There are many factors contributing
to the fast and sustained growth of plastic products and
materials, which soared from 1m. tonnes in the early 1980s to
over 70m. tpa at present Ð a rate which is exhibiting a
steady growth rate every year.
Minerals have made exceptional
contributions to this growth and are key to reducing the use of
oil resources and other energies.
At present, the volume of imported
oil in China is over 150m. tpa. For the most part, it has
performed against the backdrop of soaring oil prices, resulting
in a much higher price of synthetic resin for which oil is a
Compared with energy consumption of
synthetic resin from the exploration, production,
transportation, cracking and synthesis of petroleum, the
manufacturing of mineral powder is much easier, as the amount
of investment and the energy consumption of one tonne of
mineral powder is only a tenth of that of synthetic resin.
Consequently, using large amounts
of mineral powder in plastics in a rational way bears a
significant impact on building an energy efficient society and
realising sustainable development.
Reducing raw material
The price of nearly all plastic
mineral fillers is lower than that of synthetic resin. For
example, heavy calcium carbonate (HCC) with the general
granularity of 400 mesh - the cheapest powder material
available - is priced at over 100 RMB ($14), only a small
percentage of the price of synthetic resin.
Materials other than HCC cost no
more than 1,000 RMB ($140) either. It goes without saying that
using powder material can significantly reduce the cost of raw
materials providing it meets the performance of filled plastic
The costs of raw materials usually
account for 50-70% of the total cost of plastics products. So
cost reduction forecasts are seeing decreasing overall costs
and more competitive edges in the market. This has sparked a
rash of employing mineral powders in plastics processing plants
in recent years.
With breakthroughs in modification
technology of plastics by filling powder materials, calcium
carbonate and talc are found to be not only low cost, thus
increasing productivity and reducing overall costs, but also
have obvious modification effects on the filled matrix
Although the performance of the
filled plastics will be significantly changed, alternatives can
be made regarding rigidity, toughness and intensity by
strengthening and improving provided the overall performance of
the filled plastics can be guaranteed.
Studies have shown that talc,
kaolin, and mica powder can help plastic films better block the
infrared rays, which is crucial to improve the heat
preservation of greenhouse films. Besides, precipitated barium
sulphate can add excellent gloss to polypropylene (PP)
plastics; wollastonite in powder is conducive to enhancing
rigidity of the surface of plastic material; brucite or
magnesium hydroxide generated from the chemical reaction are
capable of filling, retarding inflame, and abating smoke,
playing weighty roles in the research and development of
low-smoke non-halogen flame retardant plastics, and the
Talc is the major filler used in
the production of
car bumpers. Key properties include rigidity while
resting impact in high and low temperatures.
In spite of the benefits brought
about by the accelerated development of the plastics industry,
plastics that are discarded carelessly after use will
jeopardise the environment and ecology. Studies in recent years
have revealed that inorganic powder material, such as calcium
carbonate, is playing important role in producing
environment-friendly plastic materials.
Using such powder materials in a
scientific and rational way can help us mitigate white
pollution (pollution related to plastic products) by retracting
the plastic bags, films, etc., which may not be easily
Extensive application of powder
material would be within the reach if we shore up the publicity
and industrialisation of it. Mineral powder material, whether
in multiplying the output of plastic products or extending its
application to new fields, is a promising prospect. It will
also play a crucial and irreplaceable role in the development
of plastics industry as well as building an innovative and
conservation-minded society in order to realise the sustainable
economic growth in China.
Example mineral powders
used in plastics
||Parts per hundred resin* (PHR)
|Polypropylene (PP) flat wire
||10 to 20
||Increasing output, whitening, better
||50 to 150
||Increasing output & friction coefficient
|Ploythene (PE) film
||40 to 50
||Increasing output & environmental protection
||20 to 40
|PE bobbin & bellow
||20 to 40
|PP injection moulded item
||Calcium carbonate, talc
||40 to 50
||Reducing costs by replacing ABS
|PE greenhouse film
||5 to 10
||Improving heat insulating properties
|PE rubbish bag
||40 to 50
||Easier to incinerate
||Reducing costs, increasing stability of
||20 to 30
||Maitaining rigidity, resisting impact in high and low
|Auto parts & home appliances
||30 to 50
||Improving heat resistance
||Precipitated barium sulphate
||40 to 50
||Maintaining glaze of plastic products
|Electric cable casing (low smoke, non halogen)
||Aluminium hydroxide, magnesium hydroxide
||Flame retardant, abating smoke
|Auto motor fan
||40 to 50
||Improving heat resistance
Terms: PP = Polypropylene PE = Polythene PVC = Polyvinyl
* 5 PHR means that 5 pounds of an
ingredient would be added to 100 pounds of resin.
Despite the fact the price of mineral powder material may climb
a bit in the long run, it is still acceptable by downstream
customers. New mineral powder materials are expected to be
launched into market, like the powder materials with little
influence on the light transmittance of plastic films and no
influence at all on the extrusion of fibres of non-woven
For powder materials whose
functional characteristics are already known to us, the main
task is to learn how to make better use of them (eg.
Calcium carbonate is the most
important mineral used in plastic products. It accounts for 70%
of the 10m. tonnes of minerals consumed in plastics every
HCC is a powder derived from the
grinding of the ore, while light calcium carbonate (LCC) is
generated from a chemical reaction, also known as precipitated
calcium carbonate (PCC).
Calcium carbonate is advantageous
as a filling material over others due to the following
low price, non-toxic, flavourless, and non-irritating
high-whiteness, easy colouring, and little interference
into other colours
low rigidity, thus little friction against processing
devices and moulds
good chemical stability, thus no chemical reaction with
other matrix plastics
macromolecules of matrix plastics degrade or cross linked
good thermal stability, and the temperature of thermal
decomposition is over 800¡C
easily dried, no crystal water, and convenience in
Talc is widely used in plastics,
only second to calcium carbonate.
With millions of tonnes of talc
used every year and large amounts exported to Japan, and South
Korea, a considerable amount of talc is used to modify
The lamellar structure of talc can
improve the rigidity and heat resistance of the matrix
plastics, talc is sometimes viewed as reinforced filling. This
requires a relatively large diameter-thickness ratio of talc in
addition to a small particle diameter.
Mineral powders containing silica
sand, like talc, mica powder, and kaolin, can be used for heat
preservation in greenhouse films due to its resistance to
infrared light. Although talc is weakest in preventing infrared
light among them, it is the cheapest and most convenient for
use. For talc used for this purpose, large length-diameter
ratio is not the concern, but a small particle diameter and
ideal gloss are preferred.
In recent years, talc has been
widely used in PE films, because the refractive index of talc
is very close to that of PE matrix plastics. Compared with HCC
and other fillers, talc may allow better light transmission of
Aluminium hydroxide and magnesium
are the key fire/heat resistant fillers used to produce
electric cable casing.
Kaolin used in the plastics
industry in China can be divided into two categories. One is
the so called washed kaolin, belonging to clay. The other is
coal kaolin, a typical hard kaolinite in
China, which is in brown or black
lumps associated with coal.
Owing to its high price and
inconvenience in use, kaolin clay is only used to improve the
insulation strength of plastics after calcination. However,
recent studies have shed light on its outstanding performance
as a barrier to infrared rays, which is of great help in
retaining heat for plastic greenhouse films.
In filling plastics, kaolin clay
could elevate the tensile strength and modulus of
thermoplastics with relatively low glass temperature without
significantly diminishing its elongation rate and impact
Moreover, kaolin could function as
nucleator after added to PP, thus increasing the number of PP
crystals and curtailing the size of crystal so as to enhance
the rigidity and strength of PP.
Mica powder is used mainly to
improve the rigidity and heat resistance of plastic products,
provided the high diameter-thickness ratio of its slice is
preserved properly during processing.
Owing to its openness which lets
light pass, it is possible to apply mica powder to agricultural
plastic films. Adding mica film to inorganic filling that is
also capable of scattering light and preventing infrared rays,
the astigmatism ratio would increase considerably in spite of a
slight lessening of light transmittance ratio. At the same
time, the obstruction of infrared rays with wave length between
7 -25mm is most effective.
Acicular wollastonite as powder,
scattered within matrix plastics, is conducive to enhancing the
tensile strength and cross-breaking strength of matrix
plastics. In addition, wollastonite can allow filled plastics
to better resist water.
This characteristic, when applied
to nylon, will improve the hygroscopicity of nylon products
under damp circumstances, since the rigidity and modulus of
nylon will decrease after absorbing water.
Al hydroxide & Mg
Adding aluminium hydroxide and
magnesium hydroxide into plastics can realise triple functions
of filling, retarding flame, and abating smoke. They are the
ideal choices of low-smoke non-halogen flame retardant
Montmorillonite, a layer-silicate,
can be used to manufacture nanoplastics and has commanded more
attention from different fields in recent years.
The tensile strength of nylon6
containing 4.2% montmorillonite can increase by 50% compared
with pure nylon6. Likewise, modulus increases by 100%, and heat
distortion temperature by 90¡C. While the transparency
heightens and hygroscopicity decreases (weakening the rigidity
of nylon), the shock resistance of the material remains almost
The reason for this is that the
lamella of montmorillonite is evenly dispersed in nano scale
within nylon6, thus forming exfoliated composite
material-nanoplastics in real sense.
Mineral concerns and
Minerals used in plastics tend to
follow the same general requirements: reasonable price; minor
impurities; low rigidity; and easy handling and using.
But there are some specific
requirements that the mineral must meet in order to be fully
suitable to use as a plastic additive.
Powder material is utilised used as
a filler in uneven granular form. However, as far as the
performance of plastics is concerned, the geometrical shape of
filling is of great significance to the physical and mechanical
properties of the filled system. In this regard, first concern
should be given to the granular shapes of powder materials
before using them.
The knack of modification
technology by filling powder materials is to spread the powders
as evenly as possible to the matrix plastics, which resembles
the islands of various sizes in the sea, this is also known as
the island structure.
Generally speaking, if distributed
evenly, the smaller the diameter of the filling is, the better
the mechanical properties of the filled system.
However, the cost of processing
powders is inversely proportional to the particle diameter, and
it will be more difficult to evenly distribute powder material
of smaller diameter. Consequently, making the right choices
based on the knowledge of the particle diameter and its
distribution is all the more important.
Specific surface area indicates the
surface area of filling by a unit mass, the size of which is
directly linked to the compatibility between filling and resin,
the activation of surface and production costs.
The power of surface free energy of
filling particles is related to their distribution in the
matrix resin. With the same specific surface area, the larger
the energy, the easier for agglomeration of particles and more
difficult for dispersal. In the surface treatment of filling,
one of the major aims is to reduce the surface free energy.
The apparent density of filling is
linked with the arranging of filling particles. In the field of
plastics modification by filling powder material, the factor
truly contributing to the overall density of the filled system
is no other but the density of individual filling particles and
the forms of their existence in matrix plastics. In other
words, whether they are agglomerated, and whether there is
space between matrix plastics molecules or not.
The hardness of filler particles is
a double-edged sword. On the one hand, fillers of good hardness
can allow better abrasion resistance for plastic filling
materials, but on the other hand, using this kind of filler may
lead to serious wear and tear of the processing devices and
moulds during the processing of filled system.
When the refractive index of the
powder filler is close to or the same as that of the matrix
plastics, the influence on covering light after blending the
powders into the matrix will become relatively insignificant,
or vice versa.
Absorption & reflection
Ultraviolet rays can prompt
degradation of the macromolecules of polymers. The wave length
of infrared rays is above 0.7mm. Light waves within this
category can be absorbed or reflected by some fillers.
Employing minerals such as mica, kaolin, and talc can
effectively reduce the light transmittance of infrared rays,
thus significantly enhancing the performance of preserving heat
in agricultural greenhouses.
The processing of filled plastics
integrates heating, fusion, cooling, moulding etc. The original
thermal performance of the filler and the discrepancies between
that performance of matrix plastics and the filler itself will
influence the processing.
Since metal conducts well, metal
powders used as a filler will affect the electrical performance
of filled plastics.
Fillers made from non-metallic
minerals do not conduct, and that is to say no influence will
be imposed on the electrical performance of matrix plastics.
However, the valence bond of metal powders may be broken during
cutting and grinding, and a static charge may occur. As a
result, mutually attractive aggregates will take the shape,
which is more likely to take place in production of minute
High molecular polymer is
inflammable, but most filler materials are non-inflammable.
This fact can help to reduce
combustible concentration and retard the combustion of the
matrix if those non-inflammable materials are added to
The benefits of applying mineral
powder material to plastics are evident, whether in terms of
using scope, modification effects or the economic and social
benefits. Years of practice have manifested that innovative
application is the key to increasing use, and is also a must in
continued expansion of mineral usage in plastics.
Innovations in surface treating
technology and treating chemicals can raise the price
performance ratio of filled plastic material. The variety of
the chemical compositions of powder particles and the
complexity of surface nature means that not all minerals can be
subjected to surface treating technology and auxiliaries. The
experiences of some companies have told us that it is all the
more necessary and possible to use tailored surface treating
chemicals with higher price-performance ratio.
To use relatively cheap inorganic
powder materials as the core, and to deposit the functional
auxiliary materials on the surface of powders in the form of
molecules is not only conducive to the distribution and
dispersal of auxiliaries, but also does not affect performance
of the powder materials. Thus, a higher price performance ratio
is achievable, so is a better synergistic effect based on the
toughening theory of rigid particles.
With the same composites in PVC
sectional material, better or at least the same physical and
mechanical properties can be reached by replacing ACR with
ATM-310B. But owing to the core-shell structure of ATM, an
obvious competitive edge in the costs of using is
Most of the plastic materials
concurrently feature high surface resistivity and low
dielectric constant, and that is why electric charges, ie.
static, are easily accumulated on them. Problems triggered by
static can range from small matters, like attracting dusts or
mutually repelling with the like charges, to disasters, such as
fires or explosions.
A new approach in improving the
anti-static performance of plastics lies in the use of tint
conducting material, which is made by depositing a layer of
conductible material on the surface of non-metallic mineral
powders that do not conduct.
The true density of non-metallic
minerals is usually two or three times larger than synthetic
resin. If we can, during the processing of injection-moulded
items like pipes or sectional materials, use fillers without
enlarging the density of the items or the increment is within
reasonable scope, to add mineral fillers into plastics will
become more likely.
In the past, pursuing perfect
performance was the main concern of plastic material, with
little or even no consideration of whether they could be
absorbed by nature or recyclable after use.
The discarded plastics in every
corner of our society have not only polluted, but have also led
to a huge waste of the invaluable oil resources.
adheres to green production and green consumption, and it also
emphasises the coordination between the environment and the
phases of production, use, and post-use of products.
Using calcium carbonate is expected
to significantly reduce the use of oil resources and other
energies. Over 25% of resin could be saved when calcium
carbonate accounts for 30% in PE plastic bags, compared with
those containing no calcium carbonate.
Non-metallic minerals will
encourage degradation of plastic materials while calcium
carbonate is conducive to the burning of PE plastics. Burning
of PE plastics is still feasible since not all plastics have
recyclable values or worth recycling, and landfill requires
Experiments have shown that 100g PE
films containing 30% calcium carbonate and 1% burning
thermal-oxidative degradant additive finishes complete
combustion in four seconds, compared with 12 seconds of films
with the same weight.
Additionally, calcium carbonate
poses no negative influences on groundwater after landfill and
does not contain any detrimental heavy metals.
The history of applying mineral
powder material to plastics shows that it has already become an
indispensable material in the plastics processing industry.
Moreover, it plays a more and more important role in improving
the price-performance ratio and expanding functional
application of plastic material, conserving resources, and
protecting the environment.
To better and more efficiently
utilise the mineral powder material by bringing its strengths
into full play shall not only reduce costs, but also aim to
build an environment-friendly society by achieving sustainable
development. To scale the application of mineral powder
material in plastics to a new height, we should further
facilitate research and development, accelerate the
transformation of research achievements, and shore up
cross-industrial exchanges and cooperation.
Contributor: Liu Yingjun, senior
engineer, vice chairman and secretary general of the Committee
of Modified Plastics of China Plastics Processing Industry
Adapted from a presentation at
the 8th Chinese Industrial Minerals Conference, 7-9
September 2009, Qingdao, China.