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7 Conclusion: Key issues in ensuring effective recycling of sulfur cross-linked NR
Recycling of sulfur cross-linked natural rubber using scCO2
The rubber industry is confronting the ongoing problem of how to handle
used rubber products. In order to achieve an effective recycling system for
sulfur cross-linked NR, the following points are required so that new science
and technology can be generated from the results in the near future.
selective decross-linking reaction for mono-sulfidic linkage in NR
∑ recycling of isoprene monomer from the used NR products
∑ recycling of fillers from the used NR products
∑ recycling of zinc atom from the used NR products
∑ elucidation on the mechanism of the sulfur cross-linking reaction
In addition to the recycling of NR molecules, the author would like to
emphasize the importance of achieving the sustainable production of NR
for the environment and for the rubber industry. The two processes, the
continuous production of NR and the effective recycling of NR, are necessary
to maintain activity in the rubber industry all over the world and to preserve
the Earth’s limited resources. A total map for the utilization of used tires as
a model for used rubber is shown in Fig. 17.11.
This study was supported by the Industrial Technology Research Grant
Program in ID: 02B67006c from the New Energy and Industrial Technology
Development Organization (NEDO) of Japan. The author thanks John Wiley
& Sons and Elsevier for copyright permissions.
17.11 Total map for the recycling of tire rubber.
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Recent research on natural rubber latex
T. P a l o s u o, National Institute for Health and Welfare,
Abstract: This chapter discusses recent findings on current views of natural
rubber latex (NRL) allergy, the underlying mechanisms, risk groups and
clinical manifestations and, in the course of time, remarkable changes in
prevalence. Historically interesting milestones and the dominant role of
medical gloves are highlighted. Prevailing practices to prevent sensitisation
to NRL and to control the problems that emerged are dealt with, including
the impact of international standards and the activities of the scientific
community. The role of education combined with guidelines and obligations
to use properly controlled NRL products or, under defined circumstances,
alternative NRL-free synthetics, show that means to prevent sensitisation to
NRL have been built up and shown to be effective where implemented.
Key words: natural rubber latex, allergy, gloves, prevention, standardisation.
Introduction: The problem of natural rubber
latex (NRL) allergy
Natural rubber latex (NRL) has been used as a material for the production
of gloves for more than 100 years. NRL gloves have been known for their
superior barrier properties, durability, flexibility, modulus and elasticity
and therefore are used extensively in medicine. A dramatic increase in
protective glove use in healthcare took place in the 1980s and 1990s, due to
the implementation of the so-called ‘universal precautions’ by the Centers
for Disease Control in the US (1987) aiming at minimising the risks of HIV
and hepatitis infection. This escalating use was associated with changes in
manufacture and other features in glove use, which in part were responsible
for the dramatic increase in allergic reactions to NRL products.
It soon became evident that allergic reactions to NRL formed one of the
most significant occupational diseases among healthcare workers. Knowledge
of NRL allergy from clinical and immunological perspectives has evolved
rapidly over the last two decades. However, the scientific literature on NRL
allergy is almost entirely limited to medical devices, primarily to surgical
and examination gloves.
Section 18.2 outlines the medical background to NRL allergy. Section 18.3
© 2014 Woodhead Publishing Limited
Recent research on natural rubber latex (NRL) allergy
then discusses the current knowledge about the mechanisms of development of
allergic immune responses and the role of different NRL allergens and glove
powder. The third section also deals with changes in glove manufacture upon
responding to the demand for increased use of protective gloves, chemical
allergens, cross-reactions, diagnostic procedures in patient care and the
newly discovered role of genetic factors in NRL allergy. Presentation and
clinical pictures of NRL allergies are also discussed. Section 18.4 describes
changes in the incidence and prevalence of NRL allergy and the changing
epidemiology, revealing an ongoing gradual decrease in new cases of Type
1 NRL allergy in many parts of the world. The peak of the NRL allergy
‘epidemic’, which hit in the 1980s and 1990s, seems to have passed in
healthcare in the western world, but problems do still exist, in particular in
developing countries and in the non-medical fields.
Section 18.5 handles the key issues in reducing NRL allergy, discussing
changes in glove manufacture, education, development of international
standards and means to reliably measure the allergenic potential of NRL
products as well as regulatory activities and numerous published position
papers. Future trends in NRL allergy research are assessed in Section 18.6.
Central findings and advances in recent research efforts on NRL allergy are
summarised in Section 18.7. Suggestions for further information are proposed
in Section 18.8.
Medical background to NRL allergy
18.2.1 Basic concepts in immunology
Immunology is generally considered as the discipline of the body’s defense
against infections. The responses mounted against infectious agents, such as
bacteria, viruses or fungi, are known as immune responses. The responses can
be specific and are then defined as adaptive immune responses, developing
as adaptation to particular pathogens. The adaptive immune response can
lead to a phenomenon known as immunological memory and confer lifelong
protective immunity against reinfection by the same pathogen.
In addition, the body is ready for non-specific or innate immune responses
which in the front line combat the wide range of pathogens surrounding
us. This system is not specific for any individual pathogen nor does it lead
to immunological memory. Central components of this front-line defense
are ubiquitous phagocytic cells (macrophages), able to engulf and digest
microorganisms. Another important compartment in the non-specific host
defense is the complement system, a collection of several plasma proteins
that can be activated directly by pathogens or indirectly by pathogen-bound
antibody, leading to various effector functions important in the neutralisation
and elimination of the invaders.