacks, obtaining kenaf paper from both fractions has some advantages. Because Gurley air porosity changed dramatically with the proportion of core pulp used, it was used to determine the maximum amount of core fibers to be added to bast fibers. A proportion of up to 34% was found to have no adverse effect on air permeability. Such a proportion allowed paper strength to be preserved with an acceptable tear index (19.8 mN m²/g) and excellent tensile index (72 N m/g). Also, energy consumption was reduced if only the bark fraction was refined. The proposed strategy thus provides increased fiber yields of kenaf per hectare per year and valorizes the core fraction.