Natural rubber, film studies

Bonfils, F. Sainte Beuve, J. Laigneau, J. Koman Achi, A. Alledon, A. Sylla, S. Steric exclusion chromatography study of natural rubber film prepared from fresh field latex. J. Nat. Rubber Res. 1995,10, 143. 

A Py-GC study [7] with pyrolysis done at 500° C showed numerous peaks corresponding to the isoprene dimers, trimers. .. up to hexamers eluting in clusters of peaks. The separation was done on a methyl silicone 5% phenyl silicone type column with FID detection. The results from a Py-GC/MS study [8] where natural rubber was pyrolysed at 580° C in a Curie point Py-GC/MS on-line system showed similar results. The TIC trace of the pyrolysate with the separation done on a 60 m Carbowax column, 0.32 mm i.d., 0.25 pm film thickness, with the temperature gradient of the GC oven between 40°... 

In the presence of the tertiary hindered amine (StNCH,), the hindered N-oxyl (StNO-) and the phenol (AOX), the extent of oxidation and embrittlement were sharply reduced, with AOX being most effective (Table 1). The thioester (DSTDP) had little effect on the 3400 cm-1, -OH absorption but appeared to accelerate embrittlement. Further study of this additive was abandoned. The y-irradiation of an unstabilized PP sample wrapped in a thin, carefully extracted film of natural rubber showed a lower overall oxidation level by IR than a PP film irradiated alone (Table 1). However, when working at the higher dose rate (and so much shorter irradiation times), this effect was barely detectable. 

The objects of study were selected mixture of low-density polyethylene (LDPE) with wood flour (WF), natural rubber (NR) and ethylene-propylene rubber (EPDM). WF content is 40 wt.%. Rubber injected at 10 and 20 masses %. As composite materials based on LDPE blending performed on a laboratory mixer at a temperature of 140°C for 5 minutes and then get the film samples in a laboratory press. The sample thickness was 100 10 microns. 

Objections to the protective film theory are less clear cut. Murray (1972) has stated that if the film were to be composed only of antiozonant or ozonized antiozonant, then some rather unrealistic rates of diffusion would have to be assumed in order to form such a film in the time period observed . On the other hand the results of Andries et al (1975), who studied the surface of ozonized natural rubber compounds by attenuated total reflectance spectroscopy obtained results consistent with this theory (and for that matter the scavenger theory) but not with the re-linking and diversionary theories. 

Strained and unstrained films of natural rubber were examined by Andrews [bS, 66] who showed that the spherulitic morphology of the unstrained films changes to a fibrillar morphology with crystalline units on the order of 6 25 nm wide. This is consistent with the work of Scott [18] who showed that strain-induced crystallinity results in fibrillar structures parallel to the strain direction. A further development of this idea by Keller and Machin [62] showed the morphology of melt extruded PE sheets to be an arrangement of lamellar crystals, normal to the stress direction, arranged in fibrillar units parallel to that stress. The concept of model film studies providing information related to commercially produced materials was described in this study. 

Based on the procedures described in the previous sections, one can obtain nanomechanical maps of a wide variety of polymeric and biological materials, including carbon black (CB)-reinforced natural rubber (NR) [40], carbon nanotube (CNT)-reinforced NR [41,42], reactive polymer blend [43], block copolymers [9,21,44,45], deformed plastics [46,47], human hair [48,49], honeycomb-patterned polymer films [50-52], CNT-reinforced hydrogel [53], and diffusion front of polymer [54,55]. The detailed descriptions are also found in other literatures [56-59]. Hereafter, several example studies are reviewed. 

Miyata and Yamaoka [152] used scanning probe microscopy to determine the microscale friction force of silicone-treated polymer film surfaces. Polyurethane acrylates cured by an electron beam were used as polymer films. The microscale friction obtained by scanning probe microscopy was compared with macroscale data, such as surface free energy as determined by the Owens-Wendt method and the macroscale friction coefficient determined by the ASTM method. These comparisons showed a good linear relationship between the surface free energy and friction force, which was insensitive to the nature of polymer specimens or to silicone treatment methods. Good linearity was also observed between the macroscale and microscale friction force. It was concluded that scanning probe microscopy could be a powerful tool in this field of polymer science. Evrard et al. [153] reported coefficient of friction measurements for nitrile rubber. Frictional properties of polyacetals, polyesters, polyacrylics [63], reinforced and unreinforced polyamides, and polyethylene terephthalate [52] have also been studied. 

---