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7 Conclusion: Key issues in ensuring effective recycling of sulfur cross-linked NR

7 Conclusion: Key issues in ensuring effective recycling of sulfur cross-linked NR

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Recycling of sulfur cross-linked natural rubber using scCO2



Future trends

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.


In use


New tire





Used tire



Recovery and




Raw polymer






Natural rubber

17.11 Total map for the recycling of tire rubber.



Chemistry, Manufacture and Applications of Natural Rubber

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Recent research on natural rubber latex

(NRL) allergy

T. P a l o s u o, National Institute for Health and Welfare,


DOI: 10.1533/9780857096913.3.452

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.

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