New Third-Generation Protective Clothing from High-Performance

Chapter 13

New Third-Generation Protective Clothing from High-Performance Polyethylene Fiber From Knives to Bullets K. M. Kirkland, T. Y. Tam, and G. C. Weedon

Downloaded by CORNELL UNIV on August 6, 2012 | http://pubs.acs.org Publication Date: April 3, 1991 | doi: 10.1021/bk-1991-0457.ch013

Allied Fibers Technical Center, P.O. Box 31, Petersburg, VA 23804

Ultra high strength polyethylene fibers are finding increased use in a variety of protective clothing applications. The unique combination of properties available with high performance polyethylene fibers such as extraordinary abrasion resistance, high modulus and tensile strength, low specific gravity, excellent chemical resistance, and high cut resistance are extending the use of high performance fibers in applications where existing protective clothing was lacking. Growing awareness of the advantages offered by high strength polyethylene fibers is allowing the fiber to be used to improve existing protective clothing. Many types of hand and arm protectors making use of the superior cut and abrasion resistance of the high strength polyethylene fibers will be presented. Ballistic armor applications will be highlighted to illustrate the advantages of high performance polyethylene fiber's high tensile strength, high modulus and low specific gravity. Progress i n d e v e l o p i n g p r o t e c t i v e c l o t h i n g has never been more r a p i d than i t i s a t p r e s e n t . T h i s steady progress has been made p o s s i b l e by advances i n both polymer and f i b e r technology. Improvements i n m a t e r i a l s have g i v e n p r o t e c t i v e c l o t h i n g d e s i g n e r s more o p t i o n s which l e a d u l t i m a t e l y t o more c o m f o r t a b l e , b e t t e r performing p r o d u c t s . F a c t o r s such as a b r a s i o n and c u t r e s i s t a n c e a r e v e r y important f o r garments designed t o p r o t e c t a g a i n s t mechanical i n j u r y . The combination o f h i g h modulus, t e n a c i t y and energy a b s o r p t i o n w i t h low 0097-6156/91/0457-0214$07.00/0 © 1991 American Chemical Society

In High-Tech Fibrous Materials; Vigo, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

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s p e c i f i c g r a v i t y and low e l o n g a t i o n a r e d e s i r a b l e f o r good b a l l i s t i c performance. I t i s unusual f o r a s i n g l e f i b e r t o possess a l l o f these c h a r a c t e r i s t i c s . High Performance P o l y e t h y l e n e (HPPE) f i b e r s , however, n o t o n l y meet a l l o f these requirements b u t a l s o o f f e r additional benefits.


High Performance P o l y e t h y l e n e F i b e r s High performance p o l y e t h y l e n e f i b e r s a r e made from v e r y h i g h molecular weight p o l y e t h y l e n e polymer. P o l y e t h y l e n e i s a f l e x i b l e c h a i n macro molecule which normally c r y s t a l l i z e s o r s o l i d i f i e s by c h a i n f o l d i n g . The f o l d e d p o r t i o n s o f t h e polymer c h a i n do not make a s i g n i f i c a n t c o n t r i b u t i o n t o f i b e r strength. Therefore, p o l y e t h y l e n e f i b e r s made by c o n v e n t i o n a l methods which a l l o w t h e polymer c h a i n t o f o l d back onto i t s e l f do n o t possess o u t s t a n d i n g p h y s i c a l p r o p e r t i e s . I n c o n t r a s t , HPPE f i b e r s a r e produced by a process which a l l o w s t h e p o l y e t h y l e n e molecular chains t o c r y s t a l l i z e i n an extended, h i g h l y o r i e n t e d s t a t e . The e x t e n s i o n o f t h e polymer c h a i n i n combination w i t h t h e i r o r i e n t a t i o n along the f i b e r a x i s give r i s e t o the s u p e r i o r p h y s i c a l p r o p e r t i e s such as h i g h t e n s i l e s t r e n g t h and h i g h modulus. S e v e r a l d i f f e r e n t v e r s i o n s o f HPPE f i b e r s a r e a v a i l a b l e commercially. A l l o f t h e work presented here was done u s i n g SPECTRA (a r e g i s t e r e d t r a d e mark o f A l l i e d - S i g n a l ) HPPE f i b e r s . The key s t r u c t u r a l parameters t h a t d i s t i n g u i s h h i g h performance p o l y e t h y l e n e f i b e r s from c o n v e n t i o n a l melt spun m a t e r i a l s a r e i l l u s t r a t e d i n F i g u r e 1.(1) The molecular weight o f t h e p o l y e t h y l e n e used t o produce t h e HPPE f i b e r s i s g e n e r a l l y i n t h e range o f 1 t o 5 m i l l i o n Daltons. I n c o n t r a s t , t h e m o l e c u l a r weight of many c o n v e n t i o n a l polymers used i n f i b e r p r o d u c t i o n i s t y p i c a l l y f i f t y thousand t o s e v e r a l hundred thousand Daltons. HPPE f i b e r s , because o f t h e e x t e n s i o n and o r i e n t a t i o n o f t h e polymer c h a i n s , e x h i b i t a v e r y h i g h degree o f c r y s t a l l i n e o r i e n t a t i o n (95-99%) and c r y s t a l l i n e content (60-85%).(1) One method o f producing HPPE f i b e r s i s t h e s o l u t i o n s p i n n i n g process. I n s o l u t i o n s p i n n i n g t h e f i r s t s t e p i s t o d i s s o l v e t h e v e r y h i g h molecular weight polymer u s i n g a s u i t a b l e s o l v e n t . The s o l v e n t serves t o d i s e n t a n g l e t h e polymer chains and i s c r i t i c a l i n o b t a i n i n g an extended c h a i n s t r u c t u r e . The r e s u l t i n g polymer s o l u t i o n i s v i s c o u s enough t o be processed on c o n v e n t i o n a l melt s p i n n i n g equipment. The c o o l e d e x t r u d a t e forms an Extended Chain P o l y e t h y l e n e (ECPE) f i b e r which can be c o n t i n u o u s l y d r i e d t o remove t h e s o l v e n t o r t h e s o l v e n t can l a t e r be e x t r a c t e d by an another a p p r o p r i a t e s o l v e n t . The e x t r a c t e d f i b e r s a r e u s u a l l y subsequently drawn p r i o r t o f i n a l packaging.


216

HIGH-TECH FIBROUS MATERIALS


EXTENDED-CHAIN

t

FIBER

VERY HIGH MOLECULAR WEIGHT

• VERY HIGH DEGREE OF • MINIMUM CHAIN

ORIENTATION

FOLDING

CONVENTIONAL

FIBER

• RELATIVELY LOW MOLECULAR WEIGHT • MODERATE

ORIENTATION

• CRYSTALLINE REGIONS CHAIN FOLDED

Figure 1. Fiber Morphology. (Reproduced with permission from ref. 1. Copyright 1988. Allied-Signal.)



13. KIRKLAND ET AL.


217

F i b e r P r o p e r t i e s . The t e n s i l e s t r e n g t h o f HPPE f i b e r s i n e n g i n e e r i n g terms i s s i m i l a r t o o t h e r h i g h performance f i b e r s such as carbon, aramid, and g l a s s . Because p o l y e t h y l e n e has a lower d e n s i t y (0.96 g/cc which i s h a l f t h a t o f h i g h modulus carbon f i b e r and two t h i r d s t h a t o f aramid) than o t h e r h i g h performance f i b e r s , t h e s p e c i f i c s t r e n g t h o f HPPE f i b e r s i s extremely h i g h . On a p e r mass b a s i s t h e s t r e n g t h o f HPPE f i b e r s i s a t l e a s t 35% g r e a t e r than t h a t o f h i g h modulus aramid o r S-Glass and approximately two times t h a t o f c o n v e n t i o n a l h i g h modulus carbon f i b e r . Table I g i v e s a comparison o f t h e s t r e n g t h s o f s e v e r a l h i g h performance f i b e r s . L i k e a l l m a t e r i a l s , HPPE f i b e r s have some l i m i t a t i o n s : t h e f i b e r has a r e l a t i v e l y low m e l t i n g p o i n t , and i t s chemical i n e r t n e s s c o n t r i b u t e s t o d i f f i c u l t i e s w i t h f i b e r t o m a t r i x adhesion. The m e l t i n g temperature cannot be s i g n i f i c a n t l y improved because i t i s an i n h e r e n t p r o p e r t y o f t h e p o l y e t h y l e n e polymer from which HPPE f i b e r i s made. I t i s i n t e r e s t i n g t o note t h a t HPPE f i b e r s 147°C m e l t i n g temperature i s approximately 15°C h i g h e r than t h e m e l t i n g p o i n t o f uno r i e n t e d p o l y e t h y l e n e . The h i g h e r m e l t i n g temperature i s a r e s u l t o f t h e i n c r e a s e d c r y s t a l l i n i t y and extended polymer c h a i n formation i n t h e f i b e r . In composite s t r u c t u r e s u s i n g HPPE f i b e r s , t h e low f i b e r t o m a t r i x adhesion can sometimes p r e s e n t d i f f i c u l t i e s . Improvements i n t h e f i b e r ' s adhesion have been made u s i n g corona o r gas plasma treatments. However, t h e r e a r e a p p l i c a t i o n s where i t i s d e s i r a b l e t o have a low f i b e r t o m a t r i x adhesion. 1

Cut and S l a s h P r o t e c t i o n For employers, p r o t e c t i n g t h e i r workers from i n j u r y has become a primary concern s i n c e t h e passage o f t h e H e a l t h and S a f e t y a t Work a c t o f 1974.(2) T h i s a c t made employers r e s p o n s i b l e f o r p r o v i d i n g adequate p r o t e c t i v e c l o t h i n g and a p p l i a n c e s where necessary. One o f t h e most s u s c e p t i b l e p a r t s o f t h e body t o i n j u r y i s t h e hands. Even a f t e r t a k i n g measures t o p r o t e c t t h e hands, such as wearing gloves and i n s t a l l i n g guards, hand and f i n g e r i n j u r i e s s t i l l account f o r over 25% o f a l l i n d u s t r i a l accidents.(2) C l e a r l y , there i s s t i l l a s u b s t a n t i a l need f o r improved types o f hand p r o t e c t i o n . HPPE f i b e r s i n t h i s a p p l i c a t i o n o f f e r a number o f advantages. HPPE f i b e r s can a l l o w t h e c u t p r o t e c t i v e g l o v e t o be made more comfortable because o f t h e f i b e r ' s s o f t hand. Another b e n e f i t i n u s i n g t h e HPPE f i b e r i n c u t p r o t e c t i v e g l o v e s i s t h e improved a b r a s i o n r e s i s t a n c e o f t h e HPPE f i b e r which improves t h e g l o v e ' s wear l i f e . The h i g h c u t r e s i s t a n c e o f HPPE f i b e r s was d i s c o v e r e d when t h e s c i s s o r s used t o c u t t h e f i b e r


218



d u r i n g manufacture wore out a f t e r a few days of use. While the experience w i t h the s c i s s o r s i n d i c a t e d t h a t HPPE was cut r e s i s t a n t , a more o b j e c t i v e t e s t was needed t o q u a n t i t a t i v e l y measure the cut r e s i s t a n c e of the f i b e r . For the cut and s l a s h r e s i s t a n t c l o t h i n g a p p l i c a t i o n a t e s t method t o e v a l u a t e the f a b r i c s had t o be d e v i s e d b e f o r e s e r i o u s product development c o u l d b e g i n . A cut and a b r a s i o n t e s t e r and t e s t method was developed by A l l i e d which i s b e l i e v e d t o o b j e c t i v e l y measure the cut r e s i s t a n c e of f i b e r s and f a b r i c s . Cut r e s i s t a n c e e v a l u a t i o n . The Beta Tec (a r e g i s t e r e d t r a d e mark of A l l i e d - S i g n a l ) Automatic A b r a s i o n and Cut T e s t e r was designed t o measure the cut r e s i s t a n c e of protective gloves.(Figure 2.) In a d d i t i o n t o g l o v e s , the Beta Tec can be used t o e v a l u a t e the c u t r e s i s t a n c e of almost any f l e x i b l e m a t e r i a l . When p e n e t r a t i o n of the sample o c c u r s , the t e s t e r a u t o m a t i c a l l y s t o p s . I t i s p o s s i b l e f o r the Beta Tec t o s i m u l a t e two types o f c u t t i n g : s l i c i n g and chopping. C u t t i n g motion i s determined by cam s e l e c t i o n . The c u t t i n g arm can accommodate a v a r i e t y of d i f f e r e n t types of b l a d e s r a n g i n g from s i n g l e edge r a z o r b l a d e s t o s c a l p e l b l a d e s . I n o r d e r t o e l i m i n a t e the e f f e c t of blade d u l l i n g from t e s t t o t e s t the blade i s normally changed a f t e r each test. With the Beta Tec A b r a s i o n and Cut T e s t e r i t i s p o s s i b l e t o r e a l i s t i c a l l y t e s t f a b r i c s and o b t a i n unbiased r e s u l t s . To t e s t a f a b r i c sample on the Beta Tec cut t e s t e r the specimen i s mounted on the mandrel. E i t h e r f l a t f a b r i c s or g l o v e f i n g e r s can be t e s t e d . The t e s t f i n g e r i s clamped a t the end c l o s e s t t o the cam. F l a t f a b r i c s should be clamped a t both ends. The p r o p e r t e s t cam, r o t a t i o n a l speed, and c u t t i n g b l a d e l o a d are selected. Once s t a r t e d , the automatic counter r e c o r d s the number of c y c l e s t o specimen p e n e t r a t i o n a t which time the t e s t e r s t o p s . Cut R e s i s t a n t Gloves. Almost a l l g l o v e s can be c o n s i d e r e d t o p r o v i d e some degree o f cut r e s i s t a n c e because the g l o v e i s an a d d i t i o n a l m a t e r i a l which must be c u t through b e f o r e the c u t t i n g edge reaches the hand. Cotton, l e a t h e r , and t e r r y c l o t h a l l p r o v i d e some p r o t e c t i o n from c u t s . However, products which have been designed f o r use i n a work environment where t h e r e i s a h i g h p o t e n t i a l f o r l a c e r a t i o n must o f f e r a v e r y h i g h l e v e l of cut r e s i s t a n c e i n order t o p r o v i d e maximum protection. Examples of these work environments are p l a c e s where the hand can come i n t o c o n t a c t w i t h v e r y sharp edges; k n i f e b l a d e s , broken g l a s s , sheet m e t a l , i n j e c t i o n molded p l a s t i c s , paper and even o t h e r f i b e r s . The n a t u r a l l u b r i c i t y of h i g h d e n s i t y p o l y e t h y l e n e used t o make the HPPE f i b e r s f a c i l i t a t e s a s l i d i n g a c t i o n of k n i f e blades and o t h e r sharp edges a c r o s s the f i b e r .


13. KIRKLAND ET AL.


219

Table I. HIGH PERFORMANCE FIBER PROPERTIES

HPPE Spectra 1000

ARAMID HM

UHM*

S-Glass

Graphite HM


PROPERTY Density

0.97

1.44

1.47

2.49

1.86

Elongation %

2.7

2.5

1.5

5.4

0.6

435

400

500

665

375

12.4

7.8

9.5

7.4

5.4

25

19

25

13

57

140

850

Tensile Strength, 10 exp 3 p s i S p e c i f i c Strength 10 exp 6 p s i T e n s i l e Modulus, 10 exp 6 p s i

S p e c i f i c Modulus, 10 exp 6 p s i 714 365 480 * K e v l a r 149 - Epoxy Impregnated Strand SOURCE:

Reproduced with permission from ref. 1. Copyright 1988 Allied-Signal. VARIABLE SPEED

MANDREL (SAMPLE HOLDER)

Figure 2. The Beta Tec Automatic Abrasion and Cut Tester. (Allied-Signal.)



220


The n a t u r a l l u b r i c i t y o f HPPE f i b e r s a l s o makes a s i g n i f i c a n t contribution t o the f i b e r ' s high abrasion resistance. HPPE f i b e r has a white h y g i e n i c appearance which, f o r a e s t h e t i c as w e l l as p r a c t i c a l reasons, makes i t a good c h o i c e f o r food p r o c e s s i n g o r food c o n t a c t . Because o f t h e f i b e r ' s good chemical r e s i s t a n c e , g l o v e s made from HPPE f i b e r do not s t a i n r e a d i l y and can be e a s i l y cleaned, u s u a l l y w i t h warm water and m i l d detergent. For food p r o c e s s i n g t h e a b i l i t y t o d i s i n f e c t the g l o v e s i s e s p e c i a l l y important. HPPE f i b e r ' s chemical r e s i s t a n c e p r o p e r t i e s a l l o w t h e use o f a v a r i e t y of d i s i n f e c t a n t s including bleach i n preparing the g l o v e s f o r reuse. See Table I I f o r HPPE f i b e r s chemical r e s i s t a n c e p r o p e r t i e s . HPPE f i b e r s have a v e r y low moisture a b s o r p t i o n ( l e s s than 2%) which a l l o w s t h e g l o v e s t o be a i r d r i e d . The f i b e r ' s low m o i s t u r e a b s o r p t i o n a l s o reduces t h e p r o b a b i l i t y o f b a c t e r i a l growth on t h e f i b e r s u r f a c e . Other f i b e r s such as n y l o n and aramid which a r e used i n c u t p r o t e c t i v e g l o v e s have much h i g h e r moisture a b s o r p t i o n s on t h e o r d e r o f 5% o r more. Because t h e HPPE f i b e r g l o v e i s more f l e x i b l e , t h e u s e r ' s f i n g e r s w i l l not cramp o r f a t i g u e as e a s i l y as i s the case w i t h o t h e r l e s s f l e x i b l e c u t p r o t e c t i v e g l o v e s . The i n c r e a s e d f l e x i b i l i t y a v a i l a b l e w i t h g l o v e s made from HPPE f i b e r can be h e l p f u l i n r e d u c i n g worker f a t i g u e and s k i n i r r i t a t i o n . These problems can be t h e r e s u l t o f u s i n g g l o v e s made from a b r a s i v e o r harsh m a t e r i a l s such as metal mesh. The yarns used t o make most c u t and s l a s h r e s i s t a n t g l o v e s may be composed o f s e v e r a l d i f f e r e n t f i b e r s o r s m a l l e r y a r n s . H i g h l y c u t r e s i s t a n t y a r n s , i n many cases, a r e a c t u a l l y composite y a r n s t r u c t u r e s . I n a composite y a r n t h e i n d i v i d u a l yarns o r f i b e r s a r e combined by t w i s t i n g , p l y i n g , o r over wrapping t o produce a s i n g l e h i g h l y c u t r e s i s t a n t y a r n . By combining d i f f e r e n t f i b e r types i t i s p o s s i b l e t o i n c r e a s e t h e performance o f t h e f i n i s h e d y a r n . One way o f improving the c u t r e s i s t a n c e o f t h e composite yarns i s by c o n s t r u c t i n g t h e yarn so t h a t i t w i l l m i c r o s c o p i c a l l y a l t e r t h e c u t t i n g edge t h a t c o n t a c t s t h e y a r n . Past experiments on c u t t i n g human s k i n showed t h a t even m i c r o s c o p i c d u l l i n g o f t h e c u t t i n g edge w i l l s i g n i f i c a n t l y reduce t h e a b i l i t y o f t h e blade t o c u t . ( 3 ) S e v e r a l methods can be used t o induce t h e m i c r o s c o p i c d u l l i n g o f t h e c u t t i n g edge. Two o f t h e most common a r e combining t h e f i b e r s i n t h e composite yarns w i t h e i t h e r s t e e l monofilament w i r e o r m u l t i - f i l a m e n t g l a s s f i b e r . I t i s important t o note t h a t t h e s t e e l o r g l a s s alone would n o t make v e r y e f f e c t i v e c u t r e s i s t a n t g l o v e s because t h e s t e e l w i r e would n o t be f l e x i b l e o r s t r o n g enough t o s u r v i v e t h e k n i t t i n g process and t h e g l a s s f i b e r would f r a c t u r e d u r i n g k n i t t i n g . A l s o , t h e g l a s s


13. KIRKLAND ET AL.

221


Table

II.


CHEMICAL PROPERTIES

% Strength Retention A f t e r 6 Months Immersion S p e c t r a 900

AGENT

Aramid

Sea Water

100

100

10% Detergent S o l u t i o n

100

100

Hydraulic

100

100

Kerosene

100

100

Gasoline

100

93

Toluene

100

72

Perchlorethylene

100

75

Glacial Acetic Acid

100

82

1M H y d r o c h l o r i c A c i d

100

40

5M Sodium Hydroxide

100

42

Ammonium Hydroxide (29%)

100

70

Hypophosphite S o l u t i o n (10%)

100

79

91

0

Clorox

Fluid

Immersed in various chemical substances for a period of 6 months, HPPE fibers retained their original strength. SOURCE: Reproduced with permission from ref. 1. Copyright 1988 Allied-Signal.



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f i b e r g l o v e would have poor a b r a s i o n r e s i s t a n c e and a bad hand. Combining d i f f e r e n t m a t e r i a l s i n t h e composite y a r n produces a s y n e r g i s t i c e f f e c t which makes the composite y a r n much more c u t r e s i s t a n t t h a n i t s components. Gloves made from t h e h i g h l y c u t r e s i s t a n t yarns a r e made p o s s i b l e by t h e i n v e n t i o n o f c o m p u t e r - c o n t r o l l e d k n i t t i n g machines. T h i s type o f k n i t t i n g machine can k n i t a seamless g l o v e a u t o m a t i c a l l y . I n a d d i t i o n t o t h e speed a t which t h e machine can k n i t , t h e computer a l l o w s tremendous f l e x i b i l i t y i n t h e s e t up and p r o d u c t i o n o f many d i f f e r e n t t y p e s o f g l o v e s . The k n i t t i n g machine can be s e t up t o k n i t tubes w i t h e l a s t i c c u f f s a t t h e w r i s t and tube end. These tubes can be worn on t h e arm or l e g s t o p r o v i d e these areas o f t h e body w i t h a h i g h l e v e l o f p r o t e c t i o n from a c c i d e n t a l c u t s and s l a s h e s . P r o t e c t i v e Sweater. A f u r t h e r development which e x p l o i t s t h e technology used i n t h e c u t r e s i s t a n t g l o v e s as w e l l as t h e a b r a s i o n and c u t r e s i s t a n t p r o p e r t i e s o f HPPE f i b e r s i s a k n i t t e d sweater f o r m o t o r c y c l e r i d e r s . The HPPE y a r n used i n t h e c u t and s l a s h r e s i s t a n t sweater i s e s s e n t i a l l y t h e same y a r n which i s used i n the c u t r e s i s t a n t g l o v e s . An important d i f f e r e n c e between t h e sweater y a r n and g l o v e y a r n i s t h a t t h e o u t s i d e o f t h e sweater y a r n i s over wrapped w i t h n y l o n or p o l y e s t e r . U s i n g t h e n y l o n o r p o l y e s t e r y a r n i n t h e o u t e r cover a l l o w s t h e y a r n t o be dyed. Because o f t h e chemical i n e r t n e s s o f HPPE f i b e r i t i s almost i m p o s s i b l e t o dye. A l e a t h e r j a c k e t w i l l s c r a p e , c u t and wear o u t w i t h r e l a t i v e ease. However, t h e sweater made from HPPE f i b e r offers a s i g n i f i c a n t l y higher l e v e l of cut, slash and a b r a s i o n p r o t e c t i o n and i s much more d u r a b l e . (4) Another advantage o f t h e c o n s t r u c t i o n o f t h e sweater i s t h a t t h e garment i s c o m f o r t a b l e because t h e k n i t t e d c o n s t r u c t i o n a l l o w s b e t t e r a i r c i r c u l a t i o n through t h e garment than i s p o s s i b l e w i t h a l e a t h e r j a c k e t . T h i s i s p a r t i c u l a r l y important i n areas where i t i s h o t and humid such as t h e South and West. A l e a t h e r j a c k e t would l i k e l y n o t be worn when i t i s h o t o r humid because i t would be uncomfortable. The sweater made from HPPE f i b e r s c o u l d be worn because i t would breathe and t h e r e f o r e be more c o m f o r t a b l e . A f i n a l advantage t h a t the sweater made from HPPE f i b e r o f f e r s i s ease o f c a r e because i t can be washed r a t h e r than d r y c l e a n e d . The HPPE f i b e r sweater may a l s o f i n d a p p l i c a t i o n i n law enforcement o r p o l i c e work. The sweater would be p a r t i c u l a r l y u s e f u l where t h e need f o r p r o t e c t i o n from k n i f e c u t s o r s l a s h e s i s g r e a t e r than t h e t h r e a t from bullets. The k n i t t e d f a b r i c i s e f f e c t i v e a t p r o t e c t i n g a g a i n s t c u t s and s l a s h e s , however, t h e sweater f a b r i c would be i n e f f e c t i v e a g a i n s t puncture t h r e a t s such as k n i f e s t a b s because o f t h e open n a t u r e o f t h e k n i t t e d construction.



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M e d i c a l Glove L i n e r . Another g l o v e a p p l i c a t i o n where HPPE f i b e r i s u n i q u e l y s u i t e d i s i n the m e d i c a l f i e l d . The need has never been more acute f o r b e t t e r forms o f hand p r o t e c t i o n f o r h e a l t h care p r o f e s s i o n a l s . I n t h e p a s t , the main reason f o r u s i n g s t e r i l e g l o v e s and c l o t h i n g was t o p r o t e c t the p a t i e n t from the d o c t o r . Today, t h i s s i t u a t i o n i s , i n many cases, r e v e r s e d . Because of A c q u i r e d Immune D e f i c i e n c y Syndrome (AIDS) v i r u s the need t o p r o t e c t the h e a l t h care workers from the p a t i e n t has become a major concern. The Center f o r Disease C o n t r o l estimates t h a t the number o f diagnosed cases of AIDS w i l l i n c r e a s e a t the r a t e of 10,000 per year. By the end o f 1992 over 365,000 cases o f AIDS w i l l have been diagnosed i n the U n i t e d S t a t e s . (5) Another l e s s w e l l p u b l i c i z e d , but f a r more p r e v a l e n t t h r e a t t o h e a l t h care workers i s the danger posed by o t h e r i n f e c t i o u s d i s e a s e s such as the H e p a t i t i s B v i r u s . The O c c u p a t i o n a l S a f e t y and H e a l t h A d m i n i s t r a t i o n e s t i m a t e s t h a t approximately 300 h e a l t h c a r e workers d i e a n n u a l l y from H e p a t i t i s B i n f e c t i o n s . (6) Many o f these workers c o n t r a c t i n f e c t i o u s d i s e a s e s through c u t s on t h e i r hands and f i n g e r s . Another r o u t e of i n f e c t i o n i s through a c c i d e n t a l needle s t i c k s . (6) The f i r s t e x t r a p r e c a u t i o n s taken by h e a l t h c a r e p r o f e s s i o n a l s a g a i n s t a c c i d e n t a l l y i n f e c t i n g themselves was t o wear m u l t i p l e p a i r s of l a t e x rubber g l o v e s . ( 7 ) Because of the i n c r e a s e d use of the l a t e x g l o v e s , both the demand f o r the g l o v e s and t h e i r p r i c e have r i s e n d r a m a t i c a l l y . I r o n i c a l l y , the use of m u l t i p l e p a i r s o f l a t e x g l o v e s add o n l y a minute amount of a d d i t i o n a l p r o t e c t i o n from a c c i d e n t a l n i c k s and c u t s . The i d e a l s i t u a t i o n would be t o p r o v i d e a glove which would i s o l a t e the hands from the environment and a t the same time p r o t e c t the hands from a c c i d e n t a l n i c k s and c u t s . T h i s i d e a l g l o v e should i n t e r f e r e t o t h e a b s o l u t e minimum degree w i t h the m o b i l i t y and s e n s i t i v i t y o f t h e f i n g e r s . (8) I n a d d i t i o n , the g l o v e should a l s o be comfortable even a f t e r b e i n g worn f o r extended p e r i o d s . One of the f i r s t g l o v e s which attempted t o meet t h i s d i f f i c u l t l i s t of requirements was a l i g h t metal mesh g l o v e made from v e r y s m a l l c h a i n m a i l . T h i s g l o v e a f f o r d e d maximum p r o t e c t i o n from a c c i d e n t a l n i c k s and c u t s , but s a c r i f i c e d t a c t i l e s e n s i t i v i t y . A l s o , the micro c h a i n m a i l glove was v e r y expensive. With HPPE f i b e r s i t i s p o s s i b l e t o produce a g l o v e l i n e r which w i l l meet most of the requirements s e t f o r t h above. The HPPE f i b e r g l o v e l i n e r p r o v i d e s a h i g h l e v e l of c u t p r o t e c t i o n w h i l e a f f o r d i n g enough t a c t i l e s e n s i t i v i t y t o touch a q u a r t e r and determine by f e e l i f the c o i n i s heads o r t a i l s . The HPPE f i b e r g l o v e l i n e r i s worn underneath the standard l a t e x surgeon's g l o v e and i s over 30 times more c u t r e s i s t a n t than t h e l a t e x surgeon's glove and 15 times as c u t r e s i s t a n t as a l e a t h e r work g l o v e . By making the g l o v e l i n e r separate



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from t h e l a t e x g l o v e , t h e g l o v e l i n e r can be reused. Tests have shown t h a t t h e HPPE f i b e r g l o v e l i n e r s can be s t e r i l i z e d f o r reuse up t o twelve times w i t h o u t adversely e f f e c t i n g the glove l i n e r ' s c u t r e s i s t a n c e . U n f o r t u n a t e l y , t h e HPPE f i b e r g l o v e l i n e r , because o f i t s k n i t t e d c o n s t r u c t i o n , does not p r o v i d e p r o t e c t i o n from a c c i d e n t a l needle s t i c k s . The HPPE g l o v e l i n e r has been t e s t e d i n c l i n i c a l t r i a l s and w i l l soon be commercially a v a i l a b l e . I n addition t o the increased p r o t e c t i o n against accidental n i c k s and c u t s , t h e s u r g i c a l g l o v e l i n e r from HPPE f i b e r p r o v i d e s o t h e r b e n e f i t s . During market e v a l u a t i o n t r i a l s , o p e r a t i n g room personnel r e p o r t e d t h a t t h e HPPE g l o v e l i n e r s a r e warm and wick p e r s p i r a t i o n away from the s k i n , keeping t h e hands d r y and c o m f o r t a b l e . The g l o v e l i n e r can be worn w i t h b l e a c h s t e r i l i z a t i o n o r Dakins s o l u t i o n which some d o c t o r s and surgeons apply t o t h e i r hands b e f o r e p u t t i n g on t h e l a t e x g l o v e . HPPE f i b e r g l o v e s have been s t e r i l i z e d by a v a r i e t y o f methods such as e t h y l e n e o x i d e , r a d i a t i o n , and steam a u t o c l a v e . When t h e s t e r i l i z a t i o n process r e q u i r e s h i g h heat i t i s important not t o exceed 121°C (250°F) because of HPPE f i b e r ' s low m e l t i n g temperature. A disinfectant s o l u t i o n made from 5% sodium h y p o c h l o r i t e can be used t o d i s i n f e c t t h e glove l i n e r w i t h o u t e f f e c t i n g i t s c u t r e s i s t a n t p r o p e r t i e s . I t i s recommended t h a t t h e g l o v e l i n e r s be a i r d r i e d and never machine d r i e d t o i n s u r e t h a t t h e f i b e r i s never s u b j e c t e d t o temperatures above 121°C (250°F). Chain Saw Cut P r o t e c t i o n . Another type o f p r o t e c t i v e c l o t h i n g b e i n g developed from HPPE f i b e r s i s c h a i n saw cut p r o t e c t i v e chaps. E a r l y c h a i n saw c u t p r o t e c t i v e chaps were made w i t h over 22 l a y e r s o f b a l l i s t i c n y l o n . L a t e r chaps were produced w i t h m u l t i p l e l a y e r s o f aramid m a t e r i a l . The HPPE chaps a r e made from two l a y e r s o f nonwoven f a b r i c . The nonwoven f a b r i c c o n s t r u c t i o n i s capable o f p r o t e c t i n g t h e user from i n j u r y from c h a i n saw c u t s a t c h a i n speeds i n excess o f 3200 f e e t p e r minute. Armor Systems HPPE f i b e r s because o f t h e i r h i g h s t r e n g t h t o weight r a t i o , good energy a b s o r p t i o n , and h i g h modulus a r e a n a t u r a l c h o i c e f o r b a l l i s t i c p r o t e c t i v e c l o t h i n g . HPPE f i b e r s can be used i n two types o f b a l l i s t i c armor systems. The f i r s t type o f b a l l i s t i c c l o t h i n g , s o f t body armor, makes use o f t h e h i g h f l e x i b i l i t y a f f o r d e d by HPPE f i b e r s . The second type o f armor which e x p l o i t s HPPE f i b e r ' s energy absorbing p r o p e r t i e s i s hard composite armor.



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S o f t Armor Systems. The e a r l i e s t types o f armor were g e n e r a l l y made from hard r i g i d m a t e r i a l s such as metals. Because o f t h e hard and r i g i d nature o f t h i s t y p e o f armor i t was assumed t h a t t h e b e s t method o f p r o t e c t i n g the human body from m i s s i l e s was t o use hard m a t e r i a l s which r e s i s t e d p e n e t r a t i o n and spread t h e impact load.(9) The i d e a o f spreading t h e impact l o a d was c o r r e c t , however t h e use o f a hard r i g i d m a t e r i a l as t h e primary p r o t e c t i v e l a y e r proved t o be u n d e s i r a b l e . A hard, r i g i d m a t e r i a l alone does not make e f f i c i e n t use of an e f f e c t i v e method o f energy d i s s i p a t i o n , namely m a t e r i a l deformation and breakage.(9) One o f t h e major f a c t o r s i n armor d e s i g n a f t e r performance i s comfort. The t h r e e f a c t o r s which seem t o have t h e g r e a t e s t i n f l u e n c e on t h e comfort o f an armor system a r e weight, f l e x i b i l i t y , and b r e a t h a b i l i t y . M e t a l armor i s d e f i c i e n t i n a l l t h r e e areas. With t h e i n v e n t i o n o f s y n t h e t i c f i b e r s g r e a t improvements i n armor d e s i g n have been p o s s i b l e . The f i r s t l a r g e s c a l e use o f s y n t h e t i c f i b e r s i n armor systems was woven n y l o n 6,6 used i n combination w i t h s t e e l p l a t e s t o produce •'Flak J a c k e t s " d u r i n g World War 11.(9) The next improvement came when g l a s s f i b e r and r e s i n composite armor c a l l e d Doron r e p l a c e d t h e s t e e l p l a t e s . ( 9 ) Aramid f i b e r s p r o v i d e d a quantum l e a p i n armor system technology because o f t h e i r balance o f p h y s i c a l p r o p e r t i e s . Aramid armor systems perform w e l l , however w i t h t h e i n v e n t i o n o f HPPE f i b e r s , f u r t h e r improvements i n t h e form o f s i g n i f i c a n t weight r e d u c t i o n s and i n c r e a s e d b a l l i s t i c performance a r e p o s s i b l e . Because o f t h e s u p e r i o r s t r e n g t h t o weight r a t i o o f HPPE f i b e r s i t i s p o s s i b l e t o produce armor systems which p r o v i d e p r o t e c t i o n e q u i v a l e n t t o o t h e r armor systems but a t a lower weight, o r a l t e r n a t i v e l y a s i g n i f i c a n t l y h i g h e r l e v e l o f p r o t e c t i o n a t t h e same weight. The low d e n i e r (a measurement o f l i n e a r d e n s i t y ) o f t h e HPPE yarns and t h e f i b e r ' s n a t u r a l l u b r i c i t y combine t o produce f a b r i c s which can be made i n t o l i g h t w e i g h t , f l e x i b l e b a l l i s t i c armor. Ballistic p r o t e c t i v e products made from HPPE f i b e r s a r e s u p e r i o r i n comfort when compared t o many o t h e r types o f b a l l i s t i c armor. The i n c r e a s e d comfort o f HPPE armor encourages i t s continuous use on a r o u t i n e b a s i s . No matter how good an armor system i s i t can not p r o v i d e p r o t e c t i o n i f i t i s t o o uncomfortable t o be worn. The chemical r e s i s t a n c e o f t h e HPPE f i b e r s a g a i n i s an advantage f o r m i l i t a r y body armor. Chemical r e s i s t a n c e i s important i f t h e armor i s exposed t o chemical agents, e s p e c i a l l y t h e type used i n decontamination d u r i n g chemical o r b i o l o g i c a l w a r f a r e . In a t y p i c a l b a l l i s t i c v e s t t h e b a l l i s t i c r e s i s t a n c e i s o b t a i n e d by u s i n g m u l t i p l e l a y e r s o f woven f a b r i c . The number o f l a y e r s necessary i s determined by t h e l e v e l o f t h e t h r e a t which must be stopped. The h i g h e r t h e t h r e a t , t h e g r e a t e r t h e number o f f a b r i c



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panels r e q u i r e d t o d e f e a t i t . F a b r i c c o n s t r u c t i o n and y a r n s i z e a l s o i n f l u e n c e the b a l l i s t i c performance o f t h e armor system. Conventional f a b r i c c o n s t r u c t i o n s u t i l i z i n g h i g h performance f i b e r s can be p e n e t r a t e d by b a l l i s t i c p r o j e c t i l e s when the y a r n i n t h e p r o j e c t i l e path i s pushed a s i d e w i t h o u t ever f u l l y engaging t h e p r o j e c t i l e . T h i s phenomena i s dependent on s e v e r a l f a c t o r s such as p r o j e c t i l e v e l o c i t y , y a r n t o y a r n f r i c t i o n , p r o j e c t i l e t o yarn f r i c t i o n , p r o j e c t i l e shape, and f a b r i c c o n s t r u c t i o n . To f u l l y u t i l i z e t h e b a l l i s t i c d e f e a t i n g p o t e n t i a l o f HPPE f i b e r s i t i s important t h a t p r o j e c t i l e s not p e n e t r a t e the f a b r i c s i m p l y by pushing the f i b e r s out of the way. The tendency o f the p r o j e c t i l e s t o s l i d e between the f i b e r s can be reduced by u s i n g lower d e n i e r yarns. F a b r i c c o n s t r u c t i o n i s another f a c t o r which e f f e c t s the a b i l i t y of the p r o j e c t i l e t o engage t h e f i b e r s . P l a i n weaves perform b e t t e r than s a t i n weaves because the p l a i n weave minimizes the l a t e r a l movement o f t h e yarn.(10) Therefore, l a y e r s of p l a i n weave f a b r i c s made from lower d e n i e r yarns p r o v i d e b e t t e r b a l l i s t i c p r o t e c t i o n a t the same weight than a comparable system of p l a i n weave f a b r i c s made from l a r g e r y a r n s . To o p t i m i z e the i d e a s of d e c r e a s i n g y a r n s i z e and reduced y a r n m o b i l i t y a nonwoven 0°, 90° HPPE f i b e r laminate bonded w i t h an e l a s t o m e r i c r e s i n was developed. The patented c o n s t r u c t i o n c a l l e d S p e c t r a S h i e l d (a t r a d e mark of A l l i e d - S i g n a l ) i s the s t r o n g e s t , l i g h t e s t weight b a l l i s t i c armor i n the world.(11) ( F i g u r e 3.) By l a y i n g two sheets of i n d i v i d u a l f i l a m e n t s p e r p e n d i c u l a r t o each o t h e r and then l o c k i n g the f i l a m e n t s i n p l a c e w i t h t h e e l a s t o m e r i c r e s i n the maximum number of f i l a m e n t s are a v a i l a b l e t o engage the p r o j e c t i l e upon i t s i n i t i a l c o n t a c t w i t h the p a n e l . The u n i d i r e c t i o n a l c o n s t r u c t i o n does not r e q u i r e the f i b e r s t o overcome the b u i l t i n crimp a s s o c i a t e d w i t h yarns i n a woven s t r u c t u r e . Another advantage of the u n i d i r e c t i o n a l c o n s t r u c t i o n o f Spectra S h i e l d i t that i t e f f i c i e n t l y disperses b l u n t trauma and minimizes i t s e f f e c t s . Damage i n c u r r e d i s l o c a l i z e d which r e s u l t s i n good m u l t i p l e h i t performance. The advantages of the u n i d i r e c t i o n a l c o n s t r u c t i o n are not i n i t s performance alone. The process f o r manufacturing The 0°, 90° u n i d i r e c t i o n a l l a m i n a t e s reduces f i b e r h a n d l i n g such as t w i s t i n g and weaving which minimizes f i b e r damage i n c u r r e d d u r i n g manufacture. The 0°, 90° laminates of HPPE f i b e r a r e a v a i l a b l e i n two forms: w i t h a f i l m c o v e r i n g f o r s o f t body armor and without the f i l m f o r hard composite armor.(11) ( F i g u r e 4.) The b a l l i s t i c performance o f HPPE f i b e r i s not e f f e c t e d by l o n g term exposure t o temperatures as h i g h as 71°C (160°F). HPPE f i b e r t e s t panels have been kept at 71°C (160°F) f o r over 60 days and b a l l i s t i c a l l y



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WOVEN FABRIC

SPECTRA SHIELD

Figure 3. Conventional Fabric compared to Spectra Shield. (Reproduced with permission from ref. 11. Copyright 1989 Allied-Signal.)




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13. KIRKLAND ET AL. Table I I I .


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E f f e c t o f Temperature on B a l l i s t i c Performance o f HPPE composite armor

Temperature°C 23 80 100 120

V50

(m/sec) 604.7 594.7 593.4 558.7

F i b e r SPECTRA 900, AD = 4.4 ADT =6.0 m a t r i x A i r f l e x 105 an e t h y l e n e - v i n y l a c e t a t e copolymer, a product o f A i r Products and Chemical I n c .


SOURCE:

Reproduced with permission from ref. 11. Copyright 1989 Allied-Signal.

t e s t e d a t ambient temperature w i t h no l o s s i n performance. (Figure 5.) When t h e p a n e l s were t e s t e d a t e l e v a t e d temperature a s l i g h t decrease i n performance o f approximately 8 % a t 120°C (250°F) was measured. (Table I I I . ) From F i g u r e 5 i t can be seen t h a t f o r most p r a c t i c a l a p p l i c a t i o n s v a r i a t i o n i n ambient temperature w i l l not a d v e r s e l y e f f e c t t h e performance o f t h e HPPE f i b e r b a l l i s t i c armor.(11) Hard Composite Armor Systems. Hard armor i s p o s s i b l y the o l d e s t type o f b a l l i s t i c p r o t e c t i v e c l o t h i n g . When one hears t h e term armor, a hard p r o t e c t i v e c a s i n g i s what u s u a l l y comes t o mind. Modern hard armor i s much more s o p h i s t i c a t e d than e a r l i e r metal armors. Most modern hard armor i s u s u a l l y composed o f s e v e r a l d i f f e r e n t m a t e r i a l s which a r e o r g a n i z e d i n a complex s e r i e s o f l a y e r s . F o r p r o t e c t i v e c l o t h i n g t h e most common type o f hard armor i s used i n helmets. Another l e s s w e l l known a p p l i c a t i o n o f hard armor t e c h n o l o g y i s i n t h e supplementation o f f l e x i b l e armor systems used t o p r o t e c t a g a i n s t c r i t i c a l t h r e a t s i t u a t i o n s such as h i g h powered ammunition o r i n bomb d i s p o s a l . The h i g h s t r e n g t h t o weight r a t i o , toughness, and u l t r a h i g h modulus o f HPPE f i b e r s a l l o w s them t o p r o v i d e a h i g h l e v e l o f b a l l i s t i c and impact p r o t e c t i o n a t a lower weight than i s p o s s i b l e w i t h many o t h e r m a t e r i a l s . The lower weight o f HPPE armor systems, e s p e c i a l l y i n helmets, can s i g n i f i c a n t l y reduce wearer f a t i g u e . Even a s m a l l r e d u c t i o n o f t h e weight o f t h e helmet a l l o w s t h e wearer t o c o n c e n t r a t e more on t h e s u r r o u n d i n g s i t u a t i o n and l e s s on how heavy and uncomfortable t h e helmet i s . Composite armor produced from HPPE f i b e r s weighs 30 % t o 50 % l e s s than f o r t h e same performance l e v e l as aramid m o n o l i t h i c composite armor.(12) (Figure 6.) One a p p l i c a t i o n which has b e n e f i t e d immensely from the i n t r o d u c t i o n o f HPPE f i b e r s i s t h e p o l i c e r i o t helmet. Before a v a i l a b i l i t y o f HPPE f i b e r s s t a n d a r d r i o t helmets were made from a f i b e r g l a s s and epoxy composite. T h i s c o n s t r u c t i o n was much h e a v i e r than t h e


230

V50


(ft/sec) 2000.


1800-. Shot A f t e r Exposure 1600Shot a t Temperature 1400-

1200-

1000-

800 SKIN BLISTER TEMPERATURE 600 "

HIT

400 -

200 -

70

100

130

160

TEMPERATURES

Figure 5. Ballistic Performance V 50 vs. Temperature. (Reproduced with permission from ref. 11. Copyright 1989 Allied-Signal.)


13. KIRKLAND ET AL.


231


NORMALIZED V50

0.5

1.0

1.5

2.0

COMMOSITE AREAL DENSITY .22 CAL,

2.5 (PSF)

17 GRAIN FRAGMENT SIMULATING

PROJECTILE

Figure 6. Ballistic Performance of High Performance Polyethylene vs. Aramid composites. HPPE is Spectra 1000 and Aramid is Kevlar 29. (Reproduced with permission from ref. 12. Copyright 1989 Allied-Signal.)



232


same helmet r e i n f o r c e d w i t h HPPE f i b e r s . A f i b e r g l a s s r i o t helmet p r o v i d e s l i t t l e , i f any, b a l l i s t i c protection. The use o f aramid f i b e r s was e x p l o r e d , b u t they were found t o be t o o heavy. The new r i o t helmet made w i t h HPPE f i b e r s i s l i g h t e r weight than t h e g l a s s f i b e r o r aramid f i b e r r i o t helmet. Even a t t h e l i g h t e r weight t h e HPPE f i b e r helmet p r o v i d e s b a l l i s t i c p r o t e c t i o n and s u p e r i o r impact performance.(13) Combat helmets f o r m i l i t a r y use may a l s o b e n e f i t from t h e use o f HPPE f i b e r s . The standard aramid combat helmet c u r r e n t l y made from K e v l a r 29 weighs t h r e e pounds. A combat helmet b e i n g developed from HPPE f i b e r s w i l l weigh s l i g h t l y over two pounds.(13) Decreasing t h e weight o f t a c t i c a l armor reduces f a t i g u e and i n c r e a s e s m o b i l i t y which t r a n s l a t e s i n t o a h i g h e r probability of survival. Hard composite armor from HPPE f i b e r s can be produced by a v a r i e t y o f methods. The m a t r i x systems can be epoxy, v i n y l e s t e r , p o l y e s t e r , o r l a t e x r e s i n . The f i b e r r e i n f o r c e m e n t can be p r o v i d e d by e i t h e r woven f a b r i c s o r t h e 0°,90° u n i d i r e c t i o n a l l a m i n a t e s . The u n i d i r e c t i o n a l laminates without the polyethylene f i l m are used which a l l o w s t h e i n d i v i d u a l l a m i n a t e l a y e r s t o be c o n s o l i d a t e d u s i n g heat and p r e s s u r e . Another advantage t o t h e HPPE f i b e r u n i d i r e c t i o n a l prepreg system i s t h a t i t i s moldable which makes manufacture o f some types o f armor e a s i e r . For HPPE f a b r i c s t h e m a t r i x m a t e r i a l can be a p p l i e d e i t h e r by wet l a y up o r t h e f a b r i c can be preimpregnated w i t h m a t r i x f o r l a t e r use. Again t h e v a r i o u s l a y e r s o f m a t e r i a l a r e c o n s o l i d a t e d u s i n g heat and pressure.(14) E a r l i e r i t was s t a t e d t h a t t h e poor f i b e r t o m a t r i x adhesion was a disadvantage f o r HPPE f i b e r s . F o r composite armor systems t h e low l e v e l o f f i b e r t o m a t r i x adhesion i s a c t u a l l y an advantage. T h i s i s because t h e low l e v e l o f f i b e r t o m a t r i x adhesion a l l o w s t h e d i s s i p a t i o n o f t h e impact energy by t h e b r e a k i n g o f t h e f i b e r t o m a t r i x i n t e r f a c e . The performance o f HPPE h a r d armor a g a i n s t .22 c a l i b e r fragment s i m u l a t i n g p r o j e c t i l e s i s shown i n F i g u r e 7. The p r o t e c t i o n a f f o r d e d by HPPE armor a g a i n s t some common hand gun and r i f l e ammunition i s shown i n Table IV. The amount o f t h e HPPE f i b e r r e i n f o r c e d hard armor r e q u i r e d t o d e f e a t t h e t h r e a t a t t h e g i v e n v e l o c i t y i s shown i n pounds p e r square f o o t . F o r comparison purposes 11 pound p e r square f o o t d u a l hardened s t e e l o r 9 pound p e r square f o o t aramid composite armor i s r e q u i r e d t o d e f e a t t h e 7.62 M-80 b a l l round.(14) Where t h e b a l l i s t i c t h r e a t possesses h i g h k i n e t i c energy o r i s a hardened armor p e n e t r a t i n g p r o j e c t i l e i t may be necessary t o combine t h e HPPE armor w i t h a s u i t a b l e hard " s t r i k e f a c e " . The t y p e and amount o f t h e h i g h hardness m a t e r i a l r e q u i r e d i s h e a v i l y dependent on t h e t y p e o f t h r e a t which must be d e f e a t e d . Use o f HPPE



13. KIRKLAND ET AL.

1.0


1.5

2.0

233

2.5

AREAL DENSITY (PSF) Figure 7. Normalized V 50 ballistic performance of High Performance Polyethylene and Aramid composites. HPPE is Spectra 1000 and Aramid is Kevlar 20. (Reproduced with permission from ref. 15. Copyright 1988 Allied-Signal.)


234


f i b e r f o r the b a c k i n g o f t h e armor system can reduce the over a l l weight o f the system. To improve the Table IV.

Threat


9 mm 5.56 7.62 7.62

HPPE Composite Armor A r e a l D e n s i t i e s t o Defeat Common B a l l i s t i c Threats

Description

F u l l Metal Jacket mm M-193 b a l l mm M-80 b a l l mm AK-47 S t e e l Core

SOURCE:

Velocity (fps) 1450 3250 2750 2400

Nominal Weicrht (psf) 0.8 4.0 4.75 5.25


performance of s o f t body armor, p a n e l s o f t h e HPPE f i b e r composite armor can be added t o augment t h e p r o t e c t i o n of t h e v i t a l areas such as the c h e s t . A g a i n , t h e amount pf HPPE composite armor r e q u i r e d depends on t h e t y p e t h r e a t t o be defeated. Because t h e e l e v a t e d temperature performance o f HPPE f i b e r r i g i d composite armor systems may be cause f o r concern an e v a l u a t i o n o f t h e armor performance was conducted. The HPPE f i b e r and l a t e x m a t r i x system was used t o f a b r i c a t e f i v e i d e n t i c a l p a n e l s which were heated t o t h e t e s t temperature and h e l d t h e r e f o r one hour. The p a n e l s were t e s t e d w i t h t h e r e s u l t s shown i n Table V and p l o t t e d i n F i g u r e 8. Again armor from HPPE f i b e r can perform a t e l e v a t e d temperature w i t h o u t a s i g n i f i c a n t l o s s i n b a l l i s t i c performance. I n a d d i t i o n t o the b a l l i s t i c a p p l i c a t i o n s o f HPPE f i b e r i n hard armor t h e r e are many non b a l l i s t i c s p o r t i n g a p p l i c a t i o n s o f t h e technology such as p r o t e c t i v e head gear. Many o f t h e requirements f o r t h e s p o r t i n g a p p l i c a t i o n s may not be as c r i t i c a l as t h e b a l l i s t i c armor requirements; however, a h i g h l e v e l o f impact p r o t e c t i o n a t a low weight i s d e s i r a b l e . HPPE f i b e r s can e a s i l y meet the requirements when used as t h e r e i n f o r c e m e n t i n these helmets. Helmets f o r almost every s p o r t i n g a p p l i c a t i o n are b e i n g i n v e s t i g a t e d . To date helmets o r p r o t o t y p e s have been t e s t e d i n a p p l i c a t i o n s such as: r a c i n g c r a s h helmets, p o l o helmets, rock c l i m b i n g helmets and w h i t e water helmets. Conclusion The v e r s a t i l i t y o f HPPE f i b e r s has been demonstrated by t h e range o f a p p l i c a t i o n s i n which t h e f i b e r i s f i n d i n g use. However, f o r many a p p l i c a t i o n s no s i n g l e f i b e r by i t s e l f can meet a l l of the requirements. Every h i g h performance f i b e r has a t l e a s t one p r o p e r t y where i t s performance i s weak. Means must be d e v i s e d t o minimize t h e f i b e r ' s weak areas and s t i l l o b t a i n maximum performance. In High-Tech Fibrous Materials; Vigo, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

KIRK1AND ET AL.


235

Table V.


HPPE COMPOSITE BALLISTIC RESISTANCE AT ELEVATED TEMPERATURE

Prepreg:

HPPE / Latex

Resin:

Latex

Fabric:

S p e c t r a 1000, 650 d, 34X34 P l a i n Weave, Treatment B

F i b e r Weight F r a c t i o n :

92%

Number o f L a y e r s :

34

Areal

1.54 l b s / s q u a r e f o o t

Density:

Fabrication Conditions:

225 F, 20 M i n u t e s , 176 PSI

Threat:

.22 c a l . Fragment, 17 G r a i n

Temperature ( F)

V50 (FPS)

%

Loss

70 (Room Temp.)

2052

Control

150

2008

2.14

180

1972

3.90

212

1968

4.09

230

1951

4.92

A thermocouple was embedded a t t h e c e n t e r p l y o f t h e l a m i n a t e . The p a n e l s were c o n d i t i o n e d one hour i n an oven a t each t e s t temperature. SOURCE:





236

Figure 8. High Performance Polyethylene composite ballistic resistance at elevated temperature. HPPE is Spectra 1000 and Aramid is Kevlar 29. (Reproduced with permission from ref. 15. Copyright 1988 Allied-Signal.)


13. KIRKLAND ET AL.

High-Performance Polyethylene Fiber 237


Improvements in the performance of products such as protective clothing which are made from high performance fibers can come from two areas. First, the search for the ideal "Super Fiber" which can meet all requirements can continue. Second, a more realistic and immediate solution can be found in hybridization of the various fibers and materials. This is an approach which has been used very successfully in the past. The same methods show great promise for the latest group of high performance fibers. It would probably be accurate to say that fourth generation protective clothing will not be composed of a single type of fiber, but be a highly engineered and complex marriage of several different fibers and materials. Literature Cited 1. 2. 3.

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

D.S. Cordova, D.S. Donnelly, Spectra Extended Chain Polyethylene Fibers. Allied-Signal, c. 1988 p.1 David C. Bennett, Health and Safety at Work, "Hand Protection" May 1981. p.32. John R. Sorrells, et a l . Some Cutting Experiments on Human Skin and Synthetic Materials. National Bureau of Standards, Washington, D.C. October 1973. p.17. Kaleidoscope, Winter 1988, Issue 3, Vol. 3, Allied-Signal. c. 1989. p.3. Center for Disease Control Outlook on AIDS. Chemical Week, June 7, 1989 p.44 New Products to Prevent Accidental Needle Sticks, Sunday New York Times, March 27, 1988. Peter Truell, "Demand for Rubber Gloves Sky Rockets" The Wall Street Journal. Thursday June 9, 1988. p.6. H.M. Taylor, "Gloves" Textiles. Vol 18. no. 1982. p.20. T.A. Abbott. "Ballistic Protective Clothing" Shirley Publication. S 45 p.41. D.C. Prevorsek, et a l . "Ballistic Armor from Extended Chain Polyethylene Fibers" Allied-Signal. c.1989. p.1. Ballistic Applications of Flexible Spectra Products. Allied-Signal. c.1989. p.1. Rigid Composite Armor Performance and Applications. Allied-Signal. c.1989. p.4. Kaleidoscope. Vol.2 no.2 Summer 1987. Allied-Signal. c.1987. p.2. Rigid Composite Armor Performance and Applications. Allied-Signal, c.1989. p.2. L. C. Lin et al., "Ballistic Performance of Lightweight Spectra Composite Hard Armor." c.1988 Allied-Signal. pp.3-5.

RECEIVED July 16, 1990


New Third-Generation Protective Clothing from High-Performance

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