More papers were presented by Dutch hemp researchers than by those from any
History & Status of Hemp Cultivation
A presentation by a company called Hemp-Flax discussed the history
and status of hemp cultivation in the Netherlands. They explained that
until several decades ago, hemp had been the most important fibre crop in
the country. Rembrandt’s paintings and Dutch world exploration would not
have been possible without hemp for canvas and ropes.
Since the late 1980’s, the Dutch government has supported hemp research in
order to help establish a cooperation between farmers and industry, and to
bridge technological gaps.
In 1994, Ben Dronkers founded Hemp-Flax as a private company. He purchased
a modern flax processing plant and contracted with Dutch farmers for the
cultivation of 140 hectares of hemp. Although no pesticides or fungicides
were used, losses caused by pathogens were insignificant. 500 hectares have
been contracted for 1995.
Function of Cannabinoids
An interesting study was presented by David Pate of the International
Hemp Association. Pate explained that cannabis is a “virtual factory”
for the production of metabolic compounds, and that the compounds which
make up the active drug ingredients are unique to the genus and are termed
Although Pate has researched the function cannabinoids serve in cannabis,
he admits to having no comprehensive explanation for why cannabis produces
them. He did however, outline four intriguing theories.
The first is that the sticky compounds may present a physical line of
defense against insects, which is coupled with the insect repelling
aromatic qualities of the resin.
Since it has been demonstrated that cannabinoids have anti-biotic
properties, they might also serve as a protection against microorganisms
and discourage fungal growth.
The third explanation is that cannabinoids act as protection from heat and
dryness in the same manner as the waxy coating on a cactus. This theory is
supported by the fact that strains of cannabis with a high level of resin
production tend to come from areas of high altitude, low geographic
latitude, and low humidity.
Finally, there seems to be a correlation between UV-B radiation and the
amount of resins produced. UV-B radiation has a significant negative
biological impact, and cannabis plants with high levels of cannabinoids
absorb and neutralize more of the damaging UV-B rays than low-potency
Although David’s theories are somewhat speculative, they do provide the
possibility that strains of cannabis with high THC could have agricultural
benefits over the low-THC varieties to which most farmers are legally
Breeding & Agriculture
There were two Dutch studies presented at the Bioresource Hemp Symposium
which dealt with the breeding and agriculture of cannabis hemp.
Hayo van der Werf of the DLO Research Institute for Agrobiology and Soil
Fertility presented the main results of the Dutch research program on
the crop physiology and agronomy of hemp. He explained that the prices of
many arable crops have been falling in recent years as the European Union
has reduced food crop subsidies in order to fight production surpluses.
As a result of this, crop rotation on Dutch farms has become limited to a
few profitable crops such as potato and sugar beet. This short crop
rotation has increased the incidence of disease and also lowered overall
yields, while at the same time increasing the use of biocides and soil
The development of a new crop introduced into current rotations would help
to solve these problems. Van der Werf explained that the new crop would
have to be profitable, produce for a large non-food market, require little
or no biocides, and help reduce disease in current crop rotations.
After six years of study, the report concluded that hemp grown for paper
pulp seems to meet all of these needs. Although fungus can cause
significant damage in rainy years, the problem may be solved through
further breeding. Hemp requires little or no biocides, and even suppresses
weeds and some soil-borne diseases.
An interesting piece of information came out of a study introduced by
Etienne de Meijer of the Centre for Plant Breeding and Reproduction
Research. He outlined the results of a four-year study into using hemp
for paper pulp production in Holland.
The conclusions of this study were similar to the one brought forward by
Van der Werf. What is interesting however, is that the study states that
“there were no strict relationships between the cannabinoid profiles and
non-chemical traits.” This would indicate that some varieties of cannabis
are high in both THC and fibre content, but also that hemp can be a useful
crop even if it is legally constrained to varieties low in THC.
Innovations in Pulping
Gertjan van Roekel of the Dutch Institute for Agrotechnological
Endeavours (ATO-DLO) presented a new technology for pulping hemp fibres
that combines the best of traditional mechanical and chemical pulping
His paper begins with a look at the history of papermaking. He explains how
paper used to be made of rags derived from hemp and flax clothing. At the
time of the industrial revolution, the demand for paper outstripped the
supply of rags, and so inventors and industry developed new processes to
use the world’s most abundant source of natural fibres: trees. This trend
has persisted, and now less than five percent of the world’s paper supply
is made from annual plants like hemp, wheat straw, and sisal.
Roekel goes on to describe modern papermaking techniques. He states that
the average hemp pulp and paper mill produces around 5000 tonnes per year,
compared to a minimum of 250,000 tonnes for a wood fibre pulp mill. This
vast difference in scale means that most modern hemp pulp mills are
designed to produce only specialty papers for which they can charge a great
deal more per tonne.
Examples of such specialty papers include cigarette paper, coffee filters,
insulating and greaseproof papers, and specialty art papers.
The typical technique used to process hemp fibres into specialty paper pulp
is called Kraft chemical pulping. This process involves cooking the hemp
fibre in a mixture of sodium hydroxide and sodium sulfate, and then beating
it for up to twelve hours in a machine specially designed for long fibres
called a Hollander Beater. Bleaching methods often include chlorine
compounds which are discharged into the environment.
Although this process does produce a fine grade of paper, it is not
economically feasible to use it in the production of “regular” grade
printing and writing papers, which is the fastest growing area of demand
for hemp paper.
Modifying the Mechanical
Mechanical pulping entails separating the fibres by exposing them to
shearing forces rather than chemical energy. The new pulping technology
introduced by Roekel involves adding small amounts of alkaline and some
catalysts to the mix, thereby improving the lignin removal. This improved
process is called chemi-mechanical pulping.
The main difference between chemical and chemi-mechanical pulping is that
chemi-mechanical pulping does not completely remove the lignin while
chemical pulping does. (Lignin is the biological glue which holds the plant
together.) Since wood fibre contains up to 30% lignin this can mean a
serious difference in the quality of wood pulp. Hemp bast fibre however, is
at most 4% lignin, and so this is not really a factor.
A major environmental advantage of the chemi-mechanical process is that it
doesn’t require extensive chemical cooking, so that it uses less energy and
chemicals than traditional processes. It also requires less bleaching, and
uses hydrogen peroxide to whiten the paper instead of chlorine.
Studies at Wageningen Agricultural University have shown that waste from
chemi-mechanical pulping does not contain toxic elements, and that all
components can be degraded biologically, except for a fraction of the
lignin, which it is hoped further studies will find a solution for.
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