INTERNATIONAL NETWORK FOR BAMBOO AND RATTAN
(INBAR)

TRANSFER OF TECHNOLOGY MODEL
(TOTEM)

CORRUGATED BAMBOO ROOFING SHEETS

Research Centre for Forest Ecology and Environment,
Forest Science Institute,
Chem, Tu Liem,
Hanoi.
Vietnam

CONTENTS
TRANSFER OF TECHNOLOGY MODELS (TOTEMs)

4

CORRUGATED BAMBOO ROOFING SHEETAS AT-A-GLANCE
6
PART ONE: INTRODUCTION
1.
2.
3.
4.
5.
6.
7.
8.
9.

Corrugated bamboo roofing sheets
History of the development of corrugated bamboo roofing sheets in Vietnam
General development attributes and advantages
Suitable agro-ecological regions
Target groups
Benefits
Scope for small enterprise development
Requirements for success
Potential improvements and research needs

Concluding remarks

8
8
8
9
9
10
10
10
11
11

PART TWO: MANUFACTURING OF CORRUGATED BAMBOO ROOFING
SHEETS (CBRS)
1. Introduction to CBRS manufacturing
2. Production of CBRS

13
13

2.1 Preparation of raw materials
2.1.1 Cross cutting and splitting of culms
2.1.2 Slivermaking
2.1.3 Mat weaving
2.1.4 Preservation of bamboo mats

13
13
13
13
15

2.2 Resin manufacturing
2.2.1 Resin synthesising equipment
2.2.2 Raw materials
2.2.3 Resin manufacturing

15
15
15
16

2.3 Resin application
2.3.1 The resin applicator
2.3.2 Procedure

16
16
17

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2.4 Pressing
2.4.1 Laying up
2.4.2 Equipment

17
17
17

2.5 Trimming

18

3. Comprehensive input requirements
3.1 Capital costs
3.2 Tools and machinery
Appendices

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19
19
22-25

3

TRANSFER OF TECHNOLOGY MODELS (TOTEMS)
Transfer of Technology Models (TOTEMs) are focussed educational tools providing relevant
information and distance training on one specific area of bamboo/rattan management, processing
or utilization. They are a means of technology transfer between similar regions throughout the
world, with the emphasis on South-South transfer for livelihood development. They enable those
involved in the management and use of bamboo and rattan resources to more efficiently and
effectively develop and use skills relating to these resources.
TOTEMs are primarily intended as practical information resources and teaching aids for those at
the local extension level in their communities, who can utilize them to assist local community
development. Each TOTEM consists of a detailed written report of the technology, a PowerPoint
presentation, a film, and, where relevant, a set of technical photographs. They also include
information on target users, financial analyses of sample set-ups from the partner country
preparing the report and information on where to source particular technologies (such as
equipment). The TOTEM thus provides all the information required for establishing similar
technologies within interested countries and regions.
•

The report contains all the technical details of the particular processes involved, as well as
other relevant information for establishing the technology such as costs of business
establishment, running costs and cash flows.

•

The PowerPoint presentation contains details of the relevant technologies and their
applications, and is intended to provide an overview of the potential of the technology for
development.

•

The film provides a visual guide to the processes involved and helps to bring them alive in
the minds of the learners.

The different parts of the TOTEM are targeted at slightly different audiences, via the local
extension workers. The report and film are intended to be the main means of extension to the
individuals and communities who will implement the technology and who will directly benefit
from it. The PowerPoint presentation is primarily intended as a tool for the extension worker to
sell the technology and its role in development to those who provide the infrastructural, policy
and financial support for its implementation, such as government departments, donors and NGOs.
There is considerable flexibility, however. Local extension workers will be able to incorporate the
TOTEMs in their own work as they wish and adapt and develop the TOTEM to suit their
particular requirements and conditions.
This TOTEM on the production of corrugated bamboo roofing sheets has been produced by the
Forest Science Institute, Hanoi, Vietnam. It may be used alone, or in conjunction with the
TOTEMs on the bamboo splitting and slivering unit and matboard production unit, both of which
have been produced by the Indian Plywood Industries Research Institute, Bangalore, India.
The report part of this TOTEM describes the technology for establishing facilities and producing
corrugated bamboo roofing sheets for rural development in regions where bamboo is available as
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a raw material. It is intended to be used in conjunction with the illustrative film included in this
TOTEM package
The first part of the report introduces the technology, discusses its history, its development
attributes, its benefits and it’s applicability. The second part of the report provides detailed
information on the technical aspects of producing roofing sheets. Appendix I details the method
used in China to produce corrugated bamboo roofing sheets. The costs of producing a standard
size of roofing sheet are shown in Appendix II and the equipment costs are shown in Appendix
III. A bibliography is given in Appendix IV.

This TOTEM is one of the first to be produced by INBAR/FSI and your feedback is most
welcome - kindly contact INBAR or FSI with your comments or suggestions.
© International Network for Bamboo and Rattan 2001

Note 1: This TOTEM has been edited at INBAR and differs from the form in which it was received from
FSI, Hanoi.
Note 2: All financial calculations are in Vietnamese Dong. At the time of writing 1 USD = 14, 600 VND.

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CORRUGATED BAMBOO ROOFING SHEETS AT-A-GLANCE
What are corrugated bamboo roofing sheets?
Corrugated bamboo roofing sheets (CBRS) are an excellent alternative to corrugated
asbestos, iron, plastic or zinc roofing sheets. They are produced from natural materials
and are attractive, durable and resilient to adverse weather conditions and pest attack.
They can be produced in a range of standard sizes and can be used to roof dwellings,
stores, animal pens and other buildings.

How are they produced?
CBRS are produced by pressing firmly together woven bamboo mats that have been
impregnated with an adhesive resin. The corrugations are formed by pressing them
between corrugated pressing plates in the pressing machine.

What is the market for corrugated bamboo roofing sheets?
The market for CBRS is somewhat variable in different regions of the world but depends
to a large extent on successful marketing strategies. CBRS is popular in rural areas where
the low prices are attractive. The potential to increase the use of CBRS in more affluent
areas is enormous, and there is considerable export potential in the markets of the more
affluent countries where their eco-friendly nature could be a major selling point.

What is the role of a corrugated bamboo roofing sheets unit in
rural development?
The unit itself will provide employment to a range of people and there will be extra
employment generation in its forward and backward linkages, such as cultivation and
harvesting of bamboos, primary processing, mat weaving, marketing and retailing. A unit
producing 500, 000 m2 of sheets per year will require a total workforce of over 200
people. The need for a sustainable supply of raw materials will encourage the proper
management of bamboo stands, and the establishment of new plantations, with their
associated environmental benefits.

How do I establish a corrugated bamboo roofing sheets-making
enterprise?
A corrugated bamboo roofing sheets manufacturing unit requires a regular supply of
bamboo mats, electricity, labour and access to markets. An enterprise with a capacity of
500, 000 m2 per year can be established for approximately USD $26, 000 in Vietnam but
costs will vary in other countries.

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PART ONE

INTRODUCTION

DEVELOPMENT ATTRIBUTES, TARGET GROUPS and
BENEFITS of a
CORRUGATED BAMBOO ROOFING SHEETS
MANUFACTURING UNIT

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1.

Corrugated bamboo roofing sheets

Corrugated bamboo roofing sheets (CBRS) are produced from woven mats of bamboo
that are soaked in adhesive resin and then pressed firmly together. The corrugations are
formed by pressing the mats between two corrugated pressing plates. The sheets can be
produced in a range of sizes to suit particular requirements and can easily be trimmed for
special situations. Bamboos are the only raw material used for the sheets. The sheets are
durable and stable and resistant to pest attack, severe weathering and fire.

2.
History of the development of corrugated bamboo roofing
sheets in Vietnam
The Centre of Experiment and Transfer of Techniques of the Forestry Industry, part of
the Centre of Forest Industries at the Forest Science Institute of Vietnam, has been
producing and developing corrugated bamboo roofing sheets on an industrial scale since
1992. Bamboo mats have been produced here since 1982, and the technology for
producing both mats and roofing sheets has been transferred to many processing
enterprises, where they have been widely used. Many regions (communes, districts) have
been established in Vietnam to specially supply raw bamboos for the units. Many of the
units do not just produce roofing sheets. The technology for producing roofing sheets is
almost the same as that for producing mats, and the equipment required is very similar, so
most of the units produce roofing sheets, matboard and bamboo flooring concurrently.
In the earlier days of the first “Doi Moi” period in Vietnam when the service sector was
developing strongly there was very high demand for the roofing sheets and matboard for
the construction of temporary bars and restaurants. At the same time, CBRS have been
used in many public locations and the demand for their use in the construction of
temporary houses for workers was also very high. There is now considerable competition
from corrugated plastic, metal and cement roofing sheets in the cities, but in the
countryside, especially in the poorer, mountainous areas, CBRS are still widely used
especially because they are competitively priced.
The technology was first developed in China, from where much of it was transferred to
Vietnam. The Indian Plywood Industries Research and Training Institute in Bangalore
has also developed roofing sheets technology.

3.

General development attributes and advantages

The main development attributes of the technology are as follows:
•

Increase in area of bamboo plantations will benefit the environment and protect
precious forest resource through substitution of bamboo wood for timber.

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•
•
•
•

Rehabilitation of degraded forests and other waste lands.
Creation of employment opportunities in bamboo cultivation, splitting, mat weaving
and the CBRS unit itself.
Opportunities for family members, particularly women, to spend their free time
weaving bamboo mats at or near their homes.
The CBRS unit is not a capital-intensive project but is labour-oriented and develops
the small-scale industry in rural and mountainous regions.

The main advantages of the technology are:
•
•
•
•

4.

CBRS are an environmentally friendly and safe alternative to asbestos, zinc or
corrugated iron roofing panels.
The sheets are also quieter in the rain than metal roofing panels.
The sheets are durable and strong with excellent internal bond strengths and high
resistance to weathering and biological agencies such as insect attack.
They have a natural appearance.

Suitable agro-ecological regions

The CBRS technology is suitable for bamboo growing regions that can supply the raw
material for their production. Regions of natural bamboo forest are suitable, but CBRS
could also be produced in areas where bamboo is grown on plantations or in homesteads.
Management of plantations and natural stands is highly desirable, both to guarantee a
standard level of supply to the unit and to maximise the benefits of the plantation to the
owner and cultivators. The technology is especially suitable for areas where bamboo
plantations are desirable for the restoration of degraded forests or wastelands such as
abandoned shifting cultivation areas, or where bamboos can be grown to reduce soil
erosion, particularly on steep slopes in high rainfall areas.

5.

Target groups

There are three main target groups of the CBRS unit. The first are those who will be
employed by the unit itself. Unskilled, semi-skilled and technically trained personnel will
all be required. The second group are those who weave the mats from which the sheets
are made. Many of these people are women who will be able to weave at home in their
spare time and who will benefit from the regular income. The final group are those who
will cultivate and harvest the bamboos. This group includes ethnic minorities in
mountainous regions, homestead owners who may cultivate a few bamboos on their plots
and plantation workers. If the unit is established as a cooperative venture within the
community it will also benefit the community as a whole and lead to increased
prosperity. Finally there will be increased opportunities for transporters, wholesalers and
retailers.

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6.

Benefits

The environmental benefits of the unit are considerable. The use of large quantities of
bamboo in the production of mats promotes the sustainable management and increased
area of plantations of bamboos. The cultivation of bamboo is also beneficial for soil
conservation and afforestation activities and plantations are often encouraged as part of
social forestry programmes.
As already noted, the employment opportunities for a range of people in rural areas are
considerable. A unit producing half a million square metres of roofing sheet per year will
create employment for 200 people, most of whom will be required for the production of
bamboo mats. More economic activities will be created in the region, particularly in the
marketing and selling of the sheets, and the social and cultural conditions of the
communities involved should improve as a result. Opportunities for export should also be
explored to earn foreign exchange.

7.

Scope for small enterprise development

There is considerable scope for the development of small CBRS-producing enterprises.
Corrugated bamboo roofing sheets are particularly popular in poorer, rural, mountainous
regions due to their inaccessibility, the proximity of natural raw materials and the low
cost of the sheets. Given some effective marketing the sheets could easily be popularised
in more affluent areas and in affluent countries, where eco-friendy products are very
popular. In this case the establishment of a vigorous sales department within the unit, or
at a local or community level to pool resources from a number of units and act on their
behalf would be beneficial.
The establishment of a corrugated bamboo roofing sheets unit requires an estimated
capital investment of approximately USD $25, 500 in Vietnam (Appendix III), although
costs would vary depending on the country, and the region. It may be possible to apply
for incentives/benefits offered by the government for the establishment of small-scale
enterprises - check with your local government office or business advisory centre for
details.

8.

Requirements for success

The essential requirements for a successful corrugated bamboo roofing sheets unit are:
•
•
•

Start-up capital
Land
Regular supply of raw bamboos for weaving into mats

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•

9.

Access to appropriate machines and equipment for the production of mats and sheets
and some technically trained personnel to install, manage and maintain the unit.

Potential improvements and research needs

Many aspects of the production of CBRS still require improvements. Some of the most
pressing are:
•
•
•
•
•
•
•
•

Improved harvesting and management of bamboo stands.
Improved equipment for splitting bamboos and further research on its mechanization
Improvements in the methods of drying bamboo mats.
Mechanization of synthesizing and gluing.
Improved training, dissemination and transfer of the technology to interested
countries and region around the world
Investigations of new, practical applications of CBRS.
New designs of housing in rural and mountainous regions using bamboo roofing
sheets.
Proper marketing approaches to bring the benefits of the sheets to the attentions of a
wide range of potential consumers.

Concluding remarks
The production of corrugated bamboo roofing sheets is a commercially viable and
socially effective means of utilising bamboo resources to produce value added items for
the benefit of consumers and producers alike. The development of bamboo roofing sheets
enterprises offer considerable income generating opportunities for different categories of
resource-poor people. The technology has strong forward and backward linkages and its
implementation will benefit a wide range of rural people involved in all stages of CBRS
production. The technology is ideally initially implemented in a new location with the
support of state agencies, NGO’s or private enterprises to ensure the linkages are properly
in place.

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PART TWO

MANUFACTURING OF
CORRUGATED BAMBOO ROOFING SHEETS

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1.

Introduction to CBRS manufacturing

There are two methods of producing corrugated bamboo roofing sheets. The method
described here involves one pressing cycle and involves the following steps.1 .
1.
2.
3.
4.
5.
6.
7.

Splitting of bamboo culms into thin slivers
Weaving of slivers into mats
Application of adhesive/binder to mats
Assembling of mats in preparation for hot-pressing
Hot pressing
Cutting to size
Finishing

The process of producing corrugated bamboo roofing sheets is illustrated in figure 1 on
page 14. The stages of the manufacturing process of CBRS are described below.

2.

Production of CBRS

The equipment required for the processing of bamboo culms into corrugated bamboo
roofing sheets are: cross cutting equipment, splitting and slivering equipment, glue
synthesizing equipment, loading-unloading instrument, gluing instrument, drying
equipment, hot press and trimming equipment (Appendix II1).

2.1. Preparation of raw materials2
2.1.1. Cross-cutting and splitting of culms
Bamboo culms are sectioned and the nodes discarded. Only internodes with a minimum
length of 0.4 m are selected for splitting. Internodes are split into splits 20 mm wide and
then soaked in water. They are removed from the water 1-2 hours before slivering.
2.1.2. Slivermaking
Slivers 0.5-1 mm thick and between 15-20 mm wide are produced, either by hand
slivering or in a slivermaking machine. They are then allowed to dry to 18-20% moisture
content and may be bleached or preserved by smoking or sulphur treatment.
2.1.3 Mat weaving.
1

Another method is used in China that involves a more complex process but that produces stronger boards
with lower moisture content. Brief details of this method are given in Appendix I.
2
A more detailed description of crosscutting, splitting and slivermaking is given in the INBAR-IPIRTI
TOTEM on the splitting and slivering unit.
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Bamboo Mats are woven by traditional hand weaving techniques: Mats are usually
woven in sizes of 1x2, 1x3, or 1x4 m and are 1-2 mm thick. The size is chosen depending
upon the dimensions of the pressing plate.
Figure 1: Main stages in the process of producing corrugated bamboo roofing sheets

Cross cutting
and
Spitting
Tools:
Knife and hand
saw or mechanical
splitting machine.

Slivermaking

Drying slivers

Weaving bamboo
mats

Tools
Knife or mechanical
slivering machine.
Sliver dimensions
0.8-1.2 mm thick
15-20 mm wide

Slivers are dried
under the sun to
18-20% moisture
content

By hand

Resin synthesising
Resin mixing
Resin application
Tools
A 500- 1,000 litre can or an
underground brick tank

Resin is diluted for use
in the application tank

Tools
Resin synthesising
equipment
Ingredients: Phenol,
sodium hydroxide,
formalin.

The excess resin is allowed to
drain away from the mats
Drying
Glued bamboo mats are
dried under the sun to a
moisture content of 1820%

Laying up
Three, five or seven layers
of mats are placed together
for pressing

Hot pressing

Trimming
With a bench type
double circular saw

Tools
Hot pressing machine with
corrugated pressing plates

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Transfer of Technology Model: Corrugated Bamboo Roofing Sheets Unit

Storage or sale

14

2.1.4. Preservation of Bamboo Mats.
Bamboo mats are rolled up in groups of 10 mats (1x4 m mats), 15 mats (1x3 m mats) or
20 mats (1x2 m mats) and stored in a dry-aerated store. If the mats are to be stored for
over about three weeks they should be treated with preservative chemicals, such as a 1%
solution of a mixture of boric acid and borax in a 1:1 ratio. Mats should be checked
regularly for signs of fungal or insect attack and retreated at intervals of about 3 months.

2.2 Resin manufacturing
2.2.1 Resin synthesizing equipment
The resin synthesizing equipment used at FSI is made by inox, and is double layered - the resin
container is surrounded by an outer jacket containing cooling water.
Figure 2. Glue synthesizing equipment
2

1

7

Key

3
6
4
5

1. Resin vat
2. Thermometer
3. Cold water container
4. Water outlet tap
5. Resin outlet tap
6. Mixing propeller
7. Water inlet tap

d
D
Usually the resin synthesizing equipment is produced with capacities of 50, 75, 100 and
150 litres. The energy used may be supplied by firewood, coal or electricity.
2.2.2 Raw materials
The raw materials required for phenolformaldehyde resin are phenol, formalin and
sodium hydroxide.
Phenol: Phenol is a white crystalline solid with a melting point of 430C.
Formalin: Formalin is the liquid form of the gas, formaldehyde. It contains 37%
formaldehyde by weight with methyl alcohol as a stabiliser.
Sodium hydroxide: Sodium hydroxide is available in white pellets and flakes.

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The following proportions are used:
Proportion by weight
100
200
25-28
72-75

- Phenol (98%)
- Formalin (37%)
- Sodium hydroxide (98%)
- Water

2.2.3 Resin manufacturing: Molten phenol is first placed in the manufacturing vat. The
formalin is then added and the mixture stirred continuously. Sodium hydroxide dissolved
in the required quantity of water is then added and stirring continued. The temperature of
the mixture then rises as the reaction takes place. Once the temperature has stabilised the
mixture is heated to 600C. After this the temperature is maintained at 85-880C. The
reaction should take about one hour and then the mixture can be cooled by circulating
cold water around the mixture.

2.3 Resin application
2.3.1 The resin applicator.
The resin applicator should be made of a 200-300 litre can or an underground brick tank
as shown below (figure 3).
2
3

4

1
5

1. Resin application tank
2. Loading and unloading pulley
3. Draining rolls of bamboo mats
4. Gutter (allows resin draining from treated mats to flow back into the treatment
tank)
5. Rolls of bamboo mats being treated

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2.3.2 Procedure
The resin is poured into the resin applicator and diluted with water in the ratio 1 part
resin: 0.5-1.2 parts water. The bamboo mat rolls are dipped into the resin for about 2-3
minutes. They are then removed and the excess resin is allowed to drain away for about
30 - 45 minutes.
Mats are then dried to moisture content of 18-20% either under the sun or in a drying
machine such as a band drier. If using a machine-dryer keep the temperature around
550C.

2.4 Pressing.
2.4.1 Laying up.
To produce corrugated bamboo roofing sheets, each sheet is usually laid up with 3, 5 or 7
layers.
2.4.2 Equipment
A suitable hot press has been designed and produced by the experimental factory, Centre
of Forest Industry, FSI with the following parameters:
- Dimension of pressing plate (m)
- Pressure (tonnes)
- Number of pressing floors
- Number of pistons
- Pressing pressure (kg/cm2)

1.1x1.1
200
1-2
2
25-30

1.1x1.5
300
1-2
4
25-30

1.1x2.1
500
1-2
6
25-30

The dimensions of the corrugated plates are based on a theoretical relationship between
thickness (a), wavelength (λ) and height (h) in order to ensure the quality of the surface
and gluing force are optimum (Figure 4).
Figure 4: The corrugated characteristic of corrugated Bamboo roofing sheets
λ
a
h

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In Vietnam corrugated Bamboo roofing sheets are produced with the following
dimensions 800 x 2000 x 5/7 mm and with a corrugation characteristics of
a = 5/7 mm, h = 20 mm, λ = 80 mm
The corrugations are achieved by using corrugated pressing plates montaged onto the
standard plates used for matboard.
The following pressing regime is used
- Pressing regime

Temperature (oC)
130-150

Pressure (kg/cm2) Pressing time (s)
25-30
420

- Pressing diagram (figure 5)
P (kg/cm2)

T (s)
30 s
T1

120 s
T2

180 s
T3

60 s
T4

30 s
T5

- The total time for one pressing cycle is T = 420 seconds
T = ∑Ti = T1 +T2 +T3 + T4+ T5
T1 = 30s, mat loading
T2 = 120s, pressure raising
T3 = 180s, pressure maintenance
T4 = 60s, pressure lowering
T5 = 30s, Roofing sheet unloading

2.5 Trimming
The pressed roofing sheets are finally trimmed to size on a circular bench saw.
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3. Comprehensive input requirements
The following is a very brief summary of the costs of establishing and running a CBRS unit,
and the profits to be made from it.
3.1 Capital costs
The capital cost of establishing a CBRS unit producing 500, 000 m2 of roofing per year is
375 million VN Dong (USD$25, 600). The costs of producing a single, 5-layered corrugated
bamboo roofing sheet, 0.8 x 2.0 m in size, is shown in Appendix II.
3.2 Tools and Machinery
The tools and machinery costs in Vietnam are shown in Appendix III. They are generally
the same as those for the bamboo mat board manufacturing unit. The INBAR-IPIRTI
TOTEM on the bamboo mat board unit contains a more detailed analysis.

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APPENDICES

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Appendix I
Method of producing CBRS used in China (taken from Ganapathy et al.,1996).
Four layers of urea formaldehyde (UF) bonded mats are used The top layer is overlaid
with UF resin-impregnated, reprocessed paper. On top of this, phenol formaldehyde (PF)
resin is impregnated by hot-pressing. The production process is:
•
•
•
•
•
•
•
•

Drying of mats to 8-12% moisture content
Application of UF resin
Overlaying UF resin-impregnated, reprocessed paper
Pressing between two corrugated cauls in a specially designed press
Laying up
Overlaying PF resin-impregnated film
Hot pressing in a specially designed press
Trimming

Sheets produced by this method are significantly stronger and more durable than by the
method presented in this TOTEM. The crest modulus of rupture is about 57 MPa,
compared to 32-38 MPa for sheets produced by the simpler method. It is, however, more
involved, and the extra strength and durability may not, in fact, be required for the
particular uses to which it will be put.

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Appendix II
Cost of producing one, 5-layer corrugated bamboo roofing sheet, 0.8 x 2 m, in a unit
producing 500,000m2 per year in Vietnam
No
1
2
3
4
5
6
7
8
9

Item

Unit

Raw Bamboo mat
mat
Glue
kg
Surface covering
Energy
KW
Employment
sheetSubsidiary material
Organization Expenses
Precautions
Equipment and construction
Subtraction
Total

-

Unit price
VND
4,500
7,500
10,000
750
2,000
500
500
500
2,000
-

Quantity
2.5
1
0.5
3
1
1
1
1
1
-

Amount
VND
11,250
7,500
5,000
2,150
2,000
500
500
500
2,000
28,600

In Vietnam the selling price for such a sheet is 32, 000 Dong, which give a pre-tax profit
of 3, 400 Dong per sheet, or 11.8% of the production costs.

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Appendix III
Equipment costs
No
1
2
3
4
5
6

Name of the equipment

Unit price
mill. VND

Hot press
Corrugated plates
Glue synthesizing equipment
Gluing instrument
Loading-unloading instrument
Trimming equipment
Total

INBAR - FSI
Transfer of Technology Model: Corrugated Bamboo Roofing Sheets Unit

120
25
15
5
10
25

Quantity
1
2
1
1
1
2

Amount
Mill VND
120
50
15
5
10
50
250

23

Appendix IV

Bibliography
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