Table of Contents
Capelle, A. 1996. Hemp: Specialty crop for the paper
industry. p. 384-388. In: J. Janick (ed.), Progress in new crops. ASHS
Press, Arlington, VA.
Hemp: Specialty Crop for the Paper Industry*
- PRIMARY PRODUCTION
- Genetic Collection/Optimization
- Harvesting/Postharvest Treatment
- PULP PROCESSING
- After Treatment
- PAPER PRODUCTION
- Table 1
- Table 2
- Table 3
- Table 4
- Table 5
- Fig. 1
- Fig. 2
- Fig. 3
- Fig. 4
- Fig. 5
In 1994 a four year research program to evaluate the feasability of the
cultivation of hemp (Cannabis sativa L., Cannabinaceae) as a raw
material source for the paper industry was finalized. Three aspects, primary
production, pulp processing, and paper production, based on an integrated chain
model from farm to factory were studied (Fig. 1).
This research program was part of a broader business concept study as a basis
for starting a commercial hemp pulp processing unit. In this paper a summary
of the research results will be presented. For more detailed information see
van Berlo (1993).
Since 1986, a collection of commercial available germplasm including old
cultivars and wild material was initiated. The research objectives which
culivar was best suited for paperpulp production under Dutch condition. The
stem composition and content of cannabinoids were used as the selection
Based on earlier studies it was concluded that a late flowering resulted in a
higher yield. In field trials carried out in successive years, several
cultivars (Kompolti Hybrid TC, Kompolti Sárgaszáru, Kompolti
Hyper Elite, Kozuhara, and Fedrina 74) were evaluated. 'Kompolti
Sárgaszáru' and 'Kompolti Hyper Elite' proved to be the best
suited in regards to yield and fiber quality. Yield in dry matter varied
between 11 t/ha for peat soil and 17 t/ha for clay soils. The bast fiber
content varied between 12% and 35%, the woody core varied between 50% and 75%.
The total of the two fractions remained more or less constant at 85% of the
stem dry substance. Cannabinoids content of the different accessions varied
between 0.06% and 0.22% for THC, in comparison with 10% THC for drug types.
Growth trials were carried out at three different locations (peat soil, sandy
clay, and heavy clay) in a three year period (Fig. 2). Hemp gives the best
results when cultivated on light soil at a soil pH of at least 5.
Fertilization of 12 kg N, 15 kg K2O and 4 kg P2O5 is needed per ton of dry
matter. Seeding should start from mid Apr., as soon as soil conditions make it
possible. On heavy clay soils compaction must be prevented as this severely
hinders the growth. Hemp can be grown as a row crop with optimum distance 12.5
cm between the rows and a plant density of 900,000 plants/ha. At a seed weight
of 19 mg and an emergence of 85% a quantity of 20.1 kg seed/ha is required for
No herbicides are necessary as the crop suppresses weeds. On weed infested
soils, plant density should be relatively higher and the row distance less. No
major diseases have been identified, however during wet seasons, Sclerotinia
and Botrytis, result in lower yields. Spraying with fungicides had no effect.
The best harvest time is from the beginning to mid Sept. depending on the
Harvesting and postharvest treatment with existing equipment is a decisive
factor in the production of hemp pulp. If the farmer can carry out most of the
needed activities with already available equipment, the direct costs will be
low thereby promoting a succesful adoption of this crop. The following
harvesting techniques were studied: topping, cutting, windrowing, chopping,
press baling, and ensilage. In topping, most of the leaves and flowers from
the top of the plant are removed prior to harvesting. The cutting has to be
done in such a way that as little sand as possible is picked up, while
maintaining optimum yield. It is best carried out with a so called row
distance independant cutter bar in front of a forage harvester.
After chopping the hemp can be ensiled at the farm. To optimize the processing
of hemp into pulp over the year drying and ensilage was studied as a
conservation storage technique. Ensilage is appreciable cheaper than drying
and more reliable. The paper quality of ensiled hemp is slightly less than of
the dried hemp, but still of acceptable quality.
The hemp stem consist of about 65% corefibers and 35% bast. The corefiber
consist of 40% cellulose, 24% hemicellulose and 22% lignin, the length is 5.5
mm. The bastfiber is 75% cellulose, 9% hemicellulose and 5% lignin with a
length of average 20 mm. As the differences between these two fractions merit
a separation into two separate raw materials, research was carried out into
Separation can be carried out before of after storage at farm level or at the
pulping facility. As harvest takes place in Sept., a rather wet period, dry
separation was discarded. Two options were selected, sieving and flotation.
Flotation proved to be a feasible technique with a selectivity of more than 90%
Four pulping processes were investigated for hemp (Table 1). Depending on the
end application of the pulp, thermomechanical pulping (TMP) of the whole stem
is possible. A more optimal result was reached when the core fraction from the
earlier in core and bast fraction separated stem was thermomechanically pulped
and milled in a refiner and the bast fraction, together with an alkaline
(pre)treatment, was extruded in a double screw extruder (Fig. 3, 4). Extrusion
has the advantage of 30% less energy consumption, while the length of the fiber
was better controlled by fine tuning of the extrusion conditions. A patent was
filed for this process by ATO-DLO.
In most cases, especially for short lived applications, there is no lignin
removal. The desired color of the paper can be adjusted by bleaching with
peroxide (Fig. 5); when pure cellulose is the end product, an ozone treatment
An important factor to be considered in pulping (Table 1) is the cost of waste
water treatment. In waste water treatment, biological oxygen demand, aquatic
toxicity, and the color of the water are important factors. In principle the
waste water contains easily degradable components such as sugars, fatty acids,
and alcohols while lignin an almost non-degradable component is responsible for
the color. A combined anaerobic-aerobic treatment with an upfront dilution
process to remove the resins, effectively solves the problems.
Different types of paper were produced from the pulped hemp. The traditional
applications for hemp papers vary from cigarette paper to art papers and
represent a total volume of about 120,000 t/year worldwide, making up about
0.05% of the world pulp volume. However, for these applications a chemical
pulping is necessary. For wider bulk applications, such as printing and
writing papers and corrugated board, cost is the decisive factor (Table 2).
The properties of chemomechanical core and bast pulp compare very favorable
with the traditional wood pulps (Table 3, 4).
We conclude that hemp pulp is very competetive with the usual pulps when
printing and writing paper application is taken into consideration (Table 5).
The building of a pilot unit with the capacity of about 5,000 t/year for
upscaling studies is now under consideration.
van Berlo, J.M. Dec. 1993. Papier uit hennep van Nederlandse grond. ATO/DLO,
*Special thanks to Mrs. M.J.J.M. van Kemenade for ATO-DLO at Wageningen, the
Netherlands for making available all relevant information.
Table 1. Comparison of four pulping processes investigated for hemp.
zCTMP = chemithermomechanical pulping.
|Pulping process ||Temp. (°C) ||Time (h) ||Fiber/ |
|Thermomechanical (TMP) ||120 ||2 ||10:1|
|Akaline TMP (CTMP)z ||120 || || ||Extruder <4% NaOH|
|Soda ||165 ||0.5 ||10:1 ||2% NaOH|
|Organosolv ||195 ||0.5 ||9:1 ||Ethanol/water = 1.2|
Table 2. Cost of chemical and chemomechanical processes for hemp vs.
chemical processing for softwoods.
| ||Hemp ||Softwood|
|Process ||Chemical ||Chemomechanical ||Chemical|
|Pulping ||2,100 ||530 ||820|
|Papermaking ||1,900 ||800 ||800|
|Total cost ||4,000 ||1,330 ||1,620|
Table 3. Chemomechanical characteristics of bast pulp vs wood pulps for
printing and writing grade blends.
zSR = standard reflection, ISO = international standardization
|Fiber ||Beating degree (SR)z ||Density (kg/m3) ||Tensile strength (Nm/g) ||Burst strength (kPa.m2/g) ||Tear strength (mN.m2/g) ||Brightness (ISO)z ||Opacity (ISO)|
|Softwood sulphate ||30 ||720 ||91 ||4.0 ||11 ||90 ||75|
|Hemp bast ||50 ||550 ||48 ||4.2 ||12 ||82 ||76|
Table 4. Chemomechanical characteristics of core pulp vs wood pulps for
printing and writing grade blends.
|Fiber ||Beating degree (SR) ||Density (kg/m3) ||Tensile strength (Nm/g) ||Burst strength (kPa.m2/g) ||Tear strength (mN.m2/g) ||Brightness (ISO) ||Opacity (ISO)|
|Aspen APMP ||56 ||709 ||53 ||2.5 ||2.2 ||82 ||73|
|Hemp core refiner ||59 ||714 ||59 ||2.7 ||2.8 ||78 ||75|
Table 5. Economics of hemp assuming high yield, small module scale, and
no recovery system. Investment is calculated for a 5,000 ton/year
zNon-bleached standard kraftpulp, price is used as a reference.
|Operation ||Annual cost/tonne (US$)|
|fiber crop ||130|
|pulping operation ||400|
Fig. 1. Integrated research module for hemp.
Fig. 2. Hemp field in the Netherlands.
||Fig. 3. Pulping hemp fibers.
Fig. 4. Necessity for new technology in hemp pulping.
Fig. 5. Bleached hemp products.
Last update August 21, 1997