Surface morphology of asymmetric latex film prepared from blends of natural rubber and poly(methyl methacrylate) latexes

Abstract

Colloidally stable latex blends of natural rubber (NR) and poly(methyl methacrylate) (PMMA) latexes containing up to 50 wt.% PMMA can be prepared by mixing commercial NR ammoniated latex concentrate and monodisperse PMMA latex dispersion. The clarity and tackiness of the films obtained depend on the PMMA content; films become opaque and non-tacky at >30 wt.% PMMA content. The morphology of these films shows asymmetric distribution of the PMMA particles across the thickness of the film. There is preferential enrichment of PMMA particles at both the air/polymer and glass/polymer interfaces and a predominating NR interior. More PMMA particles are accumulated preferentially at the glass/polymer interface than at the air/polymer interface. The accumulation of the PMMA particles at the interface is strongly dependent on the size and concentration of the PMMA particles. The formation of these asymmetric latex films is explained in terms of the surface energetics, compatibility, T g and density of the polymers, stability of the component latex, surface chemistry and particle size of the latex particles used. Copyright  2001 John Wiley & Sons, Ltd. KEYWORDS: asymmetric latex film; natural rubber latex; poly(methyl methacrylate) latex; latex blend film morphology; natural and synthetic latex blend INTRODUCTIONSynthetic latexes are used extensively in the paints and coating industry. This application requires the latex particles, on drying, to form a continuous film. However, good filmforming latex lacks mechanical strength in its film. Thus, low-T g latexes have good film-forming abilities but the films possess a low Young's modulus. Various techniques have been used to overcome this problem. For example, filmforming aids frequently have been employed to provide a coherent film.1,2 Another approach is the synthesis of waterborne core/shell latex particles with a high-T g polymer core and a film-forming shell that are able to form a film of elastomeric matrix containing a high-modulus inclusion.3,4 Another technique is by physically blending two polymer latexes with different T g values 2,5 in which the soft particles deform and fill the voids between the hard particles. A blend of a low-T g latex with a high-T g polymer is used in latex-based impact modifiers for polymer resins. In polymer blending, one anticipates obtaining different properties in the blend than those of the individual polymer components. Although polymer blending 7 has been studied for many years, much less attention has been paid to synthetic latex blends. One of the main interests in latex blends is the drive towards zero-volatile organic compounds in the organic coating industry.2 Analysis of morphology and transparency of latex blend films by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has provided insight into the interaction between hard and soft latex particles.8 -10 Although diffusion at the particle/particle interface of miscible polymer components during film formation is studied extensively, 11 -15 little is known ab...

Preparation of poly(methyl methacrylate‐co‐butyl methacrylate) nanoparticles and their reinforcing effect on natural rubber

“…The hardness values (shore A) of neat NR, NR/PMMA, NR/PMBMA1, and NR/PMBMA‐CA1 films are presented in Figure . The hardness of NR/PMMA film increased sharply compared with NR, as the PMMA nanoparticles tended to aggregate in the NR surface . While, the hardness value of NR/PMBMA1 decreased obviously, indicating that fewer PMBMA1 nanoparticles migrated out of NR surface and thus gave better compatibility compared with PMMA and NR.…”

Thermal analysis and topographical characterization of films of styrene‐butadiene blends

“…51 Although the addition of nonfilm-forming (hard) particles to a film-forming latex is known to generate voids in the film. 15,19,68 Such voids are created because hard particles cannot deform to fill the interstices after moisture evaporation. If the mobility of soft latex polymer chains is sufficiently high, the film-forming ability in a binary blend is controlled by the number of contacts between hard particles.…”

Studies of latex blends of natural rubber/poly(methyl methacrylate-co-2-ethylhexyl methacrylate) and their comparison with incompatible natural rubber/poly(methyl methacrylate)

“…Although the polarity of PMMA, the water absorption of NR/PMMA blend begins decrease beyond the addition of 10 phr. This is may be explained that the incompatible PMMA particles are considerably accu mulated on the film surface, hindering the water mol ecules into the NR inner [4]. However, it is clearly noted that the water absorption values of modified films from copolymers are superior to that of modified films from homopolymer (PMMA).…”

“…Because of excellent weather resistance and mechanical strength of PMMA, the PMMA/NR blends have been attracting significant attention from academic and practical fields [3]. However, the blending is highly incompat ible and immiscible due to the mismatch of the polar ity and hydrophilicity [4].…”

“…Besides, the polymer diffusion mostly occurs at temperature above glass transition temperature (T g ) of polymer [20]. Ho et al [4] have reported the accumulation of incompatible PMMA particles on the film surface in the NR/PMMA latex blend. This is mainly due to the big differences in hydrophilicity and T g (PMMA, T g > 100°C; NR, T g < -60°C), the un deformed and polar particles were easily trend to immigrate into the film surface through water channel during the film form ing [21][22].…”