Natural rubber structure analysis

The determination of the various types of geometric isomers associated with unsaturation in Polymer chains is of great importance, for example, in the study of the structure of modern synthetic rubbers. In table below are listed some of the important infrared absorption bands which arise from olefinic groups. In synthetic "natural" rubber, cis-1, 4-polyisoprene, relatively small amounts of 1, 2 and 3, 4-addition can easily be detected, though it is more difficult to distinguish between the cis and trans-configurations. Nuclear magnetic resonance spectroscopy is also useful for this analysis. 

With improvements in elemental analysis, the structure of many simple molecules was elucidated. Elemental analysis, however, didn t help solve the structure of cellulose or natural rubber, materials that we now know are mac-romolecular in nature. In fact, it contributed to a general misconception. For example, natural rubber was found to have a composition equivalent to CSH8, but this only corresponds to the repeating unit of the polymer and says nothing about its long, chain-like structure. 

The usefulness of analytical pyrolysis in polymer characterization, identification, or quantitation has long been demonstrated. The first application of analytical pyrolysis can be considered the discovery in 1860 of the structure of natural rubber as being polyisoprene [10]. This was done by the identification of isoprene as the main pyrolysis product of rubber. Natural organic polymers and their composite materials such as wood, peat, soils, bacteria, animal cells, etc. are good candidates for analysis using a pyrolytic step. 

Chapter 5 summarizes the investigation of lignocellulosic flax fiber-based reinforcement requirements to obtain structural and complex shape polymer composites. This chapter discusses in detail the possibility of forming complex shape structural composites which are highly desirable for advanced applications. Chapter 7 focuses on the structure and properties of cellulose-based starch polymer composites, while Chapter 8 focuses on the spectroscopic analysis of rice husk and wheat gluten husk-based polymer composites using computational chemistry. Chapter 9 summarizes the processing, characterization and properties of oil palm fiber-reinforced polymer composites. In this chapter, the use of oil palm as reinforcement in different polymer matrices such as natural rubber, polypropylene, polyurethane, polyvinyl chloride, polyester, phenol formaldehyde, polystyrene, epoxy and LLDPE is discussed. Chapter 10 also focuses on... 

A TEM photograph for DPNR-gra/l-poly(NDMA) is shown in Figure 14. 10, in which a gloomy domain is natural rubber and a bright domain is poly(NDMA). As it is clearly seen, the natural rubber partiele of about 1.0 pm in diameter was dispersed in a poly(NDMA) matrix of 10 mn in thickness to form a nanomatrix structure, while it did not contain poly(NDMA). Furthermore, a volume fraction of poly(NDMA) matrix was estimated by image analysis of the photograph to be about 3 w/w%, which corresponded to 1.81 w/w% estimated from the NDMA content shown in Table 14.2. These results indicate that the graft copolymerization occurs only on the surface of... 

Dan and co-workers [47] in their investigation of the structure and stability of chlorinated natural rubbers (CNR) applied high-resolution Py-GC-MS coupled with FTIR and thermal analysis techniques. 

Dan and co-workers [8] studied the structures and thermal and thermo-oxidative stabilities of the gel and chlorinated natural rubber from latex. The polymers were analysed by chemical analysis, high-resolution pyrolysis-gas chromatography-mass spectroscopy (HR-Py-GC-MS) coupled with Fourier-transform infrared spectroscopy, and thermal analysis techniques [dynamic thermal analysis and thermogravimetric analysis (TGA)]. 

Natural rubber (NR) is a well studied elastomer. Of particular interest is the ability of NR to crystallize, specifically the strain-induced crystallization that takes place whilst the material is stretched. Moreover, in many elastomer applications, network chain dynamics under external stress/strain are critical for determining ultimate performance. Thus, a study on how the strain-induced crystallization affects the dynamics of a rubbery material is of outmost importance. Lee et al [1] reported their initial findings on the role of uniaxial extension on the relaxation behavior of cross-linked polyisoprene by means of dielectric spectroscopy. Nonetheless, to our best knowledge no in-depth study of the effects of strain induced crystallization on the molecular dynamics of NR has been undertaken, analyzing the relaxation spectra and correlating the molecular motion of chains with its structure. Broadband dielectric spectroscopy (BDS) has been chosen in order to study the dynamic features of segmental dynamics, because it is a comparatively simple technique for the analysis of the relaxation behaviour over a suitable frequency interval. This study is important from a basic and practical point of view, since an elongated crosslinked polymer at equilibrium may be considered as a new anisotropic material whose distribution of relaxation times could be affected by the orientation of the chains. 

The properties of elastomeric materials are controlled by their molecular structure which has been discussed earlier (Section 4.5). They are basically all amorphous polymers above their glass transition and normally crosslinked. Their unique deformation behaviour has fascinated scientists for many years and there are even reports of investigations into the deformation of natural rubber from the beginning of the nineteeth century. Elastomer deformation is particularly amenable to analysis using thermodynamics, as an elastomer behaves essentially as an entropy spring . It is even possible to derive the form of the basic stress-strain relationship from first principles by considering the statistical thermodynamic behaviour of the molecular network. 

In the case of polymerization of substituted dienes such as 2-methyl-butadiene (isoprene), the structure of the resulting product may be more complicated because it is possible to create polymers with structure of type 1.2 and 3.4, as well as 1, 4 cis and 1, 4 trans. Moreover, structures head to tail and head to head t3 e may be formed. The results of the analysis of S5mthetic polyisoprene have shown that, in general dominating is the head to tail arrangement and the 1, 4 trans configuration. The natural rubber is 1,4 cz5-polyisoprene, whereas gutta-percha and balata have 1, 4 trans structure. 

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