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Method for making extrudable polyvinyl alcohol compositions    
United States Patent5051222   
Link to this pagehttp://www.wikipatents.com/5051222.html
Inventor(s)Marten; F. Lennart (Macungie, PA); Famili; Amir (Schnecksville, PA); Nangeroni; James F. (Allentown, PA)
AbstractA method for extruding polyvinyl alcohol which includes adding sufficient energy to the polyvinyl alcohol to both melt it and essentially eliminate the crystallinity in the melt, and simultaneously removing energy from the melt at a rate sufficient to avoid decomposition of the polyvinyl alcohol and rapidly cooling the extruded melt reduces the heat history and improves the resulting color of the extrudable polyvinyl alcohol.
   














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Patent Text Patent PDF Print Page Summary File History
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Inventor     Marten; F. Lennart (Macungie, PA); Famili; Amir (Schnecksville, PA); Nangeroni; James F. (Allentown, PA)
Owner/Assignee     Air Products and Chemicals, Inc. (Allentown, PA)
Patent assignment
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Publication Date     September 24, 1991
Application Number     07/402,167
PAIR File History     Application Data   Transaction History
Image File Wrapper   Patent Term   Fees
Litigation
Filing Date     September 1, 1989
US Classification     264/143 264/40.6 264/101 264/185 264/211.22 264/211.23 425/144 425/203 425/204 425/376.1 425/378.1
Int'l Classification     B29C 047/80
Examiner     Thurlow; Jeffery
Assistant Examiner    
Attorney/Law Firm     Michael, Simmons; James C. Leach; Marsh; William F. ,
Address
Parent Case    
Priority Data    
USPTO Field of Search     264/141 264/143 264/237 264/211.21 264/22 264/23 264/24 264/25 264/26 264/27 264/28 264/29 264/30 264/31 264/32 264/33 264/34 264/35 264/36 264/37 264/38 264/39 264/40 264/41 264/42 264/43 264/44 264/45 264/46 264/47 264/48 264/49 264/50 264/51 264/52 264/53 264/54 264/55 264/56 264/57 264/58 264/59 264/60 264/61 264/62 264/63 264/64 264/65 264/66 264/67 264/68 264/69 264/70 264/71 264/72 264/73 264/74 264/75 264/76 264/77 264/78 264/79 264/80 264/81 264/82 264/83 264/84 264/85 264/86 264/87 264/88 264/89 264/90 264/91 264/92 264/93 264/94 264/95 264/96 264/97 264/98 264/99 264/100 264/101 264/102 264/103 264/104 264/105 264/106 264/107 264/108 264/109 264/110 264/111 264/112 264/113 264/114 264/115 264/116 264/117 264/118 264/119 264/120 264/121 264/122 264/123 264/124 264/125 264/126 264/127 264/128 264/129 264/130 264/131 264/132 264/133 264/134 264/135 264/136 264/137 264/138 264/139 264/140 264/141 264/142 264/143 264/144 264/145 264/146 264/147 264/148 264/149 264/150 264/151 264/152 264/153 264/154 264/155 264/156 264/157 264/158 264/159 264/160 264/161 264/162 264/163 264/164 264/165 264/166 264/167 264/168 264/169 264/170 264/171 264/172 264/173 264/174 264/175 264/176 264/177 264/178 264/179 264/180 264/181 264/182 264/183 264/184 264/185 264/186 264/187 264/188 264/189 264/190 264/191 264/192 264/193 264/194 264/195 264/196 264/197 264/198 264/199 264/200 264/201 264/202 264/203 264/204 264/205 264/206 264/207 264/208 264/209 264/210 264/211.24 264/40.1 264/40.6 264/185 264/349 264/101 425/203 425/204 425/376.1 425/144 425/378.1
Patent Tags     making extrudable polyvinyl alcohol compositions
   
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 Technical Review Submit all comments and votes
 Claims Submit all comments and votes
 


We claim:

1. In a method for extruding polyvinyl alcohol which is at least partially crystalline, the improvement which comprises

adding at least 0.27 KW hr/kg of specific energy to the polyvinyl alcohol to both melt it and substantially eliminate the crystallinity in the melt by shearing the areas of crystallinity, and

simultaneously removing energy from the melt at a rate sufficient to avoid decomposition of the polyvinyl alcohol.

2. The method of claim 1 in which about 0.3 to 0.6 KW hr/kg of specific energy is added to the polyvinyl alcohol.

3. The method of claim 1 in which about 0.35 to 0.45 KW hr/kg of specific energy is added to the PVOH.

4. The method of claim 1 in which the polyvinyl alcohol melt is rapidly cooled to yield an essentially gel-free polyvinyl alcohol.

5. The method of claim 1 in which the polyvinyl alcohol is 85-99+ mole % hydrolized.

6. The method of claim 1 in which the polyvinyl alcohol is mixed with a plasticizer.

7. The method of claim 6 in which the plasticizer is glycerol.

8. The method of claim 1 in which the polyvinyl alcohol is mixed with a dispersing agent.

9. The method of claim 8 in which the dispersing agent is glycerol mono-oleate.

10. The method of claim 1 in which the polyvinyl alcohol is mixed with sufficient mineral acid to provide an extruded polyvinyl alcohol which as a 4 wt % aqueous solution has a pH of 5.5-7.0.

11. The method of claim 10 in which the acid is phosphoric acid.

12. In a method for melt extruding 85-99+ mole % hydrolyzed polyvinyl alcohol, the improvement which comprises adding 0.27 to 0.6 KW hr/kg to the polyvinyl alcohol to yield a melt and to shear the areas of crystallinity in the melt, and simultaneously removing sufficient energy from the melt to avoid decomposition of the polyvinyl alcohol.

13. The method of claim 12 in which the polyvinyl alcohol melt is extruded as a strand which is rapidly cooled and cut into pellets.

14. The method of claim 12 in which 0.35 to 0.45 KW hr/kg is added to the polyvinyl alcohol.

15. The method of claim 12 in which 1 to 30 wt % polyhydric alcohol plasticizer and optionally 0.05 to 1.0 wt % dispersing agent are added to the polyvinyl alcohol.

16. In a method for making extrudable polyvinyl alcohol pellets by melt extruding a polyvinyl alcohol composition containing a plasticizer, the improvement which comprises adding 0.35 to 0.45 KW hr/kg of specific energy to the polyvinyl alcohol composition to obtain a melt and to shear any areas of crystallinity in the melt and simultaneously removing energy from the melt at a rate sufficient to avoid decomposition of the polyvinyl alcohol.

17. The method of claim 16 in which the polyvinyl alcohol composition also contains phosphoric acid added in about a 1:2 molar ratio with the sodium acetate content and, optionally, 0.5 to 1.0 wt % dispersing agent.

18. The method of claim 17 in which the plasticizer is glycerol and the dispersing agent is glycerol mono-oleate.

19. The method of claim 18 in which the polyvinyl alcohol is 85-99+ mole % hydrolyzed.

20. The method of claim 16 in which the plasticizer is a polyhydric low molecular weight alcohol.
 Description Submit all comments and votes
 


TECHNICAL FIELD

The present invention relates to melt extrudable polyvinyl alcohol compositions and a method for their preparation.

BACKGROUND OF THE INVENTION

The end use areas of polyvinyl alcohol (PVOH) have been limited despite its excellent strength, adhesive and barrier properties. This limitation is partly due to the fact that vinyl alcohol polymers in the unplasticized state have a high degree of crystallinity and show little or no thermoplasticity before the occurrence of decomposition which starts at about 170.degree. C. and becomes pronounced at 200.degree. C.

The crystallinity of PVOH with a degree of hydrolysis in the 98-99+ mole % range is 30-40% depending on the manufacturing conditions. The higher the heat history experienced by the PVOH resin, the higher the crystallinity as described by K. Toyoshima (Polyvinyl Alcohol Properties and Applications edited by C. A. Finch, John Wiley & Sons Ltd. London 1973). The crystallinity of 87-89 mole % hydrolyzed PVOH is in the 12-18% range and is fairly independent of the manufacturing conditions used.

The melting of PVOH occurs by first melting the small and less than perfect crystals which melt at a temperature approximately 100.degree.-120.degree. C. lower than that of the perfect crystal. Thus a melt is generated by consecutive melting of crystals having a higher and higher melting point until only the perfect and highest melting crystals remain. These perfect crystals are extremely difficult to melt in an extruder as "particle flow" of these crystals is believed to occur. Particle flow is a phenomena which is widely known in the compounding of polyvinyl chloride and was first reported and described by A. R. Berens and V. L. Folt (Trans. Soc. Rheology 11, 95 (1967)). The theory developed by A. R. Berens et al. and adapted by the present inventors to the case of PVOH would predict that the perfect crystals would flow in the PVOH melt created by the melting of the less than perfect crystals and the amorphous material and remain virtually intact at the outlet of the extruder. The gels observed in the extruded PVOH products have been found to consist of unmelted crystalline areas. The crystals making up these areas are believed to be the perfect crystals and thus those with the highest melting point. Increasing the heat during the extrusion process to melt these perfect crystals would result in the formation of degraded and crosslinked material yielding gels having a structure similar to the crystalline-origin gels, the only difference being the presence of a chemical link instead of a physical one. Gels lead to imperfections in the final product which contribute to increased leakage of gas or liquid through the formed product and significantly reduces the mechanical and physical properties.

Resolution of this extrudability problem has been sought through the use of external plasticizers, such as ethylene glycol, trimethylene glycol, propylene glycol and 2,2,4-trimethyl-1,3-pentanediol (U.S. Pat. No. 3,148,202). However, the use of external plasticizer cannot provide sufficient lowering of the melting point to fully overcome the problem of thermal decomposition without leading to significant loss in physical properties such as tensile strength and elongation. Also, the tackiness of any article produced with high plasticizer levels leads to articles having little or no commercial value. Moreover, the addition of plasticizer contributes little, if anything, to resolving the problem of gels in the final product.

Water based extrusion or molding processes have been suggested to help lower the melting point and disperse the crystalline areas thus rendering a uniform and gel-free melt at a low temperature. This technique in essence forms a high solids solution of PVOH which is then cast into a film from which the moisture is removed through evaporation to form a solid, water-free sheet. This process can also be extended to tubular film blowing to produce a biaxially oriented film. However, the film thickness is limited by the rate by which the water can be removed from the film without the creation of air voids. In addition, the necessarily slow drying step results in the reappearance of crystallinity which may be advantageous depending on the particular application. The films produced in this manner are expensive because of the energy cost required to remove the water from the film and, most importantly, the films are prevented from being utilized in the area of coextruded structures. Further, the technique does not allow for injection molding or blow molding of articles as water removal under these circumstances is extremely difficult if not impossible. Thus, the number of end products which can be produced using the water based technique are extremely limited.

The prior art has addressed the problems associated with the melt processability (extrusion) of PVOH. The majority of the art deals with the use of external plasticizer to reduce the melting point of the polymer for